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lsarccc
2008.01.04, 04:18 PM
I am building an AAA cell discharger, it uses a microprocessor to control the individual discharge of each of the 4 cells. By using power transistors and the PWM feature of the processor the discharge rate can be varied to mimic the actual pattern of current draw experienced on the track. The idea is that I will program the processor to play a set 20second pattern of varying discharge rates that mimic a lap of a circuit. The cells will lap round and round the virtual circuit with a pattern of low to high load mixed with rest periods until each cell reaches a rest voltage of 0.9v when the discharge will stop.

At set points each lap the voltage of each cell will be sampled and sent out to software on a laptop via RS232 (undecided but perhaps each cell will be sampled 10 times each lap).

The device will also have a 3 line 20 character LCD that will display individual cell voltage and calculated indication of internal resistance and the current lap.

I expect that the highest current draw on each cell will cause the cell voltage to drop appreciably, the resolution of the voltage measurement is around 0.002v. At a point in each lap I plan to hit each cell with a big current draw, the voltage will drop - this indicates the internal resistance of each cell. Then I'll stop drawing current and sample the voltage rising back to it's rest state using a rate of 1000 samples a second to try and snapshot the rate the voltage rises back. I think the amount the voltage drops and the rate of recovery might be a useful indication of the performance and status of each cell.

The idea is to have a test rig that can test various cells and care and charging patterns and automatically store the data in a database with reporting and perhaps some php and mysql magic to make the data available on the net.


My questions:
I am assuming that using a varied discharge rate with rest periods to mimic race usage is superior to a static discharge rate; also that using a switched load mimics the car esc more accurately and the test data should match real world usage more accurately. This is based on nothing more than intuition and I wondered if anyone can support or dispel my assumption with experience and hopefully facts?

Does the PWM drive frequency matter? What is the drive frequency of a Mini-Z esc?

In my limited research it seems that no other application of cells cares about the internal resistance of the cells as much as we do? Use of rechargeable cells in cameras seems to be the biggest application that gives data and they just test at a fixed discharge rate that tends to be lower than what we are using. Is my proposed approach to measure the internal resistance and recovery capability of the cells valid and useful?

What current drain range should I emulate? I was thinking 0-4amps - is that reasonable?

I hope this project will take 2-3 months to complete, any suggestions help very very very welcome. :)

a7i20ci7y
2008.01.04, 06:45 PM
Which microprocessor are you going to use? I recently tried a PWM project using a PICAXE but found it's abilities to be somewhat limited.

lsarccc
2008.01.04, 06:55 PM
PIC 18F4331 - it's well up to the task, I'll run it at 20Mhz, it can do 200,000+ 10bit resolution samples per second and built in 8 PWM channels with 14bit resolution and a EUSART for hi speed comms.

lsarccc
2008.01.09, 02:03 PM
OK - not much help so far with my questions, so I decided to help myself :)

Clearly the drive frequency of the esc does matter, the lower the freq. the less efficiently the esc operates and more power the esc/motor will draw from the batteries. I'll be discharging through a resistor which is a completely different kind of load to a motor, but I guess I can only emulate the real world so far. One thing I can do is use the same drive frequency.

http://lsarccc.com/images/ext/6pwmfreq.JPG
I measured the pwm frequency of an iWaver 02 and an AWD...

iWaver 02 - 238Hz
Kyosho AWD - 640Hz

I was surprised at how low the iWaver frequency was - I suspect the iWaver board may be a bit hard on commutators.

So my conclusion is to drive the discharger pwm load at 640Hz.


I have started building a telemetry rig to measure the current drawn as the car goes around my local track, that 'trace' will become the basis for the discharger cycle.

So far I have the basics for the receiver sorted...
http://lsarccc.com/images/ext/6telemetryrx.JPG

lsarccc
2008.01.09, 05:06 PM
OK, my core assumption for doing this is that using fixed discharge rates may be flawed when measuring the performance of cells as used in toy car racing. We know that the way we put the charge in can affect the chemistry? of the cell and the performance, so intuitively I think that when we test the cell by varying the discharge rate we may get different results.

So I've been googling away and my findings so far has thrown up some stuff that supports the idea that the result will be different but nothing that suggests that pulsing the discharge will have any other effect.

This is a crossection of my reading list so far:

A simplified explanation of Peukert - involving beer! (http://www.amplepower.com/pwrnews/beer/)
More on Peukert with a graph (http://www.axeonpower.com/performance.htm)
Battery testing for electric vehicles is done with variable pattern load with standards (http://www.axeonpower.com/testing.htm)
This suggests that intermittent but constant discharge simply extends the run time, but voltage recovery is interesting (http://www.engr.newpaltz.edu/~bai/Research/mlpd04_battery.pdf)

Any more info from people that know about batteries in the RC car context very welcome :)

mk2kompressor
2008.01.09, 07:04 PM
ok arthur you are my new best friend :D ;)

are you deffo coming to the hurda challenge?
i have all the paperwork from my 12hr duracell experiments,we'll speak there :)

a7i20ci7y
2008.01.09, 07:13 PM
I'm not sure anyone is going to know enough to really answer your questions. Experimentation is in order and I would be very interested in the results, just out of curisosity if not performance gains (all the tweaks in the world can't save my car from my driving :D ).

