The Beetlebot is a classic DIY robot by Jérôme Demers. It doesn’t use any complicated electronics and can be built from parts you probably already have lying around. Rather than relying on transistors or integrated circuits to navigate, this design uses nothing more than a pair of switches and some clever wiring to avoid obstacles in its path.
Parts
Most of the parts you need can be salvaged from junk electronics or bought cheaply online.
- An old computer mouse
- 2 1.5V DC motors
- Wire
- Paperclips
- 2 AAA batteries
- AAA battery holder
Optional:
- Craft wire
- Switch
Step 1: Disassemble the Mouse
The first step is to take the mouse apart so you can use it as its body. You don’t have to use a mouse for this, you could simply use the battery holder as its body or anything else you can scavenge.
Step 2: Mount the Switches
Next, cut out a space at the front to mount the switches. They should be positioned at an angle, with the two NC contacts closest together. They need to be able to take a knock, so secure them in place with some hot glue.
When a switch is triggered, it reverses the motor’s direction.
Step 3: Attach the Motors
Now make some holes either side for the motors. The angle of the motors is up to you, but the more spread out they are, the faster the robot will move.
Once you’re happy with the angle, fix them in place with some more hot glue.
You could also put a little dab on the end of the motor shaft to give it some grip, or use some heat shrink tubing.
Step 4: Fit the Batteries
Fit the battery holder in place with some hot glue. If there's no room for a battery holder you could use some battery contacts on their own instead - or experiment with two 9V batteries if you’re feeling adventurous!
Step 5: (Optional) Add a Rear Wheel
To stop the back from dragging, your robot might need a rear wheel. I fashioned one from the scroll wheel that came with the mouse, and some metal tubes I found in my parts bin.
I wanted to reuse as much of the mouse as possible, but you could make something simple using a paperclip and a small bead, and hot-gluing it to the back of the body.
Step 6: Wire It Up
Start by soldering the the two NC contacts together on the switches, then take a piece of wire or paperclip and solder the two NO connections together as well.
Then solder the [+] tag of one motor to the remaining C connection on the switch, and do the same with the [-] connector of the other motor to the other switch. (Don’t worry if you’ve got these the wrong way round; you can swap them later.)
Now connect the remaining motor tags together using a wire across the middle.
Solder a wire from the positive output of the batteries to the NC connection on the switches. Then connect the negative output to the NO contacts soldered together earlier.
The final connection is the third wire from the battery holder, connected to the shared positive/negative end. Connect this wire to the joined motor tags.
Step 7: Add Whiskers
To trigger the switches reliably, we need to give the robot some whiskers. Bend some paperclips or craft wire into shape, and attach them to the switches with solder or spade connectors for something more robust.
Step 8: Test It Out!
Now everything's in place you can insert some batteries and test it out. It should scoot along pretty quickly and be able to avoid obstacles you put in its way.
If it’s not moving fast enough, try adjusting the angle of the motors and make sure you’re using fresh batteries.
Step 9: (Optional) Add a Switch
To finish off, you could add a switch so you don’t have to keep removing the batteries to turn it off.
To disable the robot completely, we need to interrupt the connections to both motors using a DPDT switch. A SPDT switch will stop it from moving forwards, but the motors will still activate in reverse when a switch is triggered. Good enough if left on a desk, but if something accidentally triggers a switch, it will shoot backwards.
This is because only one battery is used to power both motors for each direction. When one side is in reverse, both batteries are in use.
