Polar table design

New Home Forum ZenXY Advice – ZenXY Polar table design

This topic contains 49 replies, has 7 voices, and was last updated by  Jeffeb3 3 days, 13 hours ago.

Viewing 20 posts - 31 through 50 (of 50 total)
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  • #78158

    Bill
    Participant

    Actually Ryan, you’d be really helpful with coming up with the parametric gear pieces for different sized center gears. 🙂 Remember the small one that goes in the stepper should match the teeth for the big, eight piece one. No need for a timing belt on the theta, it just bumps right up and meshes with the big guy.

    #78166

    karltinsly
    Participant

    I’m thinking about using a lazy susan as the base. I happen to have an ikea one here, but although its action is plenty smooth, I can’t see an easy way to mount the slip ring – the base is connected to the bearing with a bolt right in the center. I think I’ll order a lazy susan bearing – I’m thinking of one of these:

    https://www.amazon.com/Aluminum-Turntable-Bearings-Restaurant-Decorations/dp/B07HF12P9B/ref=sr_1_14?ie=UTF8&qid=1543974462&sr=8-14&keywords=lazy+susan+hardware+aluminum

    https://www.amazon.com/Aluminum-Rotating-Turntable-Bearings-Dining-table/dp/B01MQY8U5R/ref=sr_1_3?ie=UTF8&qid=1543974462&sr=8-3&keywords=lazy+susan+hardware+aluminum

    Once I have a spinning platform, the radius gantry can be any kind of linear motion setup – V1-style conduit, smooth rods, or profile.

    I was thinking that the carriage from the ZenXY would work fine. Just need to design brackets to hold the conduit the correct distance apart and to mount the motor and idler.

    Thoughts?

    #78167

    karltinsly
    Participant

    I went ahead and ordered one of those lazy susan bearings, along with this slip ring:

    https://www.amazon.com/gp/product/B07FL8NR8M/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

    Where am I going to find the time to build this thing?

    #78170

    Jeffeb3
    Participant

    Thoughts?

    That makes a lot of sense. Considering some of those lazy Susan mechanisms are about $5 on Amazon, I think it’s hard to beat with bearings. I like Ryan’s gantry piece for the zen xy, but I’m not sure the spacing is exactly right for the belts. I think it’s wider than the idlers. If I had my choice, I’d leave the side that has the teeth and remove the side with the several zip ties and the bolt. Then just zip tie the ends together, like the Y axis on the mp3dp. You might have to cut through some of the gantry though to make room.

    #78171

    Jeffeb3
    Participant

    Give me a few days before you need it, and I can get sandify to output gcode so that Y is really an angle and X is really the linear axis (or flipped, whichever).

    I think this might even end up being simpler than the ZXY. I may be jinxing it…

    #78192

    karltinsly
    Participant

    Give me a few days before you need it, and I can get sandify to output gcode so that Y is really an angle and X is really the linear axis (or flipped, whichever).

    I doubt it will be very soon, but I will let you know. I’m curious though why Sandify would need to be modded at all. Doesn’t it already output polar code?

    #78206

    Jeffeb3
    Participant

    The polar code isn’t gcode, it’s a list of angle, normalized radius. The radius is always between 0,1 and there are no G commands in it. The simple example is this, which will spiral out from the center and make 100 turns before it reaches the outermost edge:

    0 0
    628 1

    So it will take 100 turns (2 * pi * 100) and end up at the outside edge. (That’s Bruce Shapiro’s explaination, I like it).

    So for a Marlin machine with angle and length, the same thing might be

    G1 X0 Y0
    G1 X628 Y250

    Assuming the linear rail is 250 max, and that radians are a good unit for the angle. It might not be, because there are some limits in resolution in Marlin, so we might have to pick something crazy like 1/10th radians or even degrees *gasps*.

    #78207

    Jeffeb3
    Participant

    Another possible solution is to make Marlin do the conversion between x,y and theta/rho. It does it for deltas, so it could do it for your machine. I have no idea how much code is involved in that. Sandify would remain simpler (rather than just have a “Karl’s machine” button), and you could possibly reuse your gcode on the cartesian machine.

