Gears

[JammyONE]

I've got 4 100mm wheels and I'm running at 12v.

[jonny]

Ah I see, I'm planning to run on 13.2v Which is why I'm going for a lower ratio

[team_mayhem]

12v id run 5:1 still fast and will have fair bit of push nice and controllable aswel as being single stage so easier and cheaper to make

[typhoon_driver]

Little bit of advice, don't be a snippy little so and so if I ask a simple question to get some background on an exceptionally general question. If you want help then a little manners goes a long way

[JammyONE]

Sorry I didn't mean to sound rude. But just to show you what my knowledge of gears is like. 8:1 may sound good to me but at the end it's just a number, I know what stage mean but that's it.

[maddox10]

A speed 900 is rather powerfull. So module 1. (module=size of teeth)

The axle is 5mm, meaning Z12 (12 teeth) as a minimum.
Smaller as that and the inner diameter of the gear gets too small .
Formula for this. Module*Z-(2,5*module)= 1*12-(2.5*1)= 9.5mm

Mechanical guideline, single stage, max ratio 8 to 1. (wormgears are an exception)

Max size for the wheel-gear is 12*8= Z96. But that's a problem in itself.
Because a gear has an outer diameter module*z+(2*module).In this case 96+(2*1)=98mm.
The wheels can't have any wear and tear. Or you're driving on the gears.

Therefor, 12 to 90 is the practical maximum to be used. Means gearratio 7.5-1

Then the rest of the calculations.

RPM of a speed 900 @12V 6600 rpm 100mm wheels.

6600/7.5 * (diameter in meter*pi)*60/1000= 16.57 km/h theoretical.

[blazerbotics]

for help figuring out ratios http://howto.killerhurtz.co.uk/calculator.htm