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Drivetrain

Drivetrain

Almost all robots in Eurobot rely either on a differential drive system or on omnidirectional wheels. This year we have combined both to cancel out one weakness of the differential drive concept. With a conventional differential drive you only have two driven wheels. If they are in the back you can accelerate fast, but braking action is very poor, and vice versa, if the they are placed in the front. The usual compromise consisted of putting the differential drive in the middle of the robot, which resulted in poor performance all around.

drivetrain rendering 670

This seasons solution uses a differential drive in the back and actively driven omniwheels as front wheels, which allows the robot to accelerate and brake very fast.

 

The results are braking look like this: 

And here we have not even added traction control.

 

Normally such a drive system would require four motors, two on the differential drive and two on the omniwheels, but we have not got enough space or motors to pull this off. However, if you place the omniwheels directly in the same line as the driven wheels of the differential drive, they can have the same speed.

 

The math of this solution can easily be shown with a thought experiment:

 

  • Imagine the robot driving in a straight line. Obviously all wheels are turning at the same speed.

  • Now imagine the robot rotating around one of its differential driven wheels. The omniwheels on the same side is also stationary.

 

All other movements are a superposition of those two scenarios.

 

For all who need math to accept a proof; here you go:

omnidrive expl 670

The system in action: