VEXPro 2014: After The Season

[Travis Hoffman]

Anyone want to take a stab designing an "electric cylinder" linear actuator product compatible with FIRST-legal motors and made with lightweight yet strong materials?

http://www.nookindustries.com/Produc...FeY-MgodlDMAZw

[nuclearnerd]

Originally Posted by Travis Hoffman

Anyone want to take a stab designing an "electric cylinder" linear actuator product compatible with FIRST-legal motors and made with lightweight yet strong materials?

Princess Auto is a popular auto parts and surplus store in Canada. They sell a Chinese brand of electric cylinder (complete with limit switches and potentiomenter feedback!). I picked one up at the beginning of the season, but we never modified it to use FRC legal motors because our design didn't end up needing one. One unanswered question was whether we could speed up the (really slow as stock) extension speed:
http://www.princessauto.com/pal/en/E...ator/8272551.p

[Thad House]

2 more suggestions, and they are both about CAD.
1. Make the parts default to standard, not metric. Since the parts are made in standard, all the metric dimensions get really weird. I know this would be hard to change for all the current stuff, but maybe next time.
2. Fix the hexes. Maybe this is something only I do, but usually I like constraining hex shaft to the hex bores. For some reason, the hex bores in all the VexPro parts are all over the place in dimensions, so it is next to impossible to directly constrain hexes.

[DampRobot]

Originally Posted by Thad House

2 more suggestions, and they are both about CAD.
2. Fix the hexes. Maybe this is something only I do, but usually I like constraining hex shaft to the hex bores. For some reason, the hex bores in all the VexPro parts are all over the place in dimensions, so it is next to impossible to directly constrain hexes.

This is probably because the nominal size of the hexes varies. For example, I'm pretty sure the bearing fits are .500", the gears, sprockets, and pulleys are about .502" nominal, and the spacers are probably a bit larger than that.

I'd rather have the VP CADs be the correct size. I like hexed things based on features concentric to the shaft (like the hub OD) and then make one part of the hex on each of the two parts parallel rather than making two parts in each of the hexes coincident.

[T^2]

Originally Posted by DampRobot

This is probably because the nominal size of the hexes varies. For example, I'm pretty sure the bearing fits are .500", the gears, sprockets, and pulleys are about .502" nominal, and the spacers are probably a bit larger than that.

I'd rather have the VP CADs be the correct size. I like hexed things based on features concentric to the shaft (like the hub OD) and then make one part of the hex on each of the two parts parallel rather than making two parts in each of the hexes coincident.

This is correct. Knowing that the shaft is, say, .497, and the bore .503, is important for certain design considerations. As Damp mentioned, using angular/parallel constraints is just fine.

Also, I agree that the CAD files should all be imperial. Sometimes, I get constraint failures when trying to attach, for example, a metric hub to an imperial wheel, due to dimensional differences that result from the two standards.

[mikemat]

Versaplanetary Gearboxes: We use them all the time. They are awesome for prototyping and iterating designs. The two 10:1s with bag motors on our intake had no issues all year. The 50:1 for shooter angle did have the pins back out a few times on the 10:1 stage, but we were running our entire arm off a cim into a planetary. If that's the only thing that goes wrong, I'm impressed.

VersaWheels and Hubs: No issues here either, though the VEX tread was quite soft. We wore through the rubber after our first competition.

Gears and Sprockets: Both show minimal wear, even after 5 competitions. We had a wheel try to eat the aluminum part of a field door, and the sprocket still looked fine.

[Juan Martinez]

vex 3 cim gearbox
the pressfit gear for the encoder started to wear out after 1 competition on our comp bot so the press fit would slip affecting our autonomous driving and we had a field day trying to figure out what the problem was
vex 2 cim gearbox
we used 1 for our catapult pull back we know it was not meant for the load that it experienced but the little bearing and c clips on the shifter shaft kept breaking i'd like to a different type of system used for the bearings

[mman1506]

I found a production product using a versa planetary.
http://novakon.net/parts-store/bedmills/pdb-torus-pro/

https://www.youtube.com/watch?v=LFkS3cvaeUI#t=424

[artdutra04]

Originally Posted by T^2

Also, I agree that the CAD files should all be imperial. Sometimes, I get constraint failures when trying to attach, for example, a metric hub to an imperial wheel, due to dimensional differences that result from the two standards.

There shouldn't be any problems due to differences in measurements, because inches are actually a derived unit from metric.

[T^2]

Originally Posted by artdutra04

There shouldn't be any problems due to differences in measurements, because inches are actually a derived unit from metric.

You're right; I had a total brain fart there. Any ideas why I can't align a VersaHub (live axle .5hex) mounting pattern with the pattern on the 4in omni wheel?

[asid61]

Originally Posted by T^2

You're right; I had a total brain fart there. Any ideas why I can't align a VersaHub (live axle .5hex) mounting pattern with the pattern on the 4in omni wheel?

Yeah, I've noticed this problem a lot. On the versahubs (I think) the mounting hole pattern is 0.9376" radius instead of 0.9375". It makes mating these things to custon versakey stuff nearly impossible, because other versa products are just 0.9375" radius.

[Thad House]

Those issues were the same issues as I was talking about with the hexes. You can constain to the axes of the circles, but trying to constrain any further then that is impossible because the dimensions are slightly different. CAD doesn't like being off by .001.

[BBray_T1296]

Just a question (does not necessarily belong in this thread). We have never tested this, but how much psi does the stock (0.75" bore) piston require as a minimum for reliable shifting (on the fly and stopped) on the ballshifter? We always ran ours at 60psi, but how low could we have gone?

[mman1506]

Originally Posted by BBray_T1296

Just a question (does not necessarily belong in this thread). We have never tested this, but how much psi does the stock (0.75" bore) piston require as a minimum for reliable shifting (on the fly and stopped) on the ballshifter? We always ran ours at 60psi, but how low could we have gone?

We found issues shifting reliably when we went under 30 PSI.

Originally Posted by BBray_T1296

Just a question (does not necessarily belong in this thread). We have never tested this, but how much psi does the stock (0.75" bore) piston require as a minimum for reliable shifting (on the fly and stopped) on the ballshifter? We always ran ours at 60psi, but how low could we have gone?

A rule of thumb minimum I've heard is 40psi for shifting. Saves a decent amount of air volume and still gets the job done.