Tuesday, 29 January 2013

Rostock arms and bearings upgrade

Well the Rostock isn’t even finished and I’ve begun upgrading parts of it.

The printed arms to me aren't the best, even in a tinted PLA (one of the more rigid colours) it is still quite flexible, I also didn't like the idea of PLA bearings, these will wear out quickly.

The following solution was suggested to me on the #reprap IRC  channel

These are a race car part. "Traxxas Rod Ends Large w/ Steel Hollow Balls 5347, Revo 3.3"  just search e-bay and you will find them.  Nicely they also come in packs of 12, which is just how many you need for a Rostock

The inside diameter of the Plastic part is 3.5mm and 10.5mm deep. The inside diameter of the Steel is 3mm (not documented but needed by us)

Assembling these together was a little tricky. One side of the plastic is bevelled (shiny circle around the hole) they go in that side. I held the bearing with some long nosed pliers just sitting on the bevelled side then snapped them in place using the plastic as a lever.  

Next is the arms between the ends. Some people are using m4 thread rod as their arms with these, but this is heavy and easy to bend.

I found a local supplier of 3.5mm solid carbon fibre rod.  Now this rod was not the best quality, ie it was a little bent, but when cut up into 6 * 236mm lengths I was able to discard the worst bits. (236mm is what is required to make the arms the same length as the originals)

I glued the arms into place, the fit was so snug I had to ensure there was no air trapped in the end (ie you would let the arm go and it would spring out due to compressed air being trapped). Also make sure that the two ends are on the same plain. Ie The flats are level.

The top original arm weighs 16g, the new carbon fibre arms weighs 6g, and is a lot stiffer and in my view a lot better looking.
That also a weight saving of 60g! (6 x 10g) (important when you considering putting an extruder directly onto the carriage vs a Bowden cable type system)

The arms fit where the old ones did.  There are new single lugged plastics if you want to reprint, but I didn't want to.

NB this was originally connected with 2 * 12mm m3 bolts. Here I am using one 20mm m3.  To be exact the order pictured here is M3 bolt head, 3m washer, Printed lug, embedded m3 nut,  Traxxas steel bearing, m3 lock nut. The second m3 nut is still embedded in the other side but the thread is just sitting indented in it, not threaded in.

NB this is still a work in progress, looking at its range of movement a second m3 nut before the bearing to move the arm towards the centre of the gap will be required.

Update: I’m not happy my with my attempts to attach these to the original plastics
So I am printing a set of http://www.thingiverse.com/thing:31642

Wednesday, 9 January 2013

Sprinter, Arduino 1.0.3, Sanguino-0101r1 and Pololu USB AVR Programmer

I recently learned that Sprinter is Arduino 1.0.3 compatible (has been for a while)

So I had to give it a try on my Sanguinololu 1.3a.

As per usual download the Arduino software from here, to suit your OS
Then download and install the Sanguino-0101r1 files from here

Grap a copy of the latest Sprinter from github 'git clone https://github.com/kliment/Sprinter.git'

Edit sprinter configuration.h to suit the board and any other changes you need.

One of the things I wanted to get working was installing a new boot loader via the Arduino GUI using my Pololu USB AVR Programmer vs cmd line as I have been doing.

After some debugging I found that there was no hardware settings for the Pololu USB AVR Programmer

So I added the following to programmers.txt (as documented here)

avrispv2.name=AVR ISP v2

Then set your programmer to AVR ISP v2, and your serial port to /dev/ttyACM0 (linux naming convention)

Then Burn Bootloader works, uploading the new boot loader and setting the fuses.

One thing to note is that the upload baud rate has changed to 57600 from 38400 in the new boot loader. This means if you have a older boot loader, you will not be able to use Arduino 1.0.3 to upload new firmware via the boot loader. (without changing settings, or using the new bootloader)

Now switch your serial port to /dev/ttyUSB0 and your board to Sanguino W/ ATmega644P and upload your new firmware via the new, faster, bootloader.
Sprinter compiled and uploads without issues.  

Tuesday, 8 January 2013

12v to 24v converter and mount

I wanted a way to mount the converter where I had my Soild state relay inside the frame. Firstly as there was a nice space there and secondly it holds the cover over the back of the mains plug in place.

I had to design my own thing again...  Getting quite good at simple scad things


I added a 50mm fan to the converter, as I've been told it runs warm. Attached with 3 bolts onto the other side of the heat sink. There should be 4 but as per usual I was one bolt short.

It is now mounted on the frame, and the input power and fan have been wired up.

I haven’t found any official documents on how its meant to be wired up.

But I did find this in the mendelmax google group .

  • Connect the Input lines of the step up to the PSU. 
  • Connect the the + line of the HBP to the + out on the step up.
  • Connect the - line on the HBP to the - pin on the D8 FET on the RAMPS board.
Also with a warning

"It's been discussed previously on this group that the step-up
converters can't handle full bed power. They're pre-set to 19v since
they don't burn up at that output voltage."

The concerns I have with this way of wiring it is there are no fuses between the power supply and the HBP, and its a 24volt kapton heater, how badly is 19v going to slow it down or cripple it?