Perhaps you can make the frequency a variable so you can select a fequency to match the ESC you're interested in using? I realize the test is for the batteries, not the ESC; however, if the frequency matters for real world results, you'd want to simulate your real world equipment, what ever it may be. The best batteries at 640Hz might not be the best at 238Hz? I don't know.

lsarccc
2008.01.10, 01:56 AM
:) It's nice to have friends - especially ones that have data!, very interested in the duracell stuff Matt :D Yes, I need to PayPal Jonny - will get that sorted this week. (I will need to tap someone up to borrow a set of the correct offset wheels for the Hurda shell - I'll speak to you/Jonny more on that elsewhere.)


I think you're right Atrocity but there has to be a few Radio Amatures and EEs out there - you know the kind of people that really know what they are doing! I'll put in variable frequency into the discharger - I guess it has more effect in the circuit when you have a load with inductance like a motor. If we compare different frequencies we may find out something - as you say we don't know so let's try.


Here's the tale of reflex charging which I take as a great example of battery myths! (http://www.rcbatteryclinic.com/burp.html) (I totally believed in my reflex charger for many years :o)


I'm sure the telemetry bug can be done with a PICAXE easily enough and the receiver could be done with an off the shelf PC/USB experiment board rather than the fancy affair I'm building. I'll post extra detail of the telemetry bug maybe you'll pick it up as a project and improve on my slacker design :)

Wolf
2008.01.10, 04:45 AM
It seems it will be a great project and also good thread for battery discharging.

Since we are also in this sector and carrying out a very similar project (infact three projects) at the moment we'd also like add our two cents may be it helps.

First you must be prepared for variable drive frequencies. As you've already pointed our all manufacturers has different drive freqs and I even suspect AWD and MR02 has different drive frequencies as well. MR02 might have (never measured yet) higher freq than a MR02 to increase efficiency and topspeed. On the other hand AWD might have lower freq to increase punch and torque. This is a common issue in larger scale EP racing and we've applied this logic to our new version of Spinner. Very soon new updated Spinner will be announced with programmable drive & brake frequency (it will also have adjustable dead band but it is not very related with this issue).

Emulation seems to be a good idea and your assumptions (especially lap based approach and telemetry) are pretty good. On the other hand what we believe is constant current discharging give more accurate results when it comes to comparing cells.

Last but not the least timing of the motors is an important topic in MiniZ area when we are discussing efficiency. I wonder how many of us aware that we are using motors with reverse timing. Did you ever noticed that your motors runs better and faster when going reverse? Or awd chasis goes almost same speed with MR02 despite of a shorter gear ratio? I guess all manufacturers uses mass produced cans and brushes but this results in such weird conditions.

I'd like to watch this thread closely and we hope we can help.

Regards

byebye
2008.01.10, 06:52 AM
I'm gonna sticky this so it stays at the top!

Kris

lsarccc
2008.01.10, 08:31 AM
Hey thanks for the sticky Kris, the pressure's on for an interesting result!

My 1/10th touring car speedo can be programmed with varying frequencies across the throttle range from 500Hz to 6.5Khz I suspect that the clever Japanese have decided on that range as the optimum for a racing model car application at 1/10th scale.

@Wolf I notice the published spec for the Spinner is 1.2KHz which sounds good to me - a bit off topic but would you care to comment about the factors that led to that choice? I presume the power being switched and rpm range of the motor and the switching losses of the FETs in use set the best frequency for the esc? Be good to hear it more definitively in the context of Mini-Z style cars :)


I'll test my MR02i frequency tonight and perhaps the iWaver 02M, there's a good chance the frequency changed when they upgraded the board.

So I guess we're looking at variable frequency 200Hz - 10KHz and a fixed current mode now.

Wolf
2008.01.10, 12:13 PM
lsarcc,

We've tested Spinner before the release with mostly modified motors since it is designed for open racing. Motors like Anima, Speedy, 3Racing, Chili. We've tested with different track shapes and gear ratios. Unfortunately there is nothing called "best frequency". As I mentioned the effects of the frequency above you are stucked in torque,rpm dilemma. Since typical tracks have 10-12metres of straight and relevant in-track curves we saw that 1.2khz is a nice (or optimum) freq to release the product. As you also pointed out it is higher freq than current PCBs which leads not only better top speeds but also longer run times due to low gate losses of FETs.

New spinner which is under test at the moment will have variable frequency between 0.25 to 3khz. We are trying to optimize its steps at the moment.

How do you plan to emulate the brakes? I think (and also afraid :) )this project might lead to a full dyno for ESCs, motors, batteries instead of a discharger :)

lsarccc
2008.01.10, 01:53 PM
Wolf - you raise so many good points in your posts I have to focus a little bit (I am too easily distracted!) but perhaps we can revisit some things another time/project :)

How do you plan to emulate the brakes? I think (and also afraid :) )this project might lead to a full dyno for ESCs, motors, batteries instead of a discharger :)

Yes - things could loose their clarity, I'd like to go through the thinking again...

We are talking about discharging batteries.

I think an automated way to discharge cells unattended and log the values direct into a database with some kind of frontend to compare discharge curves would be a good thing - for me thats a no-brainer. The easier it is to record the data the more data we can do quicker. If the data is in the same format we can graph and compare easier and the data has more value.

I believe that the way we charge our cells affects the performance, for example a higher charge rate means more punch on the track, so I think it's intuitive to believe that how they discharge might reveal something. So this introduces the idea that we should try in some way to emulate real use.

All the data I have seen is based on a fixed discharge rate with currents that are lower than what we might see in a race. I am open to the idea that this is because fixed rate is the best test for comparison, but I believe that fixed rate is used because it is easy and the main markets are for cameras and other digital devices which focus on capacity more than voltage/Internal Resistance. I think that mixing the discharge rate and letting the batteries have some recovery might reveal effects on IR/punch missed by fixed discharge.

A good measure of performance in RC cars is internal resistance and the speed the cells can recover their voltage - we can measure that with some fidelity using a good pic chip.

Data on Internal Resistance is from manufacturers only. I don't think you can compare numbers. A way of measuring the IR that is comparable and might have some relation to the punch seen on the track would be great.

I recognised from the start that I couldn't emulate everything and so a line must be drawn somewhere...

I guess that the things we can emulate are:
1. Important: Varying discharge rate based on something like a real race - including periods where the cells can rest.

2. Less important: The cells aren't powering a torch bulb, they are in a dynamic circuit with pwm. I assume the cells 'feel' that the discharge has a frequency (Maybe I can see this with an oscilloscope). Maybe the pulsed discharge does something then again maybe it's irrelevant like the reflex charger story. Perhaps the cells don't feel the pwm or effects of the motor inductance so much and this is irrelevant! In any case it's fun to emulate so we will do it and test.

I think the discharger will emulate the current flowing from the cells, regenerative currents will be ignored (not sure Mini-Z escs do that?) and so braking will appear as a rest period with zero discharge.

We'll measure time, instantaneous voltage, rest voltage, voltage under max load and rate of voltage recovery after high load. Because the load is varying, the capacity (as runtime in seconds) is troblesome but I think I can see ways round it.

That is it for this project :)

Does this make sense and limit the scope of the project nicely?



We will do another project where we measure the pulse width of the throttle channel to work out throttle demand and marry that to the rpm of the axle over time (spooling up) and somehow relate the demand of the driver on the throttle with the response of the motor spooling up (and down) to push a car of known mass through a known gearing and tyre diameter (and making more assumptions about more things than we should :rolleyes: ) to try and produce a workable dyno... we'll throw the data out of 433Mhz or 2GHz RF telemetry link and stick that in a database too. For the future, I think it requires a proper collaboration!

(But if you need a little telemetry link to help debug that Spinner drive freq - drop me a pm maybe I can help...)

edits and edits - how many typos :o

mk2kompressor
2008.01.10, 02:07 PM
damn no bowing smiley :eek:
how are you working out the internal resistance?

Wolf
2008.01.10, 02:29 PM
After a long day (its 9pm and still working) I'm also in a mood for distraction.
Forgive my short post. I'll edit or add tomorrow.

- I aggree with the scope and assumptions.
- One of the reasons why I do like constant discharge rates is; you can compare matched cells between companies. Many matchers has many accronyms. VRS, VDS, XXMAX, bla bla. They all mean same thing Virtual Race Smulation and also indicate something that you can not compare the results of brand X to brand Y. That's why I always sticked to constant ampers. I know, this is not a technical reason but still a valid hobbiest excuse. May be constant ampers would be included as an option.

- Infact variable discharge may be even better considering AAA. The reason we see low constant discharge rates on manufacturer infos for AAAs is they not designed for it. You can easily draw 35-40A from a sub-C for several minutes but you can not even draw 3-4A for several seconds from a AAA

- Yes. We would be interested in a 2.4 telemetry. Infact we have access to those modules and test boards but have no time to work on it to fit our needs. Just send me an email.

- Meanwhile we already have the software you needed. I've written it a year ago for C1. It reads from RS232 according to our protocol and stores detailed data in a mdb and then graphs it. You can compare the graphs of both charge and discharge.

- I totally aggree with IR issue. This how sub-c classified.

Pass for tonight.

lsarccc
2008.01.10, 02:38 PM
damn no bowing smiley :eek:
how are you working out the internal resistance?

Hmmm - I haven't finished thinking that through properly...

The minimum is that you let the cell rest, measure a voltage - hit it with a big discharge current. Take the dischage away and immediately start measuring the voltage. The voltage drop is due to the internal resistance and for me indication enough of the punch of the cell - punchier cells have higher voltage and hold that voltage better under load. The exact value of IR is not necessary as long as all cells are subjected to the exact same load?

