compact transmission

[Aren_Hill]

i've got an interesting predicament. I've been redesigning and improving our swerve drive from last year, and i've decided to leave dewalts behind and move on to something with nicer ratios. But the problem is the odd constraints on the transmissions size and placement.

A. The output shaft needs to be vertical
B. It would need to accommodate 2 small cims and maybe a big one also
C. It needs to be as short as possible meaning from the back of the motors to the outer plate of the transmission, hopefully around 6 inches in total length, I forget the length of a cim but the shorter the better
D. 3 or more speeds capable of being shifted without pneumatics, servo's or one of the small motors in the kit will be used. preferably servo's
E. customizable ratios.

Any advice?

[MrForbes]

Are you really sure it needs 3 speeds?

[Aren_Hill]

As compared to normal drivetrains the needs are different for this swerve in particular.
The front 2 wheels would have a gearbox driving them same with the back 2. and by pointing these sideways (shortways on the sizing box) and running the 2 sets in opposite directions it turns in place. But dragging 4 2.5" tires around like that requires alot of torque so we need an extra low gear for that. In addition to that i'd like a normal driving gear say 7 fps, then a really quick gear of 10+fps

[Lil' Lavery]

Originally Posted by Aren_Hill

A. The output shaft needs to be vertical
B. It would need to accommodate 2 small cims and maybe a big one also
C. It needs to be as short as possible meaning from the back of the motors to the outer plate of the transmission, hopefully around 6 inches in total length, I forget the length of a cim but the shorter the better
D. 3 or more speeds capable of being shifted without pneumatics, servo's or one of the small motors in the kit will be used. preferably servo's
E. customizable ratios.

Any advice?

The best piece of advice I can give you is, ease up on your constraints. What you're asking right now is rather unrealistic for use on a FIRST robot. Ignoring the DeWalt transmission, 3+ speed transmissions have been rather large (same with any multi-speed for that matter) compared to your current requests. Here are a handful of links to pictures/white-papers on various 3/4 speed transmission used by FIRST teams in the past, each of which violate one or more of your design constraints.
http://www.chiefdelphi.com/media/papers/1580
http://www.chiefdelphi.com/media/photos/26744
http://www.chiefdelphi.com/media/photos/26830
http://www.chiefdelphi.com/media/photos/17476
http://www.chiefdelphi.com/media/photos/17478
http://www.chiefdelphi.com/media/papers/1539

Good luck, and I certainly hope you can pull off your design successfully at your current restraints, and I hop these pictures provide some helpful hints into possible directions to pursue.

[camtunkpa]

Aren,

I can offer two bits of advice. While your constraints are tight, I think you might be able to pull off a three speed transmission one of two ways. I'm thinking you'd have to use either custom planetary sets or ball shifting. The planetary transmission will take a bit more R&D, but could also be as easy as modifying a dewalt transmission to the gearing you want to achieve. There is some good information on how planetary transmission work on www.howstuffworks.com. As far a the ball shifting option, 222 has been using ball shifting since 2004. We have come away from the three speed the last 3 years because of the game. Here is our current iteration of two speeds http://www.chiefdelphi.com/forums/sh...ght=tigerdrive

We use 3/8" face 20 D.P. gears with a 14.5 degree pressure angle. I could see a three speed being built with about 1.5" between the plates or maybe a little less using the current gears. You could always use different D.P. gear and face widths to more suit your needs, but you're going to be running a fair amount of power through the gearbox and I wouldn't go much smaller without some major calculations to back it up. Anyway best of luck to you. If you have any questions about ball shifting you can either contact me or team222badbrad and we will help you to the best of our ability.

[Aren_Hill]

As of right now I am meeting with a Representative of Forest city Gear on Wenesday to talk with him about hopefully making a custom Planetary transmission that will integrate 2 cims with an empty spot for the big one if we end up with weight for it.
The necessity of a 3 speed also ends up on the robots final COG as this year our 2nd gear with dewalts was 10fps which with the sudden turns of a swerve drive can lead to some scary tipping even with a good COG we never tipped over however.
So if next year we end up really short i may go with 2 speeds like 4 and 10.
Which in that situation I would most likely use a dewalt and only use 2 speeds set where i want them.

edit:
http://www.chiefdelphi.com/media/photos/26104
Thats the closet thing i've been looking at but im attempting to avoid the dewalt

[Lil' Lavery]

If you only use two-speeds, a ball shifting method (like 222) would be quite do-able. A 3-speed might be possible if you could manage to shift it with a servo accurately, although that would be a much greater challenge and likely far less reliable, especially for your middle speed.

[=Martin=Taylor=]

Originally Posted by Aren_Hill

i've got an interesting predicament. I've been redesigning and improving our swerve drive from last year, and i've decided to leave dewalts behind and move on to something with nicer ratios. But the problem is the odd constraints on the transmissions size and placement.

A. The output shaft needs to be vertical
B. It would need to accommodate 2 small cims and maybe a big one also
C. It needs to be as short as possible meaning from the back of the motors to the outer plate of the transmission, hopefully around 6 inches in total length, I forget the length of a cim but the shorter the better
D. 3 or more speeds capable of being shifted without pneumatics, servo's or one of the small motors in the kit will be used. preferably servo's
E. customizable ratios.

Any advice?

Why are you so fixated on coaxial swerves? From the looks of your drivetrain last year it seems you were running each module on an independent Dewalt. Why not just put the transmission inside the modules?

