Adding a winch to scale the tower! Two 775s run through a 97:1 reduction that will be able to lift Bob around 12 inches/second while under load. Not shown: the ratchet and pawl that will prevent back-driving (the rope will start the match un-spooled, so the winch only needs to run in one direction).
The overall shape of the gearbox is a little funky – kind of an “L” shape. That’s because the drum of the winch needed to fit down between the drive gearboxes near the center of our robot. There was no room for the 775s there, so we used the gear spacing to move the motors out and up to where there’s more room.
Here’s a video of the winch running (sorry for the vertical orientation – I was caught up in the excitement of the moment): https://www.youtube.com/watch?v=95u0-QNm7u4
What is the material of the white plastic looking gears? Curious why you guys went with those.
They appear to be from a Fisher Price Powerwheels gearbox, which was a staple of the FRC KoP for many seasons. Pretty sure they are nylon.
They are indeed from a Fisher Price gearbox! Mainly used them because they were lying around, and because they’re so light. The first couple iterations of our winch used VersaPlanetaries, but with all VP stuff now out of stock, the only way we were going to get the reduction we wanted in the weight we had to spare was though a custom gearbox. This weighs just about 4 pounds, motors included.
This is what our climber would look like if it worked consistently.
Looks very well built! I love custom gearboxes like this. I’d also love to see the rachet and pawl. It sounds better than using a socket wrench Thanks for sharing this!
Looking nice. Can’t wait to see it in action at the Michigan championship.
No problem! Here’s the ratchet attached to 60-tooth gear. Big thanks to our sponsor Lakeshore Cutting Solutions in Zeeland who waterjet cut this for us.
A couple more pictures:
Gearbox plates shown with two copies of the ratchet and pawl (why not have an extra just in case?): http://i.imgur.com/JpiDqYV.jpg
Gearbox structure assembled: http://i.imgur.com/oZToaec.jpg
Ah cool. I see it now in the original picture too. Looks awesome.
Looks great, there is some serious lifting torque produced in that gearbox. Planning on lifting the other alliance members? According to the JVN calc it could lift 3 150lb robots in under 4 seconds:)
I should clarify here - the first couple iterations were designed but not built. When we finally got some free time to start building a climber, all the VP stuff had gone out of stock, forcing the redesign.
The stall load is theoretically right around 1000 pounds, but I think we’ll stick to just lifting ourselves so we can keep the current draw at a manageable level haha. Right now we’re looking at about 15 amps per motor under the expected load.
(And always obey the curve: http://motors.vex.com/bb-775)
Nice, I love the design.
I highly suggest steel gears for the final stage, we were using the vexpro gears and broke several teeth during the Bayou Regional which is the reason we were not able to hang during the quarter finals.
Our stall torque was just slightly higher than your calculated,
Unfortunately Andymark does not sell 18 tooth steel gears with a 1/2 inch hex bore.
While the final stage gears might not be able to take the stall torque generated by the 775’s, the ratchet means that the motors should never need to be be stalled.
It’s not even just stall torque - it’s torque under load, particularly with the long cantilever on the shaft. Pulling your robot up with one of these should work for awhile, but before you know it, you could snap teeth on that pinion gear, fall from the tower, and lose your regional. Happened to me in 2013. Still bitter.
If you could somehow double the face width of that gear (second pinion / output gear) that would help I think. Maybe you’ll be okay with this, I dunno.
What’s wrong with ratcheting wrenches?
How much does the entire apparatus weigh? Our team has been experimenting with mechanisms under intense weight constraints, and I’m interested in how much such a wickedly powerful custom gearbox setup such as this weighs.
Thanks for bringing up the gear tooth failure issue! If we end up breaking teeth, the plan is to buy some steel replacements from Boston Gear and hex-broach them ourselves. Also, I’m sure the winch could tear itself apart in many different places if it actually tried to lift 1000 pounds.
The entire winch system here comes to 4.7 pounds (was hoping to get closer to 4, but oh well). That doesn’t include speed controllers, though.