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Newbie needs some help!

Posted by Shane_P 
Newbie needs some help!
June 22, 2014 07:45AM
Hi, I'm building my first printer (prusa i3, ramps 1.4, LCD) with our students. We have completed the build and wiring, uploaded Marlin. Using Prontoface, the printer is recognised and connected. I wanted to test if everything was OK and move the motors manually but the problem is nothing happens when I try to jog the motors using Prontoface. Can anybody suggest the next steps we need to take or point me to some resources to guide us and get our printer going?
Re: Newbie needs some help!
June 22, 2014 07:52AM
How to wire a stepper motor: [www.automationtechnologiesinc.com]
Use a LED to identify wire pairs, (3 links): [www.youtube.com] [www.youtube.com] And [forums.reprap.org]
Tips for beginners: Stepper Motors, bipolar series gets up to speed faster than parallel [www.youtube.com]
Determining what wires to pair up on a stepper motor. Match coils for 8 wire stepper. [reprap.org]
Calibration of stepper motors [www.youtube.com]
How to measure Stepper Motor Voltage [forums.reprap.org]
POTs Calibration – RAMPS 1.4 [bootsindustries.com]
Re: Newbie needs some help!
June 22, 2014 08:00AM
Hi A2, thanks so much for the quick reply.

Re: Newbie needs some help!
June 22, 2014 11:28AM
Also check the endstops with an M119 command. Some people have reported that stepper motors do not move or only move in one direction when the firmware thinks that the endstops are triggered due to the signal being inverted.....
Re: Newbie needs some help!
June 22, 2014 09:51PM
Hi Vreihen

What do you make of this??? I'm really not understanding some of this.

Reporting endstop status
x_min: open
x_max: open
y_max: open
z_max: open

Re: Newbie needs some help!
June 23, 2014 06:37AM
If your Y and Z carriages are not touching the min endstop switches, then they are reading backwards and need to be fixed. Assuming mechanical switches, you can swap the wires between the NC and NO terminals (or vice-versa), or you can invert the signal in firmware. Test each switch individually with a finger and several M119 commands to verify that each is working.....
Re: Newbie needs some help!
June 23, 2014 06:11PM
Hi Shane, Ive just built my own i3 as well and had to set up my end stops to get the motor working and get them moving in the right direction too. I found it best to do all the changes in the Marlin firmware rather than swapping wires and frigging it by swapping over wires.

Firstly, to make each of the motors move in Pronterface it first needs to know where the end stop datum position is for each of the X, Y and Z axes, so lets start with the X axis. I'm assuming your end stops are mounted as follows: X Axis on the left looking from the front, Y Axis at the back and Z Axis at the bottom, these are known as the MIN positions. So in your Marlin Firmware Configuration.h file you should ensure the following:
// Sets direction of endstops when homing; 1=MAX, -1=MIN
#define X_HOME_DIR -1
#define Y_HOME_DIR -1
#define Z_HOME_DIR -1
According to your info above the X Axis end stop is not reporting "Triggered", so , you should first select to HOME the X axis by selecting the home button (dont just select to move the motor) and then the motor should move in one direction, preferably towards the end stop micro switch. As soon as it moves (either direction) then manually press the X Axis micro switch with your finger to make sure the motor stops on command (if it doesn't stop, immediately remove power). Now you know it moves and stops on command. If it moves in the correct direction (towards the micro switch then next time let it travel all the way to hit the end stop and then you can move it both ways manually in Pronterface as it now knows the datum X Axis Zero point. If it moves in the wrong direction (away from the micro switch) then find the following line in the Configuration.h file in marlin firmware and amend as follows: "#define INVERT_X_DIR true", change to "#define INVERT_X_DIR false" or vice versa, and re-upload to try again.

As for your Y axis, then its already reporting as "Triggered" before its moved, so you can try to un-trigger it first by manually holding it depressed with your finger and then try the Home Y Axis button (as above for the X Axis). If it moves then release the micro switch and it should stop again. This would confirm you have wired the micro switch incorrectly, but I would simply change the Firmware again as follows:
"const bool Y_MIN_ENDSTOP_INVERTING = false"; to "const bool Y_MIN_ENDSTOP_INVERTING = true"; this will reverse the logic of the micro switch end stop.

Then its the same procedure for the Z Axis.

Hope this helps.
Re: Newbie needs some help!
June 24, 2014 03:11AM
Hi Vince, Thanks, that worked a treat. Everything is going in the right direction as it is supposd to. I'm having trouble with the z axis jamming though if I try to home it. There is a very slight bow in the threaded rod, do you think that would cause this?

Re: Newbie needs some help!
June 30, 2014 05:30PM
Hi Shane, I'm no expert but I don't think a slight bow in the threaded rod will make any difference. If the Z Axis is jamming then I'm guessing that it must be an issue with both Z axis motors not running at the same rate, so this means the threaded rods do not turn at the same rate and the X Axis twists causing the jam. On your RAMPS board, where the 2x Z Axis Motors connect to the board there is the Polu driver with the silver heatsink, next to the heatsink is a small cross head potentiometer which controls the motor current. First, switch off all power, then turn this Z axis potentiometer no more than 1 quarter turn clockwise to increase the current and see if that helps the motors run smoothly. If it does help, then this will probably make your Z Axis motors more noisy and they may need turning down again because they are now drawing too much current, so try 1/8th of a turn anti clockwise to reduce the current a bit. The rule of thumb with these potentiometers for all Axes is to reduce the current until the motors just start to play up and stall occasionally, then apply small increments clockwise (no more than 1/8th turn at a time, and always with power off) until the motors run smooth all the time. Then, as a final adjustment, give them just one more 1/8th turn clockwise for good measure. DO NOT run any of the motors (inc the extruder) with too much current or you will damage the motors and the Polu drovers too.
Hope this helps.
If your Z axis threaded rod nuts dont stay put in the plastic X Axis holders, then come back to me for a simple mod to make them stay put.

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