Winches
 

Hello all,

I am trying to find a winch online that can be modified to use with a cim motor.

My main criteria are that it can be turned forwards and reverse, to allow for the level of rotation to be adjusted. I also want it to use a worm gear, that way the tenstion in the arm will not affect it's position if the motor is not actively fighting it.

So far I have been able to find some good winches online that can satisfy these requirements. But the one of the most crucial things that we need in a winch is turning out to be a lot harder to find than I expected, that being the ability to release a clutch (if you will) allowing the cable to turn freely. If we could find something that could do all of this available to purchase online, that would be awesome! But we are open to possibly making our own from scratch (possibly with an existing gearbox) if we really have to, as we have the tools to do that (lathe, cnc mill, mills, etc..)

Stay warm and good luck,
3734

Re: Winches
 

You may want to consider doing something along the lines of what the guys at iR3 are doing for Robot In 3 Days.

They're basically using a gearbox with a shifter that shifts between an engaged gear (for rotating the winch) and disengaging from the gear into a neutral position for release of the "catapult".

It's pretty straightforward if you've worked with shifters before, and as far as "custom" goes it's not too custom, there exist parts that make it pretty simple.

It's probably easier to do than modifying a COTS winch to your specifications.

Re: Winches
 

Thanks for the reply!

I do recall seeing that, I'll have to try and find the video again. do you know where I can get one? Also, if the motor is turned off but the gearbox is not in neutral, will the catapult be able to move at all?

Re: Winches
 

You can find several types of shifters both at Andymark and VEX pro. I am not sure if they all backdrive or not, but I highly suspect that they do.

Re: Winches
 

The video can be found on their channel in the iR3 section (http://www.youtube.com/user/robotin3days?feature=watch)

The gearbox they're using is made by them, it's the Modulox Lunch Box gearbox (http://www.andymark.com/product-p/am-0846.htm) however they've modified it a bit by adding a cylinder to push a dog gear for the shifting on the final drive axle, and have an encoder at one point.

Yes, if the motor is off and the gearbox is not in neutral it will almost definitely move. To counteract that, the iR3 team basically has an encoder on the gearbox and uses a closed-loop algorithm to essentially hold the winch back until they're ready to release into neutral (to my understanding). AKA, theres an encoder, and in fraction of a second, if it notices the force of the catapult pulling up on the winch (and thus moving the axle), the program will compensate for this force on the axle by the catapult by turning on the motor until it reaches the position it should be at. This is done at such a quick pace that it's not even visible and seems that the winch is completely steady. When ready to launch, just shift into neutral.

The two noteworthy videos are:
http://www.youtube.com/watch?v=4WZ1t...EBsIGLxVsJdhL5
http://www.youtube.com/watch?v=eLzEN...EBsIGLxVsJdhL5

Re: Winches
 

If you can't necessarily make your own custom shifter like they did, I suspect you can do something along the lines of take a dog shifter from, say, VexPro or AndyMark, and take one of the drive gears off.

The dog shifters offered by WCP in conjunction with VexPro have a dog gear that, if you take off one of the drive gears, should toggle between drive and neutral. This is true for pretty much any dog gear shifter you'll find, if you can find others (I think AM uses dog shifting)

Re: Winches
 

I'm no programmer and wonder if the algorithm can truly hold back the force necessary to keep it stationary. In the video shown, there is a reference to Anthony Lapp helping them with the shifting mechanism, using a spring. It sounded to me that there is a latch of some sort involved. In 2010, we used a ratchet gear setup to prevent backdriving.
If its just shifting into neutral by removing one of the stage gears, with some fancy programming, then this should be a cinch! :)

Re: Winches
 

Thanks for the reply!
This was definately very helpful and remains a viable option for us and others, and is definately doable.

I of course want to keep our options open, so I have to ask, is there anywhere we can get something similar to this with out any back driving?

I am intrigued with the idea of using a gearbox with a worm gear, but I do not know where to get the equivalent of a stand alone dog clutch to use in apsuch a design.

Re: Winches
 

I advise considering other options too. What is maximum amount of linear distance winding that is needed? If it is not that large, you can pull a flexible tension element other ways besides wrapping it around a drum.

Consider how you might combine the way a bow string works with a turning disk plate, and you could discover a much more easily triggered mechanism for shortening a cord and instantly releasing stored energy, without having to accelerate any drum (or disk plate) rotation, wasting stored energy.

-Dick Ledford

Re: Winches
 

You *could* use an Andymark WormBox as the input on one of the shifter gearboxes, essentially preventing the winch from back driving. However, that would probably reduce the speed of the output to something too slow to be usable, so it would be necessary to replace the gears in the shifter to have no reduction, rather than the stock reduction used.

Re: Winches
 

This would probably be the easiest way.

The strength of 3D printed parts is always in question, but given that AndyMark's wormgear gearbox uses plastic gears, you can probably CAD up some gear to do what Whippet is saying and have a 1:1 ratio.

Use 100% infill and ABS and it should be sturdy enough.

Re: Winches
 

According to my research the WormBox is a) relatively efficient (compared to other worm gears) and b) easily backdriveable. I've never used one but saw a few postings that stated this was the case. I'd be careful if you plan on using it as your only means of backdrive prevention, as not all worm gears are anti-backdrive.

Re: Winches
 

What would you recomend to use as a replacement that is not backdriveable? Our team has decided that we want to avoid the robot in 3 days approach of using the motor to fight the force of the catapult, so the best way to do this (from what we can tell) would be to use a worm gear gearbox with a clutch.

The two biggest problems with this would be:
1. Finding an appropriate gearbox that can not be back driven
2. somehow utilizing a clutch with the gearbox.

Number two Is proving to be the hardest for us right now, as we have never built a clutch and do not really know where to go to look for one. I saw a picture from 2010 a few days ago of what seems very doable but I am struggling to find it.

Any help with either 1 or 2 would be appreciated.

Re: Winches
 

If you look at one of robot in 3 days recent videos they have added a ratcheting wrench to the gearbox so it doesn't backdrive.

Re: Winches
 

Mman is correct.

They found it to also be a bad idea so they stuck in a sears ratchet wrench on one of the hex axles to stop it from backdriving - super cool.