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Old 01-11-2005, 07:38 PM   #1
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Default (same thread in rookie zone) Setting up a car for vehicle dynamics research

Hi, everyone. Sorry to repost, but this forum seems to get more traffic than the rookie zone.

I am a mechanical engineering student and am specing some components for a car to be used in research at my university. I am totally new to RC cars and would like some advice. I know what I want to achieve, but having no experience with these motors, I do not know how much of a difference in performance I could expect to receive from different motors.

The car we are using is an HPI Super RS4. It's big, but it has to be because it will be loaded with some sensors (and an extra battery pack to power them) as well as a relatively large weight which may be adjusted to give us control of the location of the vehicle's center of gravity. The guys who used the old car last year complained that it accelerated too slowly. The new car will be just as big and heavy, so I need to improve its acceleration performance. Here's the old setup:
Trinity Midnight 2 27-turn motor (can't find torque numbers or dyno charts for it anywhere)
Sanyo 2400 6-cell Ni-Cad battery packs (2)
Futaba MC230CR ESC

I'm not sure what the output gear ratio is. I didn't have time to count the pinion teeth, although I imagine the spur gear is an 81 since that seems to be the most common size.

From what I have read, more turns means better acceleration. 27 is already a lot of turns, so should I bother trying to find anything higher? Would moving to a 36 offer a noticeable improvement in acceleration, given the huge (by racing standards)weight of my car? How about if I go to an 8.4V battery pack (or even 9.6 for that matter)? How quickly will the extra voltage damage the motor and ESC? How much can I gear down the motor before I burn it out? We don't need the car to run for long in our experiments, and it won't be used in all that many tests, either. Better still, we're on a pretty good budget, so if I need to replace a cheap stock motor, that's no big deal.

I know there were a lot of question marks in there. Sorry for that, but I have never dealt with this equipment before and don't have time to learn by trial and error. Thanks in advance for your help.
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Old 01-11-2005, 08:17 PM   #2
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More turns equals more torque and better efficency. Less turns equals more rpm and a little less torque but more overall power.

I would look for a 19turn spec motor and then gear it down to get the acceleration back. This will produce overall grunt over the 27turn "stock" motor. Not sure how much motor that esc will handle though.
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Old 01-11-2005, 08:34 PM   #3
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Im not sure what data you guys are looking for eg. cornering,accel, ect.. The 19t will be faster than a stock motor in both aspects of speed and acceleration as will a 12 turn motor assuming it geared properly. You cant pull the pinion off the stock motor stick it on the mod and assume it will accelerate without burning up you will have to gear it lower to make up for the lack of bottom end but remember more RPMs more speed. You can pick up an economical mod or 19turn spec motor cheap but check your speedos specs for motor limit and cell limit first, im not sure on the futaba.
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Old 01-12-2005, 08:48 AM   #4
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Gearing for any motor is pretty much trial and error, you want it to top out near the end of the longest straight. After that you can fine tune it. A brushless setup might be your best bet for torque. How many accelerometers will there be?
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Old 01-12-2005, 01:02 PM   #5
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Default Re: (same thread in rookie zone) Setting up a car for vehicle dynamics research

Originally posted by AUengineer

The car we are using is an HPI Super RS4.
Trinity Midnight 2 27-turn motor (can't find torque numbers or dyno charts for it anywhere)
Sanyo 2400 6-cell Ni-Cad battery packs (2)
Futaba MC230CR ESC

AUengineer- The Futaba MC230CR is limited to 20 turn motors (95A max fwd amps/45A max rev amps). I would stick with a 27-turn stock motor so you don't fry your ESC. The Midnight 2 is a high RPM stock motor (about 30K RPM), don't gear it too high because you will be adding extra weight that will draw more current during your testing. The 2400 mAh packs you have are good and will do the job (don't add or remove cells, you will kill the ESC that way). From what you posted your equipment will be fine to do these tests. Good luck.
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Old 01-12-2005, 02:12 PM   #6
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Another ME! Excellent. What school do you go to? What year are you in? I graduated with my BSME in '97 from New Jersey Institute of Technology.
I'd love to hear more about your research and what some of your goals are. Any way I can help, I'd be glad to lend a hand.

For starters, I would try to source a new ESC and a motor and try to pump some more voltage through it. You can pick up a used ESC with very high current capability for around $30 (I bought a used Novak TC2 for $30, which can run virtually any motor and use 7 cells). A used machine wound modified motor in good shape should also run you no more than $10-$20.
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