Motor Selection

[vtome]

Our team is having a problem deciding on drive motors for our bot. Our design goal is to be able to accelerate the 130 lbs bot at 5ft/sec2 in 5sec. We would like to do this using the two CIM motors. We are planning on using the 9" wheels

There seems to be alot of information on using motors in lifting application but not in drive application. How do we calculate if this will work using the motor curves?

Thanks.

[Jeremy_Mc]

i'll tell you now...since they've improved the drill motors, i would go with them. according to some recent threads, they're faster and have more torque than the chipua's (i haven't personally calculated it, but these people seem to know what they're talking about considering no one really disputes it...and people usually do if they're wrong).

plus they come with a transmission/gearbox that you can use with them...so we're thinking they're they easiest to use and the best choice. (i'm not so sure you'll be satified with the gear box's efficiency/gear ratios so you might want to explore in that area...)

*jeremy

[Ken Leung]

Drill motors can easily handle the job for the drive system, even if they are last year's. This year the new ones have about 30 to 40 more power than last year, and you are allowed to use a 40amp breaker.

Keep in mind, that in the acceleration and time you said, after 5 seconds you are going to be 25ft/sec, and that's a speed so fast that its uncontrolable, and even rish popping your circuit breaker at that gear ratio.

The way the motor would work is that it will take a few seconds to accelerate to their top speed, and keep running at the top speed until they encounter outside force working against it. So, You would rather gear your drive motor by calculating how fast it would go in free speed. Keep in mind that, in the past, anything beyond 15 ft/sec is too fast already, and I doublt you will see any teams trying to go that fast this year. And the more friction you have inside your drive system, the slower the free speed will be.

So, I recommend you just try getting to 15ft/s first, before trying for 25. Figure out the max rpm of the motors, plan to lose about 20% of the speed just by friction in the system, and figure out what ratio you need to move a 9" wheel at 15ft/s. You might find out that you are popping circuit breaker because you are drawing to much current at the start. When that happen, you might want to program your drive train to start off in a slow speed and slowly accelerate up to full speed, or you might find out that you will need 4 motors instead of 2.

Remember that if you are going that fast, you will get pretty much very little torque out of the motor, and might find your robot having trouble even going up the ramp, or pushing bins around. My recommendation is, don't try to go that fast. 10ft/s is a good number to shoot for that's really fast already. I would even say a good pusher would have a speed of about 5~8 ft/s.