ExtroH 3D绘图仪

In the process of documenting this design I suffered a serious PC failure when the boot SSD of my computer failed to do the booting thing. Most of the data was on a secondary drive which is fine but I've lost some of the notes that I made and for other reasons I've had to swap over to Linux which has interrupted things as I re-install & configure Linux versions of things I used to use. I had done some filming and editing for an assembly video but realistically that will take a while to prepare and I wanted to get an initial release out.

So: some of these instructions aren't as detailed as I would have wished and some aren't available yet. If you're really keen to build one but you're not confident to proceed without details instructions please wait before you invest time & money in parts, I won't be able to help you much as I'm going to spend time building the instructions for everyone.

In particular I was not able to assemble all of the notes I made on which screws are needed & where so apologies, you might need to buy a selection of the different lengths shown below and it might be a bit confusing to see what's needed in each place. If you're happy to look into the OpenSCAD code it should be possible to see what goes where.

The main structural components are v-slot extrusion, main rails are 20 x 40mm and the pen arm is 20 x 20mm. Note: this time I've actually used v-slot rails! For ExtruDraw I bought the wrong type and didn't realise, this does mean that you might have to buy new rails if you already have an ExtruDraw but the v-slots are much better.
The 2020 extrusion is 50cm long, the 2040 extrusions are 70cm long - I bought all of these as standard lengths and they allow a drawing area just over A3 (42cm x 29.7cm) at 51cm long by 32cm wide.
Other parts are:

• 16 screws to fix the plotter feet to the board, you will need to choose the length and type to suit your baseboard
• M3 socket cap screws:
  • M3x6mm
  • M3x8mm
  • M3x10mm
  • M3x20mm
  • M3x25mm
  • M3x35mm
• M5 socket cap screws:
  • M5x35mm - 11 for the main carriage & pen carriage v rollers and construction
  • M5x25mm - 3 for the pen lift v rollers
• Mini V rollers: these have a diameter of 15.3mm (6/8") and a height of 9mm with 5mm bore
  • 12 needed in total (3 each for the 2 main carriages, 3 for the pen carriage and 3 for the pen lift)
• Pulleys: 20 tooth size
  • 4 smooth idler pulleys for the main carriage - 3mm bore
  • 2 toothed idler pulleys for the end pulleys - 3mm bore
  • 2 toothed drive pulleys for the steppers - 5mm bore (to fit your steppers)
    Note: there is a design for printable idler pulleys in the STLs, these use two ball bearings each - if you already have 3mm bore bearings of suitable size they will work but metal pulleys are recommended
• T-nuts: for M3 screws to fit into the 2020/2040 extrusion, used to fix printed parts to the extrusion
  *5m of 6mm wide GT2 timing belt for a machine of the suggested size. If you change the size of the machine you can calculate the approximate belt length from:
  • Length of the 2040 extrusion you have = L
  • Length of the 2020 extrusion you have = W
  • Belt length >= 4L+2W

Servo cable management is one of the areas where my solution might not help you very much - I have some 5mm OD stiff plastic tube that I use because I have a bunch of it hanging around (I can't remember where I got it), if you don't have this you should be able to use anything else that will let you string the cable from the base to the main carriage and from there to the pen carriage. There are mounting holes in the parts to let you mount whatever you like but you may need to design your own (if you find a good solution for this please share it)

Obviously the plastic parts are 3d printed, so a printer is the most important tool to have. If you don't have a printer I can't sell these or any other parts as a kit, I'm not set up for it so you will need to talk to a friend/library/hackerspace etc. or use a commercial service.
Most holes for screws need to be reamed to size. This can be done with a cordless drill but is best done by hand with a drill bit holder (e.g. like this https://www.printables.com/model/528598-3mm-drill-bit-handle ) to avoid PLA heating up too much.
Holes for screws to pass through need to be reamed to 3mm using a 3mm drill bit.
Many other holes have to be tapped for M3 threads, so they first need to be reamed to 2.5mm. I recommend a spiral flute tap since I find it's better at clearing chips than straight taps and again I strongly suggest reaming and tapping by hand only in PLA.
You will need Allen keys for socket cap screws: 4mm for the M5 screws and 2.5mm for the M3 socket cap screws. If you can get a key with a ball end to allow the screws to be driven from slight angles as this will help with some of the assembly. In addition you may need other sizes of Allen key for the grub screws in your drive pulleys, I would recommend having a small set to ensure you have all needed sizes. You will need a driver for whatever fastenings you use to fix parts to your baseboard and may need to drill pilot holes.
Belts have to be cut to length, for this side cutters are probably the best option.

