Monday 20 July 2009

HydraRaptor's second child

Back in March I had a visit from Marcin Jakubowski, the founder of Open Source Ecology. He was over here in Manchester presenting at a conference and asked if he could come and see HydraRaptor, as he wants to use RepRap machines on Factor e Farm. Like RepRap, his project also aims to change the world.

He asked lots of questions and made a couple of videos of my answers for his blog, which you can see here.

I volunteered to print a set of Darwin parts to help get Factor e Farm up and running with 3D printing. I was confident that I would have my Darwin running in time to churn out the parts. However, because I spent a lot of time experimenting with extruder designs in an attempt to get something more reliable, I ran out of time and had to print the parts on HydraRaptor.

Here they are, all 109 of them: -



All the parts were printed with 0.5mm filament at 16mm/s with 32mm/s moves. Most were sliced with Skeinforge set to 25% fill and larger objects have double outlines to maintain strength.

Here are some stats: -


Build time Plastic volume Quantity required Total build time Total plastic Weight Cost Percentage of total

Corner bracket @ 90%
02:44:44 29.1 cc 8 21:57:49 233.1 cc 291 g $5.83 29%
Diagonal tie bracket-chris

00:27:00 4.8 cc 20 09:00:06 96.4 cc 120 g $2.41 12%
Bed corner
01:32:06 15.5 cc 4 06:08:25 62.1 cc 78 g $1.55 8%
Z-motor-bracket-chris
01:23:12 14.6 cc 4 05:32:47 58.2 cc 73 g $1.46 7%
X motor bracket
03:56:35 37.2 cc 1 03:56:35 37.2 cc 46 g $0.93 5%
X-carriage

03:51:39 40.2 cc 1 03:51:39 40.2 cc 50 g $1.00 5%
Y housing
00:56:36 9.9 cc 3 02:49:47 29.8 cc 37 g $0.74 4%
Extruder drive block
02:30:44 26.5 cc 1 02:30:44 26.5 cc 33 g $0.66 3%
X idler bracket
02:28:06 25.4 cc 1 02:28:06 25.4 cc 32 g $0.64 3%
Y motor bracket
01:51:06 19.6 cc 1 01:51:06 19.6 cc 25 g $0.49 2%
Bed constraint
00:43:20 7.5 cc 2 01:26:39 15.1 cc 19 g $0.38 2%
Bed clamp
00:21:39 3.7 cc 4 01:26:36 14.7 cc 18 g $0.37 2%
Extruder base
01:13:19 13.1 cc 1 01:13:19 13.1 cc 16 g $0.33 2%
Z-coupler-airpax
00:14:21 2.6 cc 4 00:57:26 10.2 cc 13 g $0.26 1%
Opto bracket @ 50%
00:19:00 3.1 cc 3 00:56:59 9.4 cc 12 g $0.23 1%
X-belt-clamp
00:10:46 1.9 cc 5 00:53:50 9.5 cc 12 g $0.24 1%
Wiper-diagonal-bracket
00:43:50 7.6 cc 1 00:43:50 7.6 cc 9 g $0.19 1%
Wiper-brace
00:13:24 2.3 cc 3 00:40:11 6.9 cc 9 g $0.17 1%
X-constraint-bracket
00:38:10 6.6 cc 1 00:38:10 6.6 cc 8 g $0.17 1%
Pulley
00:12:35 2.2 cc 3 00:37:44 6.7 cc 8 g $0.17 1%
Bolt plug
00:04:36 0.8 cc 7 00:32:11 5.8 cc 7 g $0.14 1%
Tall foot
00:14:27 2.6 cc 2 00:28:54 5.3 cc 7 g $0.13 1%
Y motor coupling
00:25:02 4.5 cc 1 00:25:02 4.5 cc 6 g $0.11 1%
Z-adjuster-housing
00:24:12 4.1 cc 1 00:24:12 4.1 cc 5 g $0.10 1%
Short foot
00:11:21 2.1 cc 2 00:22:42 4.2 cc 5 g $0.10 1%
Fan base
00:22:29 4.0 cc 1 00:22:29 4.0 cc 5 g $0.10 1%
Y belt clamp
00:03:43 0.7 cc 4 00:14:50 2.6 cc 3 g $0.07 0%
Fan-leg
00:15:48 2.8 cc 1 00:15:48 2.8 cc 4 g $0.07 0%
X-motor washer
00:15:27 2.8 cc 1 00:15:27 2.8 cc 3 g $0.07 0%
Z-flag-slider
00:13:00 2.3 cc 1 00:13:00 2.3 cc 3 g $0.06 0%
Bearing 360 run
00:02:47 0.5 cc 4 00:11:09 2.0 cc 3 g $0.05 0% HDPE
Extruder PCB holder
00:09:45 1.7 cc 1 00:09:45 1.7 cc 2 g $0.04 0%
Z-opto-flag
00:08:45 1.6 cc 1 00:08:45 1.6 cc 2 g $0.04 0% Black ABS
X-carriage-bearing
00:08:39 1.1 cc 1 00:08:39 1.1 cc 1 g $0.03 0% HDPE
Y-opto-flag
00:07:43 1.4 cc 1 00:07:43 1.4 cc 2 g $0.03 0% Black ABS
Bearing 360 jam
00:02:49 0.5 cc 2 00:05:38 1.0 cc 1 g $0.03 0% Black ABS
X-opto-flag
00:04:43 0.8 cc 1 00:04:43 0.8 cc 1 g $0.02 0% Black ABS
Wiper-lever
00:04:26 0.7 cc 1 00:04:26 0.7 cc 1 g $0.02 0%
Z-flag-clamp
00:03:20 0.6 cc 1 00:03:20 0.6 cc 1 g $0.01 0%
Circlip
00:01:26 0.3 cc 2 00:02:53 0.5 cc 1 g $0.01 0%
Bearing 180-x
00:02:38 0.5 cc 1 00:02:38 0.5 cc 1 g $0.01 0% HDPE
Bearing 180-z
00:02:03 0.4 cc 1 00:02:03 0.4 cc 0 g $0.01 0% ABS




109 74:28:04 778 cc
973 g
$19.47 100.00%

The times and weights are calculated, and don't include the raft time, which is significant, or the time waiting for temperature changes and raft cooling. I weighed the parts on kitchen scales and they came out at 931g, so pretty close to the calculation. The cost shown is on the basis of ABS at $20 / Kg.

I save all the rafts for the day when we get recycling working. I weighed them in at ~ 200g, that is about 20% wastage and will bring the actual printing time up to about 100 hours.



I also wasted 150g in failed prints, for silly reasons, more on that later. It gives a measure of the reliability I am achieving at the moment, i.e. 8 parts failed out of 117 prints so 93% success rate. Of course the bigger the part is, the more chance something will go wrong, so by weight and time it is much worse .



I used plain ABS for most of the parts because it seems to bond better than coloured. I used black for the opto tabs. No guarantee that they will be opaque to IR, but I think black ABS usually is. The green parts are just ones I had left over from experiments.

I made some of the bearings in HDPE as that should be a better bearing material than ABS, lower friction and longer lasting. The black ones are "jam" bearings so I left them in ABS as they want maximum friction.



Some of the parts are my own design. Most significant are the z-axis parts described in the previous post. Here is a list of the other design tweaks, with links to the article describing them:- simplified diagonal tie brackets, X-motor washer, x-carriage bearing and the feet.

Some parts I had never printed before. The Pinch wheel extruder: -



The nozzle wiper assembly has appeared in the latest Darwin release but I can't find any assembly instructions. I leave it as a puzzle for Edward Miller, the guy who is actually going to build this machine.



Similarly the new adjustable z-opto flag assembly: -



I aimed to print these parts over the course of a week, three batches a day, but the machine had other plans and it actually took me two weeks. I will give more details tomorrow.

Sunday 19 July 2009

$8 Z-axis

About a year ago I blogged an alternative Z-axis for Darwin using four tin can steppers instead of one expensive stepper and a belt drive. The only thing missing was a source of cheap motors to make it economically viable. Some time ago Forrest Higgs pointed out a source of cheap 15° motors for $2.50 made by Airpax. I also found them available for $2 at Surplus Shed. That makes a z-axis for $8 possible, which is much cheaper than original motor, let alone the belt.

They are surplus stock, so when they are gone they are gone, but there does seem to be a lot of them around. Unfortunately it costs more than $40 to ship them from the US, so the economics don't look nearly so good this side of the pond.

They are 12V 0.4A per coil, so four wired in parallel will take 1.6A, well withing the 2A capability of the RepRap electronics. They are six wire unipolar motors, but they can also be driven from a bipolar drive by using the red and orange wires as one coil and the green and brown as the other.

The pull in rate seems to be about 200pps, which would give 200 × 15 × 1.25 / 360 = ~10 mm/s with M8×1.25 threaded rod.

The boss on the back of the motor is a bit bigger than the motors I used before so I have updated the bracket design accordingly. The motors come with a spiral drive screw on the shaft. I could not find a way of getting it off, so I made a new coupling piece that clamps over it. It has a pointer so that it is visually obvious if the motors get out of step with each other.



I have uploaded both of these to Thingiverse. The other parts needed are shown below: -



And this is how they go together: -

Friday 26 June 2009

Back to Blog

Sorry I haven't posted here for a couple of months. A few people emailed me to see if I was OK, still alive, etc. No sinister reason for not blogging, I have just been on holiday, had a few weekends away, beer festivals, BBQ's, etc, and also visited the British F1 Grand Prix.




I have also been designing a new extruder controller for HydraRaptor with a stepper motor drive. I normally build electronics straight from brain to veroboard, no schematics or planning, I just pick up the parts and solder them in. That is very quick and efficient but does not leave any design record.

I decided I wanted a micro stepping bipolar drive and the only sensible way to do that is with an off the shelf chip. They are nearly all fine pitch surface mount these days so I needed to use a PCB. It is probably 10 years since I last designed a PCB and I have never used Kicad before so it took me quite a while to get it sorted. Now that I have sent the board away for manufacture I can catch up with the blogging.