Do electric motors "warm up"?

[alvinlwh 5895]

10 minutes ago, El Gecko said:

I still think there's more going on here than we realize, or possibly a combination of things. Bearings/etc. loosening up, batteries warming up, crud getting blasted off the brushes/comm, tires warming up, all these I think could be factors here. Possibly each one is only very slight, but altogether they have a big effect. Or it could be a kind of feedback loop or chain effect, where one causes another to release.

Any or all of them could be factors. I threw this question out there just because I am curious. What I am most intrigued about is the speed seems to be faster than calculated based on gear ratio and KV, which does not take into account of drivetrain friction, air resistance, etc... Sometimes significantly so. 

[El Gecko 1344]

1 hour ago, alvinlwh said:

Any or all of them could be factors. I threw this question out there just because I am curious. What I am most intrigued about is the speed seems to be faster than calculated based on gear ratio and KV, which does not take into account of drivetrain friction, air resistance, etc... Sometimes significantly so. 

Hah, the first time I read your first post I thought "no way that's mph, he's gotta mean kph" but yeah, that super top speed is definitely the strange part here. Looking back through the thread, the only thing that jumps out at me is @M 800STD's mention of Lipo having higher discharge rate when warm. Have you tried running the cars with NiMHs just to see if there's a difference? I know the top speeds will be overall slower than lipo, but it would be interesting to see, in the same exact cars, if the grouping would be closer, or if the behavior would continue.

[alvinlwh 5895]

27 minutes ago, El Gecko said:

Have you tried running the cars with NiMHs just to see if there's a difference?

I will try but NiMHs will not fit in some of my cars. 

27 minutes ago, El Gecko said:

Hah, the first time I read your first post I thought "no way that's mph, he's gotta mean kph" but yeah, that super top speed is definitely the strange part here.

I too was suspicious of the reading, which is why I checked it on different days, and checked the GPS against my 1:1 car. 

27 minutes ago, El Gecko said:

Looking back through the thread, the only thing that jumps out at me is @M 800STD's mention of Lipo having higher discharge rate when warm.

Looking back at the thread, his reply had been edited since I first seen it. The original reply was just one word, "Lipo". However, while not discounting the possibility of it getting warmer, it is more likely it actually get colder due to the outside temperature. The battery went from >20C to <10C.

On 3/18/2022 at 11:04 PM, MadInventor said:

In full size EVs. battery performance is degraded if the battery is very cold.  I know it's cold in Scotland, but that cold ??????

Also, after 10/20 minutes of running, I expect the voltage to have dropped not increased. 

[MadInventor 3884]

Are you in a position where you could measure the speed manually ? Before I got a GPS, I measured out a 50m run and then timed the run through the 'box', firstly using a stopwatch, then afterwards with a borrowed car mounted GoPro and using the timestamps on the frames to determine the amount of time it took to cover the distance. This would perhaps be a more consistent measurement than using a GPS.

 

[alvinlwh 5895]

43 minutes ago, MadInventor said:

Are you in a position where you could measure the speed manually ? Before I got a GPS, I measured out a 50m run and then timed the run through the 'box', firstly using a stopwatch, then afterwards with a borrowed car mounted GoPro and using the timestamps on the frames to determine the amount of time it took to cover the distance. This would perhaps be a more consistent measurement than using a GPS.

At this moment, not really. I am however looking for tiny camera (spy?) that I can maybe mount on the car, and then count frames. Not sure if that will work as video editing kind of beyond me. Also, whatever equipment I have or get, the FPS might be too low for this purposes. 

As I said earlier, I had checked the GPS against a real car and it seem to be reasonably accurate. If readings seem way out of the expected range, I will do more runs, on different days to see if it is repeatable and to eliminate GPS errors, which happens time to time. . 

Mind you, I am not looking to enter the official Guinness Book of Records or anything, I am just trying this out for fun, mainly on silver cans. Elsewhere, I had said that my objective is to melt the silver cans, while seeing how fast I can push them. It also gives me an opportunity to test out a heat sensitive fan and report the result to another member interested in it. 

[M 800STD 586]

Cell temp not ambient temp.

[alvinlwh 5895]

13 minutes ago, M 800STD said:

Cell temp not ambient temp.

Will ambient temp, if low enough, not lower cell temp? 

Also how about voltage dropping after a 20 minutes run? The cell temp increase can compensate for this, or even push voltage even higher than at the start?