Missing steps on low speed ?

Hi.

I was trying to change A and R values in my M669 command because those are the only values that am not 100% sure.
Anyhow, after numerous changes i still have the same problem

This is the sequence that is executed manually :

G28 ---> executed OK, homing OK
G1 Z20 X0 Y0 F1000 ---> executed OK ( low speed )
G1 Z20 X100 Y0 F1000 ---> executed OK
G1 Z20 X0 Y0 F1000 ---> executed OK
G1 Z20 X200 Y0 F1000 ---> missing 1,5 cm to reach expected point ( 20 cm from center )
G1 Z20 X0 Y0 F1000 ---> returns to correct start position ( correct in mm )
The situation is the same on Y axis. After 100 mm, extruder misses 1,5 cm.
Btw. every other point ( 300, 400, 500 ) is also missed by 1,5 cm, not more.

If i test it with much higher speeds, the result is totally the same.
I would understand that it misses all the points but first one is hit on mm.

/// EDIT
It looks like it has to do with extruder height from the floor because if i lift extruder 20cm above the floor,
"errors" are few mm... So i guess i will have to lower whole robot construction for 10 cm, to get desired
work...

Arnix

Edited 1 time(s). Last edit at 11/22/2018 06:28AM by Arnix.

You should fill in a brief descripriton of your unique printer kinematics. ( Best place is the signature )

To me it sounds, like the angles of the arms are crossing a limit in the kinematic-equations when the arms are stretched out to the bottom.
Only DC42 will know what to do...

Hi O_lampe and thank you for reply.
I agree that DC42 will know what to do. Unfortunately, i didnt have opportunity to meet him in person,
but he helped me a lot with his comments and support. Problem is that i have bunch of tasks to complete
and fine tuning of robot is just one of them. I was looking at our skype conversation and i found few things that i
can set but am missing correct A and R value setup. As you pointed out, David is maybe the only who can help with this.
I hope he will find time to reply on my mail or on this forum. We are now stuck...

That's why i will add newest status check, so if you have some additional clue, please share.

Robot base construction is lowered down, so base --> floor is now = 100 cm
and motor shaft ---> floor = 95 cm. When the arms are in horizontal to motor shaft
distance between upper arm and endstop is 17.5 cm. Extruder ---> floor = 15 cm.
This is the main setup before the base was lowered down.
Btw. now i can reach 500 limit without problem. After 500mm i can see small ring....

[ibb.co]

Problems:
- i think we will have problem that can not be solved without encoder.
- e.g. when the extruder head hits some object or presses the extruder ( future suction cup )
on floor, robot misses few steps and then it looses it self.
- i can "fix" this programmatically in vision system and with some side sensor but this is not best solution.

PC --> duet comm
- for some unknown reason, when we send data from our vision system, extruder head lowers down
and after few simulated pickups, extruder almost reaches the floor. This happens on slow or fast speed.
Funny part is that when i run the same commands manually ( over web interface ) they work without problem...

G1/G2/G3 intermediate....Outside limit error:
Sometimes i get this error after reboot and entering first command

Homing:
- i dont know why but sometimes, robot needs up to 3 passes (3x up ) to get correct homing coordinates.
- and sometimes it fails, so i have to click again to correct this.

Speed:
- like i wrote i previous posts, i dont get this 100K setup but it works.
Any explanation on this matter is more then welcome.

Arnix

Quote

Problems:
- i think we will have problem that can not be solved without encoder.
- e.g. when the extruder head hits some object or presses the extruder ( future suction cup )
on floor, robot misses few steps and then it looses it self.
- i can "fix" this programmatically in vision system and with some side sensor but this is not best solution.
Your suction cup will benefit from a spring loaded damper.

PC --> duet comm
- for some unknown reason, when we send data from our vision system, extruder head lowers down
and after few simulated pickups, extruder almost reaches the floor. This happens on slow or fast speed.
Funny part is that when i run the same commands manually ( over web interface ) they work without problem...
When you send them manually, do you send them line by line? The difference then is the idle time between direction changes.
Reducing yerk setting or acceleration would help, but your vision system could also generate pauses ( G4 ) between each move, I guess.

With the 10:1 gear reduction you can run the motors in fullstep or halfstep mode. That could help, too.

G1/G2/G3 intermediate....Outside limit error:
Sometimes i get this error after reboot and entering first command

Homing:
- i dont know why but sometimes, robot needs up to 3 passes (3x up ) to get correct homing coordinates.
- and sometimes it fails, so i have to click again to correct this.
All my Deltas get several G28 commands before I start autocalibration. Especially since I use the stall detection method.
When the arms are way off centre before homing, I have to center the effector manually.

I hope you get all issues sorted out without the need for NEMA23 close loop stepper drivers showing up.
If you have the time, take a closer look at the mechaduino drivers. Especially the behaviour around 0:40 in the demo video will cheer you up
You can probably run external drivers, suited for the meanest NEMA23 you can fit in your system. Don't know how that would work with the onboard current shunt resistors, though...
It's open source, maybe you have to change the design a bit to fit your needs

Edited 4 time(s). Last edit at 11/24/2018 03:27AM by o_lampe.

Quote
Arnix
Homing:
- i dont know why but sometimes, robot needs up to 3 passes (3x up ) to get correct homing coordinates.
- and sometimes it fails, so i have to click again to correct this.

The usual reason for that on deltas is insufficient movement specified in the G1 S1 homing commands. See this item on our troubleshooting FAQ page [duet3d.dozuki.com].

---

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].

I will make just one fast copy/ paste reply and for rest we can hear us tomorrow...

This is the code that am using for locating and picking up.
Btw. we added Z25 just because this up/down alignment but i will try your suggestion.

x, y = object
                strCode = 'G1 X' + str(x) + ' Y' + str(y) + ' Z25' + ' F50000'
                ser.write(str.encode(strCode + '\n'))
                strCode = 'G1 Z5'
                ser.write(str.encode(strCode + '\n'))
                strCode = 'G4 P50'
                ser.write(str.encode(strCode + '\n'))
                strCode = 'M42 P60 S255'
                ser.write(str.encode(strCode + '\n'))
                strCode = 'G1 Z80'
                ser.write(str.encode(strCode + '\n'))

                if x < 0:
                    strCode = 'G1 X-450' + ' Z25' + ' F50000'
                    ser.write(str.encode(strCode + '\n'))
                else:
                    strCode = 'G1 X450' + ' Z25' + ' F50000'
                    ser.write(str.encode(strCode + '\n'))

                strCode = 'M42 P60 S0'
                ser.write(str.encode(strCode + '\n'))

Arnix