I think you can make a calculation of internal resistance value, but I think voltage loaded and unloaded is enough for our purposes? I'd never compare an IR I'd measured and calculated against anyone elses number - it's going to be meaningless.

Then we measure recovery by sampling the rate of rise of voltage after you remover the load. Fast is good!


Still more questions than answers :(

lsarccc
2008.01.10, 02:41 PM
@Wolf...

overloaded! - I need to sit with a soldering iron and smell some lead fumes.

Thanks for the comments - considered replies will follow might take the weekend to fully take it in :)

mk2kompressor
2008.01.10, 02:44 PM
im going to hook up an E.S.R meter to a pack of the duracells,hopefully tomorrow(used for testing capacitors whilst still mounted)it goes down to .01ohm so hopefully its low enough to see if my mah ratings match to the internal voltages(ive put them in packs of 4 based on the end mah after break in) :)
the results will be on my spec lists for the next meet

i was hoping you could have a look into adding something like an esr meter into the charger,there are a few circuit diagrams floating about if you google it

lsarccc
2008.01.10, 03:07 PM
I thought this was simple Kirchoffs - if you know the load resistance, the current and the voltage you can calculate the missing resistance which is in the cell?

If the current was stable I could see how to do this easily - but I'm switching the load and I'm not sure of the validity of anything...



What is your thinking Matt? That I'm wrong to assert that all that matters is Voltage or that IR values can be accurately measured easily so why not do it.


I claim ignorance on this - I have loads of reading to do :o :)

More detail please mate :)

mk2kompressor
2008.01.10, 03:46 PM
oh no im not saying yours isnt the way ;)
i was discussing what i learned in germany the other day with my uncle(tv repairman and tinkerer for years)he said i should find the internal resistance very acurately using his esr meter,it fires a signal through the battery to determine IR regardless of the v in the cell,as we are talking miliohms and the battery varies in voltage whilst under load it looks like an easier way :confused:

lsarccc
2008.01.10, 04:55 PM
You seem to be very precise in the way you go about these things - I'm sometimes tempted to be slack and cut the odd corner to get there quicker... But a good team in the forming methinks.

I have had a small box of Mini-Z stuff arrive today and 4 small scales that do upto 100g in 0.01g increments.





:)

mk2kompressor
2008.01.10, 05:33 PM
ooooooohh i like boxes of goodies,esp ones with 4 micro scales in them :eek:

i cant wait to see how all this turns out :cool:

lsarccc
2008.01.11, 08:50 PM
So I'll use the 12F675 in DIP format for this. All we're trying to do is get a trace of current draw going round a track so this will be a little 'ghetto'.

Incidentally Microchip do the rfPIC12F675F chip which is a surface mount 12F675 with a nice RF TX built in, also it's available with it's counterpart RX as a free sample from their site. I ordered 3 pairs today. Using this will allow us to make a telemetry bug a little more worthy of going into a Mini-Z!

This bug is quite easy to do and I'm sure it could be done as a PICAXE so this should be a very accessible way to play with telemetry.

The first 3 way socket links to the power and ground pins and MCLR. (blimey my soldering doesn't bear close scrutiny :o )
http://lsarccc.com/images/ext/6bug1.JPG

Then the Programming and Data and external trigger pins - all these are multi functional and could be connected to sensors to measure thins like voltage and rpm.
http://lsarccc.com/images/ext/6bug2.JPG

This plug will be the one we use to measure the current - to make it easy I have power and the link to the pin that we will use to do the analog to digital conversion in one plug block.
http://lsarccc.com/images/ext/6bug3.JPG

The el cheapo 433Mhz transmitter just tacked on top. connected to power and the pin I'll use to output the signal. The fourth unconnected connection sticking up from the TX is the aerial lead - I'll tack on a bit of wire for an aerial later. This TX and it's matching RX are easily available, about 10 as a pair from Maplin but I guess you can get them cheaper elsewhere.
http://lsarccc.com/images/ext/6bug4.JPG

So far just over 2g, but I have to add the aerial, a link to tie the MCLR pin to Vdd that I forgot about and perhaps I'll add a betterpower plug to take power from the car.
http://lsarccc.com/images/ext/6bug5.JPG

A test fit with the iWaver Enzo shell suggests the bug will fit here. Whether this is a good place to avoid intereference will need to be trial and error, you'd think putting it next to the car crystal is a bad idea. I've never had an issue in the past - I guess there is a lot of signal separation between 433Mhz and 27Mhz :). The blue thing is a ferrite ring that I will dremel a slot in for a hall effect sensor - the positive power lead from the batteries will be extended and wrapped around the ring. The three pins of the sensor will be connected to the plug in the third pic above. The coil will fit here.
http://lsarccc.com/images/ext/6bug6.JPG


More doing and less talking/thinking today :) Hopefully I'll get around to seeing if the chip will take a program and also get to measuring the pwm freq of the MR02 tomorrow.

