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1-Arm SCARA with 4 Static Steppers

Posted by nicholas.seward 
1-Arm SCARA with 4 Static Steppers
April 02, 2017 10:09PM
I really don't have time to be working on this but my mind is going crazy with this design so I had to pencil to paper. There are a few neat innovations. (I can't say that they are original but it is a beautiful culmination.)




  • It is highly printable.
  • 153mm arms similar to RepRap Morgan
  • Gear reduction similar to RepRap Morgan
  • Same kinematics as RepRap Morgan (Well...this can change arm modes but we won't start doing that until after we get some prints.)
  • Fits in a 200x225x250 box
  • Can print objects that are up to 600mm long
  • All four motors (400 steps/rotation) are static while providing a structural support and their own wire-management.
  • Prints directly on a tape covered table
  • Planning on using an IR depth probe
  • Could probably print all the parts for a self-replication run in one go.

Youtube Candy

Well...That is enough for now. I will be glad to answer questions and would love suggestions if you see something that is fishy. I plan to share my slow build here and on Google+. When I developed Simpson this forum was invaluable. This beastie is a little different story. I don't really have any knowledge gaps that need to fill. I have failed enough to have a pretty good road map in my mind. That said...I am going to give the forum one last round to see if it is worth the time. Either way, if this printer works well enough to be a daily printer then I will publish it on the RepRap site. (Big if I know. However, I am doing everything I can to make it usable...touchscreen, smoothieboard, probe...I might even use limit switches although I would prefer to turn the current down and run into a stop.)

Edited 1 time(s). Last edit at 04/02/2017 10:10PM by nicholas.seward.

ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
Re: 1-Arm SCARA with 4 Static Steppers
April 03, 2017 03:40AM
Interesting design! What firmware is used?
Re: 1-Arm SCARA with 4 Static Steppers
April 03, 2017 04:29AM
Quote
grean2007
Interesting design! What firmware is used?

I will use the RepRap Morgan firmware with very small modifications to get started. In the end I need the firmware to do lazy automagic arm mode flipping during a print. That will require a trick or two.


ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
Re: 1-Arm SCARA with 4 Static Steppers
April 04, 2017 07:59AM
I am also looking at a screw for the Z. I have parts for both ways. I think this way is a bit more compact and simpler design-wise. I am not sure I can get by with only one smooth rod. I have room and for a second if needed.




ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
Re: 1-Arm SCARA with 4 Static Steppers
April 04, 2017 10:41AM
Z rod(s)

Use a linear rail

[www.ebay.com]

In keeping with the Seward way ---- perhaps a printed rail and trolley

Motor spacing?

Doesn't seem right
--- no space for output shaft/pulley


Wally Chrome -- still a gathering dust

confused smiley
Re: 1-Arm SCARA with 4 Static Steppers
April 04, 2017 11:03AM
@comicray I actually am using a 6mm rail to save weight. I tried to get a 6mm or 1/4 inch screw but it was an order of magnitude harder to source. The linear rails are nice but you take a hit on weight, compactness, and cost. At this point I think it is just as valid as a design choice but I already have the hardware pictured.

Motor spacing works. It is super tight by design.

RE Wally: I am probably never going to revisit Wally so feel free to develop it further or dismantle it for parts.


ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
Re: 1-Arm SCARA with 4 Static Steppers
April 05, 2017 03:29AM
It is interesting to look at the cuts along the axes of the gears, how are they fixed?
Re: 1-Arm SCARA with 4 Static Steppers
April 05, 2017 10:22AM
Quote
grean2007
It is interesting to look at the cuts along the axes of the gears, how are they fixed?



There are some things missing but here is that cut. I don't know if it makes things super obvious but combining that with the youtube video should get you a full understanding of the layout.


ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
Re: 1-Arm SCARA with 4 Static Steppers
April 06, 2017 02:07PM
Are you switching versions of this design?

Perhaps driving the main hub Axle could eliminate a belt?

Perhaps another path to dive extruder motor?


Re: 1-Arm SCARA with 4 Static Steppers
April 06, 2017 03:10PM
@Cozmicray:

Nice! The colors really help see what is going on.

I have a few designs running in parallel. The one I will build first will be the pure belt version. I have ordered the parts for the screw version but there are quite a few reasons that I don't like that solution as much.

To drive the hub screw I would still need a large pulley so I opted to keep the super compact quadruple stepper stack. To me that is the best thing about the design.

Driving the extruder is an interesting idea. Getting the XYZ to all be driven from static steppers chewed through a lot of plastic. I think adding the E will widen the z height of each joint by an inch and will add a lot of crazy belts stuff to the end. I don't want to dismiss it out of hand so I will give it some thought. The real trick will be having all 4 of the large pulleys in a tight stack with the 4 slaved pulleys/arms above or below the stack. I think I have used up all my tricks on that front. To do better we would need concentric shafts.

On the concentric shaft front, I would really like a design that could print in an infinite donut but that would require bottom mounted concentric shafts like the Morgan. This design is giving up some print real estate to get a more portable printer.


ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
Re: 1-Arm SCARA with 4 Static Steppers
April 07, 2017 05:41PM
Is this correct?

Yellow -- shoulder drive
Red ---- forearm drive ??? where is drive motor??
Green --- Z drive

motor 4? ------ extruder drive?

?What firmware? software?




confused smiley
Re: 1-Arm SCARA with 4 Static Steppers
April 07, 2017 07:47PM
@cozmicray





You got all of the belt paths right. This image should show you where all the steppers are.

The firmware, as mentioned above, is going to be a modified RepRap Morgan firmware which is really just smoothieware.


ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
Re: 1-Arm SCARA with 4 Static Steppers
April 07, 2017 10:10PM

Got the arm together. All is smooth and backlash free. I have two more big parts to print and am waiting on belts from China. I should have test prints by the end of this month if all goes well.


ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
Re: 1-Arm SCARA with 4 Static Steppers
April 13, 2017 09:53AM


Now that I have a my prototype moving, I am making a laundry list of things that should be fixed before release. One huge change is slimming down the arms while making them more rigid. I am still playing with the layout but I thought this picture would help people see how the 4 static steppers can get the job done.

For those that are interested, here are some of the improvements I am doing.
*Make the arms solid. (Instead of adjustable length.)
*Connect the proximal top and bottom arm in one solid print to add torsional stiffness. (Right now I would say I can move the effector 1mm by trying to twist the proximal arms. This should not hurt print quality but need to be fixed before I target arm mode switching.)
*Add 5 belt tensioners to prevent the need for arm length adjustment and slots on stepper mounts.
*Slim the electronics box.
*Add rubber feet for the ability to print without clamping.
*Pack the steppers closer. (Right now they edge to edge. I will make them face to face and will merge their mounts.
*Move LCD up onto tower to make it easier to get to. I should also build a pivot so it can be tilted out.
*Move power plug to back middle so that it is harder to make the effector collide with it.

Things I might do
*Add a belt path for the extruder. (If I do that then I will have a place to sit a spool of filament above the central pivot.
*Reduce the pulley diameters. This could really open up the build volume. (Option one is to throw away resolution. Option two would be to use compound rations up and down the whole belt chain. The only trick is the proximal arm that is driven directly. I could have an idler on the central pivot that leads to another idler on the elbow that would lead back to the driven pulley on the central pivot. It is only another two belts, two idlers, and two tensioners.)

Things I need ideas for
*For this design to work the bottom of the electronics box has to be at least the build height below the bottom proximal arm. If the build height is 100mm and the stack is 100mm then the printer has to be 200mm tall. That isn't really a problem. However, I want a super elegant way of moving this printer around. Ideally, I could throw it in a backpack. A specialized briefcase wouldn't be the end of the world.
*Wire management. I currently have a ribbon cable which works well but I would like something a little more professional. I thought about a sequence of cable chains but that would really clutter up the design. I think +Quentin Harley has the wires go inside the arm but I think my range of motion plus the z really makes that not an option.


ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
Re: 1-Arm SCARA with 4 Static Steppers
April 13, 2017 07:14PM
Are you using standard size timing belt loops
or
must they be custom or made up?

If made up --- How do you do it?

confused smiley
RepRap Helios
April 13, 2017 07:23PM
On my current prototype all belts are gt2 6mm 250 teeth. They are fairly easy to find.

Edited 1 time(s). Last edit at 04/15/2017 11:30AM by nicholas.seward.

ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
RepRap Helios
April 15, 2017 11:29AM
FIRST PRINT!!!!!!!!!!

Here is my second print.


Edited 1 time(s). Last edit at 04/15/2017 11:29AM by nicholas.seward.

ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
Re: 1-Arm SCARA with 4 Static Steppers
April 17, 2017 11:46AM
Very cool ! I really like this design and can't wait to build one. Great work ! Might have to re-purpose my Bukito into this.,
Re: 1-Arm SCARA with 4 Static Steppers
April 21, 2017 07:08PM
Where is the design / build home forum for Helios?

A place on Concept forge?

Please post URL?

confused smiley
Re: 1-Arm SCARA with 4 Static Steppers
April 21, 2017 07:16PM
Quote
cozmicray
Where is the design / build home forum for Helios?

A place on Concept forge?

Please post URL?

confused smiley

Hold your horses there little doggie. I put pen to paper 19 days ago. You of all people should know I shouldn't jump the gun on publishing until I have a proven design with great documentation.

I am pushing hard on getting the second prototype done that fixes all the problems from the first one and then I will start churning on the documentation if it works out as intended. I am also working on full homing, bed probing, and machine characterization using one accelerometer but it takes time to get that wrapped into the firmware which isn't my strong suit.

My goal is to release files before the Bay Area Maker Faire.


ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
Re: 1-Arm SCARA with 4 Static Steppers
April 21, 2017 08:58PM
Just wanted to know where development log will be?

I followed along with Wally?
Want to follow along with Helios ? Maybe beta tester?

I realize there will be Little Helios, Big Helios, Helios mark 7 1 B 3 etc
until Epson or HP purchases it?

Perhaps VW before Mercedes with auto park, lane departure, bidet etc?

Hit or miss on your youtube and Google plus.

Tnx:


confused smiley
Re: 1-Arm SCARA with 4 Static Steppers
April 21, 2017 09:04PM
There has been an order of magnitude more feed back coming from Google+ so I will not be posting here except to answer peoples question.

Google+ Collection
This is a link of all the work I have done so far.

Edited 1 time(s). Last edit at 04/21/2017 09:04PM by nicholas.seward.

ConceptFORGE
Wally, GUS Simpson, LISA Simpson, THOR Simpson, Sextupteron, CoreXZ
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