I’m looking through ways of designing intakes to show my team for the new season and dead Axle Rollers are something that we have never really done and I wanted to know if there is a benefit to doing dead Axle over live Axle? The only example I’ve really looked into was 2910 in 2023 where all of their intake rollers were dead, are there other good examples to explore?
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Look into 1678!!! Dead axles are generally more durable and keep everything on the inside inside of the intake. Additionally, there is no risk of a bearing popping out.
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Dead axles make the axle part of the structure of your mechanism, making the whole thing more rigid. It also allows the use of larger diameter round tubing, which is much stronger for the weight than typical hex axle.
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Yeah when you use dead axles, the axle itself adds rigidity into the system. We did dead axle for the majority of our shafts this year as well.
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There’s a great write up in 6328’s build blog from last year.
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We adapted 2910’s design in the ‘23 offseason. It is a very good starting point using REV alum tube and tube nuts. The dead axle design adds a lot of rigidity and together with polycarbonate intake rollers and 3DP pulleys makes for a very light weight design. One issue we ran into though is that a full robot width OTB intake can not take full speed contact with another robot (see OCR ‘24 Final 1). High impacts can permanently yield dead axle and then your intake won’t work. Hard use can also result in tube nuts becoming loose. We are iterating on a stub axle version which we like better as it does not use tube nuts. You will learn a ton by building a 2910 ‘23 design.
I would really like to see the stub axle version, do you have an onshape link?
Another advantage of dead axles is that you can replace them by removing a few bolts, whereas live axles need to to slide sideways, which may be difficult, depending on design.
I’m going to borrow a term from 2910(?): just make sure your “dead axles” don’t become “zombie axles”. That is, be careful that they don’t start rotating, allowing the attachment bolts to come loose. We had great success last year preventing zombies with these laser cut “axle keys” (green):
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what advantages/disadvantages do you guys find with the aluminum tubes compared to poly tubes?
We use aluminum because they are way cheaper than polycarb tubes. If one gets dented, it’ll stay that way, but honestly if it were polycarb, the impact probably just would have dented the inner tube anyways.
We have many spares and generally consider each roller a consumable part to be replaced as the silicon sleeving wears (and we’ll take off the silicon and resleeve it after the comp), so spending a bunch on each individual roller isn’t in the budget for us.
Also, if you plan on having silicon on them and want to spin them over about 4K rpm (we shot notes with 2in rollers running about 7k rpm) , you’re gonna need to TESSA tape the ends so the silicon doesn’t expand from the centripetal force.
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Here you go.
The Onshape
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I would recommend using Andrew’s configurable dead axle roller design. Multiple teams used these rollers last year to pretty good success.
https://cad.onshape.com/documents/b75886a5660c38eee7d50e47/w/58faeca16d5b2008a9485b5c/e/6274f59b451ed6222cd7523d
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did you guys have any issues with weight, or did the inertia of the aluminum aid rather than hurt?
If you are not careful the total weight of all your rollers can creep up on you, but we had no issues. We did use the rollers to shoot as well as intake and the extra inertia didn’t hurt any.
To be honest I don’t think there is a big difference between aluminum and polycarb. I would pick the material that you can source easiest and like to work with.
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I mean, they’re definitely heavier than polycarb, but we were only 95 lbs so it wasn’t a concern this year at least.
If you’re using it to shoot, you want the rigidity of aluminum. If you’re using it for an intake, you probably want it to be ploycarb so it can more easily take a hit. If you’re using it for moving it around in your robot but it’s not going to get hit and it’s not going to be the end shooting roller, then make it out of whatever you can source.
We were using it to intake, and then also shoot, so aluminum suited that decently, and we just had to be careful with our intake not to fight over notes.
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Straight up, I can think of only one case for live axle over dead axle for intake rollers, with two sub-cases, neither one common in the last few years since COTS rollers have been easy to procure. That is, a “vectored” intake.
- Old school, we put bigger wheels near the ends of the shaft that tended to push the game piece toward the center. Rather common in 2014 Aerial Assist, I saw a few in 2016 Stronghold.
- A bit later, mecanum wheels that did the same thing better. I know to the day when I first saw mecanum wheels used to push a game piece parallel to a shaft: 18 March 2015, FRC 179 Children of the Swamp at Bayou Regional. They were in the pit next to us (3946). I was like “what is this magic?” and they were happy to share.
- In following years, mecanum “vectored” intakes became pretty common, especially as decent quality 3d printing became affordable and small mecanum wheels became COTS item. It might come up again, but it seems unlikely.
Curiously, if you remember my “green beard” whoami, (That’s what we called profile pictures back then when CD was a qbulletin site) that was taken 2 days after I saw 179’s mecanum manipulators.
OK, I came up with another unusual use case: if you have live axles and a lot of live axle wheels laying around and very little money, a live axle driving those wheels might be more cost efficient.