Mini-Z, Kyosho Mini-Z Racer, MR-03, MR-02, MA-010, Forums, News, Pictures, Parts, and Shop - Mini-ZRacer.com
Forums, Mini-Z, MiniZ, Kyosho Mini-Z, Kyosho MiniZ, Kyosho Mini-Z Racer
Mini-Z Hop-Ups, Mini-Z Parts, MiniZ Hop-Ups, MiniZ Parts, Kyosho Mini-Z Hop-Ups, Kyosho Mini-Z Parts, Kyosho MiniZ Hop-Ups, Kyosho MiniZ Parts, Kyosho Mini-Z Racer Hop-Ups, Racer Kyosho Mini-Z Parts
Old 2006.08.31, 11:34 PM   #1
locwan
Registered User
 
locwan's Avatar
 
Join Date: Jul 2006
Location: Markham, Ontario
Posts: 274
Question What size/uf capacitors do you use??

What uf capacitors are you using with a FET stack/external ESC modified cars to reduce voltage ripples, increase punch response, and reduce glitching due to drops in current to the servo?

What's the ideal capacitence? Some use less than 1000 micro farads, while others recommend using 4700 micro farads. How much is really needed? And where are you connecting the capacitors to for the most effectiveness?
locwan is offline   Reply With Quote
Old 2006.09.02, 01:33 PM   #2
locwan
Registered User
 
locwan's Avatar
 
Join Date: Jul 2006
Location: Markham, Ontario
Posts: 274
hmm, I'm surprised no one has responded yet. No one knows what the ideal capacitence is for the mini-z chassis?
locwan is offline   Reply With Quote
Old 2006.09.02, 01:53 PM   #3
Mojar7070
Racer4Life
 
Mojar7070's Avatar
 
Join Date: Feb 2006
Location: Vallejo, CA.
Posts: 213
I don't think a lot of people use a capacitors on mini-z's. No need to, at least I don't need it. PNracing has a capacitors rated at 4700 uf. Tha's the only one I know.
__________________
-My Gallery of Cars-
Mojar7070 is offline   Reply With Quote
Old 2006.09.02, 02:08 PM   #4
locwan
Registered User
 
locwan's Avatar
 
Join Date: Jul 2006
Location: Markham, Ontario
Posts: 274
Quote:
Originally Posted by Mojar7070
I don't think a lot of people use a capacitors on mini-z's. No need to, at least I don't need it. PNracing has a capacitors rated at 4700 uf. Tha's the only one I know.
Really? I could be wrong, but I was expecting some of you that have experience with fet stacks or external esc to use some sort of capacitor to reduce current ripples caused by hot motors.

What kind of fets do you use with your setup? I've been having some glitching problems with my fetted car lately after the install, and have been suspecting it to be caused by the motor being able to pull larger current in quicker with the new fet stack, hence causing a drop in voltage being supplied to the servo and receiver.
locwan is offline   Reply With Quote
Old 2006.09.02, 02:47 PM   #5
Mojar7070
Racer4Life
 
Mojar7070's Avatar
 
Join Date: Feb 2006
Location: Vallejo, CA.
Posts: 213
I use the 4562's fets on my mod car. It does have some glitch, and I think thats just a characteristic of the 4562 fets. You have a good point about the larger current pull. I only my mod 10 min. at a time, so that I don't overheat the motor or the board and haven't had any problems with my mod car. As a matter of fact it's been running really well. It has 2x3 4562 fets, 35T turn custom motor, Atomic VDS body. It is dailed.

What motor are you running on your fetted car??

Here's a couple of pics.
Attached Images
File Type: jpg P1040011.jpg (28.0 KB, 91 views)
File Type: jpg P1040013.jpg (28.4 KB, 66 views)
File Type: jpg P1040014.jpg (28.1 KB, 65 views)
__________________
-My Gallery of Cars-

Last edited by Mojar7070; 2006.09.02 at 02:51 PM.
Mojar7070 is offline   Reply With Quote
Old 2006.09.02, 03:03 PM   #6
locwan
Registered User
 
locwan's Avatar
 
Join Date: Jul 2006
Location: Markham, Ontario
Posts: 274
That's a very nice looking car.

