How should the VESC "feel" on a board?

General topics and discussions about the VESC and its development.
benjamin
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Re: How should the VESC "feel" on a board?

Postby benjamin » 29 Dec 2015, 13:50

The acceleration (torque) that you feel is directly proportional to the motor phase current, so you can't compare it by measuring the battery current or the power level (current * voltage). At the given power level on your 10s setup you were probably going faster, which is why the power was higher for a given torque.

The motor current is always higher than or equal to the battery current, and the slower you go the higher the motor current is compared to the battery current. Based on what you report it looks like everything is behaving correctly, and it looks like the ezrun ESC has no way to limit the current and only operates in duty cycle mode (as expected from a hobby esc). Based on the resistance of your motor and the battery voltage, the current can reach 1000A or more from a standstill if you give full throttle and the battery resistance is low enough. This will give more torque, but it is not efficient and wears out the components.

You can increase the current limit a bit more on the vesc if you'd like, but I wouldn't run that motor on so high currents since it can cause problems for the tracking algorithm and damage the vesc.

Regarding slowing down in hills, I would expect that since your setup is geared for 50 km/h and you have a single motor (assuming you have 83mm wheels). 245kv is a bit high for the VESC and that motor size, so that is why it will overheat and limit the power. Some things that you can do are:

* Change the gearing (this is the best option since it will give you more torque without using way too high currents).
* Decrease the motor kv.
* Add cooling to the vesc (the motor will probably overheat in long hills with your setup, so this is not optimal).
* Change to a dual motor setup.

rogerd
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Re: How should the VESC "feel" on a board?

Postby rogerd » 29 Dec 2015, 15:37

Thanks Benjamin. I did some more testing just now. I decreased the battery cut off limits as they were too high, which improved things a bit.

I'm on 100mm wheels so geared for around 38mph.

Going slightly down hill the board felt nice and the max FET temp was around 78. Coming back up the "very gentle" incline it hit around 95 degrees and the top speed was severely limited - assume the temp protection was kicking in.

I assumed that on 6s with 16-42 gearing which worked very well (24mph on the flat and not far off the same up hill), that going to 10s and dropping down to 15-42 gearing would be fine and add on a chunk of top speed, but it seems not.

I'll have to rethink this a bit. I can't really justify going dual motor - it's a heck of a cost increase.

rogerd
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Re: How should the VESC "feel" on a board?

Postby rogerd » 30 Dec 2015, 16:39

What do you think of this? trying an SK3 6734 192kv motor - going down from a 245kv motor.

My calcs less me on my current setup that will bring the top speed down from 38mph(61kph) to 29mph (around 45kph). A drop of around 24%

I could go lower again but it would bring the theoretical max speed down to 23mph which is what it was before I jumped from 6S to 10S! so I don't really want to do that.

benjamin
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Re: How should the VESC "feel" on a board?

Postby benjamin » 30 Dec 2015, 20:34

That motor would probably generate about half as much heat for a given load on the vesc since there is a square relation between current and heat generation, so it should help a lot. There will probably be some hills that are too steep even like that if the vesc is in a closed box without cooling and it is warm outdoors, so maybe you can try to find some way to transport heat away from the MOSFETs. (E.g. some air flow or some kind of heatsink).

If you are light it might work well in steep hills anyway.

arvidb
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Re: How should the VESC "feel" on a board?

Postby arvidb » 01 Jan 2016, 15:41

Since mechanical power is speed times torque, for the same output torque on 10s as on 6s, keeping the power constant, you need to gear down proportionally (i.e. by 6/10).

You can do that by going to a ~150 rpm/V motor, or dropping from a 16T pinion to a 10T pinion, or a combination thereof. A 13T pinion with your 192 rpm/V motor should give you the same torque and top speed as you 6s setup, at the same power (192/245*13/16 ≈ 6/10).

Also, as benjamin said, in contrast to the hobby ESCs out there, the VESC is aware of the amount of current going to the motor and will limit it to the set max value. So you should get a gentler, more controlled acceleration with the VESC, the level of which determined by the current limit you have configured.

rogerd
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Re: How should the VESC "feel" on a board?

Postby rogerd » 28 Jan 2016, 09:48

Update: SK6374 192kv motor installed (was 245kv) and reduced from a 15t to a 14t motor pulley and the board now pulls like a train! Thanks guys.

arvidb
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Re: How should the VESC "feel" on a board?

Postby arvidb » 29 Jan 2016, 02:27

Thanks for the update! It's one thing to make theoretical calculations, and another to hear that the result actually works in practice. ;)

duggyboard
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Re: How should the VESC "feel" on a board?

Postby duggyboard » 08 May 2017, 03:01

Sorry to dig this thread up.

I've noticed an identical thing in my own scooter with similar set up (sk3 6374 192kv, 12s 5.2ah multistar lipo). The take off is very gentle for a motor of its size and at maybe 20kmh it has a significant hit of power that throws you off nearly every time.

I figured it was some kind of cross over point where the current the motor is drawing dips below the VESCs motor current limit giving the setup its full power. What do you think? The take off is a little disappointing for a huge motor on 12s.

Thanks!

Hummie
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Re: How should the VESC "feel" on a board?

Postby Hummie » 09 May 2017, 06:44

Duggyboard Sounds like you should decrease the battery amp max and put the motor amps up.
Vedder why recommend only 90 motor amps for a 63mm motor and not up to 160 if people want low speed power? Maybe the original poster would've been happy with his 245kv version and original gearing with the higher settings no?

rew
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Re: How should the VESC "feel" on a board?

Postby rew » 09 May 2017, 08:09

The VESC will overheat at 90A, and even faster at 160A. So you could put the motor max at 90A, so that you can have short bursts of more power for small hills and stuff like that. But for a long hill or continuous fast moving, the VESC will overheat. Other ESCs will then release the magic smoke, but the VESC will try to reduce the power level to a point where things remain safe.

I don't think that putting the motor current limit at 160A is a good idea. The theoretical max current that can be measured is 160A. That's peak value. Setting the motor current to 160A RMS means an even higher peak value. Not being able to measure the current in those regions means that control algorithms and protections break down.


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