pic: ABS-101 Front

[asid61]

Anyway, some explanation:
I've admired 192's gearboxes for a long time. I've tried (and failed) to try and make a better gearbox design that would either a) be lighter or b) be more space-efficient. The 192 design solves both of these problems quite well, so I ended up just copying everything I could about their gearbox. The cim mount belt tensioners, the flipped cims, and the overarching form are all copied from 192 using the thread on CD about their 2014 gearbox.
Because I've never actually made a ball shifting gearbox before, I copied the dimensions of the vex ball shifting shaft for the shifter shaft and just used vex ball shifting gears for the secondary. The output shaft was custom cadded so that a 1/2" hex shaft could fit inside it, and so that the WCD style sprockets stay inside the gearbox.

Spces:
Total weight: 1.75 lbs without the motors and motor screws, 10.25 lbs with motors including plates, screws, sprockets, gears, pulleys, spacers, bearings, shafts, and the pneumatic cylinder. This is ~0.2 lbs heavier than 192's gearbox, which I think is due to the use of a longer 0.75" shaft for the ball shifting shaft, the sprockets in the gearbox to make it WCD-compatible, and the all aluminum timing pulleys in place of plastic. Of course, it is still a pound lighter than COTS gearboxes and it saves space by hanging the cims over the 2x1, and the WCD-compatibleness is worth the 0.2lbs/ gearbox to me.

Speeds: 2.83:1 and 6.29:1 for a 2.2x spread. Speeds with a 3" wheel are 9.0 and 19.9fps according to the JVN design calc. It's a 3-cim gearbox, so I decided to go fast. You can lower the speed by an fps or so by making the large pulleys larger.
The primary is a 12:24 belt rediction, followed by shifting 14:44 and 24:34 ratios, allowing for use of COTS vex gears. The 24t gear is lightened with some small pocketing as well as the large pulleys.

Eveything in the gearbox is from SDP-SI (GT2 5mm pitch belts and pulleys), Vex, or has to be custom made. The way I designed it, you can layout all the curves on the gearbox using a scribe and rule, and the holes / slots can all be made with a manual mill (technically, although it would be easier to redesign it with rectangular plates if weight isn't an issue). Holes need to be in the right place though.

CAD files for this gearbox and all parts in it are located here: https://drive.google.com/file/d/0BzU...ew?usp=sharing They are in SolidWorks 2013 format. There is a folder labeled "STP" with a .stp file of the gearbox in it for those who do not use SW.
Feel free to do what you want with it except sell it. Then I want a 10% cut.

After uploading the pics to CD, I had to redo the motor mounts a little bit so that I could source the belts from SDP-SI. It looks almost the same, but it's a little different.

Please give design advice or comments.

[JesseK]

This looks really nice and compact, though I wonder how you plan to keep the output shaft attached? Or is that an inner race of a hex bearing?

[Joe G.]

Originally Posted by JesseK

This looks really nice and compact, though I wonder how you plan to keep the output shaft attached? Or is that an inner race of a hex bearing?

192's gearbox, the setup that I believe inspired this one, used a hex sleeve as it's output shaft, and a separate hex shaft permanently mounted to the drivetrain for the center wheel. This allows the gearbox to be removed without removing any wheels.

[asid61]

Originally Posted by Joe G.

192's gearbox, the setup that I believe inspired this one, used a hex sleeve as it's output shaft, and a separate hex shaft permanently mounted to the drivetrain for the center wheel. This allows the gearbox to be removed without removing any wheels.

Correct on all counts. I updated the description.

[Rauhul Varma]

Nice job!

The biggest thing that stands out to me is the shield doesn't seem particularly useful, necessary nor easy to make. Having a large slot for the chain leaves a lot of room for material to be sucked into the gearbox and once debris in there, a shield can actually speed up the wear of the gears; this is why 192 makes their drivetrain almost 100% sealed (and maybe 100% this year). Additionally, if you look at 254 they do not use shields on their gearboxes and have (obviously) had a lot of success. I would consider reevaluating your use of one here.

(One last thought: machining holes in your plates to mount the shield will be more difficult than it was on 192's 2014 gearbox as your plates curve out)

Anyways good job, I'm curious to see how the 5mm GT2 belts do!

[asid61]

Originally Posted by Rauhul Varma

Nice job!

The biggest thing that stands out to me is the shield doesn't seem particularly useful, necessary nor easy to make. Having a large slot for the chain leaves a lot of room for material to be sucked into the gearbox and once debris in there, a shield can actually speed up the wear of the gears; this is why 192 makes their drivetrain almost 100% sealed (and maybe 100% this year). Additionally, if you look at 254 they do not use shields on their gearboxes and have (obviously) had a lot of success. I would consider reevaluating your use of one here.

(One last thought: machining holes in your plates to mount the shield will be more difficult than it was on 192's 2014 gearbox as your plates curve out)

Anyways good job, I'm curious to see how the 5mm GT2 belts do!

I can remove the polycarb shield if needed, and because it's on the bottom of the gearbox I might do that (it's not a safety concern).
If we did use it, we would velcro it to the plates, so I didn't add mounting holes.
And if we ever make this gearbox, it will be in a few weeks to months at best. I'm one of two machinists, and the other one can't work for a while due to school. Mainly I put it up on CD to get opinions and release the CAD.
Thanks for the input!

[Dunngeon]

Originally Posted by asid61

I can remove the polycarb shield if needed, and because it's on the bottom of the gearbox I might do that (it's not a safety concern).
If we did use it, we would velcro it to the plates, so I didn't add mounting holes.
And if we ever make this gearbox, it will be in a few weeks to months at best. I'm one of two machinists, and the other one can't work for a while due to school. Mainly I put it up on CD to get opinions and release the CAD.

Thanks for posting the CAD!

[asid61]

Originally Posted by Dunngeon

Thanks for posting the CAD!

No problem. Though you should double check the gear spacing and the belting if you do decide to use this. I only gave 0.001" clearance on the gear spacings, and some of the parts are difficult or time-consuming to machine (read: shifter shaft).

EDIT: Also, you'll need to fix the output shaft to your specification. Right now it's necessary to use a roll pin I think, and those are hellish to get in apparently.

EDIT2: You can't use this with a 3.25" wheel. When at the lowest tension point, it intereferes. You have to use a 3" colson for this to be effective, or greatly increase the C-C distance of the motors. I'm reuploading the corrected CAD files right now.

[asid61]

Redid the gearbox to use 24t pulley in place of 26t, so that a 3" wheel can be used and not interfere with the cims. A 3.25" wheel will not work. The speeds are the same as before.
Weight is 1.75lbs, because I extended the output shaft a little bit so that you can use a 10-32 screw like a roll pin to keep the second shaft in place. You can also use e-clips to constrain the secondary shaft if you like. There was also an error with the shifting shaft spacing which was fixed.
Reuploaded to the Google Drive folder at the top.

[RonnieS]

Anyone wan't to post the link to the 2014 192 thread on theirs?
-Ronnie

Never mind, found it quickly on accident haha.

[asid61]

Originally Posted by Ronnie314

Anyone wan't to post the link to the 2014 192 thread on theirs?
-Ronnie

Never mind, found it quickly on accident haha.

In any case, here it is for those who want to see it:
http://www.chiefdelphi.com/forums/sh...d.php?t=126357

[mplanchard]

A beautiful model. Well done. Marie

[asid61]

Originally Posted by mplanchard

A beautiful model. Well done. Marie

Thank you!

[asid61]

Reuploaded with a few marginal improvements including adding an encoder to the small shaft and a mounting hole pattern to match the vex ball shifters/ WCP shifters.