asid61
07-10-2014, 09:43
http://www.chiefdelphi.com/media/img/089/089bad59d3d7c18943dff98f86bee6c6_l.jpg
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/0BzU34PeNVT0QeVJTS2QxaEZTdTQ/view?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. :P
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.
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/0BzU34PeNVT0QeVJTS2QxaEZTdTQ/view?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. :P
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.