Repeated Failure of MK4i Intermediate Shaft Screw

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So this is what it takes to get some more speedio videos? Anyone else been having any problems with their modules? Keep ‘em coming pat.


Until further notice pre-assembled modules sold by AndyMark will have red Loctite on the 12-24 screw (as well as blue on all other appropriate screws like usual).
Big thanks to @PatrickW for jumping on this so quickly and taking care of our customers as well as his.


Didn’t notice the addition of the flange until this morning.

New Version

Old Version

I’m assuming this flange OD matches the inner bearing race OD for added support.

Nice extra added touch. Glad to see continuous small improvements are always on your mind and being implemented. Excited to get these new shafts swapped in as soon as we get em.


Any ideas when we can get the updated shafts? We are competing/hosting week one and would love to not deal with this failure condition. We had seen some issues with this screw backing out on our test chassis earlier in the season and assumed it was a team assembly issue. Would be happy to pay for expedited shipping and provide feedback in the next week :slight_smile:

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Production of the new shafts began this morning. The new shafts will be tested on multiple robots tonight and tomorrow. Assuming there are not any issues during testing, the shafts will be in stock on the website starting at 12:00 PM EST on Friday (2/24/23). The product page of the V2 shaft is live. The shafts will be available at the sale price of $1 through the end of this years competition season. The quantity limit per order is 12.


Top 10 W’s of the 2023 season

  1. This
  2. This
  3. This
    4-10. This

Will / have teams who ordered these modules be emailed regarding this?

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Honestly, as a team strongly considering buying SDS modules for next year provided the money is there from our sponsors, Its reassuring that this is the kind of customer support we can expect. yes, it costs a dollar but given the time and materials cost most likely exceeds that cant really complain.


We loctited down our bolts, still didnt work well

Add 8825 to the list of teams with this problem. We only have a few hours of practice on a flat field in and lost 2 of these screws. We do struggle with students over tightening things. I have to remind myself how many screws I stripped before I could feel a screw or bolt yielding, knew how much torque was reasonable and when to grab the torque wrench. But I can’t tell you if that was the issue for us.
Good news is that we have 4 spare shafts because we could not get enough Falcons, Neos and Spark Maxes for our second bot.

@PatrickW, this is amazing turn around time. You guys are awesome.

I know it is hard to anticipate how quickly you will be able to box/ship orders until you know how many orders you have. Given that we we are approaching week 1 events, we are considering doing a group order to cover several teams and shipping them directly to the hotel that we will be staying at. But, if you anticipate being able to clear the shipping backlog quickly, then we will just have each of those teams buy their own replacements and ship them to their own build site.

The last thing we want to do is create chaos for you in your shipping department. But if there was some way that we could know what the estimated shipping backlog was (in terms of days) then we could decide at the time we place the order whether to ship to our week 1 hotel or to our build site. I don’t know if that is possible to do.


I may be splitting hairs here but I want to ask the experts floating around here if using this screw would be better. McMaster-Carr
It is a stainless version that has 70,000 lbs yield vs the 130,000 of the one linked above. It is only available in 3/4 so the modules will have to be disassembled to install.
So is having a yield strength closer to the 30,000 or so of the aluminum threads helpful? Seems like letting the screw flex would spare stress on the aluminum threads. Aluminum has poor fatigue performance and I would bet that the loctite fatigue is even worse in this situation.
It is highly unlikely that we will get the new shafts and have time to install them before our competition in 2 weeks. So I need to do the best we can with the better screws. I plan on drowning them in loctite and adding locktite to the gear. I normally train the students to be sparing with the loctite so that it only gets on the threads because you may not be able to remove a screw that has too much. Normally it only takes a little to stop vibration from loosing a screw.

Did you use red or blue loctite?

It will have no effect in this situation. The Young’s Modulus (springyness) of stainless is much closer to steel than aluminum. The deflection of the threads when torqued don’t depend on Yield strength. When shearing the threads, The Aluminum will still shear first. If you are using Loctite on Stainless and Al, you should probably be using a primer/activator. Loctite doesn’t like to cure on passive surfaces like stainless and aluminum.


I’m curious if there will be an option to overnight ship these (at the buyer’s cost, of course). We have a week 1 event as well out of state, so trying to figure out how to get these in our hands.


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Intermediate Shaft v2 sold out. Any estimates on a second round? I’m trying to decide if we disassemble and install 3/4" screws or wait for these new shafts.

The SDS site says they will go in stock tomorrow at 12:00PM EST.


If you want to fix this properly without waiting for the new shaft self locking helicoils is probably the best way to go if you have the ability to drill and tap.

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Blue loctite i believe, it may have been red loctite 241 though @Flightbudz can you confirm?

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