Motors too long - how to place them?

[RiO]

I am considering building a sumo robot with some rather powerful motors. Unfortunately they are too long to fit along one side of the robot together. Could you please comment on your experience or ideas re choice of the motor placement scheme:

My primary choices are:
1) put motors along the robot and attach right-angled gears (hard to find proper gears)

90 gears.JPG (9.25 KiB) Viewed 680 times

2) put motors side by side and use gears to pass rotation (I want to avoid making custom gearbox)

_sumo gears 2.JPG (9.31 KiB) Viewed 679 times

3) put motors side by side and attach the wheels directly but not symmetrucally, so one is ahead of the other (I am not sure in balance of the robot).

assymmetric sumo.JPG (8.77 KiB) Viewed 680 times

[slurp]

Which motors are you going for? How big are they? Have you decided on your wheels yet? The Joint Strike Minisumo idea with the wheel around the motor may help.

If you're going for a right angle gearbox you could consider mounting vertically too.

regards,
Colin

[RiO]

Actually I am designing a 3kg sumo and consider using these motors:
http://banebots.com/pc/MP-36XXX-545/MP-36016-545

It is 93mm long with gearbox.
The Joint Strike scheme may not work for me because I will only have 7mm of shaft to play with and I need to load about 10-20kg of weight per shaft (using magnets or vacuum). In non-symmetric layout I'd use banebots' wheels which are 20mm wide and then support bearing blocks for the other end of the shaft.

[slurp]

Looking at that you've got 93mm of motor and gear box with another 55mm of shaft. My first consideration would be an alternative gearbox, or as a secondary option shortening the shaft if I had the right tools.

I've not looked too closely at the motor details, I'd hope they have enough for you to consider gearbox interfaces, then you can choose something more suitable for your needs. They're not generally cheap at this size but you might find something that will give the reduction and change of angle required.

Bevel gears tend to give low reductions, while worm wheel will give higher (non-backdrivable). In all you need to choose carefully but materials and speed can be a big on the worm wheel. I think PeterW has posted some images of one of his minisumo where the speed was too high for the gears - they shed a lot of material! With a bit of care it should not be a problem.

regards,
Colin

[RiO]

Colin,
I will explore the custom gearbox option as you suggest.
Meanwhile what is your opinion on option 3 (non-symmetric)?

[slurp]

I'm fairly sure I've seen this before, I just can't think where.

Have a think about where your centre of rotation is going to be, turns clockwise and anticlockwise are going to differ. This might make thing interesting but not insurmountable. Speaking of which, I'm fairly sure PeterW's Insumountable has a non-symmetrical layout but they drive tracks... so one has the idle wheel to the front, while the other has it to the back.

regards,
colin