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bemoore
2009.03.03, 03:25 PM
I'm searching for a motor with performance similar to Kyosho's Eco, and I thought I'd try looking at 1/32 scale slotcar motors (my other hobby). But I'm having trouble understanding some of the test data I'm finding for various motors. I'm an electrical engineer, so I understand the parameters, but some of the motor data on Atomic's site doesn't make sense to me. RobinZ compiled a lot of the data from Atomic and provided the following charts:
http://farm3.static.flickr.com/2165/2483879727_c3eeeb70f6_o.jpg

So I went to Atomic's site & grabbed some of their data. I really like the looks of their data, because it looks like the motors were tested over the entire RPM range, as opposed to measuring a couple of points and connecting them with straight lines. But lets consider the Kyosho stock motor. Atomic's data shows that the no-load current draw is 2.54 amps (at 15601 RPM), and 7.04 amps at 732 RPM. That's WAY above what everone else is reporting, which is around 0.45 amps. Also, their torque measurements have the units g/cm. I don't understand this either. Torque should have units like g-cm, N-cm, in-lb, in-oz, etc. It should be a force (or weight) times (not divided by) a distance. So, I assume that the units are g-cm, and so I created a formula to convert to power (Watts). My power calculations don't match Atomic's numbers. My calculated max is 4.47W (at 11764 RPM) and Atomic's is 10.73W (also at 11764 RPM). Given what I've seen from 10W slotcar motors, I feel that the Kyosho motor is not that powerful. 4.47W sounds more realistic, but since slotcars are considerably lighter, it's hard to do a direct comparison. In addition, my power calculation formula agrees with measurements I find for slotcar motors. Here is a table for a slotcar motor:

http://slotcarillustrated.com/portal/forums/picture.php?albumid=79&pictureid=745

This table shows a peak power of 18.72W at 15000RPM. My calculations show a peak power of 18.85W at 15000RPM.

Can someone explain the numbers I'm seeing? Is Atomic using some units I'm not familiar with? Atomic has the best collection of motor data I've found, so I'd like to be able to use it.

Thanks.

RobinZ
2009.03.18, 05:40 AM
Hi,
indeed, there is something with the data;

- I checked the Power with an assumed Voltage of 4 AAA batteries and the given current and efficiency and arrived at power figures about half the Power values given in the tables (of which you think it should be more realistic). I used P=U*I*efficiency. In fact there is a factor of about 0.45 which could indicate an error with pounds vs kg or the factor 2 in the calculation of the angular speed (2*Pi*n), but Im not sure.

-the unit g/cm is wrong; probably g.cm was meant. Using this torque and the given engine speed 'n' I also arrived at Power values about half the ones given in the table and which approximate the one as calculated with the formulae above using current and voltage.
(P=T*2*Pi*n)

It still is very nice data for those who want to compare performance specs.
Thanks Atomicmods!

best,
RZ

bemoore
2009.03.18, 08:20 AM
I've found g/cm used for torque in a number of places, sometimes by people (or companies) who should know better. I've even seen it printed on a motor.

I agree that the Atomicmods data is nice, and I strongly suspect any inaccuracy affects the data for all the motors, not just some. That makes the data fine for comparisons to other motors in their database. However I was trying to compare them to slot car motors, and the data isn't as useful in that case.

Cherub1m
2009.05.02, 01:13 AM
Does anyone know the specs on the new Atomic Standard (World Cup spec US) motor?

Like how many turns it is. It sure dont feel like a 70 turn motor, that motor is very fast.

Cherub1m
2009.05.04, 09:43 PM
Does anyone know the specs on the new Atomic Standard (World Cup spec US) motor?

Like how many turns it is. It sure dont feel like a 70 turn motor, that motor is very fast.

Can anyone give an answer to this and back it up with a reference :D

color01
2009.05.04, 11:42 PM
I've had Philip(PN) take a look at it, it's a low-50-turn motor. Hence the speed. ;)

Cherub1m
2009.05.05, 08:01 PM
I've had Philip take a look at it, it's a low-50-turn motor. Hence the speed. ;)

Ah I see, thanks color01. I've also heard that atomic armatures are short stack. If I understand correctly a 50 turn short stack verses a 50 turn regular armature the short stack will be faster due to less wire.

color01
2009.05.05, 11:26 PM
I think most machine-wound motors are short-stack... I don't recall the Atomic USA armature looking any shorter than the PN Stock armature.

Long armatures are more often found in handwound motors, to get a bit more torque out of the arm for a slight speed loss. But yes, shorter armatures will spin faster for the same number of turns.