Choosing right stepper rmotor and gearbox

Hi to all.

Can someone suggest what kind of stepper motor and gearbox should i use to complete my model of rotary delta robot ?.

This is the temporary setup of my robot:
[ibb.co]

My goal --> regarding precision and speed
[www.youtube.com]


This is technical data and setup that I use now:
Motors --> NEMA 23 double axis, 3A ( 23HS8630 ) , green/black , red/blue
Smaller arm length --> 30 cm , weigth 80 gramms
Longer arm length -->100 cm , weigth 60 gramms
All joints --> 350 grams
Full weight of head and arms --> 2,2 kg
Power supply for motors --> 24V / 5 A ( will be changed to 10A )
Controller is Duet3d board ( limited to 2A ) but we will add external stepper driver, current could go to around 6A.

Data of motor:

Step Angle 1,8°
Rated Voltage 2.7 V
Rated Current 3.0 A
Phase Resistance 0.9 Ohm/Phase
Phase inducturance 1.8 mH/Phase
Holding Torque 1,45 Nm
Detent Torque 6.8 N.cm Max
Rotor Torque 480 g- cm²
Lead Wires 6
Shaft Diameter - each 6,35 mm
Motor Length 76 mm
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In this setup i dont have any gearbox.
Before i add one, i would like to be sure that NEMA23 is suitable for the job.

What motor and what gearbox should i use to lift 2,4KG in one second time ?
Btw. real weight will be around 2KG but we can add some extra wight for calculation purposes...

Thank you in advance !
Best regards !

Arnix

Edited 1 time(s). Last edit at 07/03/2018 04:16AM by Arnix.

Let's assume a worse-than-worst-case scenario. Let's suppose that one short arm is horizontal and it is supporting the entire 2.4kg load. The short arm is 0.3m long so the motor+gearbox would need to provide 2.4 * 0.3 * 9.8 Nm of torque, which is about 7Nm. The actual worst case won't be as bad as this, but will be more than one third of this figure. Perhaps 4 or 5Nm.

You can run the Duet at up to 2.4A. This is 80% of the 3A rated current of your motors. But motor holding torque is generally quoted using full steps, and when using microstepping you need to divide the torque by sqrt(2). So the actual holding torque of your current motors will be 1.45 * 0.8 * 0.71 which is 0.82Nm. So your current motors will need a gear ratio of at least 10:1 to provide enough torque with some extra margin.

You could reduce the torque needed by using a constant force spring or counterweights to support some of the load.

HTH David

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thank you very much for your time and effort !

So, if i keep NEMA23 motor and if i add 10:1 gearbox, i will be able to lift 2KG load from 0 to 20 cm height in one second ?
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I would not need any additional external power driver ?

Gearbox ( this should do it )
[www.omc-stepperonline.com]


You could reduce the torque needed by using a constant force spring or counterweights to support some of the load.
***
One college of mine was on German automation fair before few weeks.
Most of the delta robots that ware presented there are using some kind of "compensator" in the middle of the base.
I dont know if this is used as stabilizer or for torque reducer , or both...

[www.convitech-gmbh.com]

Btw. what do you mean with "extra margin" ?

Arnix

Edited 3 time(s). Last edit at 07/03/2018 06:18AM by Arnix.

The specification for that gearbox says the max permissible torque is 5Nm. That may be just sufficient.

The other two calculations you need to do are:

- what extra torque you need to produce the acceleration that you want to achieve

- what motor driver voltage you need to provide to achieve the maximum speed that you want to achieve. See my earlier reply in your other thread.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

HI David !

Am happy to inform you that your suggestion regarding counterweight has worked !
Instead of counterweight we have added one spring in the middle of robot.
Overall arms weight is now reduced to 100 grams ( from 1,5 KG ) :-).

Now it's much better to work and now i can see what should be corrected.
Am sending you few videos where you can see how all this works.
Of course, there is no rotary firmware on the board so geometry is missing but for test it's OK.

Tell me, how should i modify circle.nc file to try to draw a big circle ( on margins of working area ) ?
Would this be possible to run as test, before we implement rotary firmware ?
Btw. working diameter is 65x65 cm.
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This is what i get when i run G0 X600 from GCode console
[sendvid.com] --> or if this one is not working then:
[tinypic.com] ( you need flash 9 for this )

When i run G0 Y 600 ( after G28 )
[sendvid.com] --> or if this one is not working then:
[tinypic.com] ( you need flash 9 for this )

When i run on G0 Z100
[sendvid.com] --> --> or if this one is not working then:
[tinypic.com] ( you need flash 9 for this )
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It looks like i need to solve a problem with vibrations.
My 24V 10A power supply will be ready next week...

Best regards !

Edited 3 time(s). Last edit at 07/05/2018 01:14PM by Arnix.