Hmm 2am in UK... goodnight all :)

lsarccc
2008.01.12, 10:18 AM
Matt - I'm trying to learn more on the ESR meter. Very interesting, I still don't really get it. Be good to see some more info about use on batteries looks like a better/proper way to measure IR. I am becoming more convinced that the biggest problem we face is that not many applications care about IR - if cameras were affected by IR we'd be inundated with data.

I have found a reference to the patent that Tekin (makers of escs and chargers for 1/10th electric) took out for power capacitors:
Tekins Patent for using power capacitors with escs (http://www.braindex.com/patent_pdf/patents/US5744920.pdf)
Quite a bit of info there, power capacitors came and went as a fad at the end of the last millennium (in 1/10th and where I race at least), but the info in the pdf is interesting I think.


We're looking for a 1:1 car for our youngest daughter and other such major distractions happening all over at the moment. I find the odd moments to research on the net whenever I'm in a free wi-fi area, gotta love the ipod touch! I'm too tight to pay for 3G phone access...

At home for a few hours so I'll get cracking on seeing if I killed that pic chip with all the soldering I did on it last night...

lsarccc
2008.01.12, 04:30 PM
Well I ended up with more time on my hands than I expected :)

I finished the bug, including tying the MCLR pin to Vdd with a 100K surface mount resistor. Added an aerial (I carefully calculated a 1/4 wave antenna length then just ignored that and cut a semi-random length of wire based on what looks right!). I've also added a power lead separate to the power used by the programming dongle.
http://img209.imageshack.us/img209/9996/6bug9gc1.jpg


I made a dongle to connect between my USB in circuit pic programmer and the sockets on the bug. The thing in the bottom right of picture is my programmer, I chose that one because it means I can more easily reprogram trackside from my laptop. So the next thing was to try and program the pic...
http://img85.imageshack.us/img85/1189/6bug7un2.jpg

Success! The 433Mhz RX/TX pair works very simply, whatever the state of the signal pin on the TX is transmitted to the signal pin on the RX. In the picture the Board in the middle has the RX board with the output signal pin connected to an LED and the oscilloscope. The TX bug is on the rightmost board and programmed to send a fixed width pulse at fixed intervals. The oscilloscope is connected to the RX signal pin and displays a clean square trace of the signal being sent by the TX. This has proved the easiest way of testing the telemetry link, you can set up a clear signal pattern and set the oscilloscope on a long time base then jiggle the TX and subject it to revving the motor up jiggling the servo and testing distances. If you can't maintain a reasonably clear and square trace on the oscilloscope then you have an issue that you must resolve before you go to try and send a real more complex signal. Once I'm happy with all of the connections I'll pot the whole thing in epoxy which will make it very robust.
http://img85.imageshack.us/img85/7637/6bug8rt9.jpg


Here the TX is about 10meters away in line of sight and as you'd expect the trace is fine - my aerial length can't be too bad!
http://img85.imageshack.us/img85/92/6bug10qq1.jpg


Here it is sat on my MR02 ready for an interference test on the bench, this revealed some issues and I think various capacitors will be employed to clean the trace up. In the worst case I buy a sub miniature LiPo cell and use a dedicated power supply - usually I'd expect to be able to solve these issues without resolving to that.
http://img209.imageshack.us/img209/5351/6bug11dn9.jpg


Well I didn't get round to measuring the drive frequency of the MR02. But I did start the discharger itself on a prototyping board. This is the 18F4331 chip with power and a programming interface ready for me to start developing the code further.
http://img209.imageshack.us/img209/3614/6bug12ax0.jpg

Pretty successful day I reckon - settling the TX down so it transmits cleanly whilst it's in a car razzing round a track will be the next challenge.

Jonny
2008.01.12, 04:43 PM
Arthur, just superb work my friend. Matt and I have had some discussion on this and we're trying to keep up with you, we really are ;)

Anxiously waiting on the next installment!

Jonny

lsarccc
2008.01.12, 06:14 PM
Thanks Jonny - it'll be me trying to keep up where it matters (on the track) at the Hurda challenge! :rolleyes:

I'm racing 1/10th early tomorrow morning so I'd better at least look at my car, depending on how that turns out I'll start work on the forum...

mk2kompressor
2008.01.12, 06:27 PM
top work arthur,cant wait to see it for real,it looks small enough ;)

lsarccc
2008.01.13, 10:48 AM
Thanks Matt, the bugs have developed over a few years. These three gives an idea of the things I've tried. The central one hints at how small we could go with better pcb designing and making ability using surface mount version of the 12F675.
http://lsarccc.com/images/ext/6bug13.JPG

- I agree with the scope and assumptions.
- One of the reasons why I do like constant discharge rates is; you can compare matched cells between companies. Many matchers has many accronyms. VRS, VDS, XXMAX, bla bla. They all mean same thing Virtual Race Smulation and also indicate something that you can not compare the results of brand X to brand Y. That's why I always sticked to constant ampers. I know, this is not a technical reason but still a valid hobbiest excuse. May be constant ampers would be included as an option.

