Need help with clutch in drivetrain
 

Hi,

I was thinking of a robot (not for FIRST, only 3lb) that had two motors (one on each side of the drive) used for tank style steering; but, also had a much more powerful brushless motor that would be hooked up via some sort of clutch to both sides to for quick lunges in one direction.

I was originally planning on hooking up the brushless motor with a one way bearing, but realized the robot would no longer be able to go in reverse.

I really do not know anything about clutches.... Is there a cheap COTS item that would be able to achieve the motion I want?

Re: Need help with clutch in drivetrain
 

This probably is not what your looking for, but I figured I would throw it out there because I think this is a neat setup.

You might get some ideas from it!:D

http://www.youtube.com/watch?v=BWHAfaC-pPg

Re: Need help with clutch in drivetrain
 

Thanks!

I was thinking about belts because I know they would work (If I'm willing to accept some losses to friction for the slack belts just rubbing on the pulley)....

Now I just need to find a way to scale that down. The robot will ride on either 1.625" or 2" wheels and will be fully invertible (with the top and bottom identical). So, I've got to fit this down into a 1" space or so. I just hope the micro servos I have have enough torque to put sufficient tension in the belts....

Maybe If I cut some custom pulleys and use 1/8" or so round belt (similar to what teams use for conveyors from last year?).

EDIT: didn't even think of this before.... But this would allow me to completely remove the two other motors. That saves me a bunch of weight and makes the controls much easier!

Re: Need help with clutch in drivetrain
 

What's wrong with just using two brushless motors (one on each side) and just not giving them power all the time? It would be a lot simpler.

Re: Need help with clutch in drivetrain
 

Well, brushless motor controllers only run one way. So I'd have to hook up some sort of relay to reverse the direction. For this I'd need a microcontroller of some sort... Also, brushless motors don't like being stalled, so I want to limit it's use to just straight dashes. Of course... All my assumptions here may be entirely wrong ;)

Re: Need help with clutch in drivetrain
 

Instead of using another motor, could you use a pneumatic cylinder or something spring loaded to push off. This would work if you only have to accelerate quickly for a short distance, but it could give you better results depending on the application.

Re: Need help with clutch in drivetrain
 

Not entirely true. All a BLDC motor controller does is power the three phases in a particular order. For example, A-B-C in one direction or C-B-A in the opposite. What would you need a relay for? You don't need to reverse polarity to reverse direction.

Re: Need help with clutch in drivetrain
 

All the brushless controllers I have been able to find (besides ones that are HUGE. several ounces and several hundred amps) only spin the motor one way. I simply can't find a dual direction brushless controller that is even remotely small enough ( < 1 oz and about 25-30 amp).

I was thinking I could make a singled irection into a dual direction by having a relay switch the motor leads. I'd then need a microcontroller to determine if the pwm is above or below neutral, and switch accordingly.

However, if you can point me to a dual direction brushless controller in a small size, I would be extremely happy.

Re: Need help with clutch in drivetrain
 

Less than 1 oz might be a bit tough... here are some that I found that are less than 2 oz. These range from 8 amps to 90 amps.

While it isn't shown on their website, I know SeaBotix just came out with a new BLDC motor controller that might meet your weight requirements and is 80amp tolerant. It also has an extremely low profile. You can fully control the motor controller (speed, current, winding direction, etc) via I2C, RS232 and maybe even RS485. It isn't something they usually sell stand alone, but they might be open to the idea, especially if this is school related.