Quote:
Originally Posted by Rick TYler
Al and Alan, wouldn't it be more correct to say that those are the minimum possible turning radii? Because steering in this case uses the slip angle of the wheels to generate turning force (I know that's a sloppy way of wording it...) won't the actual radius will always be greater than the theoretical minimum? On a low friction surface (like Lunacy) I would think it would be much larger than the minimum, with the radius increasing with robot speed.
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Al and Alan are correct assuming very small slip angles. This would be relatively low speed small input stuff on regolith.
Rick is really on to something. One other thing to consider is how the back wheels play into this. If they are going the same speed they will induce higher slip angle. Racers often call this Push because the back wheels are pushing the forward wheels to induce understeer (or less steer than requested). However depending on CG location and the actual manuever you attempt, you could also get Oversteer. The grossest exageration of this is the guys that do drifting, rally, or Dirt track stuff.
Gelespie (spell?) has a vehicle dynamics book that is excellent at talking about how these equations may be applied and simplified (bicycle model). Assuming reltively small slip angles, the bicycle model works well for the system you have. I.E. Take the angle off of straight. The tanget of this angle times the radius of curvature is equal to your wheelbase. Thus to find the radius of curvature:
WB=wheelbase
angle=angle off of straight that your wheels are turned.
WB/(atan(angle))=radius of curvature
If you have extra weight available, place it in different locations on your machine. This should help change the oversteer/understeer effects you might get. In general the trailer will produce understeer effects (this is what I am seeing in most videos), unless you really crack the whip, and then it could result into an oversteer condition.