pic: Four Speed Three CIM Gearbox

Three CIM motors. Two ball shifters. Four speeds: 17.00fps, 12.72fps, 7.36fps, 5.51fps (adjusted speeds). Four gear stages. And probably weighs a thousand pounds.

This gearbox bolts right onto my first full sheet metal drive train that I’m still working on. I do not actually intend to build this thing. I just thought it would be a cool project to work on. Also it’s probably way too complicated and heavy for what it’s worth. My team also doesn’t have the machining capabilities to manufacture something like this right now. But, all of that aside, what do you think?

What advantage(s) do you expect from having a four-speed, 3CIM gearbox over a two-speed 3CIM gearbox? A four-speed 2CIM gearbox? Heck, even a single-speed 3CIM gearbox?

Basically, why? This seems like overkill.

And for the 2016 FRC game, OVERDRIVE 2: OVERKILL. This game is played on a 10 meter by quarter mile field in the streets of Miami. Any robot to get to the finish line in 10 seconds wins by default and gets a free ride to champs!

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It’s a cool piece of machinery, and looks pretty sick to boot. I believe you said you weren’t seriously considering this, as it has no real advantages over a two-speed in most games.

Ever considered taking that third and fourth position and turning it into a PTO? That wouldn’t be very important in a game like 2015 whatsoever, nor a game like 2014. But, for example, in 2013, 254 used a PTO to power their awesome climber.

It looks quite well done for the project. It’s not useful for competition, but it looks good anyway. :stuck_out_tongue:
Nice render too.
For the top shaft of the gearbox, instead of using a hex bearing, I would round down the end of the shaft and use a round bearing.
If you only have 2 standoffs going to the mounting plate, I would change it to 3-4.

EDIT: +1 on the PTO idea.

Did you read the description?

To me, the big “why” is why have four speeds over about a total 3:1 high-to-low ratio? If you’re going to bother with four speeds, spread them out a bit wider!

At a minimum, I would put the shifts a factor of 2:1 apart, resulting in an 8:1 overall ratio from high to low. At a “standard” 2.56:1 ratio between shifts, the total range would be 16.77:1. At 3:1 per shift, it would be a massive 27:1, which could be a real game changer in some highly defensive games or games with steep ramps. Especially if you want to reserve some CIMs for manipulators!

Another good PTO example: 1114’s hanger in 2010 (which was sickly fast :eek:)

Thanks, yeah I know it’s really overkill. So basically to answer the question of why I decided four speed, my team is working on the summer design project thing that was put out a couple weeks ago. The end game involves chasing down a mini bot on the field, so the end game team wanted to be able to travel at the mini bot’s speed (~13fps) to line up with it and a faster speed to catch up to it. We also wanted to be able to move around a little slower with more control for adjusting shots and in case anyone wants to push us. I know we could’ve gone with a two speed and controlled the speed with code, but that’s what the team decided to go with. Also, it gave me a nice challenge which is always fun.

Ever considered taking that third and fourth position and turning it into a PTO? That wouldn’t be very important in a game like 2015 whatsoever, nor a game like 2014. But, for example, in 2013, 254 used a PTO to power their awesome climber.

Our 2013 drive train gearbox used a PTO to power our climbing mechanism as well. There was something wrong with the throw of the shifter that made it not work, but it was still pretty cool. I don’t think there’s an opportunity in the game that we’re designing for to use a PTO, but I did think about it while designing this.

Description wasn’t posted when I posted my comment.

When I was playing around with the JVN calculator I was trying to get them as wide as possible. The limiting factor, though, was that the two speeds that we wanted for the end game were 17fps and 12.72fps, which put limit on how much i could work the speeds while still keeping it realistic. I guess I was just focusing on the speeds needed for this game and not the wide array that there could have been.

Hehehe…been done already sort of…

Impressive Design!
Team 368 made a 4-speed transmission in their 2005 robot, IIRC also.
Cool stuff!

Sorry for me asking, but what is a PTO gearbox?


They’re used to transfer power from the drivetrain, which usually has a lot of power to spare, to other mechanisms, usually for an endgame.
Lifting oneself in 2013 could be accomplished using all 6 cims in a drivetrain, for example.

This is really cool. If you can find the machining resources to make one I would totally do it as an off-season project. Sure it may not be the most practical thing for the competition season but you’ll learn a lot while doing it. You could also design up a 2 speed variant and make that too and do a comparison - maybe even post a white paper so we can all learn about it. Good stuff!

Under what scenario would that be useful? Once you can break traction you see no benefit to moving slower, unless somehow you needed to very precisely position your robot with fine movements.

Who says that your robot always has the same weight? I seem to recall that there was a game in which robots extended a ramp to lift their alliance partners. I also “blue skied” a robot for Ultimate Ascent which would have literally grappled its alliance partners and made a 90 point outside climb (code name Fezzik, for fans of The Princess Bride). If you wanted that same robot to also fly around the field scoring frisbees for the first hundred seconds of the match, having a multi-speed PTO transmission with a total span of 20+:1 would have been epic.

I always love these hypothetical crazy gearboxes and ratios people come up with. Practical, maybe not, but definitely awesome.

Assuming your robot was geared for 18 feet per second in high gear, and 0.67 feet in low gear (a 27:1 spread), you’d need to have a 1800 lb robot (or group of robots) to take advantage of the gear ratio and never trip the breaker in a pushing match. If the robot weighed any less, you could get away with a smaller spread and never worry about tripping a breaker.

That sounds like my kind of game!! :smiley: