Drive motor options

[Ellis]

It's a misconception that brushless motors are all super fast. Many many examples are significantly slower than traditional brushed motors. The big-gun brushless outrunners are almost inconveniently low revving.

I imagine a 16:1 p60 banebots gearbox would handle a brushless up to say 1kw peak power, beyond that the torque involved might be a bit risky? Never worked with them so don't know how tough their insides are.

[Liftoff]

The Ntm 4248 motor does around 12000rpm at 5s and 1300w, good for the given weight and size of the motor. Thats almost half the speed of a gimson or banebots so it's not going to over rev a gearbox.
The problem I'm seeing is that it will probably need a custom gearbox as I have yet to find a 10:1 ish box. If I still don't find one will have to build my own
Another plus I can think of is the relatively cheaper price of the esc when compared to a brushed one.

[daveimi]

I think a few people are coming up against the same problem (I know I am) i.e it's easy enough to get hold of a decent motor, but then trying to find an off the shelf 'box to fit is nigh on impossible.

[Liftoff]

That's very true David, however it's not too difficult to construct a simple gearbox with 10;1 ratio me thinks...I mean the motor speed is not that fast so the no of gears required is low and normal off the shelf bearings will do.
Have to start looking at some gear selling shops to get an idea of dimensions etc tho...

[maddox10]

I fitted 2850 Kv Brushless motors to Gimson GR02 24-1 gearboxes, all it took was drilling 2 3.5mm holes at the right spot.

[Daniel]

Well my reason for switching to brushless was a bit more unusual. I took Huntsman to RoboGames 2012 and during it's second fight agaist Last Rites it had all 4 motors fail due to popped out brushes and shattered magnets. Then at our Nationals in 2012 my Vendetta failed in the finals for simalar reasons. So I chucked a wobbly at the world of complex brushed motors and went brought the brushless setup. I wanted cheaper motors that are made with less parts and smaller magnets, and therefore less likely to have mechanical failures from shock.

I chose the because NTM 42-30 750kv because on 4-cell they should hit 10800rpm. With a 10:1 reduction and 100mm wheels that is a calculated 5.65m/s. Under load it's probably half that and would therefore take 1.7 seconds to drive across our 4.8m wide arena which was simalar to my previous robot. I do all my calculations in m/s because we only drive a few meters before hiting the other side of the arena, in a few seconds, so miles or kilometers per hour isn't relatable. So 10mph sounds slow, but 2 seconds across an arena sounds decent, and it's actually the same thing.

[Liftoff]

If I had to build my own gearbox, would it be ok to use helical gears? Main reason I'd consider them is space, I could use narrower helical gears having the same contact area a wider spur gear would. But not too sure about the extra forces generated by those gears..... any one who built their own boxes used helicals, or knows of some reasons not to use them?

[shakesc]

Have a look at the toughbox gearbox options on http://www.andymark.com/Gearbox-Transmission-s/55.htm

[Liftoff]

Thanks for the link Chris, that's what I had in mind, something down that line. The problem with their boxes is they are quite large for the space I have. But still, got some ideas from their assembly drawings. I could build mine much smaller and probably lighter without the need for helical gears...

[maddox10]

Helical gears have an inherent disadvantage , because these load the bearing also longitudal, not only axial. That can be solved by using 2 next to each other in the herringbone setup.

But for our application just straight gears will do nicely.