So I have a 260kv motor, a 10s3p pack and a VESC. Using the following formula… 260KV x 42.0V x 7 = 76440 ERPM …I come in way over the 60k ERPM limit. I assume if I limit the ERPMs in the BLDC tool I will be ok. What are the other implications of using a motor with too high a KV but limiting the ERPMs?
I’ve heard that motors are most efficient around 80% of the no load RPM so limiting the ERPM would essentially be cutting off part of the most efficient RPM region.
I have been ruining 270kv on 12s and limiting the erpm to 60k.
With 4:1 gearing and 97mm wheels top speed is around 33kph. But I got a bit board of that and ran 65k erpm for about a week before I changed my gear ratio and went back to 60k erpm limit.
It seemed to work fine just be sure to un-click limit ERPM with negative torque as this will apply brake above 60k. And bench test before riding. With negative torque on it will shake a lot a max rpm as it cuts in and out. It should be smooth at max rpm. Also you can add soft limit aditionally in the PPM tab. So you can do 55k start 60k end.
The only strange thing I found is going over a small crest at full speed you notice a dropoff in power on the down hill part of the crest, just feels a little funny but does not put balance off.
The high rpm motors can be run at higher voltages but you have to be careful not to over load them. Use a gear ratio that gives you a modest top speed will lessen the load on the motor and monitor the temp of the motor for a while. Limiting amps in the vesc can prevent overheating but also reduces performance.
no, most motors have the same voltage range. 10-12s. but higher kv can take more amps, power, speed.
but lower kv gives you better torque, with less amps, and less heat.
@mmaner it will work, but a motor </=200 kv would have better torque, easier to find gearing, less amp draw on your batteries. better noise i have a 85kv, 149kv, 200kv, and 245kv. and I like them in that order. lol
Here’s a relevant blog post by Vedder about it.
http://vedder.se/2014/10/chosing-the-right-bldc-motor-and-battery-setup-for-an-electric-skateboard/
@lrdesigns @saul @NickTheDude I appreciate all the info, not sure I’m actually going to do this build. I just have some of the parts so I figured I’d check. I’m currently running x2 190kb motors and it’s great.
I forgot to mention, while it does work the biggest downside was 4:1 gearing 12-48 The 12 tooth pulley wears out really fast and puts a lot of stress on the belt. And wheel pulley is huge so its close to the ground and gets hit by rocks etc.
My 270kv motor is “rated” for 6s yet I run it at 12s, which is fine for the motor so long as the overall power draw in watts is below its designed maximum the motor will not over heat. With vesc we have built in amp limits which also prevents the motor from over heating. The physical rpm limit for these motors would be over 20,000 rpm. But the erpm limit of the vesc means we can only go as high as 8500 rpm.
Motors do have an amp limit, but the voltage limit is not that important provided the load is within its power rating.
But I agree that the lower the KV the better for electric skateboards.
@mmaner I believe that this is true, but be careful revving the motor while it’s on the bench with zero load if you use FOC mode. I’m fairly certain that I fried a DRV chip this way, despite having the ERPM set (and having an optimal KV\battery config).
Aww dude, that sucks. I played with FOC for a min a few months ago. I wasn’t that impressed so I went back to BLDC. I’m a little scared of FOC, maybe when VESC 6 comes out it’ll be more reliable.
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@mmaner Now that I’ve wrapped my head around it I really love FOC and use it exclusively; just make sure to use caution on the bench w the throttle testing haha.
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Copy that. I have 2 MEB VESCs and 1 DIY VESC. @oriol360 hasn’t run FOC on his so I don’t wanna be the 1st. I’m not sure which revision of the DIY VESC I have, so u til I figure that out I’m gonna wait.
I’m thinking about a couple maytech VESCs, maybe try this in FOC.
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I’m sorry to dig up this old thread on you Mike.
I’m swapping parts around getting ready for my new redember build. So I’m left with a 12s3p from diy, 2 x 230kv motors, 2 x focbox’s and a 16/36 ratio on 83mm wheels.
You have a lot of experience here so I didn’t want to create a new thread. Did you have any ill effects from your setup in the first post? Just limit the erpm in bldc tool to 60,000 and don’t use negative torque. When no negative torque is used how does it react? Any other settings?
Cheers and thanks for any insight here.
If you limit the ERPM’s and dont run up the throttle too much without a load you should be good. The motors wont be very efficient, but it should work.
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Ok, thank you for that. I’ve never been a fan of squeezing the throttle much on the bench. I think I will throw my metr module on it so I can watch the draw. Then keep an eye out for heat build up on the motors.
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