Five bar parallel Scara

bondus

@iamthebest22 No updates I'm afraid. It works perfectly fine, I use it to print various small parts for other projects. The accuracy is not good enough for big mechanical parts, we need a calibration method for that.

It's actually a very simple mechanical construction. Some parts from my CAD files:
https://a360.co/3dNKGjZ
You have to make your own Z axis

Siamak

Good afternoon all,
Very interesting subject that I would like to get involved in.
I am a retired Mechanical Engineer and would like to use this new approach to build a CNC machine.

Is there a way to get hold of BOM please, I have downloaded the printable file in STEP and DWG, what I would like to know is, is it possible to use ARDUNO UNO with the CNC Shield to make this robot work.

Would appreciate a feedback please on proteus3d@free.fr
Cheers
Siamak

JoergS5

@siamak Arduino Uno is a 8 bit based hardware, the ReprapFirmware is not ported to it. Even if ported, the Arduino is probably not fast enough to calculate the kinematics, because for calculation some trigonometric functions are used.

A 32 bit based board is needed like Duet 2, Duet 3, Duet Mini 5+, and a port to STM32F4 and a specific LPC board exists. The Duet boards have stepper drivers themselfes, so no CNC shield is needed.

I have no BOM, but currently building a new parallel Scara printer and can tell you the material needed.

o_lampe

@joergs5 @Siamak
There were times when RRF was ported for Arduino Due/RADDS driver shield. The support stopped for RRF2, but IIRC was re-established later?

JoergS5

@o_lampe Arduino Due is 32 bit, but the mentioned Arduino Uno is 8 bit.

Arduino Due is at it's end of life, which means less support and buying costs more than in the past. There are technical limits with Due which limits portability of RRF, please see https://reprap.org/forum/read.php?2,769032,page=10 and https://github.com/Duet3D/RepRapFirmware/issues/193 statements of dc42. The mentioned SAME70-XPLD board is a possible build target in firmware and is maybe supported. But one needs stepper drivers addtionally.

Cosik created this issue in Duet3D/RepRapFirmware

closed support for RADDS/RAMPS-FD with wifi/eth #193

o_lampe

@bondus @JoergS5
What's the gear ratio of the belt drive? Is there a golden rule to find the best match for steps/degree vs. arm length?

JoergS5

@o_lampe I have no golden rule and use about 1:30, but my thoughts are:

One can calculate the resulting

precision of the result (+- 5% of 1.8 degree of each stepper => resulting tolerances for result, but precision depends on the print position also)
resulting speed (stepper speed divided by ratio)

Higher ratio means better precision, but lower speed, if the gear is perfect.

gnmrc_

Hi, I'm building a 5bar scara 3D printer because I would like to make a really competitive time in the speedboat race and 5bar scara seems the best kinematic to do so.

I have read in the first post made by @bondus that the gear reduction for the motors needs to be really precise, I was looking at this geared nema 23 for my build do you think it's good enough?

https://www.omc-stepperonline.com/nema-23-stepper-motor-l-56mm-gear-ratio-20-1-high-precision-planetary-gearbox-23hs22-2804s-hg20

Thanks in advance for your precious help,
gnmrc

o_lampe

@gnmrc_

I'm afraid they mention 1.6° backlash under 'no load' for the gearbox. That's a lot given the small angles it takes to move the toolhead.
You'd need a belt driven system with no backlash.

gnmrc_

@o_lampe
I have also found another gear box with only 0.3 degree of backlash but maybe it’is still too much(?).

For sure a servo motor directly coupled to the arm joint would be a better choice but it will make the system more complex.