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-   -   Looking to improve my stringing machine (http://tt.tennis-warehouse.com/showthread.php?t=455738)

 pkshooter 02-24-2013 11:24 AM

Looking to improve my stringing machine

So I have to do a science project this semester in science. I was hoping to make something I could actually use so I wouldn't just be throwing money into my grade. Then I had the idea that I could make a modification to my drop weight stringing machine. I'm coming to the forum in hopes that some of the math people on the forum could get me started. Hopefully some of the engineers and physics guys out there on this forum could throw so rudimentary engineering articles at me. Thanks in advance to anyone who voulenteers some info on how stringing machines work.

 struggle 02-24-2013 01:33 PM

make a WISE, but better and cheaper. I'll buy one.

 tball 02-24-2013 07:13 PM

PLAN A

I am not sure how one would control tension with an electric motor.
I saw an old prince machine which used a pneumatic cylinder. It seems like it would be much simpler design, and better amenable to controlling tension:

motor pumps the air --> the air reaches required pressure --> pulls the string. There are pressure relief valves. They will let excessive pressure off the cylinder. The ones I've seen were pre-set at manufacturing. I am not sure if adjustable pressure valves exist.

Alternatively, you can buy a tire pressure guage, overpump a bit, then open the valve until the pressue is just right -- similar to what you'll do when pumping a tire on a car. You can call overpumping a "pre-stretch" ( a sofisticated feature that only 3K+ machines provide).

PLAN B

Another alternative: get a reasonably tight spring. Calibrate its elongation under various tensions, say 50 lbs = + 1 in, 60 lbs = + 2 in.
Then attach string -> spring -> motor, and a ruler underneath. The elongation of the string will tell you the tension. If your motor is slow enough, so you can move in tiny steps.

 pkshooter 02-24-2013 08:32 PM

Thank you tball. That is genius, and sounds cheapish to build. Thank you very much, I can already see a pluses.
But how do I secure the string to the tensioner.

 diredesire 02-25-2013 02:58 PM

You can build something: Fast/Cheap/Accurate [or usable]. I'd choose two of the three. This undertaking is going to wind up consuming a LOT of money OR time OR brainpower to do the right way. If we're truly talking about being competitive with a WISE or similar, you'll need at bare minimum some electronics knowledge and/or preferably plenty of mechanical knowledge. If your greatest worry at the moment is to figure out how to secure string to a tensioner, I'd recommend choosing something else for a science project...

I'm not sure what education level you're currently at, but at the very least this will require high school-ish physics. Tool(ing) cost for this project can be very expensive if you don't know/have anyone available that is handy in a shop setting. Materials won't be super cheap if you're building out of metals (Aluminum is probably where you want to start with this).

If it were me: I'd re-create a drop weight system and/or even build something with a variable pivot point like the current SW/LF drop weight machines (any angle true-CP tensioner). This will be by far the most bang for your buck in terms of research needed. There are design documents archived SOMEWHERE, and the designer at SW is accessible and willing to talk technical.

If you really want to pursue an 'electric' tensioner, you will need to understand (at minimum) electrical fundamentals (ohms law, basic safety/wiring, power [wiring relays and basic power distribution]). I would personally go with something like a load cell or stress/strain gauge coupled with a simple microcontroller (Arduino is probably the easiest to get started with). This is probably the quickest/dirtiest way to get started, as the load cell should be roughly linear within the range of operation you're interested in (from what I gather). You should use proven designs as far as tension securing, linear grippers OR rotating drum head. No need to reinvent the wheel here unless you are trying to achieve something specific.

Electric motor feedback should be pretty simple (and cheap) and can probably be done with extremely cheap/passive components, but a motor heavy duty enough to achieve this is probably not extremely cheap. I would imagine with enough google-fu, you could probably pull up patent documents with prior art and/or design notes to blatantly rip off.

IMHO, though, this is probably a pretty overwhelming project unless you're well into high school, and you'd probably need to be pretty mathematically/scientifically talented and/or self-motivated to do your own research to pull this off. I'm not trying to discourage you at all, just realize that this is probably going to be more work than you thought from the get-go ;)

 Lakers4Life 02-25-2013 03:13 PM

If you look at the design of the Wise 2086 Pro. It's very similar to a screw type garage door opener. Most other high end machines use a chain driven tensioner.

 Irvin 02-25-2013 04:36 PM

At one time I was going to make a swingweight measurement tool. I was going to use it to measure the period of a racket swinging from a pivot but things got in the way and I dropped the project. Talking less than \$10 if you have an iPhone, iPhone etc. Interested?

EDIT: You could also use this for baseball / softball bats and other swinging instruments.

 Bdarb 03-08-2013 09:09 AM

I dont know what your project needs to show or prove, but there was a separate thread in odds/ends (I think?) about a machine that puts pressure back in dead balls. The general consensus in there was that it is relatively easy to make a similar device using PVC somehow? I'm on mobile or I'd link the thread but maybe consider that as a more mild alternative. Stringers take a reasonable amount of
Machining ability to modify without just purchasing aftermarket parts, I get the impression you're probably doing some kind of hs project and probably don't have access to necessary tools skills for such a large project. Good luck.

 Steve Huff 03-09-2013 07:34 AM

If you can make a 6 point mounting system where the supports are on the inside of the frame, that would be a real improvement. Inside mounting helps keep the racket in its original shape, and is more convenient to work around. Outside mounting, like all current 6 point machines, allow the frame to be squeezed inward, allowing for more distortion. Good luck.

 diredesire 03-09-2013 09:59 AM

Quote:
 Originally Posted by Steve Huff (Post 7260534) If you can make a 6 point mounting system where the supports are on the inside of the frame, that would be a real improvement. Inside mounting helps keep the racket in its original shape, and is more convenient to work around. Outside mounting, like all current 6 point machines, allow the frame to be squeezed inward, allowing for more distortion. Good luck.
I should elaborate on Steve's recommendation. This implies that the supports are NOT located in the same place as a 6-point outside, intuitively. A frame will compress when the mains are strung, thus rounding out the frame. If you just swap the position of the mounts to the inside of the frame, the outermost supports will do absolutely nothing. The frame will round out, and there will be no support from the outside mounts. You'd have to evaluate deformation and collect data before trying anything like this. If you wanted to make it easy on yourself, have the supports be inside AND out. There's no easy fix overall unless you come up with something completely unorthodox (as compared to current mounting "technology"). IMHO.

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