I run the atomic stock motor with a 9 teeth pinion. My fets are IRF 7317 2x2 stack. However, I do run in the basement, and there are several spots that have been known to glitch everyone's car;(probably external interference from neighbours), but the glitching has become especially severe with my fetted car.

In order for me to conclude whether the increased glitching is due to drops in voltage or not, I would have to know how much capacitence is needed in order to smooth out the current ripples. So I've pulled some caps off of a dead computer motherboard laying around at home, they are the cyclinder type that can handle 6v, with 1000uf each. I just wonder how many is needed, as they are not as compact as the ones that PN is selling.
locwan is offline   Reply With Quote
Old 2006.09.02, 04:48 PM   #7
LBRC
Registered User
 
Join Date: Mar 2004
Location: Northwest
Posts: 550
The only “glitching” caused by a 2x2 or even 2x3 FET stack is when it’s installed improperly, i.e. overheating or static damage, which happens quit a bit, since most people don’t use static protection and less than ideal soldering equipment, sort of like doing surgery on a kitchen table with a carving knife, with enough skill and luck the patient can survive but it’s a traumatic experience.

As for capacitors, especially with a modified motor, because of the amount of current involved you might as well try throwing cotton balls at the car to help the motor along and supposedly reliving current deprivation/spikes from the steering in this case. Look up the definition of Farad then calculate the amount of current actually being applied, or if your not up to the electronics and math just take your cap, charge it, and connect it by itself to a motor lead and see if you get any movement at all, then repeat the process with progressively smaller motors to see how small the motor has to be and how big the capacitor has to be to get even a micro second of help.

On the practical side the first thing I would do is try the car in another location, if location makes a difference it’s a TX/RX problem, if location and range does not make a difference, then why not first put a stock motor in with a freshly charged set of known good batteries to see if current delivery makes a difference. Remember a motor draws the current the mosfet H-bridge amplifier does not force that current into the motor. If you experience more “glitching” with a modified motor compared to a stock then the two most likely culprits would be either your batteries, or quite possibly the FETs where damaged by the handling and installation procedures used when stacking them. A hot motor with low current delivery batteries can indeed deprive the steering of power for example that’s the Iwaver’s main nearly insurmountable problem because of the week inefficient steering motor driver, the problem however is rarely an issue with a Kyosho Mini-Z. For example even with a 2x3 stack of 4562’s running a T1 in a very heavy Tagu 1/25 conversion chassis on a 1/14 scale carpet track using cheap Powerizer batteries and a 9 toot pinion I have no “glitchy” steering issues.

One problem with some of the reasoning mentioned in your other FET thread so far is that a working efficient FET stack does not draw more current from the battery, a small but important distinction is that a stacks less resistance generates less heat allowing the motor to receive power (voltage/current) that was previously being used by the inefficient single mosfet. In other words, the current drain from the battery stays the same with the same motor, the only difference is that more efficient mosfets allow more of that power to actually reach the motor instead of generating heat in the mosfet which is what destroys the mosfet when a motor draws too much power.

Most common cause of steering glitches in a Mini-Z:
  • Low TX power; can be either batteries or poor antenna (TX or car) connection.
  • Loose or unsecured servo encoder/potentiometer (pot), can also be caused by the pot being pinched too tight too. Either way it causes the same problem the variable resistance does not correctly indicate/match the servo position.
  • Signal interference/dead spots. For example this summer I have my home track setup in a 20’ x15’ screen tent and the close proximity of the insulated (ungrounded) metal poles caused a dead spot in the far right corner which was especially noticeable with a low power Epoch TX or a KT-5 with weak batteries. By grounding the tent poles I was able to significantly reduce the problem.
  • Low battery power, which actually starves the receiver circuitry causing the glitch not the steering driver itself.
__________________
Jungle Outlaw Micro Racing
If the track is wet, then the tent is leaking.
LBRC is offline   Reply With Quote
Old 2006.09.02, 06:02 PM   #8
locwan
Registered User
 
