Quote:
Originally Posted by Osseus_Dominum
Do hou have any pictures of 8 wheel drives like this? I haven't been able to find any.
Regarding your concern about lateral traction and being pushed or spun, I don't see how this would be any more at risk. An 8 colson wheel drivetrain with center drop will only ever have 4 colsons giving traction at any one time, just like this drivetrain. So why is this more susceptible to spins?
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The resistance your robot is going to be able to give is related to the amount of friction your robot has to resist that force. When it comes to lateral force, it's obvious that an omni wheel is going to present negligible friction compared to a traction wheel. Even ignoring the wheel placement for the moment (the outboard wheels will have a greater lever arm to your center of mass for resisting the applied moment), you can determine the friction from your wheels with the equation
f=μN. For our purposes here, the normal force is equivalent to the weight placed on each wheel.
When the quantity of wheels in contact with the ground is increased, the normal force on each wheel is decreased (less weight on each wheel). In the case of a 8WD with 4 "drop center" wheels, you'd have the weight of the robot on 4 wheels. 100% of the robots weight would then be placed onto those 4 traction wheels. In your corner omni 8WD, the weight of the robot is distributed among 4 traction wheels and 4 omni wheels. Assuming an even distribution of weight, you'd have 50% of the weight of the robot placed on wheels with a high coefficient of friction, and 50% of the weight of the robot placed on wheels with a low coefficient of friction. As a result, the total friction your robot generates to resist that lateral force would be less than a robot with all of its weight placed upon high traction wheels.
Now, we've made quite a few assumptions to reach this point, and many things will end up being far more complicated in reality than I've presented here. For instance, resisting a spinning moment is going to be very dependent on wheel placement, drop height, and frame interactions. But I wanted to illustrate a general point. To phrase that point differently, the advantages your design has in terms of turning itself easily also serve to make it easier for other outside forces to turn. None of this is to say your design is poor, just that it will behave differently than a drop center drive. In
some cases, team's have taken advantage of ultra-low resistance to turning and incorporated it into how they wanted their robot to behave.