Chief Delphi - Modifying Vexpro Ball Shifter transmissions

Chief Delphi (http://www.chiefdelphi.com/forums/index.php)

- Technical Discussion (http://www.chiefdelphi.com/forums/forumdisplay.php?f=22)

- - Modifying Vexpro Ball Shifter transmissions (http://www.chiefdelphi.com/forums/showthread.php?t=119498)

Sarakiro

20-09-2013 11:02

Modifying Vexpro Ball Shifter transmissions

Hello,

Last year, Team 1676 used Ball shifters as seen here: http://www.vexrobotics.com/vexpro/ge...l-shifter.html

We had two stage transmissions, and used the standard pancake cylinders to shift from high to low. These were great on the field and relatively easy to maintain, until at Lehigh, and more frequently than not at Monty, we lost air. As most of you using the transmissions probably know, when you loose air, the transmissions shift to neutral; Thus my question: Has anyone come up with a reliable way of inserting springs into the transmission to default either a high or low gear when air is lost? beyond that, has anyone come up with a way to modify the transmission without compromising the structural integrity of the transmission case? Any suggestions?

Thanks,
Let me know

Jimmy Nichols

20-09-2013 12:42

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by Sarakiro (Post 1292119)

Is the Cylinder designed with a spring return to center. We used them, but I haven't checked the specs on the cylinder?

Nate Laverdure

20-09-2013 16:56

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by Jimmy Nichols (Post 1292132)

Is the Cylinder designed with a spring return to center. We used them, but I haven't checked the specs on the cylinder?

Specs on the cylinder. Looks like there's currently no springs.

You could switch from single rod to double rod configuration and connect springs from the chassis to the unused rod ends.

T^2	20-09-2013 17:13

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by Sarakiro (Post 1292119)

As most of you using the transmissions probably know, when you loose air, the transmissions shift to neutral; Thus my question: Has anyone come up with a reliable way of inserting springs into the transmission to default either a high or low gear when air is lost? beyond that, has anyone come up with a way to modify the transmission without compromising the structural integrity of the transmission case? Any suggestions?

How did you lose air? (I'm assuming you made a type when you said "loose".) If it was through a problem with your pneumatics system, it may be more important to secure the whole system rather than trying to rig the shifters to default to one position. (Personally, I see the default neutral as a feature, not a bug, and I wonder if 1678 might be able to take advantage of it in the future...)

Our team ran with the ballshifters last year, and though we occasionally had pneumatics leaks elsewhere in the system, the gearboxes themselves didn't present any issues in that regard. If it really concerns you, I'm sure you can rig some springs to the cylinder-pin coupler.

magnets

20-09-2013 17:56

Re: Modifying Vexpro Ball Shifter transmissions

You can probably just tie a piece of surgical tubing to some other part of the frame, then around the tip of the cylinder.

However, it's totally possible to have a pneumatic system where there are NO leaks throughout the whole season, it just takes some time. Make sure the teflon tape is applied well and in the right direction, and test ALL parts with 120 psi, and make sure that they don't drop more than 20 psi over a few hours. Use soapy water to check for leaks. Also, remember to make a tubing cuts perfectly perpendicular.

artdutra04

20-09-2013 19:13

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by magnets (Post 1292186)

Also, remember to make a tubing cuts perfectly perpendicular.

These are an inexpensive way of ensuring your tubing is all cut square:

http://www.mcmaster.com/#8288a51

Lil' Lavery

20-09-2013 19:42

Re: Modifying Vexpro Ball Shifter transmissions

I don't think 1676 would argue that it's not possible to avoid leaks. I don't think they're planning on allowing the leaks to continue with this robot and most likely will do everything in their power to avoid them in the future.

However, in the event a leak does occur, I think they want a fail safe so they don't also lose their ability to drive when they lose pressure.

DonRotolo

20-09-2013 19:59

Re: Modifying Vexpro Ball Shifter transmissions

Precisely Sean.

