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Scara arm solution

Posted by idegraaf 
Scara arm solution
January 01, 2016 09:22AM
Picture says 1000 word. This arm is printable and uses just few bearing. What to you think.




Im not engineer and this is only 2-3 day work in sketchup smiling smiley
Re: Scara arm solution
January 04, 2016 01:18PM
hello,
nice work thumbs up; waiting the following, it's good to see other scara/arm projects!
For me, arms type solutions (although badly known) are much better than cartesian...
good luck for your project
Re: Scara arm solution
January 06, 2016 12:03PM
Hi,

looks nice.

But:
What´s the size and range?
Have you calculated the expected accuracy? (Steps, angular resolution, etc.).
How do you do joint bearing and tensioning?
Arm droop is estimated?
How do you tension the belts?
What belts are you using? HTD ?
Where are the limit/position switches or encoders etc.?

Just curious...

Kind regards,
Mike
Re: Scara arm solution
January 06, 2016 01:49PM
What´s the size and range?
Arm sizes is 100 & 100mm

Have you calculated the expected accuracy? (Steps, angular resolution, etc.).
No, testing and experimentation, and again ...

How do you do joint bearing and tensioning?


Arm droop is estimated?
Lets see.

How do you tension the belts?
There is the idea of tightening the belts from motors by rotating motor around one of the corner.

One folding point to another using self-made open belt connector.
Like this:


What belts are you using? HTD ?
GT2

Where are the limit/position switches or encoders etc.?
Not done yet.

No kidding ... it is not industrial.

Edited 4 time(s). Last edit at 01/06/2016 02:01PM by idegraaf.
Re: Scara arm solution
January 06, 2016 05:16PM
Size -- I think we are asking size of printing area
area between stops or singularities?

Those don't look like standard bearings, spacers, pulleys?

Lot of machining there? You got lathe and mill?

Many use standard bearings
608ZZ Deep Groove Ball Bearings 8*22*7mm
8mm bolt as shaft

Look at eBay for ZZ type bearings that fit on standard bolts (Shafts)

Spacing two bearings wide apart on joint would make nice solid joint.

Your belts are probably continuous circle belts that should be tensioned by idler
or clamp the ends in pulley if less than 1 rev necessary.

This is Pull Pull system belts don't push so one side just pulls

Look at Wally it uses string drive
[www.youtube.com]

looks like 1 to 1 ratio on motor pulley to joint pulley --- it will have same resolution as motor.
small motor pulley to large pulley gets you better resolution

Good Luck
confused smiley
Re: Scara arm solution
January 07, 2016 06:54AM
Yeah,
Although internals and bearing contact areas are not visible, art of bearing seems to be promising.
I think GT2 is comparable with HTD, so no slip which is good.

The only thing to mention is still belt tensioning and reduction ratio (as cozmicray already meant, it will be fast but not THAT accurate,... OK acceleration might also not be perfect due to low torque). But you can calculate it.
What about an excentric belt tensioning idler, which sits inside the main arm? By Fixing it in a slightly excentrically rotated position, it presses the belt towards the outside...So you can use continuous circle belts.

Kind regards
Mike

Edited 1 time(s). Last edit at 01/07/2016 06:58AM by theothermike.
Re: Scara arm solution
April 10, 2016 10:51AM
Hi! A we so me idea man, I want to build one since I was a kid. What about making gears with more teeth? It will improve accuracy and reduce accumulative errors. Are the accumulative errors always the same? I mean: if we can make a scientific rule that aproximates to the value, the printer would be super accurate and fast. Looking forwards to see videos and more pics
Cheers!
Re: Scara arm solution
April 11, 2016 12:16PM
Well design out 1Jan 2016

post picture of prototype
controller utilized
firmware utilized
inverse kinematics used for XY to arm movements


??? That's why there are few SCARA 3D printers out there

confused smiley
Re: Scara arm solution
April 11, 2016 12:27PM
Re: Scara arm solution
April 12, 2016 01:40AM
Idegraaf, do you already have a Video of it moving? Would be nice to see...! :-)
Re: Scara arm solution
April 12, 2016 02:17AM
Unfortunately not the time to deal with it.
Re: Scara arm solution
January 13, 2017 03:47AM
Hello,

Thanks for the nice model and idea Idegraaf.

I see that there are more people try to use this model. On YouTube I found a russian guy with the same model working with marlin.

Youtube Movie Russian single arm scara
Blog

I am trying to make the same one. There are a few things I don`t understand.



How does marlin scara do the homing with the endstops and/or how can I test without homing? Now I don`t have control over the machine. I tried a lot things with endstops and changing some settings.
despite the explanation in the blog, it`s still hopeless.

Can some one give me some advice or help with the idea of endstops and marlin?
Re: Scara arm solution
February 28, 2017 05:55PM
Firmware available here:
[github.com]
copy the folder "example_configurations" configuration Scara.
Adjust the settings to suit your own.
On the other firmware I have not worked Scara.
Marlin releases RC7, RC8 In parallel Scara not work!
Marlin releases RC1-RC6 work.
My site:
http://гребенюк-аа.рф/index.php/radioelectr/58-3d-printer?showall=&start=5
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