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Megatronics V3.0 + UM Tutorial & Review

Okay, it's been a while since my last post, I've had this installed for quite a while, but unfortunately haven't had time to write this out before now.

Before we get started here's a short DISCLAIMER:
You do any of the procedures explained here at your own risk. I assume no responsibility for fried electronics, house fires, blown MOSFETS and/or anger issues that might arise from improper wiring.
There may be errors here, so heavy usage of sanity is strongly suggested.

What is the Megatorics V3.0?

The Megatronics V3.0 is the latest version of RepRapWorld's 3d printer electronics, designed to be a single PCB solution. The usual approach in the beginning of RepRap development was to use an Arduino board, and hook it up with a shield of sorts, which then interfaced with the printer's components. However most of the newer electronic designs tend to have the Atmega chip on board.

[size comparison of the megatronics V3.0 vs UM V1.5.3 electronics vs Arduino Mega2560]

This kind of design is a more elegant solution since it takes up less space, so it's easier to install, and well, however you look at it - it's damn prettier. :)

There is another thing worth mentioning - there are two distinct types of "single board" printer electronics: those with integrated stepper drivers, and those which use external ones. I must say I prefer the latter. 

Using external stepper drivers makes them easily replaceable in case something goes wrong, and also with some boards (like this one) you get the option of using different stepper drivers instead of just the common Allegro chips. Namely, you can use Texas Instruments' DRV8825 or DRV8824 drivers, which can supply more current, and the boards have better thermal dissipation than the A498X-based boards. Also DRV882X boards support 1/32 microstepping. 

(The difference between the DRV8825 and DRV8824, is that the latter is a low-current model, more suitable for smaller stepper motors like NEMA8 or NEMA11)

Other notable features of the Megatronics V3.0 are the following:
  • supports both four thermistors and two thermocouples
  • SIX stepper driver slots, so you can run THREE extruders
  • integrated microSD card slot, but also supports external SD cards
  • dimensions are only 109.5x90.5x18mm (ie. really small)
  • six MOSFETs (three for extruders, two for fans, and one for the heated build platform)
  • supports various LCDs and keypads
  • priced at 80 Euro (ex. VAT)


So, since I managed to fry my old UM V1.5.3 electronics twice in a single week, I decided it was time for a newer, better solution. My orders from RepRapWorld have always been quickly delivered, with very fair shipping prices so hats off to them for that. 

The board arrived well packaged, with no instructions or documentation, since it's all online. Before installing I recommend printing out and carefully reading the Megatronics V3.0 Datasheet and Quick Start Guide.

The first thing I did was rip out everything from the bottom of my UM. Then I made a simple CAD template for the Megatronics' mounting holes so I could drill them out. I aligned the template so that the USB port aligns with the original USB port hole. That way you can't really use the integrated microSD card  without cutting out a piece of the UM's side panel (I wasn't intending to do so anyway). But, you can easily reach the board's reset switch, so that was good enough for me. The Megatronics' USB port is a tiny bit wider than the UM's stock one, so if you want it to go through the hole you must first widen it somehow. I decided it was okay if it didn't go through, since that gives you a bit more space when working with the pins and connectors on that side of the board. 

[the thing protruding from the upper right hand corner is the business end of a hex wrench, I have no clue why]

With the template in place I drilled the holes and used four sets of bolts, spacers and plastic nuts that held the original electronics to mount it. In the end I didn't use the fifth hole in the middle of the board, it seemed unnecessary.

[wow... such pretty... much amaze...]

Now that the board was in place, I installed my beefy 12V 30A PSU also to the bottom of the UM, since it can now fit comfortably. (I used to have it bolted to the back side of the UM = not so pretty.)

Before connecting any wires, I did the following in order:

1. Downloaded and installed the modified Arduino IDE which supports Megatronics from HERE.
2. Plugged in the board via USB.
3. Used the Arduino IDE to install the test firmware found on the product page.
4. After making sure everything was in order I installed Marlin, also found on RRW's software page.
5. Connected to the board via Pronterface, to confirm Marlin is running properly.

Note that before uploading Marlin you will most probably need to tweak some settings in the configuration.h file. (such as motor direction inversion, steps per mm, acceleration, jerk etc.) It would take too long to go into firmware specifics here, but I could write a short tutorial in the future if there will be interest for such a thing.  Also note that the recommended baud rate for Megatronics is 115200!

With everything setup properly, here's how to wire the board: 

  • Please note that the Megatronics board has no power switch! You need to have a power switch on your power supply!
  • Disconnect the USB cable from the board, take care your PSU is also switched off and disconnected from the mains!

