Robot clutch to disengage wheels

Question

I have a robot that moves around autonomously. Very often I want to push the robot several feet to start a test over again, or sometimes I want to wheel the robot outside to my car or to a nearby field.

Pushing my robot is pretty tough. Its 60lbs (27kg) and when I push it with the motors engaged its very difficult. I want a way to decouple the 2 back wheels so I can haul it around like a suit case. I've seen similar posts to this one where people suggested just leaving them coupled and recharging the battery. I don't really care to exert that much of my own energy just to recharge the battery. I just want to make transporting easier.

I also Want to be able to engage and disengage without the robot being on. This means that electromagnet clutches are out. Id like the solution to be under $300 and to be fairly easy to machine. I have access to a lathe, mill, welder... etc and can machine some complex stuff, but I don't want it to be like making a custom gear box.

Does anyone have any suggestions? I'm using standard dolly wheels from Northern tool. (http://www.northerntool.com/images/product/2000x2000/425/42570_2000x2000.jpg) I've considered a quick release pin but given the geometry of the dolly wheel that would be tough. The pin would hit the rim as you are pulling it out.

Thanks in advance for any suggestions.

Answer 1

How about a electronix solution, at the moment i guess your motors are controlled by a H-Bridge or similar, by rotating the motor you are generating a current which generates a magnetic field in your motor (see Maxwells Laws for more information). If your motor is not connected the only fricition you have is the friction of your gears.

So you can use a simple mosfet to disconnect your motors from their driver, if your motor uses a lot of current you may use a relay (or a IGBT) but the idea is the same.

Answer 2

If your robot's drive wheels always move in the forward direction, you may be able to design in a wrap slip clutch device. This device would tighten a beefy spring around the driven shaft when the input is turned in the forward direction, but would loosen itself and decouple from the motor when the robot is pushed in reverse. Here is an example: Wrap slip clutch article from Machine Design 1/25/2007

If your drive wheels move bidirectionally, you can probably come up with a different, more standard, slip clutch device that allows you to manually engage/disengage the tangs between the input and output shaft for when you want to push the robot. You'd need a mechanism to overcome the spring force that engages the tangs, and a method of locking it in place. However, before thinking too hard about the design, I'm concerned if you can really get any manual clutch to work given that you are challenged on space for even a quick-release mechanism.