Scribble bots from dollar store electric toothbrushes

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It’s time for that ritual I think of as “repaying the internet”. To whit, if I get information off the internet and then find a twist, I need to give some information back. This time the topic is scribble bots, or more precisely, powering scribble bots with dollar store toothbrushes.

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A scribble bot uses batteries and a motor to make markers vibrate across paper, thus leaving marks. They’re all the rage at science museums and STEM nights, letting one guilelessly sneak a few Physics lessons in on the kids.

There’s all kind of information about making scribble bots on the web, such as on Instructables and the Exploratorium website.

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Most of them have a materials list that includes a 1.5-3 volt hobby motor. The instructions often suggest getting the motor from Radio Shack or cannibalizing one from a toy such as a dancing chicken. Radio Shack is now out of business and I don’t happen to have any dancing chickens, so to my mind, finding a motor is the hardest part of the project.

Unless you have an electronics supply store around, by the time you’ve ordered a motor and maybe a switch and battery housing to go with it, things can get pricy. I wondered if there was a cheaper way to get the necessary parts. Might there be something at the local dollar store?

Indeed, there was. Our local dollar store had an array of the world’s saddest-looking electric toothbrushes. Instead of rotating a group of bristles like one’s Braun or Oral-B, these battery-powered devices jostled a stationary brush head a tiny amount, pretending to give a jolt of dental cleaning power that couldn’t be obtained by simply moving one’s hand.  Disassembling a brush revealed that it had a motor with an offset weight. This was exactly what was needed for a scribblebot. Perfect!

Toothbrush1

Here’s a typical dollar store electric toothbrush with its guts squeezed out.

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Here we’ve cut the handle away from the rest of the toothbrush. The handle can then be used to hold the motor, battery housing, and switch.

(Hang on to the toothbrush end. I have no idea what you should do with it, but it’s bound to come in handy sometime. If you make enough of these scribble bots, for example, you can spray paint the leftover brushes red or gold, glue them to a grapevine wreath, and make a hideous Christmas decoration. Or not.)

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Click image to enlarge

Here are the parts we’re sticking back inside the handle. Notice that we’ve cut the handle just short enough to reveal the offset weight, so that it can have attachments and twirl around freely.

Also note the electrical connections circled in red. These are necessary for forming a complete circuit between the battery and the motor. The connections at the motor end aren’t going to be accessible once the parts are put back in the toothbrush handle, and they may be flimsily assembled. Make sure they’re making contact when you reinstall the parts.

batteries

Toothbrush battery at left; standard AA at right

Here’s one other fun tidbit. I noticed that the supposedly AA battery which came with the toothbrush wasn’t the same size as a standard AA. It was shorter and narrower. I could force a fresh, standard AA battery into the brush handle, but the motor would no longer work. The circuit wasn’t making up. Sometimes there isn’t enough profanity in the world!

No doubt this is by design. Probably the owners of People’s Electric Toothbrush Factory Number Five don’t want shoppers to use their cheap dollar store toothbrushes indefinitely, so they’ve intentionally made it difficult to replace the batteries. We aren’t using the toothbrushes for hygiene purposes, though, so we do want to be able to replace the batteries.

standoff

If you run into this issue, remove the end of the battery holder and peer inside. I found that there was a vertical plastic standoff inside, precisely calibrated to the dimensions of the supplied battery. After removing the standoff with a Dremel tool, a standard AA battery fit and my circuit made up.

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Lousy photo of a battery holder after removing standoff. Pretend that you can see where I’ve made the modification. Also, pretend that I have a decent manicure.

Alright. We’ve sawn and fiddled around and modified a cheap toothbrush. What next? How about making some additional weights?

weights

These weights, which are made from wide tongue depressors, can help make the motion of the scribble bot more erratic.

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Here we’ve installed a weight on the protruding end of a motor. Note that we have the weight aligned with the mass of the off-axis weight already on the motor.

Some different scribble bot designs …

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A portion of a pool noodle with motor mechanism tucked inside and auxiliary weight on top.

 

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Another pool noodle design, this time with the motor at the bottom. It’s interesting to see how positioning of the center of mass affects the motion.

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A highly elegant Greek yogurt cup model with outboard motor.

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Strawberry basket, outboard motor. Classic. Add some razor blades or a scalpel blade to the tongue depressor weight and you’ll have a fighting scribblebot, as well as occasion to visit the emergency room.

In a few weeks I’ll try all of this out with children – well, except for the part with sharp blades. We’ll see how it goes. I anticipate that there will be chaos.

5 Responses to “Scribble bots from dollar store electric toothbrushes”

  1. Meggie says:

    Brett would have loved these, as a kid. Fantastic for teaching kids.

  2. Caitlin O'Connor says:

    This is so awesome! The availability of these cheap little motors (not to mention what happens when you get into arduino and pi) are making a whole new world…

  3. Martha Ginn says:

    Yep, I would anticipate chaos, too. But you most likely will be prepared for it. I on the other hand am clueless about scribblebots, but I’m glad you know what they are. Just wanted you to know I read you. ha-ha

  4. Amanda says:

    These are great! I’m curious how you cut off the tops of the toothbrushes?

  5. Tanya Brown says:

    Hi Amanda;

    I used a bandsaw to cut off the tops of my toothbrushes. One could also use a hack saw or some other device. The plastic was firm, but not at all difficult to cut.

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