locwan's Avatar
 
Join Date: Jul 2006
Location: Markham, Ontario
Posts: 274
Quote:
Originally Posted by LBRC
The only “glitching” caused by a 2x2 or even 2x3 FET stack is when it’s installed improperly, i.e. overheating or static damage, which happens quit a bit, since most people don’t use static protection and less than ideal soldering equipment, sort of like doing surgery on a kitchen table with a carving knife, with enough skill and luck the patient can survive but it’s a traumatic experience.
lol, very weird yet fitting analogy. I hope that this isn't due to permenant damage that I've inflicted on my "patient".


Quote:
As for capacitors, especially with a modified motor, because of the amount of current involved you might as well try throwing cotton balls at the car to help the motor along and supposedly reliving current deprivation/spikes from the steering in this case.
So if I understand this correctly, what you're saying is that a capacitor is actually not helping very much at all. I've gone and installed 3 1000uf caps in the mean time, and thought I experienced some sort of increase in the initial punch off the line. Maybe this is just me willingly thinking so?? I really have no way to tell for certain without being able to test the car's acceleration.


Quote:
Look up the definition of Farad then calculate the amount of current actually being applied, or if your not up to the electronics and math just take your cap, charge it, and connect it by itself to a motor lead and see if you get any movement at all, then repeat the process with progressively smaller motors to see how small the motor has to be and how big the capacitor has to be to get even a micro second of help.
Didn't think of that. Thank you. I'll try taking off the caps from the chassis and try that on a motor w/o load first.


Quote:
On the practical side the first thing I would do is try the car in another location, if location makes a difference it’s a TX/RX problem, if location and range does not make a difference, then why not first put a stock motor in with a freshly charged set of known good batteries to see if current delivery makes a difference. Remember a motor draws the current the mosfet H-bridge amplifier does not force that current into the motor. If you experience more “glitching” with a modified motor compared to a stock then the two most likely culprits would be either your batteries, or quite possibly the FETs where damaged by the handling and installation procedures used when stacking them.
Batteries! How could I have totally missed those in the whole equation?? I am running on a few sets of batteries that have been used for a long time. I suspect that they will not last much longer and are nearing the end of their useful lives.


Quote:
A hot motor with low current delivery batteries can indeed deprive the steering of power for example that’s the Iwaver’s main nearly insurmountable problem because of the week inefficient steering motor driver, the problem however is rarely an issue with a Kyosho Mini-Z. For example even with a 2x3 stack of 4562’s running a T1 in a very heavy Tagu 1/25 conversion chassis on a 1/14 scale carpet track using cheap Powerizer batteries and a 9 toot pinion I have no “glitchy” steering issues.

One problem with some of the reasoning mentioned in your other FET thread so far is that a working efficient FET stack does not draw more current from the battery, a small but important distinction is that a stacks less resistance generates less heat allowing the motor to receive power (voltage/current) that was previously being used by the inefficient single mosfet. In other words, the current drain from the battery stays the same with the same motor, the only difference is that more efficient mosfets allow more of that power to actually reach the motor instead of generating heat in the mosfet which is what destroys the mosfet when a motor draws too much power.
I see what your logic here is about the current draw, thanks for the education. However, I'm perplex at the fact that before the car had modified fets, the motor will always stop first when I run down the batteries completely, and this does not affect the car's ability to steer in any way. However, after the fet upgrade, the car will lose steering response when the batteries run down, eventually to a point where the steering will not respond unless I let go of the throttle. This effect seems to lessen if I first gradully ease into the throttle, bringing the car to speed, then the steering will respond better. So my reasoning about the current drain affecting the car was really based on this. So if the motor draws the same amount of current at the same speed, then I really don't understand why this would happen. In which case, based on the new info you've provided, I could only conclude that even if the motor is drawing the same amout of current, the decreased resistence in the new fets would allow the motor to draw it's needed current in at a faster rate. Will this not cause a drop in voltage in the circuits, especially if the batteries are weak and doesn't respond well? Does this happen to you car as well? Please enlighten me.


