Today I got the electronics working and I now have an extruder setup that works. The electronics I'm using is called Megatronics 2.0. It is basically the same as the typical Ramps 1.4 cards you can buy very cheap, but Megatronics integrates everything on one single board (arduino, stepper drivers, power in/out, temperature control + more). In addition, it also supports up to 3 extruders.
The Extruder is now basically complete. I had to decide on using either an existing design or making a new one. I don't want to spend too much time on reinventing the wheel, so I'll use a normal Wade's extruder that I'll change to fit with the 8mm hole pattern of Makeblock.
Once I had decided on an extruder type, I had to get the other hardware required. I had the 608 bearings already, some screws and nuts, but I needed a hobbed bolt to pull the plastic through the extruder. Since I organise 3DP meetups at my local Hackerspace, I called up a friend that made me a custom 8mm bolt. He also helped me solve another problem - some new steppers!
It turns out that the Makeblock steppers are too weak. I can easily hold them back with two fingers, so that won't work if you're moving a heavy platform around. The extruder also needs a powerful stepper to work well. I'm now trying with some new 78N ones, vs the 40N ones I had. Here's how the finished extruder looks with the new steppers:
Here it is from another angle:
The firmware that comes with the Megatronics board just beeps the buzzer & turns the steppers randomly. You also cannot connect to it with Pronterface or other software, so it must be replaced with your own version of the Marlin reprap software. Whenever you are bulding a non-standard printer as I am, you will have to create a custom firmware and then upload it using the Arduino IDE.
I've adjusted many of the settings in the Marlin software to fit exactly this printer. One of these settings are the dimensions. It looks like I'll be able to get 32 x 32 x 35 cm (w/h/d) of build volume. Not shabby! These settings have to go into the machine's firmware so it knows when to stop moving.
Josef Pruza has made a series of small web-based calculators that are really handy. To calculate the required Steps per millimeter value for the Z-axis, I just scrolled to "leadscrew driven systems". To calculate this for the Y-axis, I used the belt-calculator. Very convenient, so thanks Josef! When I had all settings correct, it was time to upload the firmware.
I added an endstop on the Z-axis and tested that it all worked as it should. Apart from needing new steppers, the testing turned out well. The new stepper motors all have 5mm shafts, so I'll need to solve that in some way... Now it's time for the weekend and some other building projects outdoors!