Incorporating the vex ball shifter into a WCD Drive

[Walter Deitzler]

Originally Posted by connor.worley

Remember: WCD chains the front and back wheels separately.

I was thinking either two separate sprockets or one of those double-sprockets.

[Nemo]

I'm picturing a wider custom version of the 3rd stage add-on that Vex sells. Put your two sprockets inside and change the 3rd stage ratio to be appropriate for direct drive. Sounds like a fun winter break project.

[Brian Selle]

If you are able to remove the hex output shaft pressed into the ball shifter shaft and replace it with your own, you could just add some pulleys/sprockets and a couple standoffs like the attached picture. The picture shown has 30 tooth pulleys and the clearance with the 4 standoffs is close... to get more clearance with smaller pulleys/sprockets you could rotate the entire gearbox slightly about the output shaft and use the 2 standoffs in the upper left/lower right corners (2nd picture). Would be good to work in some more support for the cantilevered gearbox.

[MichaelBick]

Originally Posted by btslaser

If you are able to remove the hex output shaft pressed into the ball shifter shaft and replace it with your own, you could just add some pulleys/sprockets and a couple standoffs like the attached picture. The picture shown has 30 tooth pulleys and the clearance with the 4 standoffs is close... to get more clearance with smaller pulleys/sprockets you could rotate the entire gearbox slightly about the output shaft and use the 2 standoffs in the upper left/lower right corners (2nd picture). Would be good to work in some more support for the cantilevered gearbox.

Attachment 13286
Attachment 13288

If I remember correctly, the output speed of the ball shifters without the third stage is a bit too fast to direct drive.

[AdamHeard]

Posted CAD of the implementation here.

This is a real rough model showing our concept for mounting the ballshifter only, it's a bit clunky now and if we ran with this we'd likely refine the mount a bit more.

Don't interpret this as a specific decision by 973 to do 8wd with that spacing, those wheels, etc... but rather focus on the ball shifter interface, and that we're switching to 1/2" hex all around in hex bearings.

Hopefully this helps a few people.

[MattC9]

Originally Posted by AdamHeard

Posted CAD of the implementation here.

This is a real rough model showing our concept for mounting the ballshifter only, it's a bit clunky now and if we ran with this we'd likely refine the mount a bit more.

Don't interpret this as a specific decision by 973 to do 8wd with that spacing, those wheels, etc... but rather focus on the ball shifter interface, and that we're switching to 1/2" hex all around in hex bearings.

Hopefully this helps a few people.

Adam, unfortunately my cad is not working could you add a picture or rendering of what y'all have come up with? Also... I see Hodgepodge and Viper, what are those? Again my Solidworks isn't working so I can not see these models.

P.S. I didn't mean to put that purple smiley next to the post... and I don't know how to take it off.

[JB987]

Adam,
Can you post a screen shot or two?

[AdamHeard]

Sheesh, nobody is ever satisfied

Here is an iso with the frame supressed, and then with the mount plate made transparent.

[BJT]

Thanks for the pic. thats essentially what we do with supershifters, but this got me past a mental block I had with implementing the 3 stage ball shifter.

[AdamHeard]

Originally Posted by BJT

Thanks for the pic. thats essentially what we do with supershifters, but this got me past a mental block I had with implementing the 3 stage ball shifter.

Yup! Trivially different from what we did w/ SSers in 09.

The biggest pain was how to cleanly attach to the face of the ballshifter w/ the extra standoff we had.

It's clear in CAD, but not in the pic. The lower hex standoff doesn't attach to the ballshifter, but rather to that .25" thick plate with a hidden flathead 1/4-20. The plate then attaches to all 3 ballshifter mount holes and is a large bearing surface on the face. This should really adequately handle the moment reaction.

Since we don't have one on hand, we were unsure of the strength of that face. We assumed that since IFI put in hex bores for standoffs, that small local face contact for moment reaction would cause damage. So right now we're assuming we need that large plate to touch so much.

[DampRobot]

Originally Posted by AdamHeard

Sheesh, nobody is ever satisfied

Here is an iso with the frame supressed, and then with the mount plate made transparent.

