Tuesday, March 31, 2015

Prusa i3 Rework: Build Log #10- Electronics and Wiring

Finally, the last part of the build- adding electronics and connecting the electronic parts of the printer together. In this step, it is paramount that you are careful- plugging in connectors backwards or reversing wires can cause lots of trouble.

First, we need five of the humble StepStick stepper drivers, powered by Allegro's A4988 chip. If you click on the picture, you can see the numbers "4988" etched onto the chip in the middle of the board. To the right of the board is a small heatsink for the driver chip. 

Another shot of the StepStick driver. If you want to start using stepper motors in any project, the StepStick is a great way to get an inexpensive and powerful motor driver set up. Those 0.1 inch pin headers plug into a breadboard, and some of the StepSticks on eBay are leaps and bounds cheaper than other stepper drivers. (EasyDriver, I'm looking at you.)

Here are the drivers, with heatsinks attached. We need just four of the drivers for the Prusa i3 Rework. One powers the extruder motor, one powers the Y-axis motor, one powers the X-axis motor, and one powers both Z-axis motors in sync. There are two Z-axis motors in order to lift the X-axis on each side, and with more force.

A closeup of the StepStick drivers, with the aluminum heatsinks.

The four drivers, plugged into the RAMPS board. Make sure that they are oriented properly (DIR pin in the bottom right, GND pin in the upper right)! RAMPS (this one is 1.4), at it's simplest level, is just a very fancy Arduino shield, designed for use with 3D printers, for the Arduino Uno. 

Here is another image of the RAMPS board, with the four drivers plugged in.

This is a mounting screw and Arduino Washer (standoff) for the control boards.

The Arduino Uno was attached to the RAMPS board, and I put on the mounting screws and standoffs in two of the holes.

A closeup of a mounting screw and standoff. There is a washer underneath the head of the screw, which is on the other side.

The boards get mounted on the rear side of the frame, on the right. RepRap says that the plugs and connectors should be facing upwards. I prefer to have them face downwards.

Here are the endstop wires, plugged in. From bottom to top, there is the X-endstop, followed by the Y-endstop, followed by the Z-endstop. Make sure that they go in this order, starting with the first set being filled with the X-endstop wires. Skip every other set of pins.

A closeup of where the endstop wires plug in. Make sure to have all wires over the next couple steps go over or around the black metal frame, not through it. The only exception to this are the X-endstop wires- I threaded mine through the black frame because they are too short. 

Now the motors have been plugged in. The orientation of the 4-pin motor connectors doesn't really matter, as long as both Z-axis motor connectors have the same orientation.

A closeup of the screw terminals for the hotend heater and the heatbed.

I connected the hotend ceramic heater, which lacks polarity, and the heatbed, which has polarity, to the screw terminals. The wires slip in between the "jaws" of the screw terminals. Use wire that has a high enough gauge for carrying the amperage for the heated bed- something at least 18 gauge. Don't skimp here, you can start fires by using wires that are too thin.

At this point, I also connected the thermistors for the heatbed and the hotend, which are plugged in above the Z-axis StepStick driver.

A quick note about the extruder fan: Yes, it is necessary. I struggled to print anything successfully without the extruder fan until I realized that I needed it. To save you some time, just plug the damn thing in and don't skip it. The extruder fan is plugged in to the left of the X-axis StepStick driver.

Your fan should "blow" onto the hotend, indicated by arrows on the sides of the fan. Test it out by putting a small piece of paper next to the fan. If it is sucked in, you have done it right. If not, then reverse the way that the connector is plugged in on the RAMPS board.  If that doesn't work, unscrew the fan and flip it over.

Here are the heatbed wires, soldered to the heatbed, and the thermistor wires. Keep in mind that the negative lead from the heatbed goes to the positive terminal of the RAMPS board, and that the positive lead from the heatbed goes to the negative terminal of the RAMPS board.

Here are the heatbed wires, pictured again.

Now, I stripped the leads of a power cord. Use one with a ground pin, as the power supply for the printer requires a ground pin. The letters next to the pins on the plug tell you which pin is line, neutral or ground. (Shown as ground symbol, N, and L on the printer power supply.)

I used a continuity tester to determine which wire connected to which pin on the plug, but I'll save you time: Green is ground, white or grey is neutral, and the other color (usually black or red) is line (hot). Don't mix these up, and strip the wires properly. Household wall electricity is dangerous if misused.

I sliced the outer plastic wire insulation from the power cord off with a hobby knife, leaving the bare wires.

I then stripped the wires with a wire stripper and wound them.

Here they are, attached to the terminals for the power supply. My power supply is 15V at 33A, and it has a fan for cooling. I find that it cools down most efficiently when tilted on its side.

Here are the 15V connections for the printer's power. Don't use wires for the 15V lines that are less than 18 AWG. Close the terminal cover when you are done with the screw terminal connections, in order to avoid electric shock.

And here are the 15V wires, attached to the screw terminal block for the RAMPS board.

Finally, all of the wires are plugged in. It's a huge mess.

Remember how I said earlier not to thread the wires through the metal frame? I ended up figuring that out the long way, as you can see here.


At this point, I had finally reconnected the wires correctly- over the frame.

This meant I could put the cable wrap on all of the wires coming from the extruder.

And I ever-so-timidly plugged in the power supply... a slight hum, and this light lit up on the RAMPS board. Success! The printer has been assembled!

This post is the tenth of ten that goes over my Prusa i3 Rework build. These posts are in the order given on RepRap's wiki page for the Prusa i3 ReworkAll of the images from the build are in this Flickr photo album.

My build log: