New threaded rod driven arm Hey, I have thought about the gear design, and I have decided it is too much trouble both to make it work and to maintain accuracy. Therefore I have changed the design to something much simpler, a threaded rod driven arm. The way it works is this: There is a pivoting holder for the nut on one parts of the frame There is a pivoting holder for the motor on another part They are connected by threaded rod, when the motor turns, the two points get closer together or move apart. When the points change distance, the arm rotates. This seems much simpler than all the gears and much more accurate. The last gear to get rid of is the base. I need to find an easy way to drive the base using threaded rod. A picture of the new experimental design is attached. https://reprap.org/forum/read.php?185,41373,41373#msg-41373 Thu, 10 Sep 2026 20:42:45 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?185,41373,238926#msg-238926 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,238926#msg-238926

Here is the QU-BD RPM. You can see that it uses one z-stepper but has 4 screws.
]]> nicholas.seward Polar Machines, SCARA, Robot Arms Fri, 23 Aug 2013 12:40:45 -0400 https://reprap.org/forum/read.php?185,41373,238917#msg-238917 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,238917#msg-238917 tom katze Polar Machines, SCARA, Robot Arms Fri, 23 Aug 2013 12:25:49 -0400 https://reprap.org/forum/read.php?185,41373,158515#msg-158515 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,158515#msg-158515 ketil Polar Machines, SCARA, Robot Arms Wed, 03 Oct 2012 18:39:41 -0400 https://reprap.org/forum/read.php?185,41373,67657#msg-67657 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,67657#msg-67657 Also, I have been thinking about GM3 motors, and I really don't want to deal with them anymore. Their shaft is strangely shaped, the speed isn't very constant, and they aren't rigid. I have also heard that they wear out really fast. I am thinking that small stepper motors would save me a lot of trouble with encoders and programming.]]> galaxyman7 Polar Machines, SCARA, Robot Arms Sun, 05 Dec 2010 14:28:29 -0500 https://reprap.org/forum/read.php?185,41373,67164#msg-67164 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,67164#msg-67164 galaxyman7 Polar Machines, SCARA, Robot Arms Mon, 29 Nov 2010 02:20:32 -0500 https://reprap.org/forum/read.php?185,41373,67118#msg-67118 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,67118#msg-67118
If the plastic itself doesn't want to play ball, then the coupler itself might be made of a material which will. Polyester resin, or machinable wax come to mind. Going 4-jaw chuck with some set screws sounds like a true PITA. Finer the pitch, the easier it is to make fine adjustments of course.

Do you have a dial indicator or dial test indicator? It's always nice to have feedback.]]> backseatdriver Polar Machines, SCARA, Robot Arms Sun, 28 Nov 2010 06:31:53 -0500 https://reprap.org/forum/read.php?185,41373,66990#msg-66990 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,66990#msg-66990 I am having trouble with the motors on the arm. The assembly kind of wobbles as it moves. I think it is because either:
1. The coupler isn't connecting the motor to the rod very well. The GM3 motor has a strange shaped shaft so it is hard to get concentric with the threaded rod.
2. The nut holder and/or motor holders aren't held to the pivot bolts well enough.
3. The motors are just crap?

Anyways, I am going to try making some more couplers, and then make some new holders for the motors and nuts so that they fit snugly onto the pivots. Hopefully this should get rid of the wobble. I should have a ton of free time soon, from Christmas to April.]]> galaxyman7 Polar Machines, SCARA, Robot Arms Thu, 25 Nov 2010 04:46:43 -0500 https://reprap.org/forum/read.php?185,41373,64586#msg-64586 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,64586#msg-64586 Kevin Simon Polar Machines, SCARA, Robot Arms Sat, 23 Oct 2010 00:59:16 -0400 https://reprap.org/forum/read.php?185,41373,61007#msg-61007 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,61007#msg-61007 galaxyman7 Polar Machines, SCARA, Robot Arms Sun, 26 Sep 2010 02:54:43 -0400 https://reprap.org/forum/read.php?185,41373,59332#msg-59332 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,59332#msg-59332 It can be found here:
[reprap.org]]]> galaxyman7 Polar Machines, SCARA, Robot Arms Mon, 13 Sep 2010 14:38:54 -0400 https://reprap.org/forum/read.php?185,41373,59282#msg-59282 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,59282#msg-59282 By the way, I made some motor holders for the GM3. I have attached the STL and STEP files.]]> galaxyman7 Polar Machines, SCARA, Robot Arms Mon, 13 Sep 2010 00:15:58 -0400 https://reprap.org/forum/read.php?185,41373,59192#msg-59192 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,59192#msg-59192
Are'nt smart parts great.]]> aka47 Polar Machines, SCARA, Robot Arms Sun, 12 Sep 2010 03:56:55 -0400 https://reprap.org/forum/read.php?185,41373,59170#msg-59170 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,59170#msg-59170 galaxyman7 Polar Machines, SCARA, Robot Arms Sat, 11 Sep 2010 19:43:23 -0400 https://reprap.org/forum/read.php?185,41373,59112#msg-59112 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,59112#msg-59112
[reprap.org] :

Quote

Talk:Easy Reliable Coupler
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Hi galaxyman7 Thank you for sharing. The Easy Reliable Coupler is a great idea. Please correct me if I’m wrong, I think it would work better if the 6 holes provided for the screws go through the 3 slots provided for the nuts. Tony

(:D]]> SebastienBailard Polar Machines, SCARA, Robot Arms Sat, 11 Sep 2010 02:45:36 -0400 https://reprap.org/forum/read.php?185,41373,58971#msg-58971 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,58971#msg-58971 What format should I upload it as?

Probably your favorite native cad file format, and perhaps .step for interoperability?
(You'll probably have to zip the cad file, to upload it.)

Also, start lurking in reprap-dev. :D]]> SebastienBailard Polar Machines, SCARA, Robot Arms Fri, 10 Sep 2010 06:09:55 -0400 https://reprap.org/forum/read.php?185,41373,57992#msg-57992 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,57992#msg-57992 galaxyman7 Polar Machines, SCARA, Robot Arms Sun, 05 Sep 2010 03:08:57 -0400 https://reprap.org/forum/read.php?185,41373,57974#msg-57974 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,57974#msg-57974
It can be adapted easily for other bore sizes, so if you want a different size, just tell me.
Hmmm ... want to upload the cad file?

http://reprap.org/wiki/Easy_Reliable_Coupler#Files

Also, you may want to add RepRap-style trapped nuts.]]> SebastienBailard Polar Machines, SCARA, Robot Arms Sat, 04 Sep 2010 21:52:08 -0400 https://reprap.org/forum/read.php?185,41373,57922#msg-57922 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,57922#msg-57922 By the way, pics are attached.]]> galaxyman7 Polar Machines, SCARA, Robot Arms Sat, 04 Sep 2010 14:38:43 -0400 https://reprap.org/forum/read.php?185,41373,55288#msg-55288 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,55288#msg-55288
Anyways, I have tested the x axis a lot, and I am pretty sure that the end supports have holes that are closer or further away from eachother than the cart. I am thinking that I will make some kind of adjustable positioning for the ends, so that the slide won't bind at the ends of its travel.

I have also installed one motor for the arm. Unfortunately the coupler is not exactly aligned, so the thing kind of oscillates between fast and slow. However, the speed of the arm with just the small hobby motors is impressive. I just need to hook up some switches now so I can stop touching the wires to the terminals every time I want to test it. I will upload a video of the arm to youtube soon. Everything is looking good!]]> galaxyman7 Polar Machines, SCARA, Robot Arms Wed, 11 Aug 2010 22:25:59 -0400 https://reprap.org/forum/read.php?185,41373,54480#msg-54480 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,54480#msg-54480
And by the way, I did get the plastic coupler to work, but I have a feeling the set screw holding the motor shaft in place will strip out the hole. I tried the large motor on the x axis, with mixed results. The motor worked fine in the middle section of the rails, but when it got to the outsides, it started to get hard to turn the rod. I don't know if it is binding, or if the threaded rod is messed up in some places. I did the end supports with my CNC, so I doubt the distance between the rails changes. I will try taking the rails off and running the threaded rod through the nuts, just to make sure it isn't messed up in any places. The motor has enough torque to get it through the middle section, and when it is in that section, the arm can go around 30 ipm without any problems. This is excellent, but if I cannot find the problem I might have to gear the motor down to get some more torque out of it.

Another problem is vibration. I think it is because of the coupler, which is not balanced. Hopefully the rubber tubing will work and lessen the vibration.

I also have to redesign the mounts for the motors on the arm. They need different mounting holes than the gm3 motors.

In summary, things look pretty good. If I attach the other printer motors to the arm, this thing should have tons of speed. I think since I don't have an extruder yet, I will use it as a plotter to test it out. Soon I will upload some drawings and stl / stp files so you guys can check my work, and maybe make one of your own!

Edit: Made a wiki here [reprap.org]
Haven't edited a wiki before so if you guys could help me out and put some of the pics in, that would be great.]]> galaxyman7 Polar Machines, SCARA, Robot Arms Sun, 08 Aug 2010 02:30:20 -0400 https://reprap.org/forum/read.php?185,41373,54368#msg-54368 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,54368#msg-54368 aka47 Polar Machines, SCARA, Robot Arms Sat, 07 Aug 2010 05:08:00 -0400 https://reprap.org/forum/read.php?185,41373,54354#msg-54354 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,54354#msg-54354 I just milled a plastic clamp coupler today, and I used a screw that went through the threaded rod to keep it on. That worked great, however, the motor shaft keeps slipping out no matter how tight I clamp it. I just want to find a design anyone could make with a reprap and not have special tools like a lathe or drill press. The problem is the hdpe is too slippery. I was thinking 2 part epoxy might work to keep the coupler on the shaft. Do you think this will work?]]> galaxyman7 Polar Machines, SCARA, Robot Arms Sat, 07 Aug 2010 01:43:55 -0400 https://reprap.org/forum/read.php?185,41373,54240#msg-54240 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,54240#msg-54240
Just a mill might be enough. Particularly if you have CNC and a dial indicator or edge finder.(It sounds as though you may not have the desired accessories/tooling?)

If you can clamp round stock in a pin vise, or V-Block you can use an edge finder or indicator to find it's center.

Once the part is centered: a center cutting end mill can be used to plunge cut. A CNC mill can be used to do a helical interpolation, or a rotary table can be used to do circular interpolation.

Otherwise: an offset boring head could be attempted, or even a drill bit. The conical bottom of the hole will do a good job of centering your smaller drill bit for the motor shaft.

Kerosene is god's gift to aluminum as a lubricant. Aluminum's theoretical cutting speed is ~1600/(rotating diameter)=RPM

In practice: to get a good finish, you may have to go slower if: the setup isn't rigid, your cutter isn't sharp, or some other source of chatter is causing a squeel.

It doesn't hurt to go slower assuming that you can feed slow & steady enough to not break the drill bit, but that's a big assumption with small diameter drill bits on deep holes. Small bits need high RPMs because they can't handle much of a chip load. Without high RPMs: it's difficult to feed slow enough to keep them happy.

If the flutes clog with chips: it will cause the drill bit to break, so it's important to "peck" at deep holes.

In a pinch you can use an endmill as an edge finder, by either visually watching for contact with the material with the spindle on, or more recklessly: the same way you touch-off a tool's length.

By zeroing your dials on one side of a round part, touching off on the other side, and dividing the difference in half: you can back up by 1/2 the difference and be centered in one axis. Then you can center in the other axis in the same way.

Another option would be to ignore center & chuck the finished product to your spindle using the drill shaft hole, and a mandrel.

Then you could chuck a lathe bit in a vise and use the table and the Z axis to turn the part concentric.(Ideal for balance reasons I guess.)