Quote:
Most common cause of steering glitches in a Mini-Z:
  • Low TX power; can be either batteries or poor antenna (TX or car) connection.
  • Loose or unsecured servo encoder/potentiometer (pot), can also be caused by the pot being pinched too tight too. Either way it causes the same problem the variable resistance does not correctly indicate/match the servo position.
  • Signal interference/dead spots. For example this summer I have my home track setup in a 20’ x15’ screen tent and the close proximity of the insulated (ungrounded) metal poles caused a dead spot in the far right corner which was especially noticeable with a low power Epoch TX or a KT-5 with weak batteries. By grounding the tent poles I was able to significantly reduce the problem.
  • Low battery power, which actually starves the receiver circuitry causing the glitch not the steering driver itself.
I've gone through this list before. Right now everything on the car itself is sound as far as I know, and I'm still searching for other possible cause. So I'm beginning to suspect that the increased glitching could be a coincendence, caused by external sources. Just so happens that the interference was increased as I finished the fet upgrade. Too bad I have no other track to test at the moment, and will have to wait a bit to find out. However, I'm not ready to rule out the possibility of an interanl cause just yet.

Thanks for you response and information, your insights are always helpful.
locwan is offline   Reply With Quote
Old 2006.09.02, 07:12 PM   #9
LBRC
Registered User
 
Join Date: Mar 2004
Location: Northwest
Posts: 550
Quote:
... However, I'm perplex at the fact that before the car had modified fets, the motor will always stop first when I run down the batteries completely, and this does not affect the car's ability to steer in any way. However, after the fet upgrade, the car will lose steering response when the batteries run down, eventually to a point where the steering will not respond unless I let go of the throttle. This effect seems to lessen if I first gradully ease into the throttle, bringing the car to speed, then the steering will respond better. So my reasoning about the current drain affecting the car was really based on this. So if the motor draws the same amount of current at the same speed, then I really don't understand why this would happen. In which case, based on the new info you've provided, I could only conclude that even if the motor is drawing the same amout of current, the decreased resistence in the new fets would allow the motor to draw it's needed current in at a faster rate. Will this not cause a drop in voltage in the circuits, especially if the batteries are weak and doesn't respond well? Does this happen to you car as well? Please enlighten me.
Try thinking of the FETs as a variable resistor going from open or 100% resistance down to almost, but never quite, 0 ohms or no resistance at WOT (Wide Open Throttle). When you stack the FETs and/or use more efficient mosfets you get closer to 0 ohms or no resistance at WOT.

Approx.
0.450 ohms for a single set of 3004’s
0.175 ohms for a single set of 3010’s
0.087 ohms for a single set of 7317’s
0.053 ohms for a single set of 4562’s
0.044 ohms for a 2x2 set of 7317’s and
0.029 ohms for a 2x2 set of 4562’s which is much closer to actual 0 than 0.450 ohms.

For practical purposes swapping a set of 3004’s with a 2x2 stack of good mosfets is literally the equivalent of removing an unnecessary ½ ohm resistor from the battery/motor circuit. Take out that resistor and yes the motor will run a little longer. At full power a ½ ohm hurtle is not much of an obstacle at all but as the batteries run out of juice it becomes a much more troublesome and when their just about spent it’s just too high, or rotating that darn rotor past the magnets takes just too much effort.

As an additional note by taking out that stock FET induced ½ ohm of resistance both top end speed and runtime are increased slightly at the same time, it’s not much of an increase but the car will literally not only be faster but run slightly longer too. However since you don’t normally run a race at WOT the effect when looked at from the batteries point of view is that the motor is using less of their power to maintain your top driving speed. In other words using less power to maintain your speed not more.
__________________
Jungle Outlaw Micro Racing
If the track is wet, then the tent is leaking.

