Rambo 1.4 board and marlin questions LR2

LowRider CNC Advice
1

#1. I only use the lcd and sd card. When I try to move the z axis the y axis moves too. What do I need to change to stop this from happening?
#2. When upping the amps, there are 5 unlabeled choices. Which one controls the z axis?
#3. In marlin it says I can change the voltage by the lcd. Which line do I need to change to make that possible or where do I need to look in the menu for that option.

Thank you for your help in advance

2

  1. This should not happen if you are using the V1 firmware for the LR2, and are either wiring the Z motors in serial or using the dual endstop firmware and have the Z motors plugged into the appropriate drivers. For firmware, you either want V1CNC_Rambo-2.0.7.2-src.zip or V1CNC_Rambo_DualLR-2.0.7.2-src.zip depending on whether you want the dual endstops.

  2. I don’t have a RAMBo myself, but these are generally in order, X, Y, Z, E0, E1. I believe for dual endstops, Z uses the Z and the E0 drivers, but I could be wrong.

  3. Voltage? Did you perhaps mean current? It might be settable in some parameters, there is Gcode that you can send to adjust this. It could be in a menu somewhere.

3

The Rambo board has two Z connections, but they are wired in parallel using a single driver. No version of the MPCNC uses both Z connections. So the order of connection is X, Y, Z1, Z2, E0, E1. For dual endstops, the wiring is:

X  -> X
Y1 -> Y
Y2 -> E0
Z1 -> Z
Z2 -> E1

In marlin it says I can change the voltage by the lcd.

As Dan indicated, you set the current for the steppers, not the voltage. It is originally set in the firmware in this line in configuration_Adv.h:

#define DIGIPOT_MOTOR_CURRENT { 138, 138, 138, 138, 138 }

If I remember correctly, a value of 138 was about 0.8A. For most people, the default setting works well. It is a balance between torque and heat. I’ve never used it, but according to the g-code reference, the M907 g-code can also be used to set the driver current. Note if you use the g-code to set the current, current changes in the firmware will be ignored unless you do a factory reset.

4

I did mean current but voltage came out. Sadly sometimes they mean the same thing in my head.

I was still having issues raising the z axis so I bumped it it up to 175. I ran everything for about an hour. Motors and mosfits weren’t hot to the touch( probably will still put some small heat sinks and a fan on them)
I might roll everything back to original with the z axis on there own drivers. I was using one of Ryan’s custom wire harness on the z before.

Yay thank you for all the info!

5

Many rigs run just fine at the default current. If your rig is requiring more current, it is worth exploring mechanical issues that might be putting more strain on the Z axis. I don’t fully understand stepper drivers, but I believe that the 0.8A of a 138 setting is the average (RMS) current, not the max current. If I’ve done my math right, your 175 setting is 1.0A RMS.

6

If you needed to bump up the Z axis current:

  1. Lube the Z screws. Reduce the amount of friction that the screws have. This will also extend the life of the brass nut.

  2. Make sure that the steppers are wired in series, and not parallel. Series guarantees that both motors always receive the same amount of current, where parallel might overpower one motor and underpower the other. This kind of gets worse as temperatures increase. The higher currents in parallel also are harder on the stepper driver chips. RAMPS 1.4 boards do 2 Z motors in parallel, because these typically run on lower voltage supplies, which are marginal for “rapid” moves with 2 motors in series. A 3D printer might need to “hop” the Z axis much faster than we ever will, particularly a LowRider. Put the motors in series, and the drivers will be happier, the motors will be cooler, and you’ll get more consistent power.

  3. Make sure that your Z axis rails are parallel and not binding. You can overpower a little bit of this with more motor power, but it’s not a great idea.

  4. If all else fails, go for more mechanical advantage, and get a shorter lead t;hread. Going to a 1 start (2mm lead) screw will increase the motor’s mechanical advantage by 4X. It will also slow down your maximum speed, but we shouldn’t be getting too close to that anyway.

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7

Can you share a photo of the controller connected to the steppers. I am not sure you have them in the right ports.

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8

I had 2 issues. #1 wired wrong #2 broken wire one of the y motor connectors. Thank you for your help

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