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Physics
Posted by Matt Leese at 03/24/2001 9:50 PM EST
Other on team #73, Tigerbolt, from Edison Technical HS and Alstom & Fiber Technologies & RIT.
In Reply to: Re: Errr... Wha?
Posted by Dodd Stacy on 03/24/2001 8:30 AM EST:
Ok, I'll try and explain a bit of the physics of why this happens (note, the example robot is two-wheel drive in the back and two casters in the front):
When traveling forwards, the pivot point of the robot is about the back drive wheels. When the back wheels stop, the back of the robot stops and the momentum of the front of the robot just drags the back with it slightly.
When traveling backwards, the pivot point is still about the drive wheels but this is now in the front. When the robot stops, the back part of the robot still has momentum but it can't just pull on the drive wheels. Instead, the momentum causes the robot to pivot about the drive wheels.
This happens in the opposite way going up an incline for the same reason. When going up an incline, there is a downward force of gravity applied to the robot that causes it to want to slide down the incline.
When the robot goes up forwards, the pivot point is in the back. The back is also being propelled and is pushing the front. The front is pulled down by the gravity and instead of just pushing on the back, the gravity causes the front to pivot about the back causes the robot to slide.
The robot doesn't slide when going up backwards because the casters are in the back and the force is pushing them away from the drive wheels so there's no pivoting.
Basically when there's momentum or a force applied towards the drive wheels on the casters, the robot pivot. When it's applied away, it will not pivot.
The difference between the casters and the drive wheels is that it's much harder to move the drive wheels in a direction perpendicular to the normal motion of the robot. This is why four-wheel drive robots don't suffer this (including our robot with four drive wheels in the back and casters in the front).
Matt who should qualify this statement with the fact that he's a CE and in Physics 2
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