Idler that engages/disengages w/ direction change

[TheTick]

Looking for a mechanism to engage/disengage a gear train when drive gear direction changes. Scale is too small for a sprag clutch.

We already have one candidate idea to throw an idler in/out axially with a helical gear. We would also like to find a way to kick an idler gear in/out in-plane with gear rotation.

 

[gearcutter]

I'm curious; why would you consider a sprag clutch in this application?
Won't the use of one lock the rotation of the gear train when the direction is reversed?

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[TheTick]

Not even considering sprag clutch, due to cost and availability (whether it works or not is thus moot).

The root issue is that there are two separate gear trains with one prime mover. Need to engage train #1 when driving gear goes CW, and drive #2 when driving gear goes CCW.

 

[gearcutter]

To me the point was not "moot" as I was attempting to understand the kinematics of the configuration. You mentioning the sprag clutch suggested that you wanted to lock the gear train in the reverse direction.........I was having trouble understanding why you wanted/didn't want this feature to be part of the system.

Posting a drawing of what you propose would help us to help you.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[MikeHalloran]

I think I've seen such things, comprising an idler gear that's free to move in an arcuate path around the driveR gear. The idler gear or its carrier needs to have a little intentional friction drag wrt the the driveR to make the driveR carry it from engagement with one train to engagement with the other train.

Do not expect long life from such an arrangement.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

TheTick,

A sprag clutch is probably the most compact device available for a "freewheel" application. So if it does not fit, I don't know what other device might, including roller clutches or ratchets.

If you have some axial space, you may consider a spring-wrap clutch:

Hope that helps.
Terry

 

[diskullman]

How about needle bearing clutches from Torrington or INA

http://www.ina.de/content.ina.de/en...up_roller_clutches/drawncuprollerclutches.jsp

Russell Giuliano

 

[NuclearNerd]

old-fashioned ratcheting clutches are generally smaller than sprag or roller clutches for the same torque capacity. If you are really Macgyvering it, you can cut apart a ratcheting screwdriver or socket wrench.

It sounds like MikeHollaran is describing the reversing mechanism on a VCR drive, which you can kind of see here:

http://www.repairfaq.org/sam/idler.gif.

VCRs needed to engage /disengage different gear trains depending on direction because the tape had to be pulled from one reel or the other during FFW or REV.