Startup torque with other ESC firmwares

Support for creating custom user applications on the VESC.
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mt37
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Joined: 09 Jun 2016, 06:25
Location: San Francisco
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Startup torque with other ESC firmwares

Postby mt37 » 09 Jun 2016, 06:51

I'm using a small BLDC motor (cheap a2212 that comes with its own unlabeled ESC for ~$10) for an application that requires as much startup torque as possible.
Since it's a pretty relevant topic to motor control in the context of e-skateboards, I headed this way and read Benjamin's article on startup torque and the tricks that can be used (I have to admit, it's quite a bit over my head so far).
Before investing in a VESC, which is quite expensive for tinkering. I was debating if I had other option. Namely :

1. Flash simonk onto my unnamed atmega8 ESC, possibly hack the firmware to replicate sensoreless BLDC startup torque features.

2. Try to implement my own Arduino based ESC [1] with added hall sensors to improve startup torque.

Any help or relevant links on both topics would be appreciated!

Thanks,
Matt


[1] http://www.instructables.com/id/BLDC-Mo ... -HD-motor/

Shack
Posts: 7
Joined: 03 Apr 2016, 11:58
Location: Denmark
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Re: Startup torque with other ESC firmwares

Postby Shack » 09 Jun 2016, 07:36

the SimonK option is definitely not a good one.. the startup torque tricks takes alot more computing power than an Atmega8 has (also SimonK is written in Assembler if I remember correctly)

the hall effect sensor option is much easier and probably better too

or you could ofcourse get a VESC :P

rew
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Re: Startup torque with other ESC firmwares

Postby rew » 09 Jun 2016, 08:07

It is not the CPU-power requirements that limit startup torque for simonk-based ESCs.

The reason VESC is better than standard is that the VESC can run the motor at max current during startup. You'd say: that's easy, but it is not: you have to CAREFULLY run the motor at max current: if you blast the full 12V at your a2212, the current would become enormous: Your motor has a resistance of 0.127 Ohms. Put 12.6V on there and the current would become 100A. I'm told that this may be a little too much for that motor... :-)

So, to get 10A of current you need 1.27V, but once the motor starts turning, say 1000 RPM, then that 1.27V is already way too little.

The VESC can measure the actual current and act appropriately.

(on this motor the ratio of the current that would flow if the full voltage is applied and the allowed current is relatively low (only 10!). On bigger motors that ratio gets bigger and bigger!).

mt37
Posts: 2
Joined: 09 Jun 2016, 06:25
Location: San Francisco
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Re: Startup torque with other ESC firmwares

Postby mt37 » 10 Jun 2016, 17:59

I was able to figure out what flavor of simonk to flash on my clone of a clone ESC.

This firmware already dramatically increases startup torque and I think it will be good for now.


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