@dc42 Thanks for the info!

The quadrature linear axis encoder configuration sounds like what I need! The only issue it that I'm limited on the number of wires I can string back to the control board and the 10 pin SPI header is quite a bit of cable, also the path back to the control board is further than the recommended 200mm

Also, I just realized that this setup is basically a servo, just replacing a potentiometer with an encoder. Is there a mode in RRF that allows you to drive a stepper motor in open loop mode targeting a potentiometer / encoder value? Essentially turning a stepper motor into a servo?

Thanks again for the help!

Hi!

The background
I have a 1HCL expansion board driving a Nema17 stepper motor. I also have a CUI AMT102-V 2048 PPR (8192 CPR) encoder hooked up to the output shaft of the mechanism the Nema17 motor is driving. The encoder is NOT attached directly to the stepper motor shaft, but further down the mechanical linkage at the output. The output shaft only rotates through 180 degrees of motion.

The reason the encoder is mounted on the output shaft and not on the motor shaft is that there's a significant amount of backlash in the mechanical system that is hard to compensate for (the amount of backlash varies with the load and orientation of the end effector).

Efforts
But due to the backlash in the system I can't seem to get the motor into closed loop mode. When trying to perform a Quadrature Shaft Encoder Calibration move M569.6 P##.# V1 , it fails due to inconsistent movement (I'm assuming this is because the backlash present in the system makes it seem like the encoder is faulty). I tried to bump the E param of the 569.1 command up to fairly large values to try and 'bypass' the backlash but it didn't seem to work.

Setup
6XD & 1HCL running 3.5.0-rc.1
Encoder is configured to use 2048 PPR (or 8192 CPR)
I have the A and B lines from the encoder hooked up to A and B on the 1HCL along with 5v and GND
Stepper Motor is 1.8 deg/step, with a mechanical reduction that results in 0.1930 degs/step at the wrist
The driver is configured with M569.1 P54.0 T2 C2048 R100 I0 D0

• Note:
  • I'm fairly certain C is incorrect here, but I've tried many different values with no luck
  • It won't accept anything less than C400 (throws Error counts/rev must be at least 2 times steps/rev)

The mechanism has a full-steps / deg value of M92 V5.1812500

Then placed into closed loop mode with M569 P54.0 D4

A Potential Solution
I was wondering if there is a closed loop mode of operation that essentially maps encoder values to rotational angles and will just blindly drive the motor in the direction necessary until the encoder position/value is reached. Or if there is a way to trick an existing drive mode into behaving this way?

Any help / suggestions would be greatly appreciated!

Photos

I've linked some photos of the robot arm & mechanism in question if you happen to be curious.

The mechanical linkage / mechanism in question (J5 - driven by a Nema17 ballscrew at the rear of the forearm)

This picture shows the Nema17 ballscrew driving a mechanism that pulls a belt

The belt drives a toothed pulley further down the forearm at the wrist of the robot

The encoder is mounted to the wrists shaft directly so the actual/real position can be measured

Hey @wieman01,

If you're interested in building your own 6 axis arm, I'd recommend looking into AnninRobotics. Chris Annin has done an awesome job putting together a pretty capable, open source, robot arm. It certainly doesn't meet your reach requirements, and having built one, the backlash is substantial enough that I don't think 3D printing would make sense / be practical (at least with traditional nozzles < 1mm).

I have version 4 of his robot arm running on 6 HCL's and a 6XD at the moment. There's more info and videos on my GitHub repo if you're interested.

It's not the cheapest build, but it was certainly fun.

Hey @JoergS5! Glad to hear you're still making progress on this massive task!

Are you planning on updating your GitHub with the code as you work on it? Or only once you have a complete, working, solution? Either is cool, just curious.

Looking forward to getting to test out the new IK once it's ready 🦾🥳

Hey @dc42, thanks for the heads up! So out0_neg isn't ground?

So the new, better, approach is...

• 12v power supplied to the 1LC Tool Board
• Power and ground wires of the servo running to out1.VOUT and out1.GND pins (with the VOUT Jumper installed for 2amps @ 12v)
• Signal wire running to io0.out

---

The config.g file

G4 S2                       ; wait for expansion boards to start
M950 S0 C"121.io0.out" Q250 ; io0.out 5v PWM capable, Q = 250Hz PWM Frequency

Interacting with the servo

M280 P0 S600  ; Moves the servo to lowest position
M280 P0 S2500 ; Moves the servo to highest position

The current set up that's working now...

• 12v power supplied to the 1LC Tool Board
• Power and ground wires of the servo running to out0 power and ground screw terminal
• Signal wire running to io0.out

The reason for the power and ground routed through out0 is due to only having a single power and ground line running from the main board to the tool board. I guess I could splice the power lines at Vin but using out0 lets me cut power to the servo using the M42 P0 S0 command.

---

The config.g file

G4 S2                       ; wait for expansion boards to start
M950 P0 C"121.out0"         ; out0 5amps @ Vin (which is 12 volts in our case)
M950 S1 C"121.io0.out" Q250 ; io0.out 5v PWM capable, Q = 250Hz PWM Frequency

Interacting with the servo

M42 P0 S255   ; Supplies the Servo with 12v

M280 P1 S600  ; Moves the servo to lowest position
M280 P1 S2500 ; Moves the servo to highest position

M42 P0 S0     ; Turns the servo off

---

I know this probably isn't the intended use case for the 1LC Tool Board but it seems to be working.

Thanks for the help, I really appreciate it!

Hey @droftarts

Thanks for clarifying that out2.tach is an input pin, I saw three pins and just assumed it was power, ground and signal.

I think it ended up being a signaling voltage issue! I tried switching the signal wire over to io0.out like you suggested and it worked! So I guess the servo wasn't responding to 12v PWM signals.

Hi!

Should it be possible to drive a 12v servo using the 1LC Tool Board? I'm powering the tool board and Duet3 Mini 5+ with a 12v power supply capable of 7 amps.
I've tried the following...

a) I originally tried running the servo off of out2 but It wouldn't move, so I figured the 0.8 amp limit wasn't sufficient to drive the servo.

b) So I tried...

• The power and ground wires of the servo routed through to out0 (because of the higher amp limit 5amps) (still at 12v - Vin == 12v)
• The signal wire of the servo running to out2.tach

---

The config I'm using is

M950 S0 C"121.out2.tach" Q250
M950 S0 C"121.out2+out2.tach" Q250 ; Doesn't work "invalid pin name"

M280 P0 S1500 ; Doesn't work, no movement, no sound from the servo
M280 P0 S45   ; Doesn't work, no movement, no sound from the servo

I've tried the same set up using out2 as well (instead of out2.tach)

The tool boards CAN address is the default 121 and I can communicate with the tool board, M115 B121 and M122 B121 commands return results as expected.

The servo's manual claims that the signal line can operate between 50-330Hz, and the operating voltage is between DC8.4V~12.6V.

I feel like I might be over looking something simple here. Any help would be greatly appreciated!