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Marlin to redeem


From Marlin to Redeem

Understanding the difference between Marlin and Redeem

Redeem is a completely new 3d printer controller. It's been optimized to run on the BeagleBone Black with a Replicape. It's written in Python with some parts in C++.

The biggest advantage of Redeem over other embedded programs, is that it actually runs on linux. It uses the BeagleBone Black's secondary microcontrollers for real-time operations, but still runs most of the computations in Linux process space. This makes it more efficient for complex computation, memory management, etc. that all software engineers have to face when writing embedded software. Here, it takes advantage of Linux providing a complete resource management platform (and a good one at that!) and lets the development focus on what's important for the features of the software. It also means that, if someone were to develop an alternative to the BeagleBone which also has dedicated realtime controllers, Redeem could fully take advantage of it and quite likely of a stronger processing platform. Python and C++ are easily ported to other processors, so it's future-proof for any electronic upgrade we'll see over time.

Hotend settings

Setting the thermistor type

One thing that Redeem does a little differently from other firmwares, is the handling of the thermistors. It relies on having a "chart file" which is part of the configuration's external files. This means, of course, that the temperature sensor possibilities are nearly limitless. You simply need to be able to provide the proper data in a file and pass it in Redeem's configuration.

Temperature PID settings

Depending on what your printer type and hotend is, there are a few defaults to be found in the default configurations provided by Redeem. However, your setup may vary widely from the stock setup those values were selected for. So, to select proper PID values, the best is to do just as you would with another firmware, a calibration phase.

In Redeem, the PID calibration is done using the M303 command. A typical example of what you would do (if you print mostly around 210 degrees) is to run M303 S210 C8 to run 8 cycles of the hotend going from cold to the target temperature, cooling down and going back up. This will allow for a good refinement, and it will give you P, I and D values to put into your local.cfg file in the terminal after the last cycle completes.

Configuring a printer on Redeem with Marlin values


So. You come from Marlin, and you had your steppers set to, for example, 1/32 microstep, and you have 18-tooth GT-2 pulleys. Your Marlin configuration looked something like this:

#define DEFAULT_AXIS_STEPS_PER_UNIT   {200, 200, 200, 900}

Good! So you know which values you needed for Marlin. Except Marlin considered a "step" to be every (in this example 1/32nd) microstep, and it needed 200 microsteps to advance by a millimeter. Redeem doesn't expect that. In fact, the default.cfg in Redeem shows this comment:

# Defined how many stepper full steps needed to move 1mm.
#   Do not factor in microstepping settings.

What this means is that you're motor dependent - not stepper-setting dependent. Which makes sense, since Redeem sets the stepping mode! So it only needs to know how much current you need, and what kind of motors are connected. If you need to figure out how many teeth your pulleys have, use this page to try out various settings until you get the same number of steps as your marlin configuration. Once you have the right number of teeth on the pulley set, change the step from 1/16th or 1/32nd to be 1/1 (full steps) for Redeem, and use the value of steps per mm it gives you in your local.cfg.

If you have a geared motor to run your extruder, I suggest you first find the step size for your other motors (assuming they're all the same type!) and just multiply by the ratio between your normal and geared motor in Marlin to set the redeem value. With the example here, Marlin's 200 microsteps per mm with 18 teeth pulleys and 1/32nd stepping gives you 5.56 (full)steps per mm for Redeem. Marlin's example here shows 900 microsteps per mm, so, 900/200 = 4.5. So Redeem's configuration for the extruder is 5.56 * 4.5 = 25.02 (full)steps per mm.

Bed leveling probe

Whether you have a delta or cartesian, you may want to be able to use your Z-probe. In Marlin, a z-probe is defined with a few entries in the config file, the rest is done for you:

#define AUTOLEVEL_GRID 24  // Distance between autolevel Z probing points, should be less than print surface radius/3.
#define Z_PROBE_OFFSET {5, 15, -1.17, 0}  // X, Y, Z, E distance between hotend nozzle and deployed bed leveling probe.

Some newer versions may have a few additional parameters about where to go to deploy/retract the probe, but that's basically it.

To add those mechanical values in your local.cfg, add the following section:

offset_x = 0.005
offset_y = 0.015
offset_z = -0.0017

TODO (discussion with sniffle on Slack:) so jon_c if you want to add this to that todo document basically for now, home_backoff_offset_z = xxx is roughly the same as making adjustments to z-probe offset or using M851 in marlin

To define the probing, it's a bit more complex. For one thing, the endstop to which your Z-probe is connected to isn't actively listened to by Redeem during normal operation. You need to enable it. And, if you have an inductive probe, you also need to power it up. And you need to redefine what the G29 code does. See Redeem#Implemented_Gcodes for some useful information.

