Chief Delphi - Modifying Vexpro Ball Shifter transmissions

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Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by Billfred (Post 1292337)

You're thinking of AndyMark's shifters (though given past rules on servos, every year we've used AM shifters we've used pneumatics).

The VexPro line is pneumatics-only.

Yes thank you. I knew there were servo operated shifters somewhere!

Re: Modifying Vexpro Ball Shifter transmissions

Absolutely, leaks in general can be fixed. The only issue is that the solution to the problem is active, such that it can be applied in the event of a leak. As everyone knows, pneumatic systems pop; It is inevitable. I have thought about the spring/elastic solution but the one drawback is that regardless of what is modified, it is subject to the conditions within the gearbox. I am thinking that the fix (if internal, which I currently favor) should be subjected to a long term test. Perhaps a pre-Prototype phase.

I did see that the transmissions came with a servo option (has anyone used it?) - I just find that I am not quite in love with servo functionality in general. And is anyone considering other transmission options?

Pardon the "loose" earlier.

I would like to hear a bit more about neutral being a feature. I can only imagine it being used in one paradigm.

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by Sarakiro (Post 1292400)

I did see that the transmissions came with a servo option (has anyone used it?) - I just find that I am not quite in love with servo functionality in general. And is anyone considering other transmission options?

Where did you see this? I can't find it on the vex pro page.

I'm not sure, but I think that team 67 might have used a motor to shift a ball shifter this year, but just ended up using a zip tie to lock it in high gear because it didn't work well, so you might want to ask them about that.

Re: Modifying Vexpro Ball Shifter transmissions

I don't know for sure if this will be an option next year, but did anybody try using an electric solenoid this last year, particularly for shifting? They were legal.

Thinking that might be a smidge easier than modding the transmission for a spring.

Re: Modifying Vexpro Ball Shifter transmissions

This thread will answer a few questions:

http://www.chiefdelphi.com/forums/sh...t=window+motor

Specifically, regarding 67's shifting this year:

Quote:

Originally Posted by Adam Freeman

We were unable to package our typical window motor shifter with the smaller chassis size. We then designed a VEX-393 motor shiter setup that ended up stalling out and frying a digital side car (or two...). After that, we tried to design a typical servo shifting system. We ran out of time before the season started to install the servo shifter, but after looking at it more closely I don't think it would have worked very well. We were trying to emulate the AM-Super-shifter servo setup, but had a hard time getting the rotation of the shift arm transferred into axial movement of the shaft that shifts the gear box. There seemed to be a lot of play in that shaft. Probably just needed some additional constraints that we didn't have time to design in.

I also looked into trying to find a suitable electric solenoid to shift with, but was unable to find one that seemed like it met all the rules and had enough power to shift.

In the end, we just zip tied the ball shifters in high gear and attempted to avoid pushing matches.

Maybe the guys at VEXpro can design one for us teams that can't seem to make room for a pneumatic system.

Regarding electronic solenoids (Adam touched upon it in the above quote, also):

Quote:

Originally Posted by AllenGregoryIV

We also looked at the possibility of electronic solenoids to shift or be brakes and couldn't find any that had enough power or worked in a way that we though would be reliable or adaptable for that application.

In conclusion, window motor shifters are very large, VEX motor shifters fry up a lot, VEXpro doesn't make servo shifters (and 67 had issues making a replacement), and electronic solenoids aren't strong enough.

Re: Modifying Vexpro Ball Shifter transmissions

As it has been said before, there aren't solenoid that are strong enough to hold the shifter in gear.

Also, solenoids have a limit to the amount of time that they can be actuated for before they burn up, which won't work with shifters.

The solenoids remind me of the mabuchi motors (from 05 maybe?), a neat idea, but they are just too small and not powerful enough to be useful, so nobody used them.

In 2012 we used the most powerful solenoid allowed by the rules to pull a pin on our ball hopper thing. It had almost no power at all (I could push it backwards with just one finger), and was replaced at competition with a cylinder smaller than the ones normally used in shifting gearboxes.

Has anybody ever used a solenoid on an FRC robot before?

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by magnets (Post 1292446)

Also, solenoids have a limit to the amount of time that they can be actuated for before they burn up, which won't work with shifters.

Not all solenoids have this limitation. Ever see a flipper solenoid on a pinball machine?

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by DonRotolo (Post 1292511)

Not all solenoids have this limitation. Ever see a flipper solenoid on a pinball machine?

Can you find one that's FRC legal like this?

Re: Modifying Vexpro Ball Shifter transmissions

I haven't asked Adam about his setup but from what he said I guessing they were running the 393s off the 6V output of the sidecar. The rules this past year allowed you to run the 393s off of a speed controller (R52 in the 2013 Robot Manual). We ran two 393s off a single talon (at about 10V) to be our frisbee flicker. We would stall them pretty regularly during testing and never fried anything. On occasion we would lose a tooth on the internal gears but we only had to replace two all year. I'm not sure how well they will hold up under stall conditions for shifting but you can definitely get more power out of them by running them at around 10V instead of the 6V supplied by the sidecar directly. Probably need to do some type of position control on them or just lower the voltage you use to stall them, it might worth considering.

There might even be a full VEX solution to translate the rotary motion to linear with a 393, a small 12 tooth vex gear and a piece of VEX rack gear.

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by magnets (Post 1292420)

I might not have been there, but I did see them somewhere. Regardless, I would stick to pneumatic shifters, personally.

Thanks. We will likely try modifying the transmission to see if there exists a desirable outcome.

Re: Modifying Vexpro Ball Shifter transmissions

so the vex pro ball shifters have a neutral position? Can the be programmed or do you only get it when you run out of air?
Thanks

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by Bruceb (Post 1292789)

so the vex pro ball shifters have a neutral position? Can the be programmed or do you only get it when you run out of air?
Thanks

You can't do it in the normal setup of using a double solenoid to control the shifting cylinder. If you switched to using two solenoids (one for extend and one for retract) you should be able to vent both sides of the cylinder and get it to shift into neutral. (I haven't tested this.)

Re: Modifying Vexpro Ball Shifter transmissions

seems like it might be useful for powering a pto that way.

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by Bruceb (Post 1292797)

seems like it might be useful for powering a pto that way.

Pretty much, yeah. If you wanted to do so I would recommend using one of Bimba's 3-position cylinders with a half-stroke at .25" and a full-stroke at .5".