Coefficients of Friction

[JVN]

Originally Posted by JoelP

For example, if my robot was in a pushing match with another robot but unable to move it, the transmission would need to put out enough torque to cause the wheels to spin before the fuses blew. If the weight limit was increased, creating a larger frictional force which would have to be overcome by a transmission that wasn't designed to put out that much torque.

This is absolutely right.
If the weight limit goes up, suddenly a transmission that would have drawn 30 amps/motor will now draw 60 amps per motor, and you're in trouble.

Originally Posted by JoelP

Of course this could be easily fixed by changing the gearing in the transmission, but I'm not looking forward to making changes and testing a new transmission in the constrained conditions of the 6 week build period, especially when my team doesn't have the resources to quickly create parts for a new transmission.

So design a transmission that leaves you some breathing room...
I always try to leave some adjustability in the final sprocket reduction between the transmission and the wheel:

• If I find the robot is going too fast, I can increase this sprocket ratio, to slow it down.
• If I find the robot is going too slow, I can decrease this sprocket ratio to speed it up.
• If I see FIRST has increased the weight limit by 30 lbs, I can increase this sprocket ratio to bring the motor-load back down to acceptable levels.

This method would allow you to design your transmission, and just tweak your final chain/sprocket reduction when you see the game.

JV