Drive motor options

[maddox10]

Technobots has a suitable range of gears, and are very dependable.

[Liftoff]

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.

Hmm, that will defeat the purpose of a light and compact setup if I had to use herringbone gears. I could maybe use helical gears and thrust bearings...but probably its better to keep it simple and do as you said...go with straight gears, any recommendations on who sells loose gears at a reasonable price, preferably within the EU not the States?

[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.

[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...

[shakesc]

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

[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?

[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.

[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.

[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...

[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]

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.

[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.

[Eventorizon]

Is there actually much benefit to running a brushless drive? The initial weight saving and power increase from the motor is obvious but with all the chain you had to add to get the necessary reduction There may not have been much weight saving. Is there anything to my logic?

It also crosses my mind that if you took a banebots gearbox, for example on 16:1 or 25:1, could it cope if you mounted a brushless motor to it?

EDIT: That said the motors on the test machine are only 750kv where as the 775's are over 1000... maybe its not an issue

[Ellis]

Brilliant information, thank you! Well now I feel a bit of a fool, seems this is already entirely possible. I'd still expect a good old brushed system with a set of BB TZ85s to be more reliable at this point, but this certainly sounds viable now.

Cue everyone using brushless for the '14 champs, lol.

[Daniel]

Found the Trackstar 80A instruction manual. There's a few things that arn't actually listed on the hobbyking webiste such as it is rated for motors < 2300kv. Also the controller can be reprogramed for brushed motors but I don't know how well that works. Here are the 9 programing options and what I chose:

1) Brake/Reverse type - 1. Reverse Lockout - Allows reverse only after 2 second pause at neutral throttle
. 2. Forward/Brake Only
. 3. Forward/Brake/Reverse - What I chose. Reverses as soon as motors brakes to zero rpm.
2) Brake Amount - I set this at 100%
3) Reverse Amount - You can chose 25%, 50%, 75% or 100%. 50% was default, so I changed to 100% or I'll drive in circles.
4) Punch Control - Basically has settings for acceleration - High, Medium, Low, Lowest or disabled. I think I had it disabled.
5) Drag Brake - How much braking when the motor coasts. I might have screwed up and set one motor at the highest, 40%, and the other at 0%. Didn't effect driving much.
6) Throttle Dead Band - The largest is 0.1500ms, default is 0.1000ms and the smallest is 0.0250ms. I left it at default because I didn't quite understand what would happen if I changed it and it seems to work as is. The largest would give more kick to start the motor but lower gives more control.
7) Voltage Cutoff - I left this default at Auto-Lipo, for obvious resons.
8 ) Motor Timing - You can select lowest for efficiency, highest for increased power, normal as default. I think I left it at default.
9) Motor Type - Brushless, Brushed Reversing or Brushed high power. I left this as brushless.

So it seems that for one of the controllers I only changed setting 1) reversing, 2) max braking and 3) 100% reversing. Took a bit to understand how to program it with a pistol radio, but wasn't hard once I understood the instruction's chinglish