So, the first thing we decided to try was a simple project to make bristlebots from toothbrush heads like this from EvilMadScientist.com.  It's simple, doesn't require a bunch of materials, and is pretty quick to do. It got a little more complicated than that, but not too much, really.

Instead of using a toothbrush head we decided to experiment with popsicle sticks and toothpicks to make the bodies and legs. This allowed us to have a lot of fun building several different body and leg designs. Some were better than others. Besides. we could only find one spare toothbrush in the house and had a whole bunch of the other stuff. The other thing we decided to do was make the motor piece separate so we could reuse it. We mounted the motor, battery, and switch onto a small piece of balsa wood and attached it to the body with a small screw. It worked fine for us, but two screws might have been better.

I liked being able to make my own robot body in any shape I wanted and use the motor over and over. – Alex

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Our steps:

Make the motor sled

• Cut a piece of balsa wood wide enough to support the vibration motor, battery, and switch. Leave a little extra room so the wires are easier to work with and leave space for a screw or two to hold the sled to the body.
• Fix the vibration motor to one end of the balsa wood. We wrapped scotch tape twice around the motor and balsa wood. You may need to hang the end of the motor off the end of the balsa to keep it from hitting wood when it spins.
• Attach one of the motor wires to the closest battery post. We soldered all of the wiring attachments.
• Attach the other motor wire to the switch.
• Connect the other battery post to the switch with a spare piece of wire. We used a slide switch that was DPDT (double pole, double throw), but yours may be different so check to see how it needs to be connected to your two wires.
• Test to see that it turns on and off. Got it? Good!
• Fix the battery and switch to the balsa wood. We just poked the posts of the battery holder into the balsa and hot glued the switch.
• Drill a small hole or two for screwing the sled to the body.

Make a body:

• This part is easy and fun. You probably don't really need any instructions for it.
• Use a hot glue gun to make a small platform out of popsicle sticks that is big enough to attach the motor sled. We made ours different shapes and sizes depending on how we wanted the legs to look.
• Drill a small hole or two in the popsicle sticks where you want to attach the motor sled.
• Glue your toothpick legs (or skewers, or appetizer forks, or whatever) to the platform body in some creative way. You can try and make the legs all perfectly aligned and the exact same height, but don't worry if they aren't. It will still move. Try different things to see what happens!
• Attach your motor sled to the body when the glue is dry and turn it on!

This was a good project to start learning how to use the soldering gun. You could twist the wires, too, but we figured it was a skill we may need later down the line. The hot glue gun was good practice for soldering, as well, and it was more forgiving than the solder. We had a ton of fun doing this and actually spent time over several days making more and more bodies just for fun.

I think that this was a good summertime activity for everyone. But remember that hot glue is HOT! I got some on my finger and it did hurt a lot. Try to make the legs even on each side as much as possible or else your bot might move slow and wobble a lot. – Alex