[team2039] Drive Train going over Bump
- From: Adam Czerwonka <Adam.Czerwonka@xxxxxxxxxxxx>
- To: "'team2039@xxxxxxxxxxxxx'" <team2039@xxxxxxxxxxxxx>
- Date: Mon, 9 Jan 2012 13:38:54 -0600
Hello Team,
Based on the great discussions I heard about drive trains this weekend, I
decided to look at how different drive trains would perform while going over
the bump. I put together scale drawings of the drive trains (with a few
assumptions made).
For the 4 and 6 wheel designs, I assumed we have 8" wheels, for the tank tread,
I assumed an angled tread pattern on both sides with 4" rollers (probably
doesn't impact the results if we change the roller size and keep the overall
tread pattern).
Here are my observations. I invite everyone to include their comments,
questions, or new ideas so we can repeat this experiment with other designs.
A brief discussion of the physics:
You'll notice that I have some of the designs reaching very high angles before
they tip over and drive down the other side of the bump. This was determined
based on principles of physics, the robot will only tip (toward the front of
the robot) when the center of gravity passes over the pivot point, or when
forces from the wheels or treads cause the tipping force. This means that this
performance is impacted by the location of the center of gravity (CG) of the
robot. The center of gravity is the average location of the weight of the
robot. The point at which the weight of the robot is balanced in every
direction. I placed the center of gravity in the middle of the frame, but
above the frame since there will be a bunch of hardware sticking above the
drive frame of the robot.
For just about all of these drive train designs, it would be ideal to have the
center of gravity very low to the ground, and near the front of the robot too
for others. I assumed a somewhat central location not knowing the robot design
yet. Much of the upper part of the robot will be designed based on functional
constraints, so we may have limited flexibility in where the center of gravity
is located. We can probably improve upon the center of gravity that is shown
in the images, but the question of how much will not be answered for quite a
while. One thing is for certain, the Center of Gravity cannot be located at
the edge of the robot, since there is no weight beyond this point to balance
out the robot weight. My advice would be as we look at robot designs, we can
assume that we might be able to improve these worst case numbers by a
conservative (that means small) amount, but it might be challenging to move
this location by much more than 6" to 12". For scale, the robot length in the
narrow orientation as drawn is 34".
I looked at the following 4 designs: 6 wheel narrow orientation, 4 wheel
narrow orientation, 4 wheel wide orientation, tank treads
Ranked from most likely to tip over to least likely to tip over we have:
4 wheel wide orientation *almost guaranteed to tip over
Tank Treads* high probability of tipping unless the center of gravity is very
low and very close to the front of the robot
6 wheel narrow drive *medium probability of tipping - might tip if we get hit
by another robot
4 wheel narrow drive* low probability of tipping
Ranked from biggest landing shock on the robot to smallest landing shock on
the robot we have:
Tank treads *unless the cg (center of gravity) is very close to the front, this
design practically has to jump over the bump, large impact on landing (16 inch
drop at front of bot)
6 wheel drive *medium impact (8" drop at front of bot)
4 wheel wide *low impact 4" drop at front of robot (high probability of tipping
over when coming down)
4 wheel narrow * low impact 4" drop at front of robot
Hopefully this will get people thinking of other configurations, and what the
impact on speed, maneuverability, pushing power, and bump performance will mean
for the robot design.
Happy Designing!
-Adam
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