pic: Four Speed Three CIM Gearbox

[hectorcastillo]

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[Lil' Lavery]

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.

[asid61]

It looks quite well done for the project. It's not useful for competition, but it looks good anyway.
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.

[Gregor]

Originally Posted by Lil' Lavery

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.

Did you read the description?

[GeeTwo]

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!

[hectorcastillo]

Originally Posted by GeeTwo

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!

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.

[Cory]

Originally Posted by GeeTwo

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!

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.

[GeeTwo]

Originally Posted by GeeTwo

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!

Originally Posted by Cory

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.

[magnets]

Originally Posted by GeeTwo

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!!

[thatprogrammer]

Originally Posted by magnets

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!!

2002 meant your robot could be several hundred pounds due to how heavy the movable goals were. 71 could drag over 900 pounds that year!

[hectorcastillo]

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.

[Lil' Lavery]

Originally Posted by Gregor

Did you read the description?

Description wasn't posted when I posted my comment.

[The other Gabe]

Originally Posted by Lil' Lavery

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.

in 2014, a 3 CIM gearbox helped my team be the most dominant team in the PNW for the first 3 weeks (ish). no one could catch up to us, and our rams on defense rekt teams with loose ball carry. we didnt have a 4 speed though... it was just all fast, all the time

[Chris is me]

I think you went quite overboard on the weight reduction on the outer plate. A pocketed 1/8" plate with no flanges, especially with the reduction being supported off of the end of the plate past the standoffs like that, will have some issues with flex and rigidity. With gearbox designs posted to CD in general there's often an overemphasis on lightening the plates as much as one possibly can, when it's really not that substantial of a weight savings over a more conservative lightening pattern or even unlightened plate.

[hectorcastillo]

Originally Posted by Chris is me

I think you went quite overboard on the weight reduction on the outer plate. A pocketed 1/8" plate with no flanges, especially with the reduction being supported off of the end of the plate past the standoffs like that, will have some issues with flex and rigidity. With gearbox designs posted to CD in general there's often an overemphasis on lightening the plates as much as one possibly can, when it's really not that substantial of a weight savings over a more conservative lightening pattern or even unlightened plate.

Thanks for the feedback. Would you suggest that I cut back on the lightening holes, add some flanges, and/or thicken the plate?