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233 telescoping arms how do they work?
i have seen pictures but i still can't figure how they work. I want to know how to make one this summer. any pics or cad would be great.
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Re: 233 telescoping arms how do they work?
Although I can't vouch for the pink team, on FRC-Designs team 75 has posted a CAD of their 2011 robot with a telescoping arm.
48 also seems to have a telescoping arm, but theirs uses a pneumatic cylinder instead of a lead screw for the telescoping motion. I would still like to hear how 233 (and 2016) did their telescoping arms. |
Re: 233 telescoping arms how do they work?
I had a chance to ask 254 a bunch of questions about theirs. Thanks to 254 for having a model out for fan boys and girls to look at and answering lots of questions. I was trying to explain some of it to people, but if somebody has a nice picture of a 233 or 254 arm, that make it a lot easier for us to develop something of our own. Figuring out a good telescoping arm that we're capable of fabricating is high on our list of generally useful things we want to learn how to do.
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About 233, not a picture but a video. Here is a picture, but you cant really see anything close up... |
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they had 2 this year on their climber.
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I'm on sketchy Internet in Germany right now so I can't post any pics, but the arm is relatively simple. Our best example would definitely be 2011, which in my opinion is the best robot 233 has ever produced.
We use three different sizes of box tube, with fancy bearing blocks holding it all together. The telescoping action is powered by a motor at the bottom and chain. The most complicated pieces are probably the bearing blocks. I believe they are cut with a wire edm and milled, and everything moves smoothly with rollers. Its hard to explain without pics, but there are blocks on the inside of the tops of the tubes, and the outsides of the bottom of the tubes. If you find a good pic this will make a lot more sense. We keep about 6 inches of overlap when fully extended. In 2010 we tried out using waterjetted delrin in place of these rollers and blocks, and honestly it just sucked so don't bother. Some other cool features of the arm include dual constant force springs that entirely counterbalance the telescoping portion, and a less slick system of surgical tube to balance the rotation. There are also delrin springs that act as shock absorbers when the arm retracts and slams closed. For rotation the whole arm sits in split bearings. But honestly the coolest addition to the 2011 iteration is how the rotation was powered. Instead of using chain like usual, there was one giant wire edm cut gear that fit directly to the arm. Now all of these features aren't entirely necessary for an effective arm, but are the result of continuous improvement over the years. Effective programming and intuitive driver control should be considered the highest priorities in my opinion. |
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thanks for the pics
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I understand the structure - the roller bearings and ball bearings etc.
How exactly are the belts driven and cascaded through the system? I'm not seeing how they are connected or function. |
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Maybe someone from 254 or 233 could chime in, or you could spend about an hour looking at old 233 posts. I remember coming across a thread where 233 explained how their arm extended and operated (2007 version). Also, 254 talked about how theirs worked in the 7 second climb revel thread. If I remember correctly (and don't quote me on this), 233 used a spring extend, while 254 didn't. |
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I remember it's a single belt going all the way through that's fixed to the stage that extends the most. I could figure out the belt path and pulleys from memory, but I'd have to spend some time drawing it out.
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A two stage system works similarly, but with the bottom and top of the first stage being idlers, and the belt being connected to the bottom of the second stage. I believe there's a pretty good paper on CD-Media which explain all of this in more detail. |
Re: 233 telescoping arms how do they work?
Also, specifics on this thread link
Spending a few minutes searching can get you a long ways along... |
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-Travis |
Re: 233 telescoping arms how do they work?
Links that helped me solve this problem:
Take a long stare at a few of these and you will figure out how they work. https://www.dropbox.com/sh/3fxabc28nvvkcr8/A2tQie9tgK specifically: https://www.dropbox.com/sh/3fxabc28n...f:DSC_0149.JPG Also: http://www.chiefdelphi.com/forums/sh...ng+a+clim ber Good luck! |
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233's 2011 Arm was a beauty to behold. Good luck to anyone who wants to make one :D
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Can we please get a CAD model of those? Or extremely detailed pictures? It's so hard to see what is going on in there :P
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Why is that when I look at 254's machine to see how they did something, I come away with more questions than answers... that machine and its mechanisms are so condensed, it's just insane.
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I can only speak for the 233 arm on this topic. First off, a gearbox is attatched to the outside of the largest box (4d0 x 4d0 x d125 al box) at the bottom of the tower. It has a shaft that transfers power to a sprocket on the inside of the box. At the top of the box is an idler sprocket which is also the tensioner for this chain. We will call this chain 1. Chain 1 is attatched to the outside of the next box (2d5 x 2d5 x d125 al box) thru what I call the "chain anchor". The motor/gearbox drives this stage in and out directly.
The gearbox has a 10 turn pot attatched which controls the limits and also the PID control for ramping up and down the power as the tower nears its limits at each end of its travel. Now here is where it gets a little tricky, the opposite side if the 2d5 box has a shaft in the bottom with a sporcket on the inside and the outside, this is what drives the final stage of the tower. It also has an idler at the top which also acts as the tensioner for these 2 chains. The chains both have a "chain anchor". The chain on the inside of 2d5 box is attached to the bottom of the final stage (1d0 x 1d0 x d125 al box). The chain on the outside of the box is attatched to the inside of the 4do box. The key is that the anchors are on opposite sides of the chain, this allows the second stage to use the anchor to drive the chain which extends the final stage at the same time. This is a very lengthy post and I may not of explained the subject completely but it has started an open line of communication. Ask any questions you may have and i can explain why Charlie did not like the delrin bearing blocks from 2k10. Mike D "233 for life" |
Re: 233 telescoping arms how do they work?
Awesome stuff. Thanks for all the info about these mechanisms.
