Sprag Clutch in Reversing Application 1

[chrispe]

Guys:

I am trying to make a very simple low power (less then 100 in-lbs max torque) all mechanical drive which couples to a lead screw at a 4:1 ratio in the forward direction and a 1:1 ratio (or lesser ratio) in the reverse direction. The motor is reversible so I thought I could use (2) sprag clutches but the problem is that all I end up with is 4:1 in forward direction and 1:1 in the forward direction. I can't seem to get the output to reverse. Is this even possible ? I would prefer a planetary and don't have the ability to add a separately articulated band brake etc. Thanks for any suggestions.

Chris

 

[crysta1c1ear]

Is it for a private project, or does it have to steer clear of patented ideas?

With a planetary gearset, the whole thing can be done with a free wheel to hold the ring gear to give a 4:1 ratio in one direction, and a clutch between sun and ring to give direct drive when the motor is in reverse.

The motor would connect to the sun gear, and the direction you run the motor would determine whether the ring turns giving the 1:1 direct drive or the ring is blocked, giving the 4:1.

In one case the sun would move like this

http://www.dekaper.com/~cc/ATV/screw1.mpg

making the gears move 1:1 like this

http://www.dekaper.com/~cc/ATV/direct1.mpg

Reversing the motor would make the clutch open
watch

http://www.dekaper.com/~cc/ATV/screw1.mpg

played backwards
making the gears move 4:1 like this

http://www.dekaper.com/~cc/ATV/sun_drives1.mpg.

(Watch the 4:1 video backwards too if you can, since you want to imagine your motor reversed.)

 

[chrispe]

cyrsta1c1ear:

Thanks for the answer, for some reason I did not see it. Your comment on patented technology is right-on. Is this solution patented or has it been around for a while ? If it is patented, do you have the number ?
My preference is to steer clear of patented technology. Thanks

Chris

 

[chrispe]

cyrsta1c1ear:

One more question, I see how everything locks in the one mode, but in the free wheel mode, what keeps the ring gear from free wheeling with the planet carrier ? thanks in advance

Chris

 

[crysta1c1ear]

That's because I didn't think it through and just answered 'off the cuff'. The other way, it doesn't work as I described it!

I had assumed the ring tried to turn in opposite directions in reverse and drive. We can take the discussion offline if you like. I'll leave my email address on my website.

http://www.dekaper.com/~cc/email.txt

 

[crysta1c1ear]

The pictures aren't quite what we want since they weren't made to anwser this, but they give an idea of a manual solution for changing the ratio.

For the ring, replace a fixed part by a rotating splined collar.

Put a lever on the collar so that it can be pushed backwards and forwards.

The lever in one position would block the gear.

The lever in the other position would cause the collar to transfer drive.

So with a lever moving backwards or forwards, the ring could be blocked or take drive from the sun and you'd have the two different ratios.
That would be a manual solution free of any patents.

For an automatic version, you'd just have to get something to move the lever to select ratios.

 

[enginesrus]

The simple solution is to use a servo system like all CNC machine tools do. I think you can accomplish the same with a stepper motor. This system eliminates all the mechanical wear parts.

 

[chrispe]

xr7755:

I guess I should have explained more of the issue. I need to advance as quickly as possible which requires a 4:1 ratio. The return is unloaded and needs to happen very fast. I am limited in motor speed, and do not want to have an incredible amount of inertia, to dissipate, I thought it best to have a ratio which automatically adjusted depending on the direction of the motor. Ideally, I was hoping for an all mechanical solution as I have some other more complicated ways that will work.