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Unread 07-01-2011, 08:47
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Re: 6WD vs 8WD

Quote:
Originally Posted by IKE View Post
So, I was very inspired by some of the physics guys up above, and have a challenge:
Assume 16m dash (approx. 54 feet- robot length), and COF of 1.0. Also assume a 4 cim power-train at 300 Watts/CIM.
What weight is your bot so that you are just barely traction limited the moment you strike the other wall? Is this less than 4 cims & a battery?

1) How long does it take to go 16m when you are traction-limited the whole way?

Ffriction = 1.0 (CoF) * Wrobot (because Ff = mu * Fnormal)
a = Ffriction / Mrobot (because F=m*a, so a=F/m)
a = G (because Wrobot/Mrobot = G, gravity)

D = .5 * a * t^2
t = sqrt(16 m * 2 / G )
t = 1.81 seconds

2) How fast are you going just before you hit the wall?

v = a * t
v = G * 1.8 seconds
v = 17.7 m/s

3) At this ultimate speed, we are barely traction limited, so:

P = F * speed (1 Watt = 1 N * m/s)
F = Wrobot
speed = v = 17.7 m/s
1200W = Wrobot * 17.7 m/s

Wrobot = 67.8 N = 15.2 lbs

So yes, less than 4 CIMs and one battery.
 


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