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Remus
10-30-2008, 03:46 PM
I'm working on a rover project that has to turn pretty sharply (in place would be ideal). It's going to be about 80 lbs. I'm planning on using this drive system:
http://www.trossenrobotics.com/store/p/5761-Motor-Mount-Wheel-Kit-with-Position-Controller.aspx
What are the advantages and disadvantages to having 4 powered motors rather than 2?

darkback2
10-30-2008, 04:54 PM
I have used both 2 and four motor setups using these motors. When you only have 2 drive wheels, and either use casters or passive wheels, the weight carried by the casters or passive wheels is taken away from the weight carried by the motors. This isn't a problem if the motor wheels are centrally located, but if they are either in the front or back of the robot, then the robot can slip in hilly situations, or in situations where traction may be a problem. Similarly having the drive wheels in the center can lead to high centering where the front or back of the robot makes it onto or over an obstacle which in turn lifts the center drive wheels off of the ground.

In those cases having four drive wheels is to your advantage. That said, this comes at a great drawback which is power consumption. Having for of these motors on Vivian means she burns through a five amp hour batter in about 30 minutes.

So, if your robot is going to be in a farely controlled situation, then using just two of the motors is to your benifit. If it is going to be in traction poor situations, then four would be better...

Then again lugging around 80lbs is going to be difficult with just two of these motors. You may have to go with 4 just to be sure your robot can actually move.

Hope this helps.

DB

Adrenalynn
10-30-2008, 05:29 PM
Agreed with DB with the additional that the 'bot can become unbalanced and flip backward in a rear-wheel only situation on launch (kinda "torque-steer").

For an 80lb bot, I'd be using scooter motors. I have two with chaindrive on Oscar. And they can be had really cheaply on fleaBay. 350wt can be had under a hundred dollars - and then you can do indirect drive and not be slaughtering the bearings with the weight like you might be prone to do on the parallax kit.

Remus
11-16-2008, 02:31 PM
Thanks for all of your advice, I think we're going to go with 4 motors.

The next question is how to we figure out how fast it can accelerate, or the minimum acceleration? If we have 4 of these, how do we figure out the acceleration based on the torque of the motors for our 70 lb rover?

Thanks again