As part of a personal project to improve my Fusion 360 skills, I have been developing a complete Hook/Lifter/Winch system that uses 3D printing wherever possible. I wasn’t planning on releasing it until I’d put it through a lot of testing, but given the difficulty some people are having sourcing the commercial kits, I’ve decided to throw it out there in case it proves helpful. Since it only requires a few small holes in the tubing, it may prove useful as a stopgap measure that allows testing while waiting for the kits to arrive.
Please be aware this is a work in progress; your mileage (altitude?) may vary, and your comments and suggestions are most appreciated.
The Hook component is on Thingiverse and the build guide is here.
The CheapLifter uses 3D-printed sliding bearings and seems to operate quite smoothly. Also on Thingiverse with build guide here
The final component is the Winch module; I am about halfway through the modelling process on this, but should have it done this weekend.
Good luck this year!
Edit: added link to the lifter.
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Love the idea. Did I miss the link for the telescoping portion of the project. Love to compare concepts.
I am working on finalizing the Lifter module. I will get it uploaded by this evening if all goes well.
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I love what you are doing here!
A suggestion on the hook: if you can tolerate the extra height, a hook where the load point is inline with the tubing will make the whole system lift MUCH better by minimizing the bending load on the bearings. Here’s one of mine! This one looks a little funny because only the outside tape measure in this experimental spoolable climber is actually carrying load. Done right, the tape measure doesn’t kink. Done wrong (my error), it crinkles a lot… I put it together backwards the first time, despite getting the CAD right. D’oh!
I’m guessing you are doing internal guides that also provide the minimum overlap length inside the tubes? Maybe looking like the Thrifty Bot ones? Dry tubes want about 2:1 L/D ratio/overlap for reasonably centered loads. Sorry if this is a cheese-chewing instruction item… Many people, even skilled engineers, are not aware of L/D ratio and its impact on sliding parts. And, its easy to miss in a design. We’ve had a bunch of downhole tools that didn’t work right because of missing this one… Lotsa $$ blown.
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You raise an interesting point regarding the issue of off-center loads with the current hook design; as mentioned in the OP, I wanted to do a lot more testing of the whole assembly before posting publicly, and determining the minimum tube overlap is on the to-do list. Given the specifications of the 2020 game and the relatively small amount of extension needed, a 2:1 overlap should not be a problem.
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I have uploaded the files for the Lifter components and edited the OP to point to them. Enjoy!
I have uploaded the files for the CheapWinch components to Thingiverse: CheapWinch - an easy-to-make, inexpensive winch for First Robotics by MadOverlord - Thingiverse
Build notes here: CheapWinch Build Instructions - Google Docs
Very preliminary, not tested, but hopefully helpful.
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Lovin’ the sneakiness of putting it inside the tube! And a slick VersaPlanetary connection!
The reason for tucking everything inside the tube is to keep all the forces away from the plastic parts. All they are doing is serving as positioning guides and spacers, as well as resisting any minor twisting torques. The main loads go through the bearings and into the tube.
Thank you for sharing this; I’m going to point it out to my team.
Thank you for the info and design insights! I was wondering if you could tell me what a L/D ratio is/how it’s calculated? I’m assuming some length to diameter sort of thing?
Calling it L/D comes from downhole tools, which are round… Thus “D”.
What you want to do is look at the dimension perpendicular to the sliding direction. For a 1" tube inside a 1.5" tube (1/16" wall), the D dimension is 1.375. The L dimension is the distance along the axis of motion from the bottom contact point to the top contact point. When L/D is 0.5, you parts will jam unless they are externally guided. At 1:1 you need smooth surfaces and very good lubrication. At 2 (L=2D) your parts will slide with little to no lubrication. For 1.5" tubing above the L for this case is 2.75".
The exact point that you lock up depends on the coefficient of friction. The roller bearings used on many climbers act like a super-low coefficient; under 0.1. If you look at the dovetail connection between a milling machine table and the saddle, you will see that its longer than it is wide. Its well lubricated, smooth, close fitting, but they still go WELL over 1.
Another aspect of L/D is how sloppy the joint acts. The longer the overlap, the less the whole assembly rattles back and forth (for the same clearance).
Here’s an example of a VERY low L/D ratio device used as a lock. This is on the order of 0.1 L/D ratio. This will lock for any value of the coefficient of friction.
This brings up an interesting point; it would be simple to create a spacer that fits between the tubes to enforce this separation (instead of doing so with tension on the cord). I’m thinking it would hug the inside of the outer tube but be thinner than the sliding bearing so it would never contact the inner tube. Alternately, it could hug the outside of the inner tube and we could move the mounting holes of the CF springs up above it.
Any flaws in this idea that you can see?
That would work if you can print the spacer thin enough. I think the TTB and GreyT are getting the length from the plug that goes in the inside tube; its larger than the inside tube and about as long as the tube is across. Plus the top part on those moves the bearing point above the end of the tube; the plug stops at the top of the tube, IIRC.
In my design, I have a slide bearing at the top of the CFS assembly, and half-bearing below it (to provide clearance for the spring on two sides), and then there is the bearing on the end of the inner tube. After reading your comments, I am thinking that removing the half-bearing is going to be an improvement as it will provide at least an inch between the two bearings.
If more is needed, probably the easiest way to do it is to drill and tap holes in the outer tube and install 1/4" 8-32 buttonheads to act as stops. However, this would only work on a 1-stage lifter.
In other news, I’ve added a bearing cover to the CheapWinch to mitigate possible cord tangling issues.
I think your bearing arrangements are solid… I’d leave them alone unless testing tells you they need fiddling with. After having looked at the Thingiverse files, you have plenty of L/D ratio 
The Thrifty Bot bottom part is a simple plug that is held in place by the bolts for the CF springs:
Do you have an assembled version where we can see the extension and retracted states? We are getting a bit lost on building this from the instructions on the google doc. Any tips or tricks would be greatly appreciated.
If you can tell me at what point you are getting lost, I can try and update the instructions to make them more clear, and add more photos. Please feel free to make comments/suggested edits in the google document; you should have that ability as long as you’re logged in to google.
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I have updated the google document with build instructions that are hopefully more clear.
I noticed I hadn’t set a couple of parameters correctly in the 2.0 stage models; I have fixed this and uploaded the corrected files to Thingiverse.