I use an EiBotBoard (a clone specifically although I have a genuine one that now stays in my EggBot) to drive this plotter which is very convenient because it's a very neat self contained part and allows you to interface with the AxiDraw Inkscape extension. This is the approach I would recommend for this plotter, it can definitely be brought from https://store.bantamtools.com/products/ebb-driver-board and it (or clones) might be available from other places also, I can't give you the source for the clone I bought since it's not available where I bought it any more.
There may be others but I can't help with them because I've never looked into them.

The AxiDraw Inkscape extension is the way I run this plotter but because I have mine set up as a portrait machine it can be inconvenient to use by default unless you do some extra reconfiguration.
Install Inkscape & the extension https://wiki.evilmadscientist.com/Axidraw_Software_Installation based on the information in this page. Next you will need to find where the Python code for the extension is installed on your machine - to find this you will need to open Inkscape: go to Edit > Preferences > System and look for the folder where the preferences and extensions are stored, you will need to open this folder and edit some files there.
This machine seems to be fairly “bouncy” (possibly because of the long belt run, possibly because I might have bad belt), with a some small amplitude but noticeable ringing on fast direction changes so if this is a problem use a fairly slow drawing speed of around 30% and the “very slow” acceleration setting; enter these settings in the extension options tab. If you don't need quality that high you can enter a higher drawing speed. 60% speed for travel moves seems to be OK but can be increased if you wish.
Machine size settings
Once you have built your machine you can find its plottable size and enter this into your configuration file. This is the [Inkscape extension folder]\axidraw_conf.py file, it contains the settings for AxiDraw plotters and you can adjust it to represent your machine.
For the simplest change for an A3 machine it's possible to adjust the AxiDraw V3A3 machine to be a portrait configuration by changing around the X and Y dimensions. If you wish or if your machine is not this size you can edit one of the machines to be exactly the size you have built. The X direction is the one that runs parallel to the line joining the two steppers
Remember to change the machine you're using to the one that you altered in the extension options tab.
Changing rotation settings
In the Axidraw.py file found in the [Inkscape extension folder]\axidraw_deps\axidrawinternal folder you need to edit a line around line 1000 which starts:
if self.options.auto_rotate and (self.svg_height > self.svg_width)
This line detects if the height is greater than width, for the AxiDraw this means that if auto rotation is enabled it will fit portrait documents horizontally in the machine. However in this machine it is portrait by default so we would like to reverse this behaviour to rotate if a landscape document is used which is what I tend to do.
Make a copy of the file and edit its name to show that this is the original, this allows you to revert the file if you need to. We will change the direction of the test near the end of the line to read:
if self.options.auto_rotate and (self.svg_height < self.svg_width)
Once this setting is enabled you can then use the auto rotation option in the settings of the Inkscape extension to plot landscape documents easily in a convenient way. It is suggested that you keep the auto rotation setting on.
Problems under Linux Mint
I had some problems getting my EiBotBoard working under Linux Mint. The AxiDraw extensions are developed under Ubuntu so it's likely that there is a difference between the distros that causes a problem that isn't seen in the other.
Once Inkscape and the AxiDraw extensions were installed according to the instructions I was able to make the Python code changes shown above to reconfigure the machine to it's different orientation. Once this was complete I proceded to add myself to the ‘dialout’ group to ensure that I could access the serial connection. However testing was met with errors saying that the extension could not connect to the “AxiDraw”. I chased this for a long time but eventually I started with some manual connections to the EiBotBoard using Python in the terminal which initially also failed until by chance I happened to specify the speed for the connection, which caused the commands I sent to be processes to be executed. This seems to be the solution

Open the ebb_serial.py file for editing
In the testPort function edit the following line (around line 280):
serial_port = serial.Serial(port_name, timeout=1.0)
to read:
serial_port = serial.Serial(port_name, 9600, timeout=1.0)
Adding the speed of 9600 explicitly seems to fix the problem, I don't know why or how

I used PLA for all printed parts, which works fine. Print parts with at least three perimeters and consider using 6 or 7 top/bottom solid layers for strength and stiffness since this is important for the h-bot kinematic.
All parts should print without supports. Some of the shoulder holes for machine screws are oriented with a narrow bore on top of a wider bore and so they may look like they need support but the geometry of these has been changed to avoid the need for supports by creating successive bridges before the bore is closed.
Start by printing one of the main rail bracket carriages, I would suggest 1_railBracketLower.stl & 2_railBracket.stl, and use these to check that your v-rollers fit around your 2040 extrusion. You should be able to fit the carriage around the 2020 fairly tightly and you will use clamping screws if you need to add more preload to the rollers. If the parts are much too small you may be using rollers of the wrong size or the wrong kind of extrusion however if you need to adjust the size of the parts to fit you can change the variable wheelRailShift in the OpenSCAD code and re-render/print until your parts fit although please note that large changes may produce parts with other clashes or problems.
The OpenSCAD code has a module called assembly which can be used to check the fit of most of the major parts, if you want to re-print any parts there is a section where all of the parts are separated into more printable orientations. If you want to print a part comment out the assembly module and uncomment the part you want to render.

The 2040 rails are both assembled in the same way but are mirror images of each other. If you wish you can assemble both sides at the same time in this way.
Start by fitting one rail foot (6) to the end of the 2040 rail with 4 t-nuts and 4 M3x10 screws, this will be the underside of the rail.
Next fit one of the stepper brackets (4) to the top side of the rail on top of the foot using 4 t-nuts and 4 M3x8 screws. Do not fit the stepper at this stage. The stepper bracket is asymmetrical but should be fitted to the rail with the counter bored holes for the screw heads facing up.

The following sections are incomplete because of the PC drive failure mentioned at the top, I'll add them once as I get going again with Linux

Main carriages
Pen carriage
Idler pulley assembly (& feet)
Pen lift assembly
Belts

Tensioning & setup
Tensioning the belt can be done by pulling the belt through the back of the pen carriage with all other parts fixed if you wish. Alternatively it's easy to change tension by sliding and re-fixing either the idler pulley assemblies or the stepper assemblies until the desired tension is achieved. When the belts are at the correct tension the longest belt runs on the outside of the H pattern will make a low musical note when plucked gently, the belts do not have to be very tight, just enough that there is no slack as this will cause backlash and imprecision.
With the belt tensioned it's important to check the orientation of the machine movement before using the full range of motion in order to ensure that it does not run into the limits of movement as this may cause damage. Start with the carriage in the centre of its range of movement to ensure that whatever direction it moves will allow free movement.
Commissioning
The following instructions assume that you have built the machine to the suggested size and that you have configured the software according to the instructions above for machine size and rotation settings.
First orient the machine with the steppers at the right-hand end of the backboard. Create a test drawing in Inkscape that is around 10cm by 7cm in landscape orientation. Create a small ellipse on the small drawing you just made, size isn't important but it is useful to have an obvious difference in the length of the major and minor axes of the ellipse so you can check orientation. Orient the ellipse with its long axis horizontal. You do not have to set up pen lift for this check but you need to have a pen & some paper in position.
Plot the ellipse using the Inkscape extension, you should see that the long axis of the plotted ellipse is parallel to the 2040 rails since the auto rotation should have rotated the landscape drawing. You should see that the ellipse is plotted to the right of and below the starting point. If this is not the case you may need to reverse the stepper connections, there are a few ways to do this.
The machine's origin is the “top right” corner of the bed when the steppers are positioned to the right hand side