Mixing for brushless escs.

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dcr raptor
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Mixing for brushless escs.

Post by dcr raptor »

Ok, so I was thinking about the possibility of using brushless motors to drive a robot, however there is one thing that may prove to be an issue aside from the possibly uncontrollable speeds which is mixing for brushless escs. As only one brushless motor can be used for each esc, will this mean that mixing will face a similar issue?
On a similar note, does anyone know how many brushed motors can be run off of a single typical esc?

Thank you in advance for anyone who can answer this question.
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Shakey
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Re: Mixing for brushless escs.

Post by Shakey »

To the first, since generally it is 1 brushless ESC per motor you will need an onboard V-tail mixer or mixing on the transmitter (Quite a few can do this, what transmitter do you have?). Also as for uncontrollable speed it just needs gearing down. I'll be testing out a brushless drive antweight soon using small brushless motors and gearboxes taken from normal gearmotors, just need to find the right combination of components. Be careful choosing brushless ESC's not all of them can do reverse and those that can may have a delay switching between forwards and backwards.

To the second it depends on the current draw of the motors and the rating of the ESC. I run one robot with 2 motors in parallel on each side of the ESC fine but if I ever stalled both motors on one side it would toast the ESC as it would draw over what it is rated, stalling is rare though as they are polulu 50:1 HP motors so a good deal of torque.
Nuts And Bots - For all your components and ready built antweights!

Alex Shakespeare - Team Shakey / Nuts And Bots / Team Nuts:
AWS 44, 45, 49, 51 & 55 Winner - Far too many robots!
EpicentrE
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Re: Mixing for brushless escs.

Post by EpicentrE »

There is no "possibly" about it; if you were running a wheel directly off a brushless motor, the speeds would be uncontrollable. Not only that, but you'd have so little torque that there would be little point attempting to push anything.

There's 2 ways brushless drive can be feasable; the first is as Alex describes, running the motor through an external gearbox (the same as we do with normal motors for drive) to bring the speed down and the torque up to usable levels. The second would be to design it in such a way that you're able to transfer the power to drive a very small wheel, or to drive a walking mechanism with a very small accentuation on the cam.

ESC wise, yes, you'd need either a mixer in your robot or your transmitter to make this feasible. The two feasable ESCs I've found while looking into this are here and here. The first is a good weight and size for ants, but can only take two cells. If you wanted to use 3 cells, you'd need to go for the second one. Although it stated 19g on the page, I think you could get this down significantly by removing the heatsink and the plastic case, but you're still looking at something far heavier than the brushed ESCs we use.

Edit: There are some reviews on the main page for the first ESC that I've linked that state they have ran it on 3 cells, so it may be feasable, especially if you're not pulling anywhere near the max current of the controller. It's the sort of thing I'd definitely want to test if I had enough money that I could buy parts specifically to attempt to make them pop :P.

"The ESC is perfect for weapon control in 1lb antweight combat Robot. I use it for the drum of Saifu (28-22 kv1900 outrunner running on 3S) and it worked right out of the packet."
"I can confirm that this esc does work on 3S, even on the heatshrink is says, "DC:3V-13V" I have used it extensively in my 1/24 losi truggy along with the turnigy 4500kv and esc is warm after 15minute runs."
"Working excellent with an 8750kv motor on 3s (Yes, it works) for a losi micro DT"
Scott Fyfe-Jamieson, Captain of Epic Robotics. Champion of AWS38/41/42.
http://www.epicrobotics.co.uk
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BeligerAnt
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Re: Mixing for brushless escs.

Post by BeligerAnt »

You can only run ONE motor per brushless ESC. The ESC measures the back EMF across the motor windings to perform the commutation. With 2 motors connected in parallel the commutation would not work. This would probably result in the release of the magic smoke in large quantities from the motors and/or controller.

Small 8-10A ESCs are about the same size and weight as typical brushed speed controllers. If you search for "SimonK" firmware, I think it has a reversing option and should improve the performance of any compatible ESC. Does mean reprogramming the ESCs and invalidating the warranty though.
Gary, Team BeligerAnt
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