If your building a fork lift style entry this year most are using gears and chain or cables and winches. If your using a single drum winch just for lifting then your hoping gravity will pull down your lifting forks .
The advantages of a two drum cable winch for lifting totes is that one drum takes up the cable while the other plays it out and vice versa.
I thought I would share the steps of constructing a simple version of this winch with everyone .
The team I mentor is planning to use a Vex Planetary Gear box attached to this style winch .
Thank you for posting this! Our team was using only one drum and this makes much more sense.
Could I ask a favor of you? We are setting up a site dedicated to helping teams find people with various FRC skills. Basically it is a searchable directory with contact options. If you’d be interested, we’d appreciate you checking it out and perhaps registering your skills at http://frcpitcrew.com
Another option that removes the requirement to machine is to use AM hex hubs. Use an extended or ‘long’ shaft on your gear box and slide your hubs on.
Keep in mind that your wire / rope on the drums may not build up or release at the same rate as the diameter changes (if it overlaps itself on the drum). Many teams use a tension spring on the pull-down side to account for any inequalities between the drums.
We’re using a single drum with a “continuous” loop of winch line to pull our forks both up and down. We have about five wraps of line around the drum. We use a small turnbuckle to make sure that the line is always tensioned properly. We used this approach successfully on our elevator in 2013 and our line never tangled or overlapped. Our drum that year was made out of ABS pipe screwed on to AM hubs. Last year our catapult winch used a 100% 3D printed ABS drum, no metal hubs required. It held up fine and we needed a lot of torque to retract our catapult. Used a hex bore on the drum because the ABS can’t take the stress concentration in a square keyway. We’re 3D printing our drum for this year’s winch and we added helix grooves in it to guide the wraps.
I will be happy to help and will post my skills on your site this weekend .Just love that photo of team 254 robot that is a great example of the two drum winch used in FRC.
I have designed and erected several telescope enclosures such as domes and roll off roof observatories and these two drum winches are simple and very effective in opening shutter doors or rolling off huge roof structures weighting several thousand pounds. So it should have no trouble with a few totes and a garbage can.
I am currently making a 3 inch version of this winch and will post photos of its construction soon .
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There is one design flaw with the winch that I original posted and I will post photos soon to correct this. It is not a flaw in the winch performance it deals
with the game itself . At the end of the game power is shut off , so if your lift is stuck up in the air your team will need to have a fast way to lower the lift manually . So I am currently replacing the nub shaft that was machined with a threaded hole that will have a 1/2 in bolt sticking through the support bearing and housing. This bolt will need to be cross drilled and cotter pin installed to prevent it from turning. This will allow the pit crew to safely ratchet the lift down with a socket and extension on a cordless drill. Sorry I guess that’s why they make erasers on every pencil. :o
This is a new and improved two drum winch design . It will allow you to use a ratchet and socket to lower the lift once the power is cut at the end of the game if your stuck with 6 totes in the air. Cable guides from home depo are simple screen door bearing / track guide mounted at bottom and top of the frame above and below your load your lifting or pulling down.The
cables are directed to top side of drum one and bottom of drum two . No slack in ether cable is allowed .Then as # one drum is lifting drum #two is spooling out and vise versa . To prevent the tote load from placing stress on the motor a constant spring force will be pulling the lift in the upward motion . You could use your Vulcan spring freebie or some KOP Latex Tubing . Hope these Ideas help other teams with there designs.
One thing to keep in mind is how your cable stacks up on the drums. If it starts piling in one spot, the radius increases and it wants to haul in more cable per turn. If your un-spooling drum isn’t keeping up, they’re going to start fighting each other…and your winch will stall or something will break.
A continuous loop design, like you say, helps avoid this, especially if your drum is wide enough and your cables aligned well, as it will only keep one layer of wraps across the drum.
Better yet…have your lathe folks cut spiral lagging (round-bottom groove) into the drum surface so that the cable always sits where it is supposed to. As a crane guy, that’s how you get pro at cables on drums.
I have posted this video to show how well the two drum winch works .
The lift we had previously prototype in alum. had to be replaced because
of its bending under attempting to lift 6 totes . The new lift painted red with new pneumatic arms should improve the overall performance of the robot. The winch shows no noticeable damage from about 4 hours of practice lifting .