running driven different sized wheels

[Danjr1]

Evening,

been doing some sketching (tried CAD and i can't get my head around it still!) and come up with a design which is a 4 wheeled rambot, where the rear wheels are 75mm robochallenege and the front are the 100mm versions. On each side, the 75mm wheel would be connected to the 100mm wheel (to provide 4WD) via timing belts and pulleys. The problem i have is how would i work out the ratio of the timing pulleys so that the wheels would spin at the same relative speed? the design uses gimsons for drive, where on the left hand side the motor would attach to the 100mm wheel and the right hand side the motor would attach to the 75mm wheel (motors would be in tandem like my current bot so the size is minimised viewtopic.php?f=240&t=4654&start=30

[Max]

If you have one Gimson directly attached to a 75mm wheel and the other directly attached to a 100mm wheel then thos two wheels would move at different rates making you go diagonally regardless of The gearing between wheels on the same side. You could fix this with travel adjusts if you have a fancy tx.
As to the ratio you want the same ratios the ratio between the wheels, 75:100 or 3:4 or 0.75:1. And then the other way round on the other side. (big pulley always on the little wheel)

[Danjr1]

If you have one Gimson directly attached to a 75mm wheel and the other directly attached to a 100mm wheel then thos two wheels would move at different rates making you go diagonally regardless of The gearing between wheels on the same side. You could fix this with travel adjusts if you have a fancy tx.
As to the ratio you want the same ratios the ratio between the wheels, 75:100 or 3:4 or 0.75:1. And then the other way round on the other side. (big pulley always on the little wheel)

cheers! can picture it now. ill scrap that idea then lol