Children birthday party with spider-bristlebots

Our kids are one year and one month apart. Every now and then we decide that the worst of the implications of this situation are over and that we can now tackle the opportunities. For the 5th and 6th Birthday we agreed to combine the parties. Their peer group overlaps and having two parties with 6 kids sounded worse than one party with 10.

Coming up with a program for such a party is a blog entry on its own. This one, however, is about a single part of the party, in which the kids would create some spider-bristlebots.

For the bristlebots we had certain goals:

Thus the following parts were needed:

For the rare material that sums up to a total of roughly 1.40 EUR per piece.

To create the spiders we needed some wool and pipe cleaners.

Putting it together

The first part is to collect toothbrushes. Or rather, avoid throwing them away. Make sure you let your party guest know early enough you need those. A four-person household like ours will not manage to collect the required amount of toothbrushes.

With the main requirements also came some additional. It should be pretty unbreakable (as it will have to work when being messed around with by little kids), the moving parts should not be easily accessible, and not tip over easily because kids would put hand-made enormous spiders on top of it.

So the idea was to use two brushes per bot and the motor hidden between them. The two brushes should give the stability needed, and by having the motor between them it’s not easily reachable. The on-off switch should be on a side so it is easy to hold it and turn it on and off again.

sketch bristle A sketch of the plan

Let’s take a first look at the parts. The battery case has a switch, can be opened easily and comes with a long cable.

battery case

The motors also have some cables and two sides. One that contains the rotating weight, and a backside for the cables.


Step one is to solder the cables together. If the cables are very long, cut them shorter. The cables for the case should be long enough so they can be reeled halfway around the case, the cables for the motor should be long enough to give you free space to put glue them on. As my kids were helping me I kept a lot of cables also to make soldering issues less impactful. You’ll be able to hide the cables later under the brushes anyways.

solder the cables

Next reel the cables of the case around it, and use a hot glue gun to fix them to the bottom of the case. Use plenty of wax, it will be the foundation for your brushes.

glue to the case

Now try to glue the motor in the centre of the bottom of the case.

fixate the motor

The final part is adding the toothbrushes. With a saw remove the brush and fixate it to the case with the hot glue. You can hide the free cables from the motor under the brushes.

toothbrush Adding the brushes

Now it’s time to test-drive the bristlebots. If they only run around in circles take a scissor to trim the brushes a little until the motions are more diverse. Each bot should kinda act like this:

Next comes the robot’s appearance.

The Spiders

Our kids' birthday is in Autumn, around Halloween. To create a matching theme, we came up with spider-bots.

The spiders are build from styropore balls, and we added some eyes. The legs are pipe cleaners, and all of it can be stuck together with hot glue. But obviously there are multiple ways to achieve a scaring spider, and it’s something that can keep kids busy for quite some time.

Watch my wife putting one together for you:

Putting together the spider

The Party!

And after all of this comes the final acceptance tests by the users

Except for some unforeseen spider mutants, it worked pretty well, and they enjoyed it!

We, however, learned that entertaining 12 kids of that age are far much more challenging than expected. Kudos to every nursery school teacher. This will probably the last combined birthday party, next year everybody is getting their own.