Question about motor gearing

[VaporTrail]

I've run TPPower 4050 series motors on 4S, one a 1570KV, the other a 2100KV. I haven't run any crazy gearing on them; the 1570 has been run on 11 through 16T and the 2100KV has been run on 11 through 13T. And that's with the stock 52T spur.

The 2100 is scary to run; geared at 13T it'll easily reach 150, early 160s at the end of a 10min run. The 1570 is a little more sane, but the motor temps can still hit 140+ all the way up to 150+ at the end of a 10min run. The batteries take a big hit too. I've had a 4S 6500mAh pack hit 138 degrees with the 2100 and maybe 128 or 132 on the 1570.

The Kuron motor isn't as brutal; temps will be around the 140+ range for the motor and maybe 120+ for the batts.

I'm always running a fan on whatever motor I'm running, so I'm starting to wonder if my gearing could perhaps be either low or possibly high? I know that undergearing a motor can also result in high temps, so maybe my gearing is too low?

My Shogun is run on a small track; decent amount of turns, maybe a 30-40yd straight. I don't usually brake for the turns, I just let off the throttle and try to coast through the apex and then get back on the gas to power out. It's not full throttle either, maybe about 1/4 to 1/2 throttle.


Am I missing something in this equation? Common sense is telling me that my motor and battery packs should be cooler, but they're not. Which leads me to think that they could possibly be undergeared. I'd love to run the TPPower 2100 motor, but I value my lipos too much to just throw em away by running that particular motor.

What do you guys think?

 

[VaporTrail]

Well, I'm still about 3 weeks out from running again, so maybe I'll slap a 14T on and try again. Hopefully I don't kill another battery.

 

[CCB-MN]

Well, I'm still about 3 weeks out from running again, so maybe I'll slap a 14T on and try again. Hopefully I don't kill another battery.

Hey VT,

I would try changing to the 14 and see how it seems. I’m seeing more and more motor heat questions and concerns lately, nothing brand specific, just hot overall.

Most brushless motors run a little warm but when you’re consistently getting too hot then usually it’s a mechanical reason that’s generating the excess stress on the motor causing the excessive heat output. (It could also be electrical too but that usually shows its head much differently so I doubt it). I would also check anything that could cause friction or binding throughout the drive system.

I’m consistently hitting 140 plus on the Kuron 825’s but that while running 6S and running pretty flat out with my ears pinned back. I do run dual fans on the motor and that has made a huge difference for me but I also don’t push more than one 6S pack through it at a time without letting everything cool off a bit. 4S I can usually get away with 2-3 packs, no real heat issues.

Friction, Tires/wheels, terrain, humidity can all can cause heat build up. I honestly don’t think changing to a 14 will hurt you but you would know soon enough if you give it a shot!

 

[Horatio]

Increasing pinion size when the motor is already struggling temperature-wise is only going to make matters worse.

You have to gear to the track.

If you're only getting 1/4 - 1/2 throttle, you certainly don't want a bigger pinion.

As you use smaller pinions and lower the gear ratio, you can end up with significantly more brutal power delivery coming out of turns and more rapid acceleration. You can tame this using the punch settings.

Overall, your temps should get lower with smaller pinions / larger spurs.

Increasing the pinion size adds load to the motor, which in turn increases current draw and thus the motor's temperature.

 

[VaporTrail]

Hey VT,

I would try changing to the 14 and see how it seems. I’m seeing more and more motor heat questions and concerns lately, nothing brand specific, just hot overall.

Most brushless motors run a little warm but when you’re consistently getting too hot then usually it’s a mechanical reason that’s generating the excess stress on the motor causing the excessive heat output. (It could also be electrical too but that usually shows its head much differently so I doubt it). I would also check anything that could cause friction or binding throughout the drive system.