When we've built these cascaded telescoping lifts/arms in the past, we've used a winch system for the first stage. What I'm having trouble wrapping my mind around with both of 233's and 254's telescoping arms is where the extra chain/timing belt, goes when these mechanisms are extended. Or are just the cascaded sections using the timing belt/chain? Always trying to come up with better solutions, and these are the type of mechanisms we're all striving to make (in some small way). |
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This section of belt (from the pulley to the bottom of the last stage) is what takes all the tension when the arm is being retracted. This way, the force exerted by the weight of the robot while climbing is just transmitted through the (large) bearings and shaft supporting the bottom pulley, and not on any of the tiny ones where the belt doubles back on itself. The beauty of using a telescoping arm for hanging, in my opinion, is that there are no moments exerted on any of the stages during retraction. |
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If I'm reading this thread right, the arms are basically a condensed version of this right?
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If I understand MikeD's post correctly, 233's multi-stage arms are essentially cascaded lifts, but the second stage does not return to the original power source (and is instead driven "passively" by a sprocket that is turned as the first stage extends). The key difference for both arms is that all the stages are nested within each other, which presents numerous challenges and advantages. |
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Yeah, the nesting sounds very hard to do. Maybe if I get bored over the summer I'll CAD up something :D |
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The question that you'll also have to answer is the orientation of the constant force springs. Do you use them to extend the arm and only pull one way with your motors? Do you use to retract the arm so they help you lift the robot, but power the arm in both directions? It's a really awesome design that I wanted to understand to put it in our 'toolbox'. |
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If somebody is still having a hard time understanding how the poof's arm works, I took many pictures which are posted here: https://drive.google.com/folderview?...&usp=sha ring
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In our application we use the constant force springs to assist the extend function only. It offsets the weight of the manipulator on the end of the tower/elevator. The motor/motors have plenty of power for lifting the robot and we use a locking type ratchet to hold the weight up after the buzzer but the idea of having the motor/motors stalled out to hold position while the tower is extended is not, in my opinion, a healthy one. This year we did an elevator and used constant force springs to assist the elevator in lifting our shooter deck, it weighed in at about 18lbs. I find it ironic that we did an elevator and the Poofs did telescoping towers this year
Mike D "233 for life" |
Re: 233 telescoping arms how do they work?
To the people who have posted in this thread: I just want you to know that after the school year ends, I'm going to devour the information in this thread, including both the pictures and written explanations. I am looking forward to trying to figure out the guts of one of these arms and working with some students to create a model of something we could build. Thanks very much for all of the posts.
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good one Sean, and you are correct on your earlier post about the passive drive of the third stage on pinks tower.
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we have done many lift's with bosch 20 series with custom sliders and cable but that has it's limitations, mainly strength and weight.
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Seconded. These are some great idea to digest! Many thanks as well! |
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EDIT: I ask because I'm only familiar with the coil style constant force springs and if you used those I'm curious how they were implemented. |
Re: 233 telescoping arms how do they work?
Try looking up negator spring or constant force spring motor. It's a really nicely packed solution to the counterbalance problem. Ill update this when I'm at a computer with some links Ect.
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EDIT: would someone familiar with the 254 system we willing to describe or diagram that system? From looking at all the pictures, I believe they use a different concept. |
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Re: 233 telescoping arms how do they work?
Thanks for all of the helpful insight.
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After looking through the pictures referenced earlier in the thread, I was able to better understand the 254 telescopic arm. It is conceptually very different from the 233 arm.
We attempted to build a nylon strap driven arm, similar in concept to the 254 design, and found it very difficult to get all the rollers, idler pulleys, and pieces of slippery UHMW from colliding with each other. In the end we ran out of time, kept the first stage, and just implemented a first level hanger. The devil is definitely in the details with these mechanisms. |
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What did 254 and 233 do to pin the chain/belt to a stage? I'm wondering if they put bolts through the chain/belt, pinched the chain/belt against a toothed surface, or did something else. I'm guessing they might have had different methods since 254 used a belt and 233 used chain.
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For #25 chain, you can fit #4 screws through the gaps between the rollers to fix it to something, although I don't know if this is how 233 does it or not. Another method is to drill a hole in the fixed structure that one end of a masterlink fits through. |
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233, in 2011 at least, machines a part that appears to 'look' like a #25 chain link at either end and uses that to fix the chain to the stages. Here's a few pictures on their flickr. http://www.flickr.com/photos/thepinkteam/5787028180/ http://www.flickr.com/photos/thepinkteam/5787033770/ http://www.flickr.com/photos/thepink...n/photostream/ |
Re: 233 telescoping arms how do they work?
Has anyone tried using these to attach chain? Specifically the K-1 style connector.
http://www.mcmaster.com/#roller-chai...hments/=p1acmb Seems like an easier option than machining an attachment for the chain. |
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Re: 233 telescoping arms how do they work?
Maybe fill it up with pressurized air (like a piston out) to make it longer, and have a spring retract it. Maybe that will work for light/medium loads
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Am I the only one that likes the lead screw method?
Its beautiful. If you ask, they're more then happy to share some drawings on that arm. I have them saved somewhere. To me, it seems a little more simple and solid then all these chain runs. Cons being I'm not sure how you'd have multiple stages. |
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I suppose another disadvantage of the leadscrew would be it's expense and inefficiency. Of course, it does look like a very elegant solution in that situation. |
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Re: 233 telescoping arms how do they work?
Stuff got moved around in my google drive, and the previous album link now does not work. I got a PM to repost the link so here it is: https://drive.google.com/folderview?...&usp=sha ring
I will have to try to find a more permanent solution for the future. |
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