16 October 2011

Updated SumPod RAMPS v1.3 Build

The SumPod RAMPS build varies very slightly from the standard RAMPS build, with the addition of the LCD connector.  In this post, I provide updated pictures of the RAMPS board, the ancillary stepper boards and the Arduino Mega.

Here are the pics, first up we have pictures of the two variants of the RAMPS board, one of which you will receive with your SumPod.  They are electrically identical:
Gold pads
Immersion silver pads

I prefer the second board type, with the silver pads, because it has a silver immersion finish; the overlay shows the resistor values and there is a fraction of a millimetre difference in component clearance (or my imagination) of the socket and pin headers at the top right of the board making assembly easier.  Other than that they are identical.

The additional 4 pin headers (each labelled 2B 2A 1A 1B) are required for stepper motors X, Y, Z, E0 and E0.  With the LCD pin header on the far right my RAMPS board looks like this:

Mounted in the Arduino Mega 1280 dev board:

With the full complement of five A3983 stepper driver boards for the dual feeder based system:

The overall board stack looks like this:

When mounting the stepper drivers ensure they are orientated correctly.  To help this legend on the underside of the driver PCBs indicate the pin function matching the legend on the RAMPS board.

Uprated PSU and Improved Stepper Performance
Currently the SumPod uses a 12VDC supply.  I am intending to use a higher voltage supply (24VDC) because superior stepper performance is possible, and besides the driver boards will run at voltages of up to 35VDC.  
Since the SumPod comes with high torque (44Ncm) hybrid steppers using the chopper current limiting stepper drivers, greater speed is possible with a higher voltage.  This is because of the natural low pass filtering that occurs with an inductor (stepper coil).  As frequency of pulses increases the amount the stepper coil energises (directly affecting torque) reduces.  Increasing the voltage proportionally improves energisation rates and hence top speed.
I realise the Mega 1280 board supports a maximum input voltage of 12V and I intend to use a DC-DC step down converter to provide an acceptable supply.

I haven't yet connected the LCD, but here are some pics and technical details:

Until next time
SumPod Guniea Pig


  1. Interesting info about the 24V for the steppers. Taking a look at the schematics it seems like you could probably get away with it. Pluggging a dc/dc converter in place of D1 that servers as a revers polarity protection can cover the arduino 12V supply. Then you might want to replace the current limiting resistors R23-25 that protect LED2-4 by the heater and fan outputs. The rest seems to be powered by the arduino. But you will have to double check. Have you seen this done else where?

    OT: the sumpod forum is acessable again from the front page. You could actually access it anyway after the site can back online but no one tried to post anything.

  2. I think you're looking at the schematic for the latest RAMPS v1.4 board, not the v1.3 (just as electrically capable and all through-hole) that comes with the SumPod. The parts are not on v1.3 and the only led on the board is powered from Arduino.

  3. Yup, disconnecting D1 will allow us to drive RAMPS 1.3 on 24V as long as the Arduino is connected to USB. That is pretty much what I have in mind. You will have to provide 6-12V to VIN from somewhere else to power the linear regulator.

    Another way is to hack the Arduino itself and replace the MC33269 regulator with something like oki-78sr-5.
    A tiny to-220 compatible 5v switch-mode supply.

    I kind of shy away from messing with the Arduino since it will be a nasty surprise if you ever replace it and inevitably forget you made it magical :o