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Repic Electronics Questions

Posted by ostamo2 
Repic Electronics Questions
April 01, 2011 03:36PM
on the wiki page for Repic the Pololu Steppers do not have the 100K resistor going to Ground and 5V+ for MS1.
But on the other RAMPS type electronics they do. Is that resistor needed?I am building these electronics on strip board until i can get stuff to etch a board and would like to do it correctly the first time.

i am also building a Prusa mendel and ordered these steppers http://www.pololu.com/catalog/product/1200. what kind of power supply would i need.
i have no heated build platform but will in the future.and i am also debating on what extruder to order.
Re: Repic Electronics Questions
April 01, 2011 10:37PM
Looking at the board, the pins are all wired directly to +5V, and are NOT jumperable. I'm guessing that it's hard wired for 1/16th step.

As it's not jumperable, you don't need the 100k resistor.
Re: Repic Electronics Questions
April 04, 2011 12:06PM
Thanks i appreciate that i just wanted to know before i put it on the strip board.

is a 12V 5 amp power supply enough for the 5 motors and an extruder?
Re: Repic Electronics Questions
April 04, 2011 08:37PM
I know it's enough for 4 motors and an extruder (I have RAMPs myself, but I know myndale and I'm very interested in the Repic). I'm guessing it'll work with 5 motors as I've seen Prusa's (which have 2 Z motors) use 12V 5A power supplies with Pololu's. That said, if your motors draw a lot of current, you might be worth looking at a slightly higher rated power supply (eg: 6-8A).

Note: A heated bed will definitely need more current, so if you're after a heated bed as well, you'll want to factor that in. 10A just for the heated bed is not uncommon (eg: the PCB heated bed out there).
Re: Repic Electronics Questions
April 10, 2011 05:31AM
Sorry for not replying to this earlier Ostamo, I haven't checked the main forums for a while. As Cefiar points out, Repic is hard-wired for 1/16th step for quieter operation. This results in lower torque, but in my experience and that of others it's still more than enough to drive Mendel.

The power requirements are dictated by the current limiting on the Pololu drivers, not the steppers, which is also why you can run a 4V stepper on the 12V supply. There's a little pot on the Pololu boards that you turn to adjust this, basically you turn it until it's the minimum you can reliably get away with. If you run the steppers at a higher current you get higher torque but also start to lose the micro-stepping until eventually you're effectively running them single-step (you can hear it too, they get that characteristic buzzing sound that you hear on youtube videos of single and half-stepped RepRaps). Run at even higher current and you risk damaging your stepper.

The Repic software doesn't support a temperature controlled heat bed yet, the hardware is there but I won't be adding the code until my own heat-bed is built. Whatever you choose just make sure that you don't exceed the rating of the power transistors, I specified VNP14NV04-E on the Repic circuit since that's what Adrian's original Pololu circuit specified, they're rated at 12A so at 12V that would support a heat-bed up to 144W. I believe the heat-beds shown on the wiki are rated at 100W or so, so that should be fine. If your heat-bed needs too much power then you can always run the signal through a relay instead, although you should probably add a protection diode across it to protect the electronics from the back EMF.

Overall Mendel is rated at 60W, so your 12V 5A power supply is right on the money, but as Cefiar mentioned you'll need something beefier to provide the ~9A or so needed for a heat-bed. Personally I use a PC power supply from an old shuttle, you short the two pins that the PC power switch is normally connected to and then you can tap 5V and 12V off the molex connectors. I haven't built a Prusa myself but given that the Z-axis steppers are connected in parallel there is no reason I can think of as to why they would together need more current than the single stepper in a regular Mendel...you're still doing the same amount of work to lift the x-carriage (if anything I'd expect them to be more efficient).

With regards to extruder selection I got an Adrian's geared with my original RP pieces but used dremeled nylocs instead of the M4 insert. This worked surprisingly well but it's not very good at quickly changing the extrude rate so there were some minor problems with my prints. It was good enough to print the pieces for a replacement Wades extruder, and that's what I'm doing at the moment, but from what I've heard others say you're probably better off going for a Wades to begin with if you have the choice.
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