Thanks for posting the pics. (It's great to be able see what you're talking about without downloading it and waiting for SolidWorks to load.)

Is that plate supposed to be flush with the 2x1 tubing? If so, there's going to be some interference between those two button head screws and the tubing wall. Also, how would you plan to remove the gearboxes in competition?

[AdamHeard]

Originally Posted by DampRobot

Thanks for posting the pics. (It's great to be able see what you're talking about without downloading it and waiting for SolidWorks to load.)

Is that plate supposed to be flush with the 2x1 tubing? If so, there's going to be some interference between those two button head screws and the tubing wall. Also, how would you plan to remove the gearboxes in competition?

The CAD is very clear here. The plate is flush, the bolts go through the tube, through the plate, into the tapped standoff.

We remove the bearing block faceplate, remove the two 1/4-20 buttonhead, and the gearbox is removed. Identical in function to our current designs. We consider the bearing block an integral part of the gearbox.

None of this is untested, all we did was make the ballshifter the same black box more or less as our current designs.

[JB]

Originally Posted by AdamHeard

The CAD is very clear here. The plate is flush, the bolts go through the tube, through the plate, into the tapped standoff.

We remove the bearing block faceplate, remove the two 1/4-20 buttonhead, and the gearbox is removed. Identical in function to our current designs. We consider the bearing block an integral part of the gearbox.

None of this is untested, all we did was make the ballshifter the same black box more or less as our current designs.

What are the gears that you are using in the third stage, standard IFI ones? One of the possible issue's I noticed with IFI's third stage is that it sits below the bottom of the plastic housing from the previous two stages, causing an issue if you want to mount the housing to the bottom of a robot with very little clearance. I was thinking about changing up the gear ratio and was wondering if that is what you did.

[Brian Selle]

Originally Posted by jb1403

What are the gears that you are using in the third stage, standard IFI ones? One of the possible issue's I noticed with IFI's third stage is that it sits below the bottom of the plastic housing from the previous two stages, causing an issue if you want to mount the housing to the bottom of a robot with very little clearance. I was thinking about changing up the gear ratio and was wondering if that is what you did.

In the CAD file he is using 34/50 for the 3rd stage. With 4" wheels this gives a theoretical 7.6/17.2 fps. If you drop down to the next IFI option of 24/60 that gives you 4.5/10.1 fps. It'd be nice to have something in between... like 30/54 which gives 6.2/14.1 fps except IFI does not have a 54T gear. It shouldn't be too hard to find a 54T gear from another source.

Having the gear hanging below the bottom of the frame shouldn't be an issue for traversing perpendicular bumps as the gear is concentric with the wheel. Parallel "ruts" might be an issue... regardless wouldn't be a bad idea to extend the mounting plates and create a guard. I really like the low CG of this design.

[scottandme]

Originally Posted by jb1403

What are the gears that you are using in the third stage, standard IFI ones? One of the possible issue's I noticed with IFI's third stage is that it sits below the bottom of the plastic housing from the previous two stages, causing an issue if you want to mount the housing to the bottom of a robot with very little clearance. I was thinking about changing up the gear ratio and was wondering if that is what you did.

Edit: above poster beat me to the punch

Look at the part names in the CAD - it's a 34:50 3rd stage. The stock 3rd stage is 24:60. The stock ratio is probably a touch slow for 4" wheels (80% speed loss gives 3.6 and 8.1 ft/s). The 34:50 reduction yields 6.1 and 13.8 ft/s. I don't know why they don't list that possibility on the ballshifter page, but any combination of gears that add to 84 teeth would work. 40:44, 34:50, 24:60 and 20:64 are the only possibilities using vex gears.

You can always cut out your belly plate to accommodate the 60T gear, it will be within the OD of the wheel regardless, so short of sliding perfectly sideways off of a ledge, it's unlikely to contact anything.

The mount Adam posted might interfere a 60T gear, depending on the OD of the standoff some modification of geometry would be necessary.