Prusa and Wade Firmware Changes for Gen 3

I’ve now got the three axes of my Prusa up and working with some temporary wiring, woo! Time for some calibration, now when I first set up my electronics I was doing it with a standard Sells Mendel in mind. To get the Prusa to work correctly I’ve got to make some changes to the configuration file of the firmware.

The first one is the z axis steps per mm, now I think that as the z axis is now directly driven rather than via a pulley and belt, this needs to be altered. The pitch of M8 rod is 1.25mm, so for every full turn of the stepper motor it should produce 1.25mm of travel. My steppers have a step angle of 1.8° (for a full step), now I think Gen 3 works in “half” steps, so for one full turn of the stepper I have (360/1.8)x2 = 400 half steps. Therefore the z-axis value should be 400/1.25 = 320 steps/mm.

The second one is the x and y axis, as I am using newer design pulleys (9 teeth rather than 10) I need to change the steps/mm. The belt pitch is 5mm, so 9x5 = 45 mm circumference. Therefore the steps/mm should be 400/45 = 8.889. (Interestingly the value given in the firmware is 8.9307 I wonder if it allows a little extra).

Thirdly is the extruder steps per mm. I am now going to be using a Wade’s extruder rather than Adrian’s. This has a gear ratio of 39/11 rather than Adrian’s which has a ratio of 59/11. I’ve had a go at calculating the steps/mm using the equation given on the wiki. For my set up, assuming a pinch wheel diameter of approx 5mm, nozzle of 0.5mm, and 3mm filament size, I make it: ((400x(39/11))/(pi x 5))x((0.5/3)² = 2.508 steps/mm.

Prusa progress

I have found the build much easier with nophead's proper printed parts. It only took me a couple of hours to get this far. I think I should have a carteasian bot up and running in the next week or two.

Switch to Prusa

I've decided to switch my build to a Prusa mendel after a long time getting frustrated drilling the cast parts. The cost of printed parts is now much less for a Prusa kit. Last week I purchased a printed set from nophead, can't be more pleased the quality is fantastic and the geometry is spot on. It has taken just a couple of hours to assemble most of the frame. Progressing well now, I'll upload some pictures soon.

Back, RDR, X-axis and Solidworks

In the past few months I have discovered that there are a few things that are very bad for progress on building a RepRap:

1. Moving house.

2. Changing Job.

3. Red Dead Redemption.

Having completed the above three I am now back building my reprap. I have almost finished the x-axis. See the below photo of my progress. Struggling to find time for the build at the moment so progress is likely to be slow for a while. Drilling and shaping the cast plastic bits is becoming quite annoying, wish I had held out and bought proper printed parts, never mind hind sight is 20:20!

From Mendel

I have also been practising using Solidworks at work, so what better to tune my skills than with the Mendel Solidworks files. See below for some videos I made using Solidworks. I have changed the model quite a bit, fixing a few errors and making the limits rights so you can only move the axes to the allowable positions. I will try and post my adjusted assembly files soon for those who are interested.

Sketch it Up

Just thought I would write a few words about using SketchUp for modelling with RepRap. I'm not sure if it's just me but very few people seem to be using SketchUp for doing their designs for the project. I really like Google's SketchUp and think it is fantastically easy to use. Capo's recent comment reminded me of the fantastic model he put together of Mendel and prompted me to have a play again myself. A quick look at Capo's blog and you can see how he has used SketchUp in a number of ways for both presenting idea's and for component design.

The below video shows Capo's model that I have coloured then animated.

Link to the SketchUp Mendel Model by Capo:
http://sketchup.google.com/3dwarehouse/details?mid=86dc5e3cc80958355ad914839c51e370

Link to Capo's Blog
http://capolight.wordpress.com/

Geared Extruder and X Carriage

I've done some more work on the extruder build. I had some problems getting the gears to mesh correctly, I found that the large gear seemed to be slightly ovalised which meant that as it turned the wheel would grind in some places and miss in others. I think I have solved this by filing down the teeth that were grinding using a triangular file (note the red marks I have put on so I know where to file) until eventually the gear wheel was circular. It's still not perfect but should be workable I think. I still need to glue the nozzle assembly in place.





I have also starting working on the x-axis. Beginning with the x-carriage. Nothing too difficult here except the captive nuts. A few of the nut locations had to be drilled to the correct shape to hold the nut, I did this using my dremmel clone with a small drill bit and file attachments, time consuming but works in the end. It is also important to remember which holes have to be drilled at an angle.

Adrian's Geared Extruder Build Part 1

The RP parts I have are for Adrian's geared extruder see the wiki here. For this you need some pats not listed on the original BOM list. There are a couple of different screws you need, nothing hard to find on ebay. Main parts you need are a short piece of M4 threaded rod. An M4 "Insert" - this is a splined piece used to grip the plastic filament. An M4 wing nut, and 3 bearings. The splined piece I got from ebay here is a bit different to the one shown in the wiki but serves the same purpose. It doesn't have a grub screw but it is internally threaded so should stay in place with bolts either side of it. It was listed as "Ripmax DYCO M4 x 0.7mm Coupling Insert" looks like it is used in the clutch mechanisms of model cars, trains etc.
After a bit of drilling and shaping the parts seem to fit together ok.