Dr. Joe's Unchain the Cracken No. 25

[Joe_Johnson]

Allow me to introduce myself.

I have been doing FIRST robotics since 1995.

I am currently a mentor on Team 88, TJ-squared.

I am also an engineer at Formlabs, a 3D printing company.

I love all three. I wish that there was more overlap between these things I love.

I am trying to fix that.

I formed a group at my work called FormFRC to design parts that are (A) useful to FIRST FRC teams and (B) print super well on Formlabs Printers and/or in our materials.

This is the 1st post of what I plan to be many more (I have half dozen in the can and will post them as soon as I am able).

Dr. Joe’s Unchain the Cracken No. 25.

A chain cracking mechanism that has it all.

Cracks 25 Chain (standard and heavy).
No added tools required.
Printed on Fuse1+ in Nylon11 CF
Includes a lot of metal bits inside (core pins, shaft keys, bearings, 10:1 Versaplanetary gearset, screws, dowels). Not cheap but the performance is amazing (in my opinion).

Geneva mechanism counts turns but also provides “hard stop” to keep you from breaking the mechanism by cranking the wrong way (after a 10:1 gearset, cranking the wrong way against a “hard stop” seems a lot like pushing pins out of #25H chain – only the crack you’ll hear is the plastic housing giving way).

Has an (almost) fool proof set of doors that make it difficult to have out of position chain before you Unchain the Cracken.

Print in place rotating knob on the crank. Feels so nice when you crank.

Presses 2 pins out at once so as long as you position a chain such that the pins are over the plates (not the links) you don’t make chain sections with dangling plates (so annoying to be making a chain section and you have to finish the work of some lazy person before you that left the plates just dangling away).

Youtube video here

GrabCAD files here

[Joe_Johnson]

[Joe_Johnson]

[Peter_Matteson]

I really like this we need better chain breaks and this fits the bill, but what the heck is the skeleton in the background of the first photo above?

[Tom_Line]

When do we get a “rechain” the cracken?

[Joe_Johnson]

Formlabs is a weird and wonderful place. Employees have access to “infinite prints” and one Formling decided to print a human skeleton found online. It’s currently sitting in the break area to my left (wearing a the longest continuous Nylon11 chain that yet another Formling could fit into an full Fuse1 build volume)

[Joe_Johnson]

I know a lot of folk like pressing pins back into chain to avoid using master links. I am not one of them. I need to clean up my Onshape file but once I do that and I publish it, feel free to design your own dang rechain mechanism

Cheers,
Dr. Joe J

[Joe_Johnson]

Here is a [link to the BOM](Unchain the Cracken No. 25 BOM Unchain the Cracken No. 25 BOM - Google Sheets) - I know it is a lot for a chain cracker but… …it’s a REALLY good chain cracker

Here is a link to the Public Onshape Doc. Have fun.

[asid61]

Dr. Joe, you maybe want to reconsider this stance. Breaking chain is already pretty easy with any number of COTS tools, but rechaining is rare and annoying even with the right tools. Your tool looks really fast with breaking, but if it could rechain, then I think it would be worth printing for many teams that are looking to use their old VP stages. And if I could spend $90 to avoid using an Allen key to work chain again I would do it in a second.

I personally hate spending $1 on masterlinks to close loops of chain, and then inevitably losing the U-shaped clip so I have to spend another dollar just for that one piece… I think a lot of teams prefer just pressing the pin back together. Rechaining tools are overwhelmingly popular.

EDIT: I missed that the BOM is actually closer to $180, though I think I could drop it to under $100 by using AliExpress for the metric stuff. Could this be printed on any SLS printer or does it need to be a Fuse? $100 in parts isn’t the worst but $200 in prints would make it untenable.

[Joe_Johnson]

Here is above referenced skeleton and chain - pay no attention to the plush racoon inside the rib cage. That is a dog toy for one of the more popular Formdog – it’s where we keep it. Don’t judge…

[Potttaaatttooo]

Finally a good use for 10:1 Versa cartridges! And a mechanism to prevent it from breaking (bc ofc the cartridge does)

[JohnFogarty]

I like the tool, but I feel like the intentional avoiding rechaining method is a pretty hot take.

I have first hand experience with 25 chain breaking on a custom drivetrain system that had master links, but then after discovering the dark soul tool rechaining with the original pins never experiencing the chain breaking again.

[Joe_Johnson]

Everyone can have whatever take they want. It is not of value to me and it wasn’t worth the extra complications it would require so I didn’t design it into the mechanism.

Others feel otherwise, that’s fine with me.