I know 469 did this last year with the Dewalts, and I've even seen a dog-shifting setup before. It would certainly keep things compact.

[Aren_Hill]

I like not having to worry about wires getting caught up. Another advantage is it makes it ALOT hard for the programming people to mechanically break anything. (we have this issue with other parts usually)
This next iteration will only have 2 gearboxes rather than 4 like last year one in front one in back.
We've weighed the pros and cons and coaxial came out on top for us.
And everything ends up a little more spread out and easier to maintain.

[=Martin=Taylor=]

Originally Posted by Aren_Hill

I like not having to worry about wires getting caught up. Another advantage is it makes it ALOT hard for the programming people to mechanically break anything. (we have this issue with other parts usually)
This next iteration will only have 2 gearboxes rather than 4 like last year one in front one in back.
We've weighed the pros and cons and coaxial came out on top for us.
And everything ends up a little more spread out and easier to maintain.

You could always use one of these. And yes, they are FIRST legal (or at least they were in 2006).

[AdamHeard]

You really need to lax the requirements or prepare to spend a lot of money and time on a custom design.

For the season, 3 speeds really isn't necessary. the easiest option (although it is past your length requirement; but a small CIM is about 4 3/4", so a shifting gearbox that is only 6" total is kind of wack. Especially a planetary) would be an andymark super shifter to power each pair. The mounting plate would have to be remade with some changes to allow a 3rd motor.

the other good option would be to put the dewalts in the module with slip rings.

Originally Posted by Aren_Hill

i've got an interesting predicament. I've been redesigning and improving our swerve drive from last year, and i've decided to leave dewalts behind and move on to something with nicer ratios. But the problem is the odd constraints on the transmissions size and placement.

A. The output shaft needs to be vertical
B. It would need to accommodate 2 small cims and maybe a big one also
C. It needs to be as short as possible meaning from the back of the motors to the outer plate of the transmission, hopefully around 6 inches in total length, I forget the length of a cim but the shorter the better
D. 3 or more speeds capable of being shifted without pneumatics, servo's or one of the small motors in the kit will be used. preferably servo's
E. customizable ratios.

Any advice?

Woah. Those are some crazy tight constraints, but it can be done... What size frame members are you mounting the swerve module to? If it's a 2 incher, I bet I can design a 2 speed gearbox that could meet your needs... Wanna have a CAD swap? Crab for gearbox?

Anyway, on to some suggestions...

A. Easy, just work on how you mount the box.
B. Ew, big CIM. It's a great motor, but keep this in mind: Those motors were from a discontinued product. If you can't find them anywhere, they're too heavy, and many FIRSTers complained about them, what's the likelihood of seeing them in the Kit again? Just saying...
C. Interesting. If you want the motors to face mount, it's fairly easy. If you want the length of a CIM to be the entire size, then you've got a fun challenge to make.
D. I'm not digging this 3 speed thing... a 4 speed is actually easier than a 3 speed, and both are totally unnecessary. If you're having turning issues with your steer setup, you should probably thin out your wheels. What tread are you all using for your bot?
E. No sweat. Also, planetaries aren't customizable... So you should try and stay away from them. They're also heavily expensive. IMO, not worth the cost.

Edit: Not to sound harsh to others, but seriously... Comments in a thread should be helpful to the question asked. Suggesting something that changes his entire design (such as a non co-ax) aren't helpful or relevant. It's like the old saying "If you don't have something nice to say, don't say anything," but instead "if you don't have anything relevant to say, don't say anything at all!" Sorry if I came off as harsh, but taking the topic away from where it's going doesn't help that much...

[maclaren]

I agree that ball shifter is the only way to go. The big thing you will need to keep in mind is the spacing between the motors so that you can access the back of the output shaft; but I guess you could have the shift rod come out the end of the output shaft and shift it that way. if you use 3/8" face width gears place thin thurst bearings between the shifting gears then you should end up with an overall length of 1-1/4" ish plus the length of the body of the CIM.

As far as customizable ratios you would be limited as to which gear pairs you could use and still maintain the approriate center to center distance. The smaller the DP that you use the more ratios that you will have available to you; However the weaker the teeth will be.

Side thought: I have a really great idea of how to solve the problem with truning a swerve drive module. But I'm not going to say what it is until my team actually makes a crab drive system so I will just leave you guys in suspense. My idea would allow me to turn a four inch wide wheel EASIER yes easier than any standard crab drive module with any other size wheel.

[Aren_Hill]

I am currently downloading inventor from first base again so i'm planning on quickly recadding the whole thing.
i've remembered the size of box i'd have to fit this in though. So thats what im basing shape off of.

The bottom plane of the frame to the top plane is 5.5" vertical distance and that box is 6" wide, with plenty of length for a transmission.

So generally what i was thinking was having the cim shafts pointing down, combining to one central input in between the two (inline). And then having the transmission go back up flush with the back of the cim, which is why the shape of planetarys would fit well. But I am liking the ball lock idea i think i may have a good way to fit it.

Once i get the cad redone i'll post some pics

edit: im not go away from coaxial you can't make me lol it worked well last year it'll work well again
Craig: the wheels will be 3.5" diameter by 2.375 wide with Natural rubber rougtop on them, they got wider from last year i dont like being pushed. 2" is the thinnest i'll go

[Aren_Hill]

Okay, so after having some talks with Craig (114manuallabor). I'm removing the 3-speed constraint. And now i get to figure out what the most compact 2 speed system is. I'm gonna take a quick look into modifying a dewalt further and using one of those due to there tiny size.