reversed cim gearbox / output shaft question
 

high speed: 18.77 ft/s
low speed: 8.46 ft/s
weight: 3.4lbs without cims, 9lbs with cims.

tl;dr: How can I extend the output shaft of the ball shifter without having to knock out the roll pin or use a coupler?

I designed this to be something that I would personally be comfortable with making during build season, so everything is cots with the exception of the gearbox plates.

The problem comes with the output shaft of the ball shifter. Even when using the long version, and using chain in tube, the output shaft still isn't long enough.

Currently, my solution is to knock out the roll pin and replace the output shaft. but removing a roll pin would fall under "something I wouldn't do during build season", or really in general.

another solution is to use a coupler, but I would like to avoid that if I can.

Has anyone come up with a elegant way to direct drive using the output of the ball shifter?

Re: compact reversed cim gearbox and output shaft question
 

That's a nice box! I think increasing the first stage reduction a tad would be a good idea to get your high gear below 18fps, below 17fps, really. I've packaged that reduction before while maintaining good tooth contact.
You also need to move your CIMs up so that the belt doesn't touch the middle pulley twice, as it appears to do now.
How is this 3lbs without CIMs!? It should be 2lbs max from what I'm seeing here. :D Are you using aluminum pulleys?

EDIT: Oh, are you using Vex pulleys? Switching to 3mm GT2 pulleys from SDP-SI will probably net you better results and let you mess with the ratios a bit; you may even be able to get them from faster sources. Of course, figuring that out before build season would be necessary. Given the design you have right now, it might be easier to switch to a 3 CIM gearbox than lower the speed.

On the extending the output:
I already spoke to Chak about this, but I think you can just press out the roll pin. What makes you hesitant to remove it? It seems like something people do fairly often in other applications.

EDIT: If you make a length of thunderhex and retain it some way other than using a roll pin in the ballshifter output socket, then you don't need to worry about high tolerances or roll pins. A shaft collar between the gearbox and 2x1 should suffice.

Re: compact reversed cim gearbox and output shaft question
 

the pulleys are staggered. The middle one is 15mm while the ones on the cim are 9mm so they dont overlap. I may be misunderstanding your comment?

whoops. my ball shifter weighed over 2lbs :D actual weight is 1.85lbs.


funny thing. The one time me and Chak had to remove a roll pin, We spent a good ten minutes hammering it, then broke a drill bit. I ended up going in with a dremel and cutting apart a steel coupler instead of taking out the pin. guess it left a bad taste in my mouth.

I'll take a look at some sdpsi pulleys. should be easy enough to increase the ratio from there. maybe shave off a tiny bit of weight as well.

Re: compact reversed cim gearbox and output shaft question
 

Sometimes pins are tapered and only come out one way.
You need a hardened punch the right size for the pin is all.

Re: compact reversed cim gearbox and output shaft question
 

The drawing indicates it's a metric roll pin size 3mm x 18mm. McMaster Carr carries that size.

Just put it in a hand arbor press, it should be easy to remove and install. A M2.5 cap head bolt from the hardware store would work to push the old one out.


http://content.vexrobotics.com/vexpr...g-20141016.PDF

Re: compact reversed cim gearbox and output shaft question
 

This. I would never use a drill bit as a bunch, it's worth investing in a set of punches for your team, we use ours all the time.

Re: compact reversed cim gearbox and output shaft question
 

Just a note that the ball shifter hex shaft is held in with both a roll pin and red Loctite. After you remove the roll pin, you'll want to heat the shaft with a heat gun to soften the adhesive bond of the red Loctite, then remove the hex shaft.

Re: compact reversed cim gearbox and output shaft question
 

After reading this thread, I now understand that trying to drill out the roll pin back then was a bad idea. :o

Has anyone ever tried to replace the vex ballshifter output in real life though?

Re: compact reversed cim gearbox and output shaft question
 

An Arbor press is the "correct tool" for the job. Applying controlled steadily increased pressure until the pin slides is far better than Hammering / Pounding the pin.

An Arbor press is also handy for removing mounting pins/collars from pneumatic actuators and setting bearings in slightly undersized holes.

A one ton arbor press can be found for under $100, it really one of those basic tools that any reasonably well equipped FRC shop should have.

A drill bit is too long for the job; it's subject to column buckling with high axial force (Euler formula). You can make a short pressing tool on your lathe for a specific job. When in a hurry I have found a steel bolt the correct sizes works well enough.

Re: compact reversed cim gearbox and output shaft question
 

I believe he was trying to drill it out, not press it out with a drill bit.
I've seen videos of people hammering them out and in before, but if it's possible to press that sounds much easier than whacking at it.

Re: compact reversed cim gearbox and output shaft question
 

I believe most spring pins are hardened spring steel (something like 1080). While you can drill it with a HSS bit, it would be a slow process. A cobalt bit(M42) would be the best option, and still ugly. Drilling it out would definitely be my last choice of methods.

Re: compact reversed cim gearbox and output shaft question
 

Having just gone through a season where I tried to use lots of press-fit bearings without a press, I can attest to this. And now that I've found that an 8mm shaft makes a wonderful press-fit into a 5/16 bore, I'll be needing a press even more.

Re: compact reversed cim gearbox and output shaft question
 

I've had a lot of luck pressing things with just a large vise (we have nice wide ones in the woodshop) but there are times when a press comes in handy.

Getting one suitable for 1/2" hex broaches like a 5 ton might be wise.

Re: compact reversed cim gearbox and output shaft question
 

An arbor press is handy for handling small jobs.

A 1/2 hex broach is nearly a foot long, it really requires a full size press that has more travel. Most small presses seem to be at least 12 Ton. If you have the floor space for one, might as well go for at least a 20 ton as they are not much bigger.

Re: compact reversed cim gearbox and output shaft question
 

I'll mention it to my team if they look at buying one, but since I've graduated, my 2 cents have become worthless. Oh well. I've got access to some large presses at work.