Hopefully some of this was helpful. I'm kind of rambling cause I don't know the source of your problem.]]> JohnnyCooper Polar Machines, SCARA, Robot Arms Fri, 06 Aug 2010 05:36:35 -0400 https://reprap.org/forum/read.php?185,41373,54190#msg-54190 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,54190#msg-54190
You can approximate a lathe with a Drill Press (Pillar Drill) or CNC Milling setup.

You clamp the lathe/drill bits on the bed/vice and put the brass rod (or hex brass rod) into the chuck.

Position the drill bits and or lathe tools correctly and you can drive the spinning workpiece onto the tool in a lathe like fashion.

Notes:-

It can be noisy and you often get funny resonance things happening if the tool lengths (the length of clamped tool piece extending out of the clamp/vice) are over long. Keep them as short as possible.

Also use lots of lubricant 3in1 oil or wd40 will do at a push if you don;t have cutting compound.

Aluminium can be a bitch to work with.
A. it work hardens and can suddenly screw up mid piece.
B. it is very soft and clogs the cutting edge of the cutting tool (drill bit or lathe tool is irrelevant).

To fix B make sure the cutting tool is always sharp and frequently withdraw the tool from the operation and clean off the swarf and junk that accumulates over the cutting edge making it blunt and graby on the work piece.

It is doable with care.
I have done this.
It is less than optimal but in a tight corner will do the job.

Think outside of the box.]]> aka47 Polar Machines, SCARA, Robot Arms Thu, 05 Aug 2010 19:26:50 -0400 https://reprap.org/forum/read.php?185,41373,54172#msg-54172 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,54172#msg-54172 galaxyman7 Polar Machines, SCARA, Robot Arms Thu, 05 Aug 2010 15:42:39 -0400 https://reprap.org/forum/read.php?185,41373,54157#msg-54157 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,54157#msg-54157
I wouldn't worry about zero backlash couplings for now. The benefits don't merit the complexity in the prototyping stage, although eventually: it will be low hanging fruit for picking up tighter accuracy.]]> JohnnyCooper Polar Machines, SCARA, Robot Arms Thu, 05 Aug 2010 13:54:24 -0400 https://reprap.org/forum/read.php?185,41373,54060#msg-54060 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,54060#msg-54060
I am turning the coupling on the lathe so that the motor end is a hot fit ie it needs to be heated before sliping over the motor shaft. when cool there is no chance of slipage.

The threaded rod end i am threading so thhat the threaded rod screws in and is locked using thread locking compound and a lock nut.

dunno if this helps any.

cheers aka47]]> aka47 Polar Machines, SCARA, Robot Arms Thu, 05 Aug 2010 04:14:33 -0400 https://reprap.org/forum/read.php?185,41373,54052#msg-54052 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,54052#msg-54052 galaxyman7 Polar Machines, SCARA, Robot Arms Thu, 05 Aug 2010 02:43:50 -0400 https://reprap.org/forum/read.php?185,41373,51804#msg-51804 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,51804#msg-51804 aka47 Polar Machines, SCARA, Robot Arms Fri, 16 Jul 2010 01:37:08 -0400 https://reprap.org/forum/read.php?185,41373,51796#msg-51796 Re: New threaded rod driven arm https://reprap.org/forum/read.php?185,41373,51796#msg-51796 It is hard to explain how it works so I uploaded some pictures along with sketches.
It is very smooth, and I can push it back and forth with my finger easily.
The only thing is one of my rails turned out to be just a little over 1/2 inch, so I will have to take a bushing to the store and find a nicely sized rail.
The two nuts that go over the lead screw are recessed in a hexagonal hole in the side of the slide. I hope they will not come out, because then I would need to redesign the slides.
Other than that, I am working on designing the circuit for the driver board, along with trying to learn the programming language for the SX microcontroller. So I have a lot to do, but I think the linear slides and lead screw are the biggest issues (speaking from experience with my CNC).]]> galaxyman7 Polar Machines, SCARA, Robot Arms Fri, 16 Jul 2010 00:11:02 -0400