Motor with a 1 way clutch, how to do it?

[Scott Shepherd]

I have a mechanism I need to make. It's essentially a take up reel. I need to have a motor that is turning a shaft (lightweight) in 1 direction. I'm good with that bit. However, at the end of the machines cycle, it sucks the material back into the machine about 1 foot and then cuts it off. So I can't have the machine pulling material the opposite direction of the take up reel. What I'd like to do is figure out a way so the motor is turning but if much pressure is applied in the opposite direction, then my added motor will essentially freewheel and let it happen.

I can't think of anything I've run across recently that would let me make that happen, so I thought I'd ask here. I know someone will know an easy, inexpensive way to accomplish it!

Any suggestions? My plan is to use an arduino to drive it so if I need to be measuring something along the way, I suppose I can put something in line that measures the movement, somehow.

[Guy Hilliard]

Scott I think you may be looking for a ratchet. A brake will allow the mechanism to retract with some force but stop retracting when a larger force is applied to the material. The ratchet may already have enough built in friction depending on your application.

[Scott Shepherd]

It hit me a little bit ago that maybe I want to put a rubber wheel on the motor and use friction to spin the motor. Then if it gets pulled backwards, it'll just slip. I think that's a doable thing.

[Dave Sheldrake]

Seat belt retraction system Scotty?

cheers

Dave

[Steve Rozmiarek]

Is it ok to have tension on the reel all the time?

[Scott Shepherd]

Yes, light tension would be fine.

[Curt Harms]

If I understand correctly, you're looking for what I've heard called an overrunning clutch. I'll bet Steve knows what I'm talking about. I'm familiar with them from forage harvesters. They were used to enable a heavy cutterhead to spin down without trying to drive the rest of the machine or coming to a sudden stop. They used two or more dogs that when spun flew out and engaged the cutterhead drive mechanism. Once power was removed and the drivetrain stopped, the dogs were no longer extended by centrifugal force so disengaged the cutterhead from the rest of the drivetrain. I don't know a source or how to make one inexpensively.

[Bill Huber]

I am not sure what you need but I do know there are one way sprag type bearings out there. I have work on equipment that have them and the will free turn in one direction and then drive in the other.

http://www.bocabearings.com/bearing-types/one-way-clutch-bearings/sprag-type-one-way-clutch-bearing-csk-

[John Coloccia]

You could just keep it simple and use a stepper motor. Just set the torque to just enough to take up the material. When the machine pulls it back in, the stepper will simply drop steps. When the machine let's go, it will re-sync and continue on it's merry way.

Another solution is to drive the wheel with a belt, tensioned by an idler. Belt is on a pulley on one side, material is on a pulley on the other side. When the machine pulls the material back in, it lifts the idler, disconnecting the motor drive. Then all you need is some sort of one way mechanism on the take up wheel to provide tension when the machine pulls it back it. Use your favorite style here...there are many many many to choose from. If this isn't clear, I'll try to explain it better, but it's a pretty standard way of disconnecting a drive motor. Our use is novel in that the material you're moving also acts to provide the force that disconnects the idler.

If you want to be really clever about it, the idler arm can double as a brake. So the mechanism starts to pull the material back in...that starts to lift the arm. Lifting the arm allows a spring loaded brake to engage the wheel. As the material is pulled harder, the arm lifts more, disengaging the idler from the drive belt. Very elegant and simple.

You don't really need the brake, but without it you'd never be able to disengage the idler any more than the bare minimum necessary to make the belt slip, and that would quickly wear out the belt. The brake allows you to completely disengage the belt.

[Jerome Stanek]

Are you talking about something like a movie projector or a tape recorder that keeps tension on the top reel as the bottom pulls the film then when reversing the top wheel drives.

[Dan Hintz]

You could just keep it simple and use a stepper motor. Just set the torque to just enough to take up the material. When the machine pulls it back in, the stepper will simply drop steps. When the machine let's go, it will re-sync and continue on it's merry way.

As long as you're not running the stepper too fast... otherwise, it'll never sync back up as the pulses are coming too fast to overcome the inertia of the shaft. Plus, you'll also have to look at how much drag you want as that is a second item that will reduce the speed at which you can reliably sync up.

[Steve Rozmiarek]

If I understand correctly, you're looking for what I've heard called an overrunning clutch. I'll bet Steve knows what I'm talking about. I'm familiar with them from forage harvesters. They were used to enable a heavy cutterhead to spin down without trying to drive the rest of the machine or coming to a sudden stop. They used two or more dogs that when spun flew out and engaged the cutterhead drive mechanism. Once power was removed and the drivetrain stopped, the dogs were no longer extended by centrifugal force so disengaged the cutterhead from the rest of the drivetrain. I don't know a source or how to make one inexpensively.

Sure do, one clever design I've seen uses balls in slanted holes and centrifugal force. Others use dogs and pawls, or like Bill mentioned, sprag bearings.

[Mike Lassiter]

Maybe you could adapt a auto starter Bendix. It's a one way drive that locks when it is under power but releases when the drive gear starts being turned faster than the drive is turning. Would have a gear on the end but possibly could adapt a pulley or whatever to that.

[Scott Shepherd]

Thanks for the input. It's a very slow turning thing. Maybe 1 RPM, I'm guessing. I've looked at units that come on machines and they seem to compensate for it by allowing some extra slack in the material, then they take a shaft, and lay it in the fold, so it's just gravity putting tension on the extra area. If it pulls the material back in to dry 12" or so, then the shaft just raises up about 12".

It's a take-up real on a wide format printer. The factory wants $3,000 for one. For what it doesn't that a long, long, long way from being remotely reasonable on the price. If it were $1,500 I'd say it was high, at $3,000....well.....I don't think so.

It can be made really basic. I'm just trying to decide how high tech to make it. I could make it sense the material movement and direction and adjust the motor accordingly, or just make it dead simple and be done with it.