Designing a Robotic Lawnmower Blade: Calculating Torque for Optimal Performance

[Brushybill]

Hello,

Some classmates and I are building a remote controlled robotic lawnmower for a design project. One of my task is to design the blade system. The blade is a small weed-wacker blade that is 12in long -- and I am estimating the weight at 1lb for now. It will be attached directly to the motor output shaft.

I am having trouble figuring out how much torque I will need to turn the blade with an electric motor. Neither my dynamics or mechanical mechanisms book gives a clear example of a bar/blade that is driven from the center and/or facing down. Can someone help me figure out the math to come up with some calculations for this problem?

-Thank you

 

[bluelava0207]

It depends on how fast you want it to spin once it's up to speed. The torque will affect how long it takes the blade to get up to speed, but once it's up to speed, the blade doesn't really affect the motor, unless there's significant drag on the blade from air (probably not). There are probably charts for your motor for torque, rpm, current, etc.