- Infact variable discharge may be even better considering AAA. The reason we see low constant discharge rates on manufacturer infos for AAAs is they not designed for it. You can easily draw 35-40A from a sub-C for several minutes but you can not even draw 3-4A for several seconds from a AAA

- Yes. We would be interested in a 2.4 telemetry. Infact we have access to those modules and test boards but have no time to work on it to fit our needs. Just send me an email.

- Meanwhile we already have the software you needed. I've written it a year ago for C1. It reads from RS232 according to our protocol and stores detailed data in a mdb and then graphs it. You can compare the graphs of both charge and discharge.

I agree with your pros and cons of fixed vs variable discharge rate. After some thought I realise that it is the hobbyist side of me wanting to make something with a pic chip driving this effort more than a deep technical belief that this will reveal some major new piece of info.

Maybe you think my telemetry approach is a bit amature now :)? Well I think that this approach is surprisingly accessible and feels more like a hobby and less like a maths exam - I hope some people will be interested in doing stuff like this. Once you've built a bug like this you can easily attach various peripherals like rpm sensors, accelerometers and use rare earth magnets and hall effect sensors to easily detect the changing positions of chassis elements. A great hobby on it's own! :) I'll drop you an email later in the week about telemetry and your database schema you use.

Ah a big Sunday dinner with the family :)

Wolf
2008.01.14, 01:16 AM
In fact being a hobbiest approach is the best thing we can have. PIC drived discharge mechanism is not only hobbiest approach but also manufacturers product. We are announcing our microprocessor controlled individual discharger this week. Hope people will like it and don't consider it as a lab rat device :)

There is wording;" Geniousity is being able to divide big complex problems in to small easy parts". That's why I think your approach is very affective and result oriented.

Meanwhile we were discussing with Ozgur yesterday (other partner of TGR who is electronics engineer), we thought using a seperate PCB + Motor with a load, with the same frequency would also give you the data you need. Ofcourse it is not extensible as yours but might be sufficient and trivial.

Waiting for your email about telemetry.

color01
2008.01.14, 01:54 AM
Isar, this is freaking genius, lol... definitely above my head as to how you got this far! And you're so right about the possibilities, you can plug in additional modules as you see fit to monitor different things... totally blown away, awesome work. We gotta see this final thing in action. ;)

lsarccc
2008.01.14, 02:17 AM
You're announcing a discharging device! That's fantastic and very interesting news. I hope you do well with it and it allows many people in the hobby to share data that has been measured with comparable devices. I know a lot of people like to have gadgets, some like to be more professional in the way they race and others like to turn their pit area into a lab experiment - I hope it appeals to all :) The dark side to this is that we wouldn't want to blight the Mini-Z hobby with the level of battery wars that has put me off 1/10th... Hmmm...

Well I think geniousity is a new word on me, "brevity" is the one I need to take most notice of - I use 20words to your 1 and our signal to noise ratio is similar :o! There is a popular sideline hobby of rewiring CDROM brushless outrunner motors for model aircraft and building your own brushless speed controller using microprocessors - I confess the sensorless brushless controller beat me - you have to be a lot more serious to get one of those to work - that was for me a maths exam of the worst kind.

Yes your argument about using an esc with a real motor is sound/common sense, I have thought about that and I dismissed it because I thought that the motors are subject to wear and then over the life of the unit the results would not be consistent but then... arrggh too early to think properly!

I will go through my task list at work and drop you a note!


Edit: Sorry color our posts crossed - I'm sat at work and listening to peoples weekend stories. I hope to get this telemetry sorted to a point others can make them very easily. It might appeal as a side hobby to some and a usful tool for chassis designers such as yourself.

Wolf
2008.01.14, 02:48 AM
In fact it is just a individual discharger with discharge rate and cutoff voltage adjustable for our battery packs. It can also be used for single cells. It doesn't have the capability to log the data (at least commercial one :) )

I aggree with the cost of batteries in larger scales and I also like way it is now for mini scale. However I think we've already reached the barriers of current plastic chasis so our products are just a little step ahead. We are trying to keep our costs and also prices down in order not create another vallet monster.

lsarccc
2008.01.14, 07:49 AM
Well that's still a nice product - I look forward to hearing more about it. TGR seems very active at the moment, I'm racing in the Hurda challenge in Stafford later this month - I suspect I'll struggle to be on pace but I'll get to see things like the Sinister and learn more off the Stafford boys and girls about these small cars :).

I have a background with 1/12th pan cars so the Sinister chassis is very attractive to me - I have 4 kids so like all parents I have pictures in my wallet where my money used to be - no real room for wallet monsters anymore :eek: !


So thinking through the next steps, I need to make the current sensor and calibrate it and also drive the car around the hall with the bug transmitting to make sure the signal is still stable.


You have pm Wolf...

