Mini dyne setup

Discuss hardware related to the VESC such as the NRF nunchuk.
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Joined: 15 Apr 2017, 00:33
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Mini dyne setup

Postby elux » 19 Apr 2017, 23:52

I mentioned a mini dyne setup that I have and I've received some questions about it so I thought I'd post it here so others can benefit from it.

It's kind of an embarrassingly simple little setup. The key is the little flex coupling (uxcell Motor Shaft 8mm to 8mm Joint Helical Beam Coupler Coupling D18L25, less than $8.00 on Amazon). A couple of little L brackets and the some careful alignment and you're good to go. The load is three power resistors that short the three phases of the load motor together. With a cheap current clamp and volt meter you can learn a lot about the motors with this setup. I also have a raspberry pi computer to run VESC tool to monitor the VESC.

These motors can be really dangerous and I cringe every time I see Benjamin holding a motor in his hand to test it.

Here are some pictures.

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Re: Mini dyne setup

Postby arvidb » 20 Apr 2017, 17:36

Thanks for describing your mini dyne! :)

How do you use it in practice? What kind of measurements can you do with it?

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Re: Mini dyne setup

Postby Quezacotl » 20 Apr 2017, 20:29

Never thought of that :shock:
Far easier to simulate the load than actually riding. It's still harder with my e-bike hub motor though.

What kind of measurements... You have a known load, and you can tune for it to perform optimally on that specific load. I would try with max load measured with my normal ride.
Adjustable load would be good, but that adds cost.

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Re: Mini dyne setup

Postby rew » 21 Apr 2017, 06:15

Yeah. I always wanted to add a VESC on the second motor, and then have it run an "application" that sets the current contrary to the current movement direction, and in proportion with the speed, square of the speed, or cube of the speed (or in between?).

constant. (this happens in real life when friction forces are the main thing).
proportional with speed is what you have now.
proportional with the square of the speed is what you get when driving a propellor.
proportional with the cube of the speed is what you get when biking for instance, when wind resistance is proportional to the square of the speed. XXX not true. The power is proportional to the cube, the braking force (current) is proportional to the square.

Anyway, with the "arbitrary power" you can simulate real-life scenarios, but also some things that do not happen in practise.

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Joined: 15 Apr 2017, 00:33
Location: Detroit

Re: Mini dyne setup

Postby elux » 23 Apr 2017, 20:02

The set up shown has 4 ohm resistors which limit the power to to a level that my little power supply can handle so it's really a light load. I also use 1 ohm resistors which will allow higher current and much more power. For that setup I use the batteries to power it and the power supply to charge the batteries.

The phase resistance of the motor is 0.028 Ohms and the phase resistance of the load is either 1 or 4 Ohms. If you measure the current then I^2R gives you the power lost in the copper (P = 3*(1 +0.028)*I^2) the iron loss is small, but you can estimate it if you like. With the known loss and the speed you can calculate the torque of the motor (T = P/(RPM*(pi/30))). If you disconnect the load and measure the phase to phase Voltage you get the back EMF of the motor (back EMF gives you the permanent magnet flux linkage). In this case it should be near the 192 RPM/Volt advertised for the motor, but there's nothing like measuring it for yourself.

You can connect a second VESC to the load motor and operate it in speed control mode. You will need to operate off a battery for this setup so it can absorb or deliver power as needed. Run both the load motor and the motor under test from the same battery. One motor will be generating and the other will be motoring so the battery only has to make up the sum of the losses. You can connect a small power supply like the one I have to support the battery state of charge. This can be a tricky setup and there are many things that can go wrong resulting in failure of either VESC and/or battery so please be careful if you try this. The passive setup shown above is much easier and it can be useful for learning about the motor or playing with VESC software .

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