  • You can choose where the 5V power for the processor will come from via a jumper. It can either be from the USB cable (so you can upload firmware/connect to the board with the PSU off) or from your PSU (in which case the PSU must be on to connect, but you can also print from SD without having an USB cable connected).
  • You can use a 12V or 24V PSU. I suggest using 12V if you are not sure what you are doing. With a 24V PSU all the outputs from the Megatronics will also supply 24V so take care.
  • Setting the current on your stepper drivers is not for the faint of heart. There's lots of info on that around the Web so find it and read it all! Different drivers are adjusted in different ways. 
  • Never touch the stepper driver pots while powered!

[A schematic of the board. The highlighted connections are the ones we will use.]

1. Plug in the stepper drivers (the extruder stepper driver goes into the E0MOT header). Be very careful when doing that, if inserted improperly they will most probably be destroyed when powered on. The proper orientation of the drivers is described in the Quick Start guide (you have to be sure the Vmot pin is at the right place). Also, note the three jumpers that set microstepping modes. You need to consult the chart for your stepper driver model and adjust the jumpers accordingly. (L or Low means disconnected, H or High means connected.)

Here is the chart for A4988 based drivers:

And here is one for DRV8825 based ones:

Your extruder and X and Y axes should be set to 1/16 microstepping, and the Z axis to 1/8.

2. Connect the motors. In case your motors (like mine) don't have the appropriate female connectors, you will have to buy some, taking care to connect the wires to them in the proper order, as shown below.

3. Connect the endstops, I only used the Xmin, Ymin and Zmin, since the max values are defined in the firmware anyway and I never use the max endstops. The endstop connectors have three pins for using optical or hall endstops, but since I have the stock mechanical ones, I only had two leads, which should be connected to the "S" and "-" pins (the "+" pin is not used).

4. The Megatronics board has 2 outputs for the print head fans. I only use one so I plugged it in the FAN1 socket, just beside the E0MOT stepper driver.

5. Plug in your hotend thermistor or thermocouple into the appropriate port (T0 for a thermistor or S1 for a thermocouple). I've switched from using UM's thermocouple to standard thermistors a while ago since the little amplifier board always got in the way of my designs somehow. Anyway, even if you are using a thermocouple you don't need that board anymore, just connect it to the S1 input. (Bear in mind that I don't know how well that would work since I have not tried, and I'm not sure if there will be too much interference from things like the printhead fan to use the thermocouple at all).

6. If you have a heated bed, connect its thermistor to T1.

7. Connect your heated bed to the "HB" terminals.
AFAIK, most Mk2 heated beds don't care for polarity, but others might, so take care.

8. Connect your hot end heater to the "E0" terminal.

9. Connect two 12 V outputs from your PSU to the "PWR" and "HBIN" terminals minding the polarity.

10. Check everything is connected properly.

11. Check again.

In the end the whole thing should look something like this:

You are now ready to turn the printer on.

If everything is okay, there should be no white smoke, no funny smell and no fire. If any of those symptoms are present you've done something very wrong.

My thoughts on Megatronics V3.0 after some use:

To sum it up in one short sentence: I think this board is awesome! 

To begin with, I think the board's cost is very appealing. Add to that the speedy and cheap shipping and good packaging and you get a nice shopping experience. After that, I had ZERO problems understanding the documentation and wiring everything up. I must say that the board datasheet and quick start guide are among the best docs I've seen in the RepRap ecosystem. (Okay I lied there, I had one tiny question but the guys from RepRapWorld responded to my mail almost instantly so I'm counting that one out.)

This board's feature set is more than good enough for all but the most hard-core experimenters out there. Also I got to ditch the UM electronics fan, and get rid of those pesky little heatsinks which kept falling off by switching to DRV8825 drivers. It has additional 5V and 12V pinouts for all sorts of stuff you want to attach to the printer (like additional fans for cooling the motors and such).

I especially like the small form factor which enabled me to put my PSU under the printer, but I did have to print some feet to raise the printer a bit since the PSU was a bit too thick.

It has status LEDs for all sorts of stuff so you can quickly check what's working and what isn't.

I see no major flaws when compared to other boards of its kind. If you don't want to use the included microSD, it's easy to wire up an external one and place it where you want. It's also easy to attach an LCD (like this one for example). The only little bad thing here is that there is no power switch, but that actually makes sense since the board was meant to be used with more powerful power supplies which can supply the heated bed along with the rest of the printer, and which should have power switches on themselves anyway. 

One could argue that it isn't an ARM-based 32 bit board like some that are starting to show up, but I don't think that's so bad, because this works out of the box, and ARM based boards still have ways to go firmware-wise. 

All in all, I give it  a  CCBR(TM) rating of 9.7 out of 10 and a shiny gold medal, because to my amazement one can do such things when one has a blog. I should have started blogging earlier, 'tis fun!

  • fair price
  • very good manufacturing quality
  • small form factor
  • good documentation
  • lots of powerful features
  • status leds
  • reset switch
  • it's black

  • it's still Atmega, so it's not a top of the line 32bit ARM board
  • no power switch 
  • nothing else I can think of

If you have suggestions, comments, or have found errors somewhere here, let me know!

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