calculating a turning radius? (I think I got it....see update)

[bignateyk]

Its been a while since ive done any calculations like this (like 4 years since i had freshmen physics...)

I have an RC car, and I wish to know its minimum turning radius (i.e. the wheels are turned as far as they can go).

What parameters would I need to calculate this? Would it depend on the vehicles speed? I assume it would depend on the distance between the axels (~280mm)?

The car is rear wheel drive, and turns only with the front two wheels. It can go ~25mph at its max speed.

Also, just using a protractor, it looks as if the wheels can turn a maximum of about 30 degrees off center in either direction.

Any ideas?

update:
http://www.personal.psu.edu/njk909/turning_radius.JPG

Thanks,

Nate

 

[IronWing]

Um, get the wheels wet, set it on pavement, drive in circle, measure?

 

[bignateyk]

Originally posted by: ironwing
Um, get the wheels wet, set it on pavement, drive in circle, measure?

I would, but eventually I want to be able to calculate a turning radius based on a wheel angle (and throttle speed, if that matters)

 

[bignateyk]

ok, I think I got it figured out to be:

r = Wheelbase/sin(theta) + TrackLength*cos(theta)

http://www.personal.psu.edu/njk909/turning_radius.JPG

see picture for how I got it... does this seem right?

This is ignoring any kind of friction and different surfaces that might cause the wheels to skip, etc...

 

[Umberger]

I assume that you're just going to neglect the difference in radius between the left and right side of the car? I don't know much about RC cars, but I would assume they don't actually run true Ackermann. Anyway, if you REALLY wanted to be rigorous, you could take that into account, but it is probably a small difference. Other than that, your picture looks right.