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Author Topic: Four Motor/cable horizontal Polargraph??
3feet
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Posts: 3
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Post Four Motor/cable horizontal Polargraph??
on: February 9, 2016, 08:48
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I've been really interested in these printing machines for a while but never had the opportunity to make and play with them. Having found this site it's great to see people here coming up with great hardware/software solutions and image production.

What i'm setting out to do is create a horizontal machine that uses 4 wires on each corner of a table top to pull around an object to draw images... something similar to these machines - https://www.youtube.com/watch?v=hrsDBdnj5E8 and https://www.youtube.com/watch?v=n0ZoGZjS6Tc

Does any one know if this can be done using the Polargraph software and hardware combo.

I have some basic experience with Arduino/Ramps 1.4 and simple linear x/y axis wall printing devices. I'll be playing with a polargraph setup over the next few days to try to get my head around it a bit to see if that helps.

Any help greatly appreciated thanks.
Robert

sandy
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Post Re: Four Motor/cable horizontal Polargraph??
on: February 9, 2016, 20:33
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The kinematics of most of the polargraph machine's movements is pretty obvious, and very simple. It's be very easy to work out two more cord-lengths stretching from the bottom of the machine. RAMPS can drive four steppers fine.

However, the firmware is a little too simple really, I don't think I'd recommend it for a new build. There's a few things it doesn't do at all well, and well-accelerated vector drawing is one of them.

sn

kongorilla
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Post Re: Four Motor/cable horizontal Polargraph??
on: February 10, 2016, 00:15
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I built a prototype along these lines late last year, and I thought a lull in my freelance work would allow me to finish it up for sharing, but little gigs keep popping up, among other (less positive) life things. Wish I could turn down paying jobs and do the work I'd like to do.
As ever with me, I took the "no programming necessary" approach to this. It's fairly hacky.

3feet
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Post Re: Four Motor/cable horizontal Polargraph??
on: February 14, 2016, 12:49
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Thanks, good to hear the positioning of the additional cords is easy to work out. How would i find more about achieving this? What approach would you recommend to take regarding software and controlling hardware?

I am hoping to get some thing working in the next month and the final work it outputs will be limited to text, atm. The hardware side is being played with now and the final design is 90% completed.

I'm keen to hear the "no programming..." approach as time is limited, as long as i can achieve something relatively robust 🙂
Robert

sandy
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Posts: 1449
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Post Re: Four Motor/cable horizontal Polargraph??
on: February 14, 2016, 21:17
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There's an algorithm in the changeLength(..) method that works out the lengths that the strings need to be to get to a particular cartesian position. Distance to the two top corner points.

If I was cobbling it together based on the existing firmware, I'd use the same algorithm to work out he distance to the two bottom-corner points. As I say though, I wouldn't base a new build on the existing firmware.

Not sure what Kongo's no programming approach is though 🙂

sn

3feet
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Post Re: Four Motor/cable horizontal Polargraph??
on: February 16, 2016, 12:06
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Thanks Sandy I'll have a look tomorrow as i now have a couple of Arduinos to play with and my drivers and motors have also arrived.

Until i can poke around i'm finding it hard to visualise how the original algorithm and the the new algorithm for the other axis work together, maths inside my head isn't working for me atm. For now I will start the build and keep trying to wrap my head around the coding side.

When you say to not use existing firmwares do you mean it is best to start from scratch and write a (polargraph style) 4 axis specific version?

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