Brushless drive ESC

[shakesc]

So my plan is a larger sensorless brushless outrunner with a lower KV and less reductions. I want to keep it simple and cheap - NTM's with angle grinder gears and 6mm chain final stage reduction.
I prefer chain as you can give it a little slack which isnt necessarily something that belts an tolerate.
Wheels are a pain. I've used 100mm alot before but really too big so will probably end up making my own around 80 - 85mm diameter.

Oh, and if anyone is interested a Gimson motor (which I'm very capable of burning out ) next to a couple of outrunners

[knightrous]

Just trying to settle this in my own head...

There seems to be two schools of thought:

1: Go for a sensored inrunner setup with a higher KV and more reductions, the advantages being it is easier for the motor to start because of the gearing and because the ESC knows were it is.

2: Go for a large stator sensorless outrunner with a lower KV and less reductions where you rely on the greater torque of the motor to get the machine moving despite the ESC not necessarily being able to remain perfectly synchronised.

The first option seems to be having more success but needs a high reduction gearbox to make it work which is expensive (Just thinking banebots or a custom setup here). The second is easier to do as it requires less reductions but may not work at all of you get it wrong.

Is that right?

Speaking for myself, Yes & No.

Sensored is the best option regardless of it being inrunner or outrunner, it's just that sensors more readily available on an inrunner motor then it is on an outrunner.
I prefer an outrunner over an inrunner due to the lower weight, need for less gearing (less weight, more effeciency, stronger reduction), better voltage coverage (2S-6S), lower amp draw (higher voltage needs less amps for the same wattage) and better cooling.

Relying on mechanical slop in the gearboxes isn't good either, that slop can stress the reductions more as they impact harder during direction change and it affects the handling of your robot (sit down and see how much your robot turns just by the movement in the slop in the gearboxes)

[overkill]

What Aaron said. People in the electric scooter community seem to like reduction with some slack in it, but they are not constantly starting, stopping and reversing. The sensored inrunners are very easy to get running but there is a limited choice of sizes; most motors are either low power 540 size or bulky 1/8 scale motors. It would be great if a motor between these two sizes with around 300 to 500W output can be found. I wouldn't bother looking at sensorless inrunners at all.

If you are already using 775 motors, the 1/8 scale sensored brushless motors are an easy conversion as they are only 5mm longer than a 775. Most of these motors are rated for 14.4 volts but I'm betting they will be fine at 22.2V in a bot that doesn't need to do much pushing with really high traction wheels.

Its likely that we can over-volt all the larger brushless motors; when I was bench testing my motors they got quite hot after 3 minutes but they barely got warm even after full length matches and that's probably because they were not running at full output for most of the match. Brushless motors will over-volt better than brushed motors as long as the output power rating isn't abused too much.

One thing to note about the Hobbyking inrunners: the few 540 sized motors that I have tried so far are much lower quality than similar looking name brands. They have lower torque and build quality and just didn't work out at all.

[overkill]

Here is my ultimate brushless motor range- these should even keep Aaron happy!



http://holmeshobbies.com/Brushless-Outrunner-Motors/

A sensored outrunner that fits anywhere a 550 motor will, with at least 4X the power output of a drill motor - that has to be about perfect for all KE spinners. The only down-side is availability; they are very popular and often out of stock.

[knightrous]

Voltages and prices don't make me feel good, but everything else is pretty awesome!
That is essentially what I want to make out of the NTM motors with the sensors placed in the mount!

[overkill]

Just make a split voltage pack like I did on Mr Mangle - you can have 4S for drive and 8S for a weapon. It wasn't hard to do and worked first time; it also means you can use cheaper 4S capable ESCs. I am happy to publish the 3D model and 2D plans for my dual power link block if anyone wants to go down that path.

I looked at similar sized NTM motors and they are usually 4S as well, plus they mostly have 4mm shafts which makes them harder to fit onto drill / Gimson / Banebots gearboxes. Its not until you get up to the NTM 42-58 motor that voltages go up to 6 or 7S.

I'm not saying the NTM motors are bad, its just that these HH motors are ready to run now, with all the most desirable features. The price is well over Hobbyking but completely in line with similar name brand motors. For builders with the money, I think these are currently one of the best options.

[knightrous]

I'm mainly looking at NTM42's as they use a 5mm shaft, which works nicely with the gearboxes I'm testing for BotBitz :P Not knocking the HH motors, it's just they are personally too expensive for me and potentially any BotBitz customers (Not to say we cannot supply our gearboxes ready to mount a HH motor to!) if we go down that path. I think you should grab a set of the HH motors and do some testing for us Nick since you've got both a robot with brushless drives and inrunner motors to compare them against You can do some good data logging on amperage use, over volting and general quality.

[overkill]

My thinking too - already emailed the supplier.