Wolf
2008.01.14, 09:58 AM
This is the product I've mentioned previously, it has some missing hardware as you can see. They will be also ready within few days.

http://mini-zracer.com/mini-zgallery/data/1252/702002.gif

I don't want to distract this thread neither I want to open a new product anouncement thread yet. So everyone; questions and comments in Ask TGR forum please.

mk2kompressor
2008.01.14, 11:54 AM
you will be amazed at the sinister chassis arthur ;)

i have a few ideas on sensor placement and operation,ill save them for the meet :)

lsarccc
2008.01.14, 01:19 PM
That is a beautiful piece of kit :cool: I think you will definitely win over the gadget freaks and pit poseurs! The variable rate and cutoff with get the racers too - nice presentation! Now a USB output and you'd get the lab rat boys too - less of them people about I guess so wise to choose that level of functionality.

I'm going to mention dead shorting - now this may be an immotive subject and I don't want to start a 'riot', but I have never seen anyone mention this. These AAAs remind me of the very flat Sub-C 3000s we were running a while back that loved to be dead shorted, but no mention of it on Mini-Z forums. Many people say don't go below 0.8v but that sounds like my grandma talking? :eek: ;) :) Dead shorting is about number 3 on my list to try with a set of say Sanyo 800s - thoughts?

Matt - you might want to save all the old CDROMs and DVD drives you can get your hands on. Under the outrunner motor there are 3 hall effect sensors - they are really small and light and linear. Start collecting them mate! (put the cdrom motors and platter motors to one side for me if you don't need them)

Edit for picture...

I guess you know what I mean but just incase:
http://lsarccc.com/images/ext/6hallsensor.JPG
The three black things under the stator.

lsarccc
2008.01.16, 02:46 PM
I was thinking about how to calibrate the current sensor and decided that I'd use this as an opportunity to test the discharge side of the discharger by using that to supply different currents to help calibration.

When I was looking at the allocation of the pins on the pic chip I realised I had enough spare to drive a graphic LCD rather than the 20x3 character LCD I originally planned. I reckon this will allow more data to be displayed and graphics LCDs are definitely more bling than character ones. Luckily I have a stock of these graphics LCDs (cost about 5 off eBay).

It wasn't completely straight forward and it took me a couple of hours to get it all to work and get to a stage where I can display what I like...

http://lsarccc.com/images/ext/6glcd.JPG

Should look neat with a load of data on display in each cell and the current run time, discharge rate, lap etc counting up.

I have started to program the pwm and will have the discharge part sussed soon, then the interesting stuff can begin... :)

mk2kompressor
2008.01.16, 03:19 PM
again no clapping smiley,well done dude :D

Jonny
2008.01.16, 05:13 PM
Crikey Arthur, :eek: Can't wait to meet up again soon. I may well be able to supply some of those hall effect sensors.

Jonny

lsarccc
2008.01.18, 09:12 AM
Cheers guys, work is progressing - I hope to make some major advances this weekend and be able to have a trace of the load going around the track next week.

I was just looking again at fixed current discharging vs fixed load discharging. (With fixed load the current decreases as the battery voltage decreases.).

I think I should make the discharger able to be expanded to do fixed current discharging in the future.

I think fixed (and static value) load is worthless.

I think a fixed load that varies in a similar fashion to the load on the track is superior.

:confused:

I'll stay on course with the variable load idea but the possibilty of adding selectable fixed currents later will be built in. I need a better current sensor/fixed current load.


My free sample rfPic chips arrived today - super tiny, I'm wanting to collaborate and create some really good telemetry bugs. Theres a good application paper on this: tyre pressure telemetry (http://ww1.microchip.com/downloads/en/AppNotes/00238b.pdf)

:confused: No comments on dead shorting cells? :confused:

LED
2009.01.06, 06:33 AM
any progress ? :)

cico
2009.11.01, 01:56 PM
hi everyone, i have finished a new design circuit, with "pwm" *i can sell the design for 100 usd if anyone is interested to produce and sell. pcb is included

quazster
2013.08.20, 08:22 AM
We made a discharger/test rig a bit over a year ago. Two of these made, first prototype in the picture. Some features:

- MCU controlled calibrated constant discharging current, 0-4500mA, 2mA resolution
- Four point measuring of cell voltage, contact losses don't effect the voltage reading
- 0.1mV calibrated voltage resolution
- DAC controlled discharging circuit with automatic closed loop correction to maintain discharging current
- Individual cell temperature monitoring
- Internal resistance measurement
- Can be coded to do PWM discharging, constant load, pulse discharging etc.
- 128x64 display
- Can be connected to LogView via USB, discharge curves directly to LogView and can be processed further in Excel etc.

Attached a picture of the prototype device and a picture of some 60 batteries discharged and plotted in Excel. Next version will have a charger circuit and SD-memorycard onboard and the goal is to make a device that does automated and identical battery break-in and testing with one push of button.

https://docs.google.com/file/d/0ByzkDr4ub7bKaEMtR3RwbEY4Mzg/edit?usp=sharing
https://docs.google.com/file/d/0ByzkDr4ub7bKZ3hOdV9iUFJPa3M/edit?usp=sharing

chad508
2013.08.20, 09:45 AM
Very interesting setup to say the least.