Quote:

Originally Posted by Sarakiro (Post 1292119)

beyond that, has anyone come up with a way to modify the transmission without compromising the structural integrity of the transmission case?

Modify them to do what? That might help us help you.

Quote:

Originally Posted by T^2 (Post 1292179)

(Personally, I see the default neutral as a feature, not a bug, and I wonder if 1678 might be able to take advantage of it in the future...)

Between my team and yours, we'd have to ask FRC 1677...:p

We lost air because of a failure. That failure mode has since been eliminated, but no doubt there are others.

I was thinking that a plain rubber band would do the trick.

T^2	21-09-2013 00:00

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by DonRotolo (Post 1292213)

I was thinking that a plain rubber band would do the trick.

I would advise against it. Our team missed a potential division win in 2011 because of rubber bands. Springs are your friends.

MrBasse

21-09-2013 13:30

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by T^2 (Post 1292247)

I would advise against it. Our team missed a potential division win in 2011 because of rubber bands. Springs are your friends.

I would assume (I don't know the situation you were in) that rubber bands had nothing to do with missing out on a win, rather how you used them caused your problems. Rubber bands are great tools when used wisely. They are cheap, plentiful, and easy to work with. At your next competition try walking around the pits to find a direct replacement for that critical spring that you used, then try finding a rubber band... Springs are not quite as friendly going around objects, you can't tie a spring to something without using another material or drilling a hole, and if a spring breaks or deforms you have to have a replacement that is the same size and strength. We never plan to use them, but rubber bands have been necessary additions to our robots all three years and have performed near flawlessly when taken care of.

Kernaghan

21-09-2013 14:07

Re: Modifying Vexpro Ball Shifter transmissions

I wonder if there is a way of modifying the ball shifter to avoid pneumatic shifting all together, even something like using window motors(servo might not be powerful enough to shift on the fly).

DonRotolo

21-09-2013 18:02

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by Kernaghan (Post 1292304)

I wonder if there is a way of modifying the ball shifter to avoid pneumatic shifting all together, even something like using window motors(servo might not be powerful enough to shift on the fly).

Absolutely there is, but for most, pneumatics are far more reliable, simpler, and lighter. These can easily be shifted with a servo, it that servo used, say, a Chap-Stick "extender" mechanism to do the actual pushing.

cmrnpizzo14

21-09-2013 19:38

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by Kernaghan (Post 1292304)

I wonder if there is a way of modifying the ball shifter to avoid pneumatic shifting all together, even something like using window motors(servo might not be powerful enough to shift on the fly).

Can't ball shifters be purchased with a servo instead of pneumatics anyways?

EDIT: 254th post goes out to the cheesy poofs. I love those guys.

T^2	21-09-2013 20:07

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by cmrnpizzo14 (Post 1292331)

Can't ball shifters be purchased with a servo instead of pneumatics anyways?

No.

Billfred

21-09-2013 20:25

Re: Modifying Vexpro Ball Shifter transmissions

Quote:

Originally Posted by cmrnpizzo14 (Post 1292331)

Can't ball shifters be purchased with a servo instead of pneumatics anyways?

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.

cmrnpizzo14

21-09-2013 21:25

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!

Sarakiro

22-09-2013 10:28

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.

magnets

22-09-2013 12:01

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.

EricH

22-09-2013 13:04

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.

ErvinI

22-09-2013 13:20

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.

magnets

22-09-2013 13:45

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?

DonRotolo

22-09-2013 20:50

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?

magnets

22-09-2013 21:06

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?

AllenGregoryIV

22-09-2013 21:49

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.

Sarakiro

23-09-2013 10:57

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.

Bruceb

24-09-2013 10:37

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

AllenGregoryIV

24-09-2013 10:49

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.)

Bruceb

24-09-2013 11:27

Re: Modifying Vexpro Ball Shifter transmissions

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

T^2	24-09-2013 23:26

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".

All times are GMT -5. The time now is 23:31.