Last edited by LBRC; 2006.09.02 at 07:16 PM.
LBRC is offline   Reply With Quote
Old 2006.09.02, 08:18 PM   #10
locwan
Registered User
 
locwan's Avatar
 
Join Date: Jul 2006
Location: Markham, Ontario
Posts: 274
Quote:
Originally Posted by LBRC
As an additional note by taking out that stock FET induced ½ ohm of resistance both top end speed and runtime are increased slightly at the same time, it’s not much of an increase but the car will literally not only be faster but run slightly longer too. However since you don’t normally run a race at WOT the effect when looked at from the batteries point of view is that the motor is using less of their power to maintain your top driving speed. In other words using less power to maintain your speed not more.

I see. So in fact, with a 2x2 stack of 7317 I'm actually able to extract that last bit of juice from the battery with its lower resistence. This would explain why with standard 3004 fets, the motor will stop responding, but there's still enough power to move the servo. In fact, this is still the case with the fet stack, but only when I'm not keeping the throttle on in the transmitter, even though the motor has stopped spinning.

However, this still doesn't explain why steering input would be slower with the fet stack when the battery gets low, and would even eventually stop responding so long as the throttle is opened all the way. Any ideas on why that would be?

Logically, the first thing that comes to mind is the lack of power from the battery to be distributed evenly in the circuit board. But since the fet stack doesn't "push" the current, but rather is letting current through, is something else on the pcb that's dictating where the current will have first priority when it comes to distribution? If so, why has changing the mosfets on the board changed this?
locwan is offline   Reply With Quote
Old 2006.09.02, 08:51 PM   #11
LBRC
Registered User
 
Join Date: Mar 2004
Location: Northwest
Posts: 550
Since the steering servo takes relatively little power to operate when everything is working correctly, your steering shouldn’t be slowing until the batteries are all but spent, and replacing the stock FETs should have almost nothing at all to do with it. If your steering is slowing while you still have appreciable battery power there is likely something else causing the problem like binding servo gears, debris shorting the circuit board contacts, high resistive short by excess solder touching something it shouldn’t, etc.

BTW since your motor does seem to be running longer at lower battery levels I’m voting for a dead spot being the primary problem. “Primary” meaning the largest of several possible contributing factors, anything form pinion gear spacing to Tx battery power can also act as straws on that proverbial camels back.
__________________
Jungle Outlaw Micro Racing
If the track is wet, then the tent is leaking.
LBRC is offline   Reply With Quote
Old 2006.09.02, 09:15 PM   #12
locwan
Registered User
 
locwan's Avatar
 
Join Date: Jul 2006
Location: Markham, Ontario
Posts: 274
The many "mysteries" of electronics. Very fascinating. Sometimes working on these little things makes me wonder if I should have gotten into electrical engineering.

Back on topic. I'm always thinking about current like water distribution in a network of water supply pipes. Water/current will naturally want to go where there's less resistence, right? If this is the case, will changing the steering fets have some sort of equalizing effect? In fact, this question might be a new topic, but I wonder if upgrading the steering fets to decrease the resistence will enhace servo resonse speed.
locwan is offline   Reply With Quote
Old 2006.09.03, 08:09 PM   #13
ph2t
Registered User
 
Join Date: Dec 2003
Posts: 503
Personally in this hobby I think the power cap is more for stability.

It can help and at times it won't do squat.

the best thing is to get the size right. Go for 6V caps, the smaller the voltage, the smaller the dialectic needed in the cap to hold the charge. Because of this a 6V 1000uF cap will be smaller than a 50V 200uF cap.

I use 1000uF at 6V on my ma-010, mainly to help against a dead spot on a homegrown track we run on. With a longer antenna and the cap it does help in these instances...

The bottom line is practical though. Just test it and see if it works. If it doesn, just piss it off. no more , no less.....

ph2t.
ph2t is offline   Reply With Quote
Old 2006.09.07, 05:06 PM   #14
benmlee
Registered User
 
Join Date: May 2006
Location: Los Angeles
Posts: 375
[QUOTE=locwan]

However, this still doesn't explain why steering input would be slower with the fet stack when the battery gets low, and would even eventually stop responding so long as the throttle is opened all the way. Any ideas on why that would be?