    #78218

    Bill
    Participant

    I bought a lazy susan bearing set like that for the 3D scanner setup I almost made a few years ago. Come to think of it, that design was awfully close to this one… 🙂

    So for a Marlin machine with angle and length, the same thing might be

    G1 X0 Y0
    G1 X628 Y250

    I assume with lots or arcs in between those two? 🙂

    #78219

    Jeffeb3
    Participant

    As the X axis moves from 0 to 628, it will be rotating the motor enough so the whole gantry will take 100 turns. A move from X0 to X3.14 would be 180 degrees. A move from X3.14 to X6.28 would be another 180 degrees. So these units aren’t going to be that great, we’ll need something finer.

    Marlin drives in a straight line, so at X314, the Y will be half of it’s final goal, or 125mm out, and it does everything else proportionally.

    #78227

    Kelly D
    Participant

    You guys are all a few floors above me in corner offices with killer views but you’re definitely making me curious about what’s inside this thing. We’ve had it for a couple of years. I think I ordered it off of ThinkGeek. It’s the one reason I need to wait for the right moment in life to surprise the wife with a sand art coffee table 😉

    #78230

    Jeffeb3
    Participant

    Through the magic of the Internet:

    (Spoiler alert!!)

    1 user thanked author for this post.
    #78234

    geodave
    Participant

    How about an upside down Delta machine? Here is a calculator for Delta sizes. http://www.thinkyhead.com/_delta/

    That video looks like a really cool method for a sand table if you come up with a design for that.

    #78236

    Jeffeb3
    Participant

    That would be a big box, and another motor. It would be pretty for the firmware though. The other interesting thing is that you could actually move the magnet away from the surface. You could even have it follow a non-flat surface… I’m not sure if that’s useful but…

    #78237

    Jeffeb3
    Participant

    I like the next video this guy has. He’s creating light patterns without the sand:

    #78242

    Kelly D
    Participant

    Through the magic of the Internet!

    Well that saves the questioning by the family. “What are you doing to it dad?!”

    Hahaa…..

    That’s pretty simple. Neato. Kinda like a spirograph…. Thanks for digging that up to indulge me. my Wifi in the basement office isn’t like yours on the executive floors…..

    #78244

    Bill
    Participant

    my Wifi in the basement office isn’t like yours on the executive floors…..

    Don’t believe everything you hear… It’s actually slower to push all those bits and bytes up to the rarefied upper stories. Down in the basement gravity works to your advantage.

    #78246

    Jeffeb3
    Participant

    I found some pretty good math for spirographs. I should be able to add stuff like this to sandify without too much trouble.

    https://github.com/jeffeb3/sandify/issues/66

    (hijacking this thread for more sandify stuff, but, oh well).

    #78274

    geodave
    Participant

    After thinking about this, these movements reminded me of the Trammel of Archimedes.  That movement by itself will not give you want you want, but might be something to consider to start with. https://en.wikipedia.org/wiki/Trammel_of_Archimedes

    I remixed someone’s thingiverse design to use only plastic parts if you want to play with the idea. https://www.thingiverse.com/thing:2927475

    Did you ever see this video of software creating gears based on movment.

    gzumwalt on thingiverse had it linked on this build he did. https://www.thingiverse.com/thing:1212665

    Gzumwalt has some pretty cool designs & challenging to print & put together.

    #78304

    Jeffeb3
    Participant

    After thinking about this, these movements reminded me of the Trammel of Archimedes. That movement by itself will not give you want you want, but might be something to consider to start with. https://en.wikipedia.org/wiki/Trammel_of_Archimedes%5B/quote%5D

    Oval table! Since the two axes are linked, you can’t really adjust the radius of the endpoint without changing the length of that linkage, but you could put the linear axis on the arm, and instead of rotating it on a circle, you could rotate it along an oval. That might be pretty fun. I don’t know how you would get the power to the linear axis.

    Did you ever see this video of software creating gears based on movement

    The most terrifying part about that is that it’s from Disney. They have their hands in some strange honeypots… But otherwise, that is some really cool software. Instead of the “open loop” way of choosing the size of the gears and lengths of the rods, you’re able to go backwards, a bit and choose the gears and rods from a pattern. The method for determining that is a good algorithm for a lot of problems too. Just put in a huge number of input and record their outputs. Compare a desired output to your database of input/output pairs, and find the closest one. Then search around the space of the closest match for inputs that match even better. Add in some simulated annealing to avoid local minimums, and you’ve got a non-linear system solver! I’ve used something similar to this to determine a camera calibration on some very inexpensive (high distortion) cameras.

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