Team Nuts' Build Diary

[Rapidrory]

So, as some of you may have seen from the team Nuts facebook group (https://www.facebook.com/nutsrobotics/), I've been working on creating a suitable sensorless brushless drive system for the heavier weight classes (researching motor tech and control seems to be the main aim of Team Nuts these days :L). The advantages of brushless are obvious: Lighter, smaller, and cheaper than equivalent brushed motors, as well as there being a wider range available. The issue has been that brushless ESCs are unable to run these motors at low speed, and struggle to start them turning whilst under load. This means that the motor has to be much more powerful than needed, and that low speed control is often lacking.

Alex and I had been experimenting at flashing a TZ85A with SimonK firmware. This had better low speed control than the Trackstars that had previously been used, but still lacked start up torque. It's viable as a cheap option for featherweight drive, and there's still some tweaking to be done with the settings, but probably not going to cut it for heavyweights.

We were then pointed to VESCs, an open source ESC developed in Sweden by Benjamin Vedder ( http://vedder.se/2015/01/vesc-open-source-esc/). His ESC makes use of current sensing and a much more powerful processor to make a sensorless brushless motor act almost exactly like a brushed motor; low speed control and plenty of startup torque, as well as many many other cool features he has added to these controllers.

The standard VESCs are spec'd for 50A @ 50V, fine for a feather but slightly low for a heavyweight. As it is an open source design, I tweaked the PCB layout slightly to increase that current rating up to around 100A, allowing motors like NTM5060s to be used. I got 30 of these PCBs made, and put two of them together over Christmas.

During all this, I had a very generous donation of Foxic 1's chassis from Craig, which I plan to use as a test bed for brushless drive in heavyweights. I also bought a pair of ~2.5KW NTM5060s to use as the drive motors.

I created some test videos of the VESCs, as can be seen below.



I also borrowed Olaf off of Chris (Shakesc) to test them in. Unfortunately i managed to kill one of the chips on the VESC the day before, and didn't have any spare so had to run one motor off the VESC and one off the TZ85 with SimonK.



Once the TZ85 with simonK gets moving, it can be seen to handle similarly to the VESC, however the first and last clip shows that it struggles to start the wheel moving under load, whereas the VESC powers through, even with ~60kg piled on top.

My final uni term starts in a week, so I'm not sure how much time I'll get to work on these. My plan is to get a few made and out for testing (I have a few beta testers lined up), so hopefully they'll be able to find any bugs or work out the best settings without me having to put too much time into it.

It's all looking very promising so far though!

[adz600]

Great work brushless heavyweight would be very interesting to see in action