QUOTE]

What LBRC said made good sense. The battery is not an infinite device. As the output current of the battery increase, the voltage drops. How much current the battery put out is a function of the circuit resistance. Having a low resistance circuit means the battery will try to put out more current, and in doing so, the voltage drops. When the battery is running low, voltage might drop enough to slow the steering or stop the steering completely. Imagine if you have a 1 turn motor, you are practically shorting the motor. There would be no voltage to run the steering or other functino. If you put a 100 ohm resistor in front of the 1 turn motor, then the motor would turn slowly, but there would be voltage for other functions.
benmlee is offline   Reply With Quote
Old 2006.09.07, 10:56 PM   #15
locwan
Registered User
 
locwan's Avatar
 
Join Date: Jul 2006
Location: Markham, Ontario
Posts: 274
That was my logic as well. My understanding of what he was trying to explain was this; that with the fet stack and it's lower resistence, the motor isn't drawing more current from the battery, but in fact is only letting all of the current that the battery is capable of producing to reach the motor more efficiently.

With that in mind though, I was pondering of what I asked earlier could make a difference in providing the circuits with a more evenly distrbuted pathway for both the motor and servo.

Quote:
Originally Posted by locwan
..current will naturally want to go where there's less resistence, right? If this is the case, will changing the steering fets have some sort of equalizing effect? In fact, this question might be a new topic, but I wonder if upgrading the steering fets to decrease the resistence will enhace servo resonse speed.
locwan is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
question about a-bbs capacitors... SSJ Char Parts and Hop-ups 1 2004.02.26 08:57 PM
Did I purchased the correct capacitors for my stock motor? Skylineboy Motor Tech 4 2003.03.13 08:25 AM
Capacitors Slonik Motor Tech 5 2002.11.23 08:21 AM
Capacitors Strider- Parts and Hop-ups 6 2002.02.06 11:06 PM
Motor Capacitors... Draconious Parts and Hop-ups 2 2001.12.11 04:02 AM


All times are GMT -5. The time now is 07:29 AM.


Powered by vBulletin® Version 3.8.3
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright ©2011 Mini-ZRacer.com
Mini Inferno Sale - Up to $85 Instant Savings!
Micro-T Hop-Ups
RC18R, M18, Micro RS4, Mini-LST, TamTech-Gear, Minizilla, RC18T, RC18B, RC18MT
shop.tinyrc.com Products

more»
Tiny RC Community News
[03/22/17] MZR was on vacation, didn't... : All kidding aside, the host experienced a bit of a server meltdown last week and efforts to restore the site to a new server took longer than anticipated. The current server is temporary until - more»
[11/25/15] Did You Hear? Our Black... : Hey Racers,
We're getting started a bit early with our Black Friday sale this year.  Generally we're not supporters of retailers opening early on Thanksgiving, but in our case, we're - more»
[06/30/15] shop.tinyrc.com: Have You... : Hey All! Just a quick reminder to everyone that we post all of our shop.tinyrc.com Newletters here on the MZR Forum. If for some reason you miss them in your email inbox, you can always see the - more»
Mini-Z, Mini-Z Racer, MR-02, MA-010
M18, M18T, RC18T, Mini-LST, Mini-T, Micro RS4, XRay, 1/18, 18th scale
XMODS, XMOD, Micro Flight, ZipZaps, ZipZaps SE, Bit Char-G, MicroSizers, TTTT, Plantraco Desktop Rover, SuperSlicks, Digi Q
Mini Inferno, Mini Inferno ST, half EIGHT, 1/16, 16th scale
Epoch, Indoor Racer, 1/43, 43rd scale
E-Savage, eSavage, eZilla, e-Zilla, HPI
Robots, Bots, Bipeds, Wheeled, Manoi, Roomba, NXT, Lego, Hacking
Crawling, Crawlers, Micro, RC, Losi Mini-Rock Crawler, Duratrax Cliff Climber
Kyosho Minium, Caliber 120, Minium Forums
Mini-Z Hop-Ups, Mini-Z Parts, Mini Inferno Hop-Ups, Mini Inferno Parts, M18 Hop-Ups, M18 Parts