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DumHed
Experienced Roboteer
Joined: 29 Jun 2004
Posts: 1219
Location: Sydney
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I think there are a few too many variables involved (motor efficiency / torque curve, different surfaces, etc)
Either way, if you have a 4WD bot, and give each motor the maximum amount of power it can put to the ground without wheel spin, the front wheels will spin, as weight is tranferrered to the rear wheels instantly.
Both motors will be making the same power, as they're starting from stall and are given the same input wattage.
The front motors will reduce torque once they speed up, but the wheels will already be spinning.
In cars it's referred to as geometric weight transfer, because it's a byproduct of the car's geometry.
This is why a car can be balanced mid corner by keeping the steering in the same place and varying the throttle input.
Changing the torque going to the wheels instantly changes the amount of load each tyre has on it, and hence its grip level.
Also don't forget that most rammer / wedge bots will also need to push other bots around, so designing around the maximum power that can be put to the ground under its own weight could leave you with an underpowered bot when you have another one sitting on top of it.
You'd be better off have a dual preset system for power, so you can drive around with power limited normally, and then go to maximum power when you need it (or can use it) _________________
The Engine Whisperer
- fixer of things
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Thu Feb 09, 2006 12:34 pm |
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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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Actually, most Pro Drag cars have *very* sophisticated suspension. Its just not designed for going over bumps comfortably like "normal" suspension is.
4-Links, Ladder-Bars and quite a few other types of precisely engineered linkages are used in the rear end of a drag car to turn the rotational torque reaction along the rear axle axis into downforce to press the tyres against the track.
Differential-Rate shock absorbers allow the front of the car to rear up easily, and then settle back slowly assist in weight transfer to the rear of the car (where the power is being applied), the "crinkle" effect of the drag-slicks tyre sidewalls is carefully considered and a lot of other factors I probably dont know about.
I have seen some of the simulation software available for the many configurations of drag-car suspension. It is very involved and takes into account linkage lengths, unsprung mass vs sprung mass, polar moments of inertia for the rotating masses and a million other factors. Your average 14-second street drag car might not worry too much about this sort of thing, but once you get up into the sub-9 second brackets, it really turns into rocket science.
Anyway, thats all about *acceleration* which is different to static-power output that mr Kero is discussing, but dont get the idea that putting 1000+ horpsepower to the ground in 8 seconds is simple just because the cars go in a straight line..
Have you tinkered with EDTSim to see what factors it takes into account in this area ? _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
Last edited by Spockie-Tech on Thu Feb 09, 2006 7:29 pm; edited 1 time in total
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Thu Feb 09, 2006 7:01 pm |
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