How does this Thrifty telescoping arm connect to a motor?
You need to add a bracket for the winch/motor. The AndyMark climber is a good example of a solution
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Are you asking about using a motor to extend the tubes, or how to retract them?
Retracting
This is intended to be retracted using a winch system. You would attach one end of a string to the innermost stage (how exactly you do this is your choice), the string goes down through the tubes, and the other end of the string would be attached to a spool at the bottom of the system. The string needs to be as long as the telescope when its fully extended. When you want to retract, you rotate the spool, and the string pulls the inner stage down.
Extension
This is not really designed for a motor to extend the tube - that is what the constant force springs are for. One way to extend is by holding the inner stage “down” until you want it to extend, and when you remove that hold down, the springs will coil up and it will extend itself.
Alternatively, you could extend the system by starting the match with your winch string fully spooled, and run your motor backwards to extend it. You still need the constant force springs here because you can’t push a rope.
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With a couple of bearing plates, you could just mount the motor to the bottom 1" or so of the tube, building a winch spool inside the tube, similar to how chain-in-tube drive trains work. Or you could put it a bit below the tube, using (for example; AM and Vex also have solutions) one TTB mega motor plate and one TTB mega bearing plate, a spool, and your favorite gearmotor configuration with a shaft a bit over 2" long, and a bearing for that shaft.
I would recommend mounting the motor a bit off center so the spool unwinds near the center of the tube. The Megaplates are only 2" wide, but you should be able to mount them about 1/2" off center. If you have limited machine capability (e.g. just a drill press or even a hand drill), you can use the megaplate as a match drilling guide, clamping it flush with the end and sides of the tube. I would also use bolts rather than rivets on a few of these holes so you can mount the arm to the robot using the same anchor points.
Added: just like @Ryan_Dognaux 's second image 
, except for the off-center bit.
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We just have ours a test drive today- Took some inspiration from the way the AndyMark attaches their motor and path for the rope.
Thrifty Mega Motor plate attached to the side of the 2” tube with a Falcon Sport Gear box- (purchase the 3” long shaft to make this easier) make a spool from 2 Thrifty Hubs and press then into a 1.5 long piece of 1.124 ID Aluminum tube- then on other side Thrifty Bearing plate-
We installed a 1/2” rod inside the tube to allow the rope to make the 90 turn through a 1.125 hole and finally on to the spool.
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For the video test setup, I just ran a versaplanetary mounted directly under the tube with my motor / bearing plates with a drum to wind the cable and a 3D printed hook that was physically bolted into the top stage. The dyneema cable was fed and tied off on the hook so when pulled down it retracts the stages and when released the stages extend.
Here are a few pictures that I took that sort of show the setup, didn’t get a picture of everything altogether.
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I’m really liking the TTB arm over the AM arm, in that it appears to have a significantly shorter “overhead length”, it has bearing support on both axes, and the bearing plates have “extra” holes for mounting it to the chassis.
Also, another thing I’ve realized as trying to package an arm that is at an angle - as far as attachments at the hook end, make sure the rope is firmly attached to the HOOK; that’s what does the lifting. The attachment to the tube just has to be enough to raise the hook on extension and compress the springs on retraction. Right now, I’m thinking of mounting a hook made of bent 3/4" x 1/4" aluminum bar to a relatively light single bolt at the top of the innermost tube, with a light duty spring to keep it oriented the direction I want to engage a rung, but then assuming a more “natural” and secure angle once the hook is engaged. The telescoping arm is ultimately just a hook delivery device (in normal or not too-unusual usage).
@Ryan_Dognaux, as soon as I saw the mega bearing plates with the same form factor as the mega motor plates, I realized quickly that it solved a problem I’ve been struggling with for far too long - centering a gearbox, a radial bearing, and a thrust bearing all on the same axis with nothing better than a drill press well enough to avoid overconstraint friction. Today I realized that together this pair of brackets has revolutionized minimal machining design. Bravo! 
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Thanks for your answer!
How do you press 2 thrifty hubs onto a tube? The hubs have a hexagonal hole and the tube’s cross-section is a circle. the hubs I’m seeing: https://www.thethriftybot.com/bearings/QTY-4-The-Thrifty-Hub-Half-Inch-Hex-p151670087
Second, do we need a bearing for the bearing plate?
Also, could you please clarify the sentence:
On the other side Thrifty Bearing plate, we installed a 1/2” rod inside the tube to allow the rope to make the 90 turn through a 1.125 hole and finally onto the spool.
Thanks again!
Thanks for your response! Does the drum come within the telescoping arm kit? If not, where can we purchase it?
Also, what is missing from the setup in the first photo? I infer that the following are missing: a thrifty bearing plate, a bearing, and bolts, but I’m not sure how the drum would connect to these components since the hex shaft doesn’t protrude the drum.
I was going to leave this one to @Ryan_Dognaux, but doesn’t seem to be typing, The spool pictured appears to be one of his thrifty inserts in a 3d printed plastic spool.
If you don’t have 3d printing, a serviceable spool can be made from two hubs (pick your manufacturer) with the extensions facing each other (that is, flanges away from each other), and spacers or shaft collars holding them together. Use any of the holes usually used to mount a wheel as your rope anchor point ( you may have to drill it out a bit).
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The hubs have a 1.125 diameter circle hub around the hex in the center- you find a piece of 1.12 inner diameter tube- cut it to about 1.5 inches and press a hub into each end. It make for a nice tight press fit.
Yes you will want a bearing fir the plate to help support the axle the “drum” will be on.
The 1/2” rod is just a piece of aluminum rod that we cut to length to fit inside the 2” tube to help with the rope making the 90 degree turn outside the tube. Honestly look at the AndyMark documentation on how they do this set up for their climber. It is better then anything I can provide.
Thank you! How did you put the aluminum rod inside the 2" tube? And is the rope attached to the rod in some way?
Any of the holes in the hub can be used to secure the rope.
I don’t know how @1493kd did it, but I’d just use a bolt through the tube. I like simple where simple works.
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Spoken like someone who has never sailed a boat in the winter…
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That would be a line, not a rope…
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Here’s an example of how we’re doing it, it puts the tangent for the spool right in the middle of the tube (you can see the inner tube plug as well, that’s as far down as it goes). In this particular case, we opted for a cutout in the tube instead of placing the spool below it. Simply put, aside from the tube, the rest of the robot is not much taller than the spool. As a result, we don’t have much room to attach the tube above it, so having some attachments below the spool as well will make that part a little more rigid. And we couldn’t move the spool down, as it would get in the way of our ball control mechanism! The geometries get a little tight, but at least this way we can fit under the low bar and extend up to the middle bar 
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A little explanation that may be totally unnecessary here - we (Thrifty) did not have any inside knowledge into the game beforehand. We set out to make a good telescoping tube kit, and we figured teams would want to come up with their own mounting features, gearbox/spool solutions, and hook designs. I think we found a way to include as much as possible while coming in at a price point that helps teams come up with a climb while not giving them a complete all-in-one solution.
I also want to point out that our clamping bearing blocks work with 2x2 and 1x1, and they have 1.875” and 2” holes for mounting whatever to them. Between these, the aforementioned plates, and the telescoping tube solution, you can pretty much do whatever you want to drive the tube kit. Let us know if there are additions to the Thrifty ecosystem you would like to see!!
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