"Round-A-Bot" - the egg-painting machine :D

Easter will never be the same again! I have used the last weeks designing an eggbot clone that makes it possible to draw on eggs or other spherical objects. When deciding for the design I trawled the internet looking at other mockups. Thingiverse had some interesting ones called the "sphere-o-bot" but these designs as too large for my 3d printer (and my-o-my those guys must take days to print!!). I therefore decided to make my own design to carve out on my CNC machine. CNC designs are so much simpler and faster to make (thus also faster to do adjustments if necessary).

I decided to go for a clone of the Eggbot pro. The simplicity of the design intruiged me - I also had the parts lying around from other failed projects, so hardware-wise I was good to go from day 1. 

As all my other stuff the machine was desined in OneShape - you can have a look at it here and fork it as you please:

Notes about the design

I wanted to keep the amount of 3d printed parts to a minimum and ended up with the couplers for the egg rotation, pen arm and adapters for different sizes of pens. For the latter part I am quite pleased with myself - this design makes it ease to shift pens for different needs (e.g. changing colors). The design make it possible to make special adapters for pens up to 16mm in diameter - which should cover most needs I hope (note that there is a variable in the Onshape model for this - just update the diameter and export the adapter to print). The adapter has a slot for inserting 3mm screw for fastening the pens. 

For the cups used to fasten the egg the last part is made of ninjaflex giving it a rubbery feel and ensuring that the egg stays as it should during the painting process. If you don't have Ninjaflex or other rubber fillament lying around there are plenty of other designs on thingiverse to pick ideas from.

The hinge connecting the pen-arm and pen motormount and the pen arm is very simple - I have made a 1mm holde in the design for inserting a metal paperclip

To make this machine please just look at the pictures and the model in Onshape - it shows quite clear what you need - all of it can be sourced from Ali Express at low expense and your local hardware store.

Notes about hardware

Apart from that you need a CNC and a 3D printer to build this thing the machine is really cheap component wise. Apart from wires, buttons, power supplies and a few nuts & bolts I ended up with the following main components

Notes about software

This I assumed would be the easiest thing of the whole project - oh my I was wrong! I started up looking for software - you need to run a forked version of the original eggbot and there is a ton of them out there. You can find references on some of the other thingiverse versions - for example here: https://www.thingiverse.com/thing:1683764
You probably need to do some configurations in the main arduino ino file before uploading. I chose to go for separate stepper motot drivers and a Nano - different boards/drivers will mean you need to adjust the pin configuration in the EggDuino.ino file.

When you have uploaded the eggduino code to your board of selection the first thing you need to check before doing anything else is to verify that you have connection with your board. Open your favourite serial terminal and connect with 9600baud (I use Termite). Then type the letter 'v' (small letter) and hit Enter. You should get a verification message from your board starting with something like "EBBv13_....."

Only when you have connection can you continue with Inkscape!

When successfull connection to the board from a Serial terminal - go on and download Inkscape 0.91 to your computer. https://inkscape.org/en/release/0.91/

When installed you go on and find the Eggbot control extension. You can find information from here (hail you  Evil Mad Scientist!!!): https://wiki.evilmadscientist.com/Installing_software.
When the software is installed you must do some configurations - in the eggbot_scanwin2.py file you need to verify the "hkey" settings in the beginning - and most likely change it to align to your own setup. 

This is where my "nightmare" started - after finally getting Inkscape extension to connect to the Nano I successfully managed to perform some basic prints on my eggduino. I then started finetuning the machine playing around with different heights on the pen motor, changing the servo up/down +++ I was ready for doing some serious painting and started getting "EBB Serial Timeout" - both when doing pen up/down and other manual movements....what happened?? I tried to do a print and now I got "Plot paused by button press after node number xx"....WTF!! I trawled the interent and found references to others having this issue and recommending to comment this part of the code (in the Inkscape extension). Phew - error message gone. But now - the prints got totally screwed up, the pen doing strange movements during print that I never asked for. Two days....two late evenings with trial and error - testing out various versions of eggduino firmware, different versions of Inkscape extension - no luck. No references to this issue on my old friend google either. In desperation I installed Inkscape on my wife's computer and the add-in. Everything worked! So there was something fishy with my laptop I assumed - started doing the configuration of the pen up/down in the Eggbot Setup tab ++ .... : "EBB Serial Timeout"  No!!! Same error as before!! Wait. What did I change? The Pen up and Pen down position? Could that be the error? Changing it back to original settings - no errors. Adjusting them to e.g. up: 80% down: 50%. "EBB Serial Timeout" And there it was....two days of pain explained! So for anyone having the same problems - look no further, check these settings first. I assume the issue is related to some timeout occuring if the pen uses too long time going from the down to the up position. Keep the difference in values between pen-up/pen-down to less than 25 and you should be ok. I am sure this timeout setting can be adjusted somewhere - if you know please give me a nudge :D

Fun-fun-fun :D 

Getting those software issues out of the way it is now time to play around with my cute little "round-a-bot" - and it is so much fun! Eggs are the perfect test candidates, you will always have fresh supply of new test items - and if something goes wrong - crack it and eat it!

Now it is time to learn more about Inkscape and how to use the Inkscape add-in to produce nice looking eggs for various occations. Firstly I will look into hatch filling (filling objects with ink) and using layers to create eggs with different colors.


  1. Hi
    Thanks for the details and files on the Round-a-Bot. I have successful made the bot (with a few modifications) but I am having trouble in fixinf the SG09 servo to the pen arm, Any chance you could let me know how you have achieved it. Un fortunately the videos do not show any detail regarding that. Look forward to hearing from you.

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