Quote:
Originally Posted by Madison
...operating with the unwritten assumption that all other things are equal.
A robot with a 9:1 ratio and 6" wheels will be slower than one with a 9:1 ratio and 8" wheels.
I give presentations about drive train design now and again and I sometimes assume a level of understanding that's not there yet, so I just wanted to explicitly note that gear ratio alone does not determine a robot's final speed.
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To further the point, the final speed also depends on a lot of other factors like the efficiency of the gearbox, friction and losses in the drive train, and the inertia the motor is trying to accelerate. If the rule were simply that a lower ratio gearbox = higher final speed, then we'd all be direct driving CIMs to our wheel. But, of course, a direct drive CIM is unlikely to generate enough torque to even get the robot started rolling, would take forever to accelerate up to top speed, and would probably blow a breaker attempting to get there. That'd be another trade-off you're making with the gearbox. A lower ratio gearbox is going to take longer to get up to its top speed. It's even going to take longer to get up to the top speed of a higher ratio, lower speed gearbox. So, in summary, simple rules of thumb are usually highly simplified and approximate.