I’m consistently hitting 140 plus on the Kuron 825’s but that while running 6S and running pretty flat out with my ears pinned back. I do run dual fans on the motor and that has made a huge difference for me but I also don’t push more than one 6S pack through it at a time without letting everything cool off a bit. 4S I can usually get away with 2-3 packs, no real heat issues.

Friction, Tires/wheels, terrain, humidity can all can cause heat build up. I honestly don’t think changing to a 14 will hurt you but you would know soon enough if you give it a shot!

This one slipped through the cracks for some reason. I thought I responded, but....

Ennyhoo...I don't think there's any binding issues; the wheels turn fairly smooth. Maybe there's something in the diffs, but the last time I serviced the diffs, they also felt smooth.

The Kuron I didn't have too much of a problem with heat or amp draw, which makes the situation even more interesting. IIRC the Kuron is a 120A rated motor, while the 1570KV Tp is rated at 125 or 127 amps. Lower KV, not much higher in amps, you would think the temps would be in the same neighborhood, but no.

Then again, I've read that some people say the TP motors can be current hogs. Maybe that's another possibility for heat? Makes me want to sell the motors and go back to Neu.

I may have the chance to run this weekend, so I'll try the larger pinion first and temp maybe every couple minutes.

Increasing pinion size when the motor is already struggling temperature-wise is only going to make matters worse.

You have to gear to the track.

If you're only getting 1/4 - 1/2 throttle, you certainly don't want a bigger pinion.

As you use smaller pinions and lower the gear ratio, you can end up with significantly more brutal power delivery coming out of turns and more rapid acceleration. You can tame this using the punch settings.

Overall, your temps should get lower with smaller pinions / larger spurs.

Increasing the pinion size adds load to the motor, which in turn increases current draw and thus the motor's temperature.

Yes, I would be very inclined to agree with you. I'm still at a bit of an impasse' though. My EB48.3 is running a 3670 size motor that's 2400KV. Gearing is 16/44 with a 3S batt. Temps after a 15-20 minute run are:

Motor: 118-125
Esc: 110-123
Batt: 108-115

To me, that's a bit high on the gearing, but it seems that the electronics are happily buzzing around with nary a care. I'm wondering if the taller gearing will tame down the power delivery a little and perhaps lower the temp because of that?

The Shogun seems to be geared correctly for the track; it has about 15% more to go at the end of the straight in terms of top speed. For torque, it can do a triple with from nearly a standstill; if I were to measure it, it would around 10ft of runway and it'll clear. Interestingly enough, the EB48 can also do the same. I suppose I can adjust punch settings, but I like to train myself to have finesse with my trigger finger.

You're absolutely right on the current draw. I wonder though: will the decreased wheel spin and longer time to reach optimal RPMs help reduce heat? Maybe some sort of balancing out? Heck, I'm even willing to try an 18T to see if it'll limit the RPM range since with that high of a gearing it probably won't even get to it's theoretical RPM rate.

 

[Horatio]

This one slipped through the cracks for some reason. I thought I responded, but....

You're absolutely right on the current draw. I wonder though: will the decreased wheel spin and longer time to reach optimal RPMs help reduce heat? Maybe some sort of balancing out? Heck, I'm even willing to try an 18T to see if it'll limit the RPM range since with that high of a gearing it probably won't even get to it's theoretical RPM rate.

Decreased wheelspin and longer time to reach 'optimal' revs are all indicators that the motor has increased load upon it.

Your motor doesn't care if it has enough torque to overcome available traction. Running on higher traction surfaces will definitely make your motor hotter, because less of the motor's energy can escape through spinning wheels and instead has to propel the mass of the car instead - which is a greater load as the motor is being forced to work harder every time you blip the throttle.

Ideally, your car should be able to reach it's maximum speed on any given gear ratio, as it meets the braking point on the track's longest straight. If your track consists entirely of bends, then apply the same logic to the fastest part of the track.

Constantly having the car where it optimally produces most power would only be helpful at 1 speed in a straight line - and even then the motor would still generate heat because our motors are not 100% efficient and the point where most power is produced isn't where they are most efficient.

