High torque that can be purchased.

[nnfuller]

So our team just finished our second and final regional this year, and i was left with one large impression, that we have yet to find a way to have a high torque requirement such as lifting our main arm not destroy gearboxes... currently our system of a Banebot 256:1 with a 60:22 sprocket reduction powered by an RS-775 is not cutting it in the slightest. We broke four transmissions at great cost to our team and increased stress of our pit crew. Please note that a disc brake was designed to reduce this stress but seemed to do little due to small amounts of backlash in the system. So my question is, how do you do it? I would like to find an off the shelf solution, but would also be open to custom solutions, provided the don't seem like they would require excess machine time or custom gears. While our fabrication team is very talented we do not have the technology to cut our own gears. Thank you for your help

[theprgramerdude]

Spur gears. And more spur gears. Take a look at the tough boxes, they can probably be stacked together in a system, driven by two CIM's, somehow stalled, and still live. Cutting your own gears is actually very easy, if you order the stock from McMaster-Carr. They just need to be cut to length and drilled.

[Trent B]

Team 2502 made a 32 or 33:1 gearbox using toughbox gears if we added another stage it would be around 100:1, if you used cimulators as well (we didnt) it would be ~90:1 with 3 stages.

Large beefy spur gears are your friend.

[DonRotolo]

If spur gears are too pricey, then chain and chain sprockets.

Our arm is powered by a window lifter motor, with about a 4:1 reduction using gears, then another 5:1 reduction using sprockets.

I can imagine using a toughbox or similar from the RS775 to 2 or 3 stages of sprocket-based reduction.

[sanddrag]

We have a 775 in a Banebots 256:1 P60 going 10:60 driving an arm, and had problems as well. We had the end of the shaft well supported, but it didn't matter. First the ring gear spun and the output carrier plate was rounding out. So, we removed the roll pins, welded where they were, and filed it flat to match the flats in the ring gear. And we welded the carrier plate to the output shaft. Didn't have any more problems with that. Then the sun gear and planet gears on the last stage stripped, and the ring gear was starting to go. Replaced all that, and it's fine again, but it's only a matter of time. We chose these gearboxes this year because we didn't have the time or money to manufacture our own solution, but, we will not be using these in high reduction or high load situations ever again.

Do you have the technology to machine your own gearbox plates and shafts? If so, you could design a spur gear box using off the shelf gears from AndyMark or McMaster.

Or, you could potentially use AM stackerboxes, if you have the space to fit it. Or maybe a GEM500. You'd probably want an AndyMark Planetary and a Fisher Price or BaneBots 550 in place of your current 775.

Another option may be something like this driven by a lesser reduction BaneBots P60, or by a drill transmission, such as a Dewalt XRP.

I saw one team using some gears from an inexpensive Harbor Freight winch to drive their arm.

Or, you could go 330 style and use the KOP plastic Fisher Price gearbox, driving two stages of sprocket and chain reduction.

[blayde5]

Our Banebots started doing the same thing so as soon as Fisher Price gearboxes got in stock in AndyMark, we jumped on the opportunity:

Basically we got this: http://www.andymark.com/ProductDetai...ctCode=am-0822 (the motor) and used their planetary GEM gearboxes and stacked multiple ones to get the ratio we want:

First stage: http://www.andymark.com/ProductDetai...ctCode=am-0449
Additional Stages: http://www.andymark.com/ProductDetai...ctCode=am-0301

After we put this beefy thing in, we don't expect to have any more gearbox problems. Be forewarned, the whole assembly for a 180:1 ratio for us weighed about 7 pounds...

[Billfred]

We used two window motors ganged together by a shaft with a (I -think-) 10:60 chain reduction. Combined with some surgical tubing counterbalancing, we've never been wanting for torque or speed on our arm (not that we've necessarily used it a lot).

[Andrew Schreiber]

Originally Posted by sanddrag

Or, you could go 330 style and use the KOP plastic Fisher Price gearbox, driving two stages of sprocket and chain reduction.

You can also use the FP gearbox through a KoP transmission (either CimpleBox or TB depending on your reduction). Once you put a standard output shaft on the FP it is pretty simple to use. http://www.chiefdelphi.com/media/photos/36316 is how we did it.

[de_]

Constant force (rotational) springs (see 1113) and long travel compressed gases shock absorbers (similiar but longer travel than van gate lifts: as per 2056) to counterbalance all the weight and off load the motor/transmission re inertia and momentum loads will definitely be on our next motor powered arm.

[Johnny]

Fisher Price motor + fisher price transmission = 123:1 reduction
Combination of sprockets and shaft i.e 60tooth-10tooth on rotating shaft, 36tooth - 12 tooth on intermediate shaft = 18:1 reduction on two shafts

Overall reduction is 2214:1

Now some estimating:
FP motor free spin rpm= about 20770 rpm
w/ reduction 20770/2214= about 9.38 rpm or .156 rps or 56.29 degrees per second

stall torque of FP motor is .5324 newton*meters
so .5324n*m * 2214(final reduction) = 1178.73 newton*meters or 869.39 foot*pounds of torque. Now depending on how many feet your arm is, you divide that by the estimated foot pounds. So if your arm is 5 feet long, you can lift something at the end of your arm that is about 173 pounds.

This kind of setup is a very nice way to lift anything with an arm and is very reliable, has lots of torque and speed. Teams like 330 have used similar setups and i'm sure you can find more examples. Sanddrag already mentioned this.

[s_forbes]

High reduction spur gearboxes are fairly simple to make (and a fun design project!) if you have appropriate tools.

We lucked out this year and had the opportunity to get parts made on a milling machine with DROs (digital read outs). We designed a high reduction gearbox to work with unmodified AndyMark toughbox gears and output shaft, which we happened to have a bunch of from past robots. The parts that needed to be fabricated were the two plates for the gearbox, the standoffs that hold the plates apart, and the idler shafts (toughbox shafts were too short).

Due to our uncertainty we designed it to work as either a 3 stage (max reduction 53:1) or a 4 stage (190:1). Additional gearing options would be possible with the different gearsets offered by Andymark. We ended up going with the 3 stage configuration driven by CIMulators and a 12:60 chain drive to the arm sprocket, giving a total reduction of about 717:1 from the RS-775s to the arm.

I've been hoping for a while that AndyMark would come out with a spur gearbox scheme similar to this that would accept FP/Banebots motors on one of the plates. This year we made our own plates, but we would have bought them in a heartbeat if we could!

[wireties]

Try pre-loading your design with stretched surgical tubing or something else. We tried the balancers used in commercial window mechanisms this year (since a student's father works for a company that donated a few). We disconnect our arm (from the motor) and let it hang freely then pre-load the mechanism using a passive mechanism (surgical tubing or balancers in our case) so that the arm will just sit in a horizontal position with no help from the motor. Then all the motor has to do is supply a delta force rather than working against gravity etc.

We "went to school" on comments in a blog by one of the Robo-Wrangler #148 mentors. It was veeery helpful! Our arm moves up and down smoothly and easily with a single window motor and I think a smaller motor would work as well.

[ebarker]

We used a P80 to mount the arm and it is also cantilevered. The math we did showed that we cannot exceed the operating limits and should have no problem. And our experience has supported that statement.

It's all math.

[Andrew Y.]

NEUTRAL BUOYANCY IS YOUR FRIEND

[JesseK]

My personal favorite method of reducing stress on a gearbox is to use a gas shock. Why? Gas shocks are more controlled that surgical tubing. You can calculate the weight needed, the geometry, etc, and know that it will never change.