I have a few questions concerning the usage of axle set collars.
Our design is a scissor lift and calls for a large amount of shaft collars to hold the cross members in place. (Somewhere around 216)
The first question is may we use vex set shaft collars? It isn’t the right size for
the Tetrix axles, but if we bore out the center to accommodate a Tetrix axle, would this be legal? I’ve been seeing that vex fasteners are permitted, so would a modified shaft collar be considered a fastener?
The second question is if we do order set screw shaft collars from a supplier such as McMaster-Carr, what Bore would we need? I’m guessing at 1/8".
The Tetrix axles are of 4.7 mm diameter. That’s pretty close to 3/16" or 5mm. I’m not sure which will work best.
Strictly, the only shaft collars you may legally use (unless there’s been a Q&A revision that I’ve missed) are those sold by Pitsco. Shaft collars are NOT a fastener and substitutes aren’t allowed.
Practically, nobody will be able to tell the difference.
Let your conscience (or, perhaps, your wallet) be your guide.
Rulebook says ‘absolutely no VEX parts’ or words to that effect…
If you’re like us, we’re using Tetrix parts drilled out to our shaft sizes (1/4", 3/8") and possibly having to drill/tap setscrew holes in ‘repurposed’ parts such as hub spacers.
But, we didn’t choose a scissor design (more like a extending boom), so our needs are simpler.
Can you thread the ends of your shafts and use common locking nuts which are the cheapest option? If threading the shafts is not an option, could you switch to all-thread rod. Do you run up against the limits of allowed materials?
I don’t have those limits committed to memory.::rtm::
Thank you for the responses, and I appreciate the idea Andrew but I believe the nuts would become loosened easily over time, unless you think we could use loctite to keep them on. What type of tool exactly would we use to thread the ends of the shafts?
Also, I found these on McMaster-Carr, could I use this part or some other part similar to its purpose?
A tap and die set cuts threads. You would need to use two lock nuts per shaft end to lock in place. I still have not checked the linear feet of all thread is allowed but cutting thread on shaft has no restrictions.
We participate in BEST robotics which provides a specific supply of materials in the KOP. We use modified 1/4-20 nuts as shaft collars.
We drill out the threads of the nut with a 17/64 or 9/32 drill bit. We then drill a tap hole in the side of the nut for an 8-32 bolt. You might be able to manufacture you own this way rather buying.
You could try the same technique with a small nut with a smaller bolt as the set screw.
Moshe,
You really need to read through R5c of the robot rules section. Shaft collars are not fasteners and so do not fall under the unrestricted use of fasteners section of this rule. I find nothing in the rules that would allow you to use anything other than the Tetrix shaft collars. 216? Really?
Once again, thanks for the quick responses, except Al’s which has a patronizing tone to his comment. And yes, I have read rule R5c but did not know whether the item “set screw shaft collar” would qualify as a fastener because it technically fastens onto axles.
I think we might try going all threaded or try to thread the end of the axles.
Andrew, why would we need two nuts per side to lock it in place? Could we use just one and use loctite to keep it on?
Moshe,
Sorry you took it that way, I did not intend it as anything but help. I am speaking from the standpoint of an FTC inspector.
From R5c 18. All mechanical fasteners (nuts, bolts, screws, etc.) of any length, any thread type, up to 0.375” (0.9525cm) diameter. The intent of this rule is to allow teams to use fasteners from any supplier that are substantially the same as TETRIX fasteners.
In the context of this wording, shaft collars are not considered fasteners(nuts, bolts, screws, etc.). I am merely trying to save you from facing this dilemma when you compete.
You may try asking on the Q&A. If they rule it as a fastener then you can proceed. The Q&A has ruled that threaded rod is a fastener.
R5c 17. Unlimited length Threaded Rod (also known as All‐Thread) not to exceed 0.375” (0.9525cm)
diameter (e.g. McMaster Carr Part #94435A317).
All GDC and Inspector responses come off as condescending, it’s just the nature of the position, I think
Komodo,
You can use unlimited length threaded rod in your robot this year. You can use an unlimited number of nuts.
Andrew’s response is slightly confusing. You can use lock nuts, or you can use two hex nuts tightened one against the other to lock both in place on the threaded-rod. Lock nuts come in different styles - the ‘Kep nut’ style that’s in the kit has a built-in form of a lockwasher (that star-shaped thing attached); locking-thread or acorn-nut where the thread depth constricts and the nut jams onto the thread as it were; or the nylon-insert kind that has (oddly-enough) a nylon insert to keep the thread from vibrating/backing.
You are ALSO allowed loctite.
For the use you’re describing, I’d use 1/4-20 nuts from McMaster by the hundreds… I’d also invest in a 1/4-20 NC die, a pair of vice-grips, and a 1" 6-point deepwell socket (when handheld, beats a die handle hollow for speed) to ‘chase’ the threads after you cut the rod. It’ll help a LOT if you can dip the end of the allthread in a 1/4" deep capful of motor oil (used is fine).
I’d also use a fiberblade to cut that many rods. Get a 10" one and mount it in a tablesaw is how I’d do that, and use the fence for length.
I like the solution from Coach Norm, too, but for your application, it may just be a whole lot faster to use two nuts per side and tighten them against each other to lock them.