You're basically going to redefine G29 using Macros. You can also simplify your life by defining a probe deployment macro (G32) and probe retraction macro (G31). This is my current macro section, for a Kossel Mini with a mechanical endstop switch being flipped into place before, and flipped back out of the way after the probing is complete.

g32 =
        M574 Z2 x_ccw,y_ccw,z_ccw ; configure the Z2 endstop to be active, including which way the motors should spin upon endstop hit.
        G1 Z5 F4000
        G1 X50 Y-25
        G1 Z28
        G1 X0 Y0
g31 =
        M574 Z2 ; deactivate any endstop input from the probe after probing is competed.
        G1 X0 Y0
        G1 Z50
        G1 X50 Y-25
        G1 Z30
        G1 X0 Y0 Z35
        G1 Z250
g29 =
        G28 ; home the printer head
        M558 P3
        M557 P0 X0   Y0   Z5
        M557 P1 X50  Y0   Z5  ; Set probe point
        M557 P2 X0   Y50  Z5  ; Set probe point
        M557 P3 X-50 Y0   Z5  ; Set probe point
        M557 P4 X0   Y-40 Z5  ; Set probe point
        M557 P5 X25  Y0   Z5
        M557 P6 X0   Y25  Z5
        M557 P7 X-25 Y0   Z5
        M557 P8 X0   Y-25 Z5
        G32 ; deploy the Z-probe
        G30 P0 S
        G30 P1 S              ; Probe point 1
        G30 P2 S              ; Probe point 2
        G30 P3 S              ; Probe point 3
        G30 P4 S              ; Probe point 4
        G30 P5 S
        G30 P6 S
        G30 P7 S
        G30 P8 S
        G31                   ; retract the probe

Delta printers

Assuming your mechanics for your arduino mega-like board were soundly calibrated and nothing changed when you plugged it into the replicape instead, you should be able to look at the configuration file you had for Marlin and extract some of the useful values and put them in your Redeem's local.cfg file to help you get started faster.

the delta values

Your delta values in Marlin should look something like this:

#define DELTA
// Make delta curves from many straight lines (linear interpolation).
// This is a trade-off between visible corners (not enough segments)
// and processor overload (too many expensive sqrt calls).
// Center-to-center distance of the holes in the diagonal push rods.
#define DELTA_DIAGONAL_ROD 214.0 // mm
// Horizontal offset from middle of printer to smooth rod center.
#define DELTA_SMOOTH_ROD_OFFSET 145.0 // mm
// Horizontal offset of the universal joints on the end effector.
#define DELTA_EFFECTOR_OFFSET 19.9 // mm
// Horizontal offset of the universal joints on the carriages.
#define DELTA_CARRIAGE_OFFSET 19.5 // mm
// Effective horizontal distance bridged by diagonal push rods.
// Effective X/Y positions of the three vertical towers.
#define SIN_60 0.8660254037844386
#define COS_60 0.5
#define DELTA_TOWER1_X -SIN_60*DELTA_RADIUS // front left tower
#define DELTA_TOWER2_X SIN_60*DELTA_RADIUS // front right tower
#define DELTA_TOWER3_X 0.0 // back middle tower
// Diagonal rod squared

Now, in redeem, the file you want to be putting those values in is:


Elias has already normally properly set the values for the Kossel Mini in the kosselmini.cfg redeem profile. But if you have another delta, you'll need to overwrite those values with the equivalent from Marlin.

But! Remember, Redeem uses meters, not millimeters as the default unit! So you'll need to divide every value in Marlin by 1000.

Endstops and home position

To define the home position on a Delta, which is typically (x,y,z) = (0,0,h) where h is the top of the the printer's moving space, you'll want to set the parameters in your local.cfg (note that all section headers are case sensitive) like so:

home_x = 0
home_y = 0
home_z = h
home_speed_x = 0.2
home_speed_y = 0.2 
home_speed_z = 0.2
home_speed_e = 0.2
home_speed_h = 0.2 

Remember to set the h to the value converted in meters you had stored under the value

#define MANUAL_Z_HOME_POS 251.20

in Marlin.

The home_speed values are given in meters per second! Do not casually change those to the values you had in Marlin or you will have bits and pieces flying off into orbit.