Ratchet Switch under load

[Monochron]

Originally Posted by EricH

the second seems to say that there's a worm drive between the ratchet and the winch--and then talks about "easily" spinning the winch!.

Huh, I didn't read it like that, but as long as you get the concept now, cool

Having a ratchet device machined might be the only solution, but we are looking into industrial grade ones that might shift easier under load. Money is a bit of an issue, but I imagine any ratchet we found would be cheaper than a transmission.

[Ether]

Originally Posted by Monochron

Having a ratchet device machined might be the only solution, but we are looking into industrial grade ones that might shift easier under load. Money is a bit of an issue, but I imagine any ratchet we found would be cheaper than a transmission.

How about a pawl?

[Derek Bessette]

Have you tried reversing the motor while you release the ratchet? This may work depending on how quick your winch is.

[Monochron]

Originally Posted by Derek Bessette

Have you tried reversing the motor while you release the ratchet? This may work depending on how quick your winch is.

From what I can tell no motors that are legal for FRC would be able to reverse like this. There are also weird alternatives like holding your tubing with a hardstop while you unwind your winch, but we haven't gone down that road just yet.

Originally Posted by Ether

How about a pawl?

A pawl and ratchet gear is an interesting idea. Making a housing that will rotate the two of them together might be a little tricky but actuating the pawl should be as simple as actuating a ratchet switch on its own.

[AdamHeard]

Originally Posted by Monochron

From what I can tell no motors that are legal for FRC would be able to reverse like this. There are also weird alternatives like holding your tubing with a hardstop while you unwind your winch, but we haven't gone down that road just yet.


A pawl and ratchet gear is an interesting idea. Making a housing that will rotate the two of them together might be a little tricky but actuating the pawl should be as simple as actuating a ratchet switch on its own.

I don't understand why reversing the motor would be illegal.

[Dan.Tyler]

I also don't understand why reversing the motor would be illegal.

If you have the power to pull your winch, simply pull it slightly more (in the direction used to store power in your launcher), hold it there while releasing your pawl or switching the ratchet clutch. Then release the motor.

[Monochron]

Originally Posted by AdamHeard

I don't understand why reversing the motor would be illegal.

Originally Posted by Dan.Tyler

I also don't understand why reversing the motor would be illegal.

"no motors that are legal for FRC would be able to reverse like this"
As in no motors that are legal to use in FRC are capable of this.

Because of how slow we need to gear our motor to be able to pull back with 100+ lb. of force, that same motor will not be able to unwind at the very high speed of our shooter.

We have not calculated this, but empirical evidence seems to confirm it. I would be surprised if there are FRC motors that wouldn't slow the rate of your shot if you left it mechanically connected to the winch system.

[AdamHeard]

Originally Posted by Monochron

"no motors that are legal for FRC would be able to reverse like this"
As in no motors that are legal to use in FRC are capable of this.

Because of how slow we need to gear our motor to be able to pull back with 100+ lb. of force, that same motor will not be able to unwind at the very high speed of our shooter.

We have not calculated this, but empirical evidence seems to confirm it. I would be surprised if there are FRC motors that wouldn't slow the rate of your shot if you left it connected.

He doesn't mean reverse as the shot motion. He means continue to drive it so the natural motion of the ratchet/pawl causes the pawl to jump one tooth. If the pawl is actively being pulled on as well during this moment it can disengage.

[Monochron]

Originally Posted by AdamHeard

He doesn't mean reverse as the shot motion. He means continue to drive it so the natural motion of the ratchet/pawl causes the pawl to jump one tooth. If the pawl is actively being pulled on as well during this moment it can disengage.

Yes, but if your motor is connected to your winch shaft throughout the shooting movement then your shooter will be forced to pull your motor as it moves forward. This will be a considerable source of drag. This is why most designs use some sort of shifter which has a neutral gear.

If you know of another way to remove the drag from the system though, that would be great.

[Dan.Tyler]

It sounds to me like they are using the motor/gearbox to turn the ratchet itself. I.e, taking the place of your hand if you were to use it as a hand tool.

And then using the lever to disconnect the motor/gearbox from the winch. The ratchet is acting as both the ratchet/pawl and the "shift into neutral" options.

To relieve the load on the lever, you simply need to drive the motor slightly forward, then actuate the clutch lever on the ratchet while releasing the motor. It will relieve any load the ratchet is holding momentarily (long enough to flip the switch) while changing directions/freespinning back the partial tooth distance.

To ensure disengagement, power on whatever you're using to flip the switch, then pulse the winch motor several times at 5-10 hz, full power, for a couple milliseconds each time. So effectively a very slow pwm at low power. It should sound like the motor/gearbox is clicking. You may have to play with your on vs off times and frequency to get it to work every time.

[AdamHeard]

Originally Posted by Monochron

Yes, but if your motor is connected to your winch shaft throughout the shooting movement then your shooter will be forced to pull your motor as it moves forward. This will be a considerable source of drag. This is why most designs use some sort of shifter which has a neutral gear.

If you know of another way to remove the drag from the system though, that would be great.

I'm sorry, you're right. I was thinking that the ratchet pawl combo also disengages the motor, but there was no basis for this thought! My apologies.

What it does buy you is the ability to move the disengage to a different portion of the system while the ratchet is taking load, meaning less force is required to pull a dog or whatever you're using (then fire with the ratchet). This is two actuations for the same thing, but could be the right choice for some teams.

[Monochron]

Originally Posted by Dan.Tyler

To relieve the load on the lever, you simply need to drive the motor slightly forward, then actuate the clutch lever on the ratchet while releasing the motor. It will relieve any load the ratchet is holding momentarily (long enough to flip the switch) while changing directions/freespinning back the partial tooth distance.

This could work I think. The only issue is the concept of a hard-stop. In order to be able to reverse the motor and relieve the tubing load on the ratchet something else will have to be taking the tubing load for that short amount of time. Because the motor cannot spin as fast as the tubing wants to shoot, we can't just reverse it real fast and try to flip the ratchet switch.

Honestly though, that just shifts the problem of releasing under load to whatever is taking the load while you reverse your motor. So many the real questions should be "what will hold and release the tubing effectively". And for that I think some kind of simple pneumatic hook would do the job best.

[Dan Richardson]

We made a video of how our ratcheting, shift to neutral gearbox works. What was not describe in this video is the mechanism that disengages the dog gear. This was accomplished by a 1.5" bore, 6" stroke cylinder on a 12" lever arm. The dog is re-engaged by the internal spring.

http://www.youtube.com/watch?v=xx3I2...u8SDSA&index=5

I'm not sure if this video will be helpful but it may depict what others were describing.

[Dan.Tyler]

Originally Posted by Monochron

This could work I think. The only issue is the concept of a hard-stop. In order to be able to reverse the motor and relieve the tubing load on the ratchet something else will have to be taking the tubing load for that short amount of time. Because the motor cannot spin as fast as the tubing wants to shoot, we can't just reverse it real fast and try to flip the ratchet switch.

Honestly though, that just shifts the problem of releasing under load to whatever is taking the load while you reverse your motor. So many the real questions should be "what will hold and release the tubing effectively". And for that I think some kind of simple pneumatic hook would do the job best.

I'm not certain you would need to relieve the loading (you may need to)after reducing it by cycling the motor.

If you do, perhaps pushing a high friction material into the winch spool, acting like a disc brake would provide sufficient relief without necessarily holding the entire load with another device.