So, geeky stuff aside. If your motor gets hot, obviously use fans to help, but also consider using a smaller opinion to lower the gear ratio.

 

[VaporTrail]

That's an interesting graph Horatio...very illuminating. I guess its back to the drawing board to try and figure out why I'm getting so much heat from my low KV motor.

 

[Horatio]

That's an interesting graph Horatio...very illuminating. I guess its back to the drawing board to try and figure out why I'm getting so much heat from my low KV motor.

It's a great graph - things are not as they seem with electric motors.

They're at their most efficient about a third of the way along the power curve.

And they produce the highest torque from the moment they start to turn. No wonder they accelerate so much better than IC engines.

 

[VaporTrail]

Hrmm...a third of the way? Then I guess I've been more or less close to the mark for most of the time. In theory I try to keep the RPM range to around 10K; usually around the 7-8K range and sometimes in the 9K. The 1570 was sitting at roughly 6 thousand-something RPM, which is why I was wondering if it was undergeared.

And yes, electric motors have that awesome clump of torque right from the get-go. My old Neu motor was an absolute beast in that regard. 1515 1.5D/f, 2700KV. On 3S it was notching the diff cups on a Jammin X1 something fierce. And that was also on a 13-15T pinion.

I'm quite tempted to go back to a Neu.

 

[VaporTrail]

In the meantime, I have this little beauty set up at 16/44. 2200KV Hobbywing G2 and a XR8 Pro. I'll see how she does on her shakedown. I may go to a 14T or even a 12, depending on how the batteries take to the load.

 

[VaporTrail]

So about a month later, I finally had the chance to test out the gearing in the Shogun. 15t pinion on a TP Power 4050 (4080 size) 1570KV motor on 4S. The motor has a fan on it. After about a 7min moderate run:

motor: 110
esc: 115
batt: 98

I also noticed just how brutal the Shogun is in terms of power delivery. It's running a MMX 6S esc. Diffs are 20K front, 30K center and 10K rear. She's an absolute bruiser. I think that may have something to do with the 52T spur.

I ran the 48.3 before running the Shogun, and it's smoother in power delivery. That has a G2 2200KV motor, 4274 size with a XR8 Pro esc. Has a 16T pinion and 44T spur. Diff fluids are 20K front, 20K center and 10K rear.

The Shogun is definitely faster, but easier to overshoot the apex and to carry too much speed into the corners. The 48.3 is slower, but rolls through the turns better and rotates better through the turn.

I think I'm going to replace the center diff of the Shogun with the Python's center diff and replace the oil with 20K. I may also replace the TP motor with the Castle 1515 to give the Shogun more/easier rollout and gear close to the 48.3's gear ratio. Then it'll be a matter of seeing how the weight difference plays a role in how they perform. I may lighten up the Shogun's diff fluid in the front and the rear to help it rotate better in the turns. Maybe 15K front and 7.5-8K in the rear; that should help offset the weight discrepancy.

 

[VaporTrail]

I replaced the 52T spur center diff with the 46T Python cente diff. Also went with a 15T pinion on the TPPower motor. Definitely better on the temp ranges for all the electronics.

I do believe the TPPower motor was undergeared after seeing the temps with the 46T spur. Next up is to try a 4274 motor and maybe drop the teeth on the pinion to 13. That should make all the electronics buzz along quite happily.

In the meantime, I have this little beauty set up at 16/44. 2200KV Hobbywing G2 and a XR8 Pro. I'll see how she does on her shakedown. I may go to a 14T or even a 12, depending on how the batteries take to the load. View attachment 5409

And regarding this little beastie...I nailed everything all nice and proper. After about a 10min race-paced run, her temps were pretty good.

Motor: 116
Esc: 138
Batt: 105

I do believe that she's ready for the competition. Handles as smooth as butter and floats through the jumps. The only thing that messes up on her is driver input. Aside from that she's golden.