Felix2010
2013.08.20, 10:13 AM
Please forgive my ignorance if this is already said quazster, but does your prototype discharger unit measure Internal Resistance, either actual or real-time? This is something I fooled with using my MuchMore CellMaster Platinum SP ED. and found the IR data told a lot about how a cell could handle high amp draw while maintaining maximum voltage (Good for Mod guys):D
Thanks for all the info and pics! Very interesting! Great job:D

quazster
2013.08.21, 03:47 AM
Forgot to add it to features, yes it has a function to measure internal resistance. For now it is a separate test, I haven't had time to code a function that does IR measurement during discharging for example every 5 seconds or every 30 seconds or whatever I want. It is easily done, only needs some coding work, and it is also in my todo-list.

Best way to match batteries quickly so far (without Excel work) has been a function that discharges 300mAh at 3A and calculates how many mWh battery gives out.

IR reading is very much dependant on the battery temperature and state of charge. This is why I have to finish the constant discharge function with repeated IR measurements.

Felix2010
2013.08.23, 02:20 AM
"DISCHARGE*** 300mAh at 3A and calculates how many mWh battery gives out.


This is great info, thank you for sharing! :):):)

ALso, you mention these as "prototypes".. Are you planning to sell any of these Discharge Stations???:D It is very cool and a interesting new way to easily match packs without doing these math:D:o:D

quazster
2013.08.23, 02:24 PM
No plans to sell now but we will most likely do a second, bit more sophisticated version just for fun. And maybe do a small batch of devices for sale, who knows.

This has so far been a nice research project to the world of AAA Nimh batteries :-)

Felix2010
2013.08.24, 11:11 PM
Excellent job on this device and thank you for the info. I for one am looking forward to possible additional updates, thanks again!:D

quazster
2013.11.06, 08:21 AM
Coded a new function some weeks back. Was sick at home and off work for few days so had time to make this work.

Functions:
- discharge at constant 3A current
- two GUI configurable mAh limits that control the result points
- three IR measurements during the discharge, first at start before the discharge begins, second at first mAh limit and third at second mAh limit
- results are displayed on the screen real time during discharge
- function gives out 7 different results from the battery, 3x IR readings, the average voltages between 0 - first mAh limit, first mAh limit - second mAh limit, second mAh limit - discharge to 0.9v, and total mAh discharged

This works really good and the batteries are easily tested and it is fast to write the results to Excel to sort the batteries with the reading of choice.

Here is a photo of some of my matched batteries and the results screen, first mAh limit is 50, second 300mAh:
https://drive.google.com/file/d/0ByzkDr4ub7bKY3NxemVzWW1kNjg/edit?usp=sharing

Jshwaa
2014.12.30, 10:18 AM
Like the concept here. How far did the design go? Did it provide any marked improvement on cell life, charge cycles, or charge/discharge performance?

Sounds like you are just trying to duplicate the discharge profile of cells running in an RC on a track. I'd like to know how you were able to capture that information so as to duplicate it, while running on a track.

quazster
2015.03.24, 07:16 AM
Like the concept here. How far did the design go? Did it provide any marked improvement on cell life, charge cycles, or charge/discharge performance?

Sounds like you are just trying to duplicate the discharge profile of cells running in an RC on a track. I'd like to know how you were able to capture that information so as to duplicate it, while running on a track.

No improvement on cell life, charge cycles or charge/discharge performance at cell level.

But huge improvement on the visibility on single cell performance, capability to choose the best of the best cells for the big A-mains, ability to detect in real time when one cell starts to go bad, also we have learned the right way to charge, discharge and store cells.

Overall we just get the most out of our batteries and get the edge over our competitors here :)

No new developments on the device, the two prototypes we made 3 years ago are working too well still, and because they just have been too good we haven't had the motivation to design any new hardware :D

Jshwaa
2015.03.24, 08:17 AM
No improvement on cell life, charge cycles or charge/discharge performance at cell level.

But huge improvement on the visibility on single cell performance, capability to choose the best of the best cells for the big A-mains, ability to detect in real time when one cell starts to go bad, also we have learned the right way to charge, discharge and store cells.

Overall we just get the most out of our batteries and get the edge over our competitors here :)

No new developments on the device, the two prototypes we made 3 years ago are working too well still, and because they just have been too good we haven't had the motivation to design any new hardware :D

That's interesting. Something I've wondered about.... If you were to keep a group of 4 cells 'together' through all charge/discharge cycles, do you think that each cell would degrade at different rates?

Do you believe any variations you experience between cells would be due to manufacturing variations, or is it due to mixing your cells between one charge/discharge cycle and the next?

It may be interesting to see if, in a 4 cell series configuration, whether or not the most positive cell or the most negative cell experiences any different loading conditions, where it may be prudent to rotate the individual placement of each cell in the 4 cell series configuration between each cycle, so that the cells would wear in evenly so to speak.

At any rate, your charge/discharge datalogger sounds like it has some interesting potential, however I'm glad you're getting the most out of it in your club. It really does all start with the cells...