OK, long story short, I got the CTC to RAMPS electronics conversion done, but I wound up reverting it. Marlin has some great stuff I wish was in the CTC, but it is missing some key stuff, mainly change filament. The CTC has a completely closed extruder. Marlin theoretically has a change filament item under the Tune menu but I have no idea how to get to Tune. It just seems to magically appear sometimes, then disappear under equally mysterious circumstances.
Anyway, I blew 10 hours on the conversion, so I'll post my problems and solutions here.
Problem 1: thermocouples
The Makerbot clones use thermocouples instead of thermistors to read the temperature of the heads. Thermocouples do not interface directly to any standard RepRap electronics. You can do it with thermocouple amplifiers, but I decided I'd rather just put thermistors on the heads, since they work fine and I have thermistors just sitting around.
Here's the thermistors being removed, they're the big lugs that were screwed into the head.
Here's my solution: I took wiring lugs, spread the wire position out to form an inverted wedge so that I could slip a thermistor in from the front, pull it tight into the position and have it held in place. I also greased it up with thermal paste and then wrapped it in kapton tape:
Problem: I didn't want to cut the connectors. So I made adapters out of RepRap style connectors soldered to various things that fit the CTC/Makerbot connectors. After putting them in place, I used hot glue to secure and insulate them.
Problem: The CTC power supply is 24 volts. Most Arduino Megas do not appreciate being run on 24 volts and mine was no exception. It ran for about 2 minutes before the voltage regulator started to overheat and fade.
As a solution, I wired up a voltage regulator on a separate board to drop the 24v down to 12, and I unsoldered D1 from the RAMPS board and wired the regulator board across it (24v out one side, 12v into the other). You can see the regulator board on the top of this photo, with the red, yellow and black wires snaking over to the RAMPS board (D1 position is under the X motor driver).
You can also see a terminal block on the bottom of that board. It's for distributing 24V to the fans. The RAMPS board does not have the capability to switch the two hotend fans on as the Mightyboard does, so I opted to just run them constantly.
The board you see there is a hunk of 1/8" hobby plywood cut the size of the mightyboard, drilled to mount on the same screws, then with the RAMPS board mounted on it to line up the USB socket in the same location.
CAUTION - If you are thinking about doing this and want to reuse the motor drivers BEWARE - I think they are compatible, but they are FLIPPED OVER. The pins come off the other side. This is a sensible move on Makerbot's side since the driver chips are soldered to thermal vias which dump heat through to the other side of the board. By flipping the board over they are able to put heatsinks directly on the thermal pad on the bottom which is FAR more effective than the other method of gluing a heatsink onto the plastic top of the chip, which does some good but is far less effective.
Anyway if you want to reuse a Mightyboard driver board in a RAMPS board, you'll have to unsolder the pins and resolder them on the other side. If you don't you will have a very bad day - I plugged in a motor board wrong once and it smoked ALL the electronics including the USB port on the hub that it was plugged into. I don't actually know if you can get the pins in alongside the heatsink and still plug it in - probably not, I'd guess the heatsink would hit the capacitor under the driver socket. I just wanted to point this out to save you from smoking a bunch of stuff.
Another problem is that the RAMPS board is quite a bit taller than the Mightyboard, and the adapters don't help either. It's a mess and you can't really get the bottom cover back on.
Anyway, in the end it worked. It would print, but it just wasn't very good and I wound up reverting. Hopefully someone can get some use out of this info.
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