Methods of Limiting power output
 

Hello all,

I won't bore you with explaining why I want to do this. I'm just going to ask how I can do it. I would like to severely limit the power output in my TC. I need to do it in a way that will keep ESC/Motor temps low.

Here is my thought process so far:

1.) My first idea was just to drastically over-gear the car for the track I am on, thus bogging down the motor, and providing poor acceleration. After a few searches, I realized this was a really bad idea and would cause high current draw, and overheating.

2.) My second idea was to just get a smaller brushless motor (like a 380 can) but again I think this is probably a bad idea. I assume the weight of the 1:10 TC would put a strain on the little motor, and again cause High load and excessive current draw.

Does anyone have any thoughts/experience on putting an under powered motor in a heavier car than it was designed for?

3.) I have a Tekin RS Gen2 ESC, and I discovered it has a Current limiter feature. I thought this would be a good idea because I could gear the car properly for the motor's "sweet-spot" and then use the current limiter to prevent the motor from generating it's potential torque. After a few searches though, it seems like there is more to Tekin's current limiter function. There was mention that it only limits during low-speed/high throttle, that it only limits for a few seconds, and other things... I don't know how much truth there is to any of that and the Tekin website doesn't have much info on it.

Can anyone confirm the specifics of the current limiter function? Also, would using this cause the motor to run hotter, cooler, or no difference? I am guessing cooler. Also, does the current limiter not apply to braking/decelerating? I assume not, since this would be a big disadvantage.

4.) I really don't know why this was my last idea, but it's looking like turning the travel down on the transponder for the throttle might be my best option. Please correct me if I am wrong, but this is what I assume happens in this scenario: If the travel is set to 50%, than pulling the trigger to the full throttle position gives 50% power. Pulling the trigger half way back would give 25% power. I hope this is accurate. If pulling the trigger half way back gives 50% power, and the last half of the pull just maintains 50% power, that seems like it would make the "feel" very bad.

Thanks in advance for any tips or suggestions.

The last method is DEFINITELY the best one, & yes, your assumption on it are basically correct. By limiting the throttle end point(say to 50% of max, like you mentioned), then full travel on the throttle trigger(or stick, for stick radios) will give you 50% of the actual max, & it should definitely allow the electronics to stay cool....:cool:

I'm assuming that when you said "transponder" you meant "transmitter". :) Grizzbob is correct, this is definitely the way to go! It works well, costs nothing, and lets you change the power to match the track and driver ability.

The motor's power output is not a linear function of the end point setting. 50% endpoint doesn't give 50% power. But that doesn't affect what you are doing; just set the endpoint to what gives you the desired result.

Regarding the Tekin current limiter: Send them an email with your questions. Tekin's customer service is excellent, and Randy often posts here on RCTech (although email guarantees that he will see your questions).

Just to point out that you'd need to setup/calibrate the esc to 100% end point first prior to reducing the end point to 50% or whatever you desire otherwise the esc could detect that 50% as full throttle if you set the 50% prior to calibrating the esc!

As I understand it the current limiter just limits the initial current that can be supplied to the motor. It's a kind of traction control used mainly in off-road applications to reduce initial wheelspin. It doesn't affect anything at full throttle. I have the same speedo in my 2wd buggy and use it this way with good results.

Yup, as stated above just turn down the end points on the radio. I do this all the time with my kids.

Thanks all for the responses. I do have a follow-up question though about turning down the throttle endpoint. Since the ESC is digital, even when the throttle is set to linear, it's not really linear (more accurately it's a series of steps, like stairs.) The smaller the steps, the "smoother" the ESC feels. If I adjust the endpoint to 50% throttle, will the smoothness remain the same, or will it effectively cut it in half? I am guessing it will cut it in half, and make the throttle a little more "Choppy" kind of like the old analog ESCs were, but obviously not that bad. My assumption is based on the fact that the transmitter will be trying to "stretch" half of the ESC's throttle map over the entire range of the trigger pull.

Yep. No clue why I said transponder lol.

I honestly don't know. But I've turned down some low turn (5.5) motors in my 4wd buggies by about 40% and never really noticed a real change in "smoothness".

I'll ask this. If you're looking at turning down the EPA by 50%, is that driver going to notice a difference in feel? Aren't you doing it to help them learn throttle management, not worry about feel? "Feel" comes after throttle management in the learning curve, IMO.

Correct. I've got a 6.5 turn in my wheeler and on small tracks I can't go any more than 75% throttle EPA or it's too much of a handful LOL. But to me, it actually feels smoother

The power increment per ESC step size will remain unchanged, but the reduced number of steps will be spread over the full range of the trigger movement, as you stated. (If the radio is digital, then the number of steps it generates will be decreased, also.) It depends on what ESC and radio you are using, but I'd guess that if they are relatively new, the step size (and therefore the power increase per step) will be small enough that you won't feel them. Let us know when you try it!

Well, I took the throttle travel all the way down to 35% and have been running it on a very small track for a while now. Maybe a better driver would say otherwise, but the throttle response does not feel "choppy" at all to me. I am sure it is, but I sure can't perceive it.

That's good news. Thanks for letting us know how it turned out!

When my kid drives my m-chassis on my tiny track I dial down the throttle EPA to about half. I drove it a few times with that setting and it was smooth.

But then, I come from the 3speed mechanical speed controller days..:rolleyes: smoking hot resisters and all...

Haha, yep. I had an rc10t with the TC conversion kit when I was a kid. It had a mechanical speedo with only like 8 or 10 metal contacts.