pic: 2x1 gearbox

[KohKohPuffs]

So probably using 1/8" stock would be better. If the spacing inside is too little to fit anything in, then perhaps using 2x1.5 (I think this exists on McMaster) stock or something higher would be better. Unfortunately doing this would cause you to most likely lose the ability to integrate the gearbox into a drive rail

[Chak]

Originally Posted by Andy Baker

Thomas,

You've got a nice, simple design here. One more tip to add to the comments already provided in the thread:

You will need more space machined in the top or the bottom of the tube to allow for inserting the 64 gear into the tube. Unless you have some magical conjuring skills, that gear can't currently be inserted into the pocket you have designed.

Sincerely,
Andy B.

Thanks. The bottom pocket is .125" wider than the diameter of the gear, so I should be able to just slide it in.

3D viewer here:https://workbench.grabcad.com/workbe...nm/link/495146
The bolts are a little bit messed up on the online viewer right now for some reason, bear with it.

[pwnageNick]

I love this design for what it's goals are (low weight, single speed drive with minimal parts).

I don't think most of the issues raised above are too big of an issue. I'm not sure I buy the thin wall being an issue for mounting the CIMs, and if the wall of the tube really did flex from the weight of the CIMs, some simple part (3D printed would be a good source) that goes between your belly pan and motors would solve that problem easily.

As far as pressing the bearings into the tube for the drive shaft, this is the only thing I could see being an issue. A simple fix would be some small 2D bearing blocks that mount to the tube for the bearings to be pressed into.

I would definitely just incorporate this into the drive tube. I don't see the benefit of it being a bolt on gearbox; at that point you might as well go with some bolt on COTS gearbox.

Maybe I missed it somewhere in the thread, but what gear is on the drive shaft? I think I saw someone say 64T. I think if you switched that up to 72T, that would probably be a more reasonable ratio for a single speed drive, and it would also easily solve any clearance issues with the CIM mounts and allow you to stick with 2x1 (which I think is necessary for it to be a viable choice to incorporate into the drive tube). A larger drive gear would push the CIMs out, allowing you to rotate the mounting holes a bit, keeping your 1/8" clearance from the gear while gaining some clearance from the top wall of the tube.

Great design, I really love it. I had worked on a similar idea before, but somehow that design ended up migrating away to having the gears on the outside of the tube (in the chassis) with a chain-in-tube setup.

EDIT: You may have had hesitation about a 72T gear on a 4" wheel; that would explain the 64T gear.

EDIT AGAIN: Disregard the part about the larger gear buying you more clearance space, I misunderstood how you had the mounting set up. I sketched everything you have out and see your dilemma.

[JesseK]

Love the concept. There are a lot of "you should do X" comments in this thread, but generally speaking this is a great design as-is.

Say your robot comes in at 150 lbs (w/ bumper/battery), and the game is similar to 2012 where typical strategies go about 20 feet in a single sprint. In other words, you've determined you need a 2nd stage for that game. 2015, 2014, 2013, and some 2016 bots wouldn't need a 2nd stage at all, so this is pretty situational.

Since this gearbox is modular, a new gearbox with the same interface should be plausible. How would you re-design the gearbox to do it?

edit: for reference, you'll want to go way back in JVN's spreadsheet history:
https://www.chiefdelphi.com/media/papers/2750

[Chak]

Originally Posted by pwnageNick

I love this design for what it's goals are (low weight, single speed drive with minimal parts).

I don't think most of the issues raised above are too big of an issue. I'm not sure I buy the thin wall being an issue for mounting the CIMs, and if the wall of the tube really did flex from the weight of the CIMs, some simple part (3D printed would be a good source) that goes between your belly pan and motors would solve that problem easily.

As far as pressing the bearings into the tube for the drive shaft, this is the only thing I could see being an issue. A simple fix would be some small 2D bearing blocks that mount to the tube for the bearings to be pressed into.

I would definitely just incorporate this into the drive tube. I don't see the benefit of it being a bolt on gearbox; at that point you might as well go with some bolt on COTS gearbox.

Maybe I missed it somewhere in the thread, but what gear is on the drive shaft? I think I saw someone say 64T. I think if you switched that up to 72T, that would probably be a more reasonable ratio for a single speed drive...

Great design, I really love it. I had worked on a similar idea before, but somehow that design ended up migrating away to having the gears on the outside of the tube (in the chassis) with a chain-in-tube setup.

EDIT: You may have had hesitation about a 72T gear on a 4" wheel; that would explain the 64T gear

Thanks! I was afraid that the gear might get caught in the carpet. A 70t gear might work though. I have no experience with large gears getting caught in the carpet. How close can the gear get to the ground and still be fine?

I'm expecting a lot of anecdotal answers, since the Vexpro Single Reduction Clamping Gearbox has been out for 2 years now!

[Chak]

Thanks for the suggestions everyone! For the third revision of this gearbox, I decided that it would be part of the drivetrain rail only. By moving it to the corner wheel, I was able to produce a drivetrain rail with gears and chains in tube.
http://imgur.com/a/QucQK

Since the gearbox is part of the drivetrain rail now, the CIM shafts are extending too far and would hit a 4" wheel. And well, if I have to space the motors back anyways, I might as well use the 3D printed CIMcoder instead of the SRX mag encoder.

Unfortunately, sticking with 3x1 means that

1. this needs a modified gear (in the render, it's a 70t)
2. this also needs a custom 17t sprocket
3. the chain barely clears the surrounding parts by .01"
4. the gear blocks the CIM mounting holes, which is annoying, but still possible. The shaft comes out with one shaft collar, so it's not that bad, but still annoying.

But hey, the drivetrain is still in theoryland, so these potential problems are okay.

[pwnageNick]

Love the new iteration!

Any chance you could get us a pic with the tube transparent so we can see some of the relationships and clearance between he tube and parts? Also a view from the other side would be awesome.

Great work, keep it going.

[Tom Ore]

Looks a bit like our 2015 frame.

http://imgur.com/BRxeabK

[Cothron Theiss]

Originally Posted by Tom Ore

Looks a bit like our 2015 frame.

http://imgur.com/BRxeabK

Is that a tank drive with Mecanum wheels? I'm not sure I've ever seen that before. How did it perform?

[Tom Ore]

Originally Posted by Cothron Theiss

Is that a tank drive with Mecanum wheels? I'm not sure I've ever seen that before. How did it perform?

Good question. The gear between the CIMs was never installed. We designed it in because early on we didn't know what kind of wheels we wanted to use. The drive team decided they wanted mecanum wheels so we never tried any other option.

[Chak]

Originally Posted by Tom Ore

Looks a bit like our 2015 frame.

http://imgur.com/BRxeabK

Did you guys use 3x1.5 rectangular tubing? What were the clearances between parts?

If I were to actually build my design, I would use 3x1.5, since fitting everything into 3x1 is a failure waiting to happen.

The third version is now on grabCAD, along with the STEP file and the "pack and go" Solidworks file.

[Cothron Theiss]

Originally Posted by Tom Ore

Good question. The gear between the CIMs was never installed. We designed it in because early on we didn't know what kind of wheels we wanted to use. The drive team decided they wanted mecanum wheels so we never tried any other option.

Ahh, that makes much more sense.

[Tom Ore]

Originally Posted by Chak

Did you guys use 3x1.5 rectangular tubing? What were the clearances between parts?

If I were to actually build my design, I would use 3x1.5, since fitting everything into 3x1 is a failure waiting to happen.

The third version is now on grabCAD, along with the STEP file and the "pack and go" Solidworks file.

You can download the CAD from FRCdesigns.com. Also, this robot made it into the "Behind the Designs" book so you can get some more info there.