Mousey the Junkbot is alive! I finished Mousey and let her zoom around the house on Friday, February 7, 2011 after a long session of soldering, gluing and Dremeling™. She looks a lot like all the other computer mouse-based robots out there on the web. This one is mine and she’s awesome!
Here are 3 ways to get step by step instructions on how to build Mousey:
- The Best of Make, First Edition by the Editors of Make Magazine, “Mousey the Junkbot” pp 150 – 163, article written by Gareth Branwyn.
- The online updates to the same article “Mousey the Junkbot” by Gareth Branwyn
- The free online instructions at Instructables.com
My blog entries are intended to supplement the instructions written by Gareth Branwyn. I have a list of tips for builders that I learned along the way. See the previous 3 Mousey blog posts for tips and tricks for building an inexpensive robot.
Summary of this blog entry:
- Use the largest mouse case you can find so that components fit easily inside the small space.
- Position the motors so that they mostly stick out of the case and down at a 60 degree angle using hot glue to hold it in place.
- Use thin, 24 gage, stranded wire so that the folded up wires in the case don’t put unnecessary strain on the solder joints.
- Use an IC socket to hold your OpAmp integrated circuit chip. The socket will take the heat of soldering and the pins will withstand the stress of the solder joints better than the fragile pins on the IC.
- Follow the bump switch instructions on the Instructables link, and don’t try my short cuts and don’t use super glue.
1. Use the BIGGEST MOUSE YOU CAN FIND!
You’re going to need all the room you can to fit all the parts and all the wires inside and still close the case. Most of the problems I encountered had to do with figuring out the best way to fit all the parts and wires inside the case like a 3D puzzle. Soldering inside that puzzle was also challenging. The alternative is to have some parts mounted outside the mouse, which gives a different aesthetic. I wanted it to look like a normal computer mouse rolling around the house. If you want a road-warrior mouse with random cybernetic parts sticking out through holes in the case, then I say embrace that theme!
2. Position the motors
Things got pretty crowded inside the mouse case as I was trying to fit all the parts inside so that the top and bottom of the mouse case would still close. In order to fit the relay and the OpAmp IC chip into the front of the mouse, in front of the battery, I had to move the motors around four times. I affixed the motors to the case with hot glue, so snapping the bond was fairly easy with a minimal amount of force using my hands and no tools. I would put the motors in what I thought was a good spot, then many steps later as I would realize I had no room to glue down the parts, so I’d have to move the motors again! In the final design, the motors were mostly sticking out of the case at about a 55 degree angle so that I had more room inside the case for all the electronic parts. The exact degree isn’t important, as long as the two motors are symmetrical.
After I was sure I’d found the best location for the motors, with just the smallest amount of the motor inside the case, I used