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Re: Mechanum Wheels?
Quote:
Originally Posted by BJC
What I believe he is saying is that the midpoint of the wheel is level with the top of the barrier. Because of this the forces exerted by the robot must be entirely up until the wheel gains some purchase on the barrier and will continue to be able to pull the robot forward (read: over) the barrier.
If when your robot is climbing the barrier where the initial wheel contact with the barrier is lower then the middle of the wheel more forces remain pushing in the forward direction. In the same way, when you are on flat ground the wheels are pushing entirely forward. As a good rule of thumb if you can get the initial contact point inside the bottom 1/3 of the wheel that wheel will fairly easily surmount the point of contact while maintaining its forward force.
This is why it was suggested to put little ramps or something in front of your wheels. So the initial contact point of the barrier to the wheel is as low to the wheel as possible and forward momentum can be maintained.
Regards, Bryan
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We did some tests with the bump and the AM kit chassis with 8" wheels and found out exactly what you are describing Bryan. Here is a tweet with a picture of the test to put a visual to this part of the discussion. The center of the 8" wheel hit the middle of the bump directly. We ended up putting a slope on the front edge of the chassis to help with horizontal forces.
http://t.co/4GxQFVqU
We used mecanum for the first time last year and had some success with them and the rest of our robot design. I always tell my students that the chassis decision should be based on our robot/game strategy. We built an offensive robot and of course tried to stay in front of our own rack, worked great. We decided not to use mecanum this year for a few reason with the main having to do with high level game strategy.
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Nate Knauss
FRC 2729 Teacher-Drive Coach 2009-?, FTC 4390, FTC 7433
FRC 87 Student 2000-2002 and Mentor 2003-2006, FRC 1647 Mentor 2006-2008, FIRST Senior Mentor 2009-2013
"We can't change the cards we are dealt, just how we play the hand." -Randy Pausch
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