Brushless drive ESC

[mattsdragons]

It seems to be the next thing with powerful brushed stuff being more awkward to get hold of in the UK, had a look at various ESC's and these seem to fit the bill but wanting other opinions?

http://www.hobbyking.co.uk/hobbyking...Truck_ESC.html

[typhoon_driver]

Won't work. You need an esc and motor with closed loop feedback so that the esc knows the exact poisition of the poles in the motor.

[mattsdragons]

Ah okay, makes sense. Still learning about brushless myself, glad to have the pointers

[mattsdragons]

Something more like this?

http://www.hobbyking.co.uk/hobbyking...Truck_ESC.html

[Shakey]

Won't work. You need an esc and motor with closed loop feedback so that the esc knows the exact poisition of the poles in the motor.

A non sensored ESC still has feedback through the use of back EMF normally. It is prefectly possible to use sensorless brushless setups and still have good performance. You'll just experience less smooth startups.

[typhoon_driver]

yes as long as the motor is a sensored motor. However I'm not familiar with the ins and outs of using a brushless for drive. As far as I know it's only been done successfully either on the continent or in the states

[typhoon_driver]

oh and there's no way that thing is taking 700 amps or whatever it's spec'd to. Those are hobby amps, not genuine. Also bear in mind that these esc are made with relatively lightweight models, not our 30lb machines.

[mattsdragons]

700 amps is laughable, it seems entirely possible to do so may be worth a bit of exploring

[Shakey]

yes as long as the motor is a sensored motor. However I'm not familiar with the ins and outs of using a brushless for drive. As far as I know it's only been done successfully either on the continent or in the states

You're wrong, back EMF can and is read from a sensorless motor. Back EMF is read from the inputs to the motor. I am actually leaning more towards sensorless setups in fighting robots. Sensored introduces more parts/components so more potential things break and often they are simple optical sensors and under certain conditions can fail (generally not built for robots tumbling all over the place). Part of my lean towards sensorless brushless is the entire motor becomes a single moving part with just windings and magnets. Not much to get knocked about and fail.

EDIT: The 700 Amps is probably the combined peak rating of the FETS. Wouldn't fully trust that.

[maddox10]

Don't try to small a motor. A 28mm won't do.

[typhoon_driver]

By all means prove me wrong but there's a good reason that CNC machines have feedback on the axis. It's not that you can't keep good position with a stepper motor, but it's to ensure that if steps are missed or there's backlash, the system can still travel the correct distance. Different application, different motor, same idea.

[maddox10]

Challenge accepted.

[PJ-27]

I've been looking at brushless drive too (Mr Mangle inspired me!) My biggest concern right now though is finding ESCs that will have good Fwd/Rev response, most truck ESCs have braking or a delay.

[maddox10]

All brushless esc's have a delay, even the sensored ones. You can't trow a brushless in reverse like a brushed motor. It has to be stopped. The only thing you can have is a minimal delay.

It will take a lot of practise to get the best from the new tech.

[Shakey]

By all means prove me wrong but there's a good reason that CNC machines have feedback on the axis. It's not that you can't keep good position with a stepper motor, but it's to ensure that if steps are missed or there's backlash, the system can still travel the correct distance. Different application, different motor, same idea.

You're right different application, different motor. Which is why this doesn't apply. CNC machines keep feedback because they need precision to fractions of a millimeter, a fighting robot does not, no matter how expert a driver your 'precision' does not warrant such control. Back EMF is a perfectly good way of measuring the motor. This isn't some few hundred steps a millimeter stepper motor, this is a brushless that probably has around 10-30 poles. The feedback in a fighting robot is not position tracking but ensuring that the motor RPM and ESC timing match to sustain torque. If you want position tracking in your robot feel free to drive with stepper motors.