Designing the ball release mechanism

When a visitor completes the challenge, they need to be served with a gob-stopper as a reward. The whole premise is that they have released it from the machine, so I need an automated way to release a gob stopper.

This actually turned out to be my biggest challenge, in terms of time I think it took longer than all the other parts of the project added together. Admittedly some of that time was leaning another level of CAD, being pushed to learn new skills is one of the reasons I do makerfaire projects, so that is fine.

The balls must be released individually and reliably. No good getting to the end and the visitor not getting the ball. I also wanted a reservoir of balls so they don’t need to be loaded before each person tries as this would look naff and spoil the illusion that the ball has come from the gob-stopper machine. I also thought it a good idea if the ball release is independent of the ball spiral arrangement and allows the project to be transported in a reduced form without that larger part for more far flung locations, or where less room or quick setup is needed.

I started by drilling a hole in the front panel of the binary number rack board. This would be where the ball would roll out when the visitor completes the challenge. From there I worked backwards. I found some electrical conduit at 25mm it fitted the gobstoppers perfectly, so designed around that.

Attempt 1

beam engine marble release mech

Based on a beam engine, with wooden dowel where the pistons would go, I made a servo driven device that clamps to the 25mm plastic conduit and pushes the dowel into it to inhibit the movement of the balls, in theory letting one at a time through. After many proto-types and experiments I got it working, however it needed too much tuning and was prone to occasional problems when a ball would not roll quickly enough and the piston hits the top of the ball rather than between them. This with some other concerns regarding practicality, reliability made me re-think.

Attempt 2

This was a totally different idea. I created a cylinder that could be rotated through 120 degrees, allowing the balls to be fed into the device at a nice feed angle, ensuring they rolled in nicely. The cylinder has a sphere cut into it and an open half to the sphere thus forming a receptive cup that takes the ball from one position to another. I drive this with a Micro Servo via I2C and a servo driver board from the RPI and .NET core.

It funny to say that although the design looks simple, it took a lot of thinking and CAD to get it working right. However the many hours of work have given me a reliable ball feed.




Then I hit a big hitch, testing I  got many more test gob-stoppers out and found that the size varies a little more than anticipated from the originals that I sampled. This meant that some were getting only just stuck in the 25mm tube. Now I had designed the system to use 25mm I was determined to get it working, so I printed some 26.6 mm tube instead and joined it in lengths to make a feed tube and a delivery tube through to the font panel of the project. Again this added several days of unexpected printing!

3D printed pipe parts

The solid tube was not satisfactory, so I ended up using some more of the clear tubing that is being used for the spiral. This has the added benefit of being see through so supplies can be checked.

Rear tubing

Rear tubing

Binary Candy–Rack part 2


Reader stand

After a bit of experimentation and debate with myself, I’ve decided on an almost vertical arrangement for the reader. This allows the numbers to be reached and slotted in easily even by 3 year olds, something I’m keen on achieving.

Using the mitre circular saw I’ve created the wedges and blocks, they will be held in with wood glue, its totally adequate for a job like this and avoids unsightly screws.


It stands up!

So now the glue is dry I’ve used the multimeter to determine the best level for the lowest possible position for the reader. I made the reader slightly wide to stop ambient light getting down into where it reads, but this means I do need to position it as low as I can to give a good position for slotting the numbers in and also seeing what they are.

It looks great and I’ve very happy with the angle I chose to go for!

Binary Candy–Binary Tiles

Making the Binary Tiles



Creating the tiles! Using circular saw and lots of careful measuring I have some rectangular tiles.
They are designed to show what the number is (one or zero) above the reader a little, be shaped to ensure they are inserted in the correct way around. They are also of a size that they are fairly big for other visitors standing behind the person participating in the task to be able to enjoy the fun with them (keep it as inclusive as possible). It is always important to thing about both the people who are interacting with your maker project and the other nine or so standing watching!
I’ve made a few extra tiles in case of accidents or losses.
In the photo above you can also make out the reflective sensors peeking through the holes in the detector board.

Now for primer on the MDF tiles…


White tiles get spray painted


Number digits
I used paper template cut out and spray paint, inverse to the background colour to make ones and zeros. I was up at midnight spray painting on neighbourhood pavement away from houses, must have had neighbours talking!
I struggled with this one, I was trying to make the numbers almost look like graffiti in style, just causally sprayed on. Problem was the engineer bit of me wanted to pefectly centre and mask off each one and touch up any imperfections and do a couple of coats each to get a pristine number.

This is supposed to be inside-out maker style project I kept telling myself. I managed to just leave them looking “casual”.

I am struggling with the style of this project!

Using UPVA glue as varnish - trick I got from my Son. Mind you, now  the house smells like a infants school!
The glue you see above will dry to be transparent and will hopefully stop the paint numbers from wearing or getting scratches or chips.


The finished numbers ready for action 9 of each should be plenty!


Binary Candy–Planning and rack build

Inside-out ethos of this project



Not quite literally inside-out, but this project is where I’m having to really wrestle with myself. At every step I want to hide the wires, the sensors, paint everything to a high quality smooth finish. However the words of a fellow maker ring in my ears, from the first Makerfaire we showed at. He said how its the only place where you get a bigger crowd around you by stopping your invention and taking the lid off than when it is running. So in this spirit I’m trying to make everything on this project look open so you see the wires on the front the painting is not finished, electronics is showing. Already I’m struggling with my instincts to make everything small, hidden and highly finished, but here goes…

Building the main binary input device “rack”

After buying some MDF and lots of cutting with the mitre and circular saws, construction really begins now for this Binary Candy project.

The main back board is cut, I’ve routed out the recesses that the MDF tiles (with the ones and zeros) will slot into.

I have found the routing left the MDF less than smooth, so I’m going to put a few layers of UPVA glue on and sand to give a smooth slot for the tiles to slide into.

I’ve forced myself several times not to paint the MDF on the detector board already to follow my home made, thrown together look I’m wanting this year.

I’ve cut some tiny Vero board squares to mount the reflective sensors. The sensors have a infrared LED that shines onto the surface in front of them and a detector that measures the reflected light. My plan is to mount these in a position where they will see the back ground colour of the tiles. Ones and zeros will have inverse colours to make them discernible from one another.
I have gone for eight bits as it gives the visitor the a good number of tiles to wrestle with, yet hopefully not overwhelming the younger visitors.

The sensors have been friction fitted through holes exactly in the middle of each digit position. I’ve fought with myself to not hide the wires in the reverse of the reader stand, instead everything is up front and on show. -ewww I’m struggling with this way of doing things! :)

All in all I’m amazed how quickly its coming together in a I already have a major part of the hardware done.
The sensor board goes to a .1mm pitch IDT connector for quick assembly. I’ve leant from earlier shows that it is best to have a quick fool proof robust way of building and dissembling the project.