bemoore

2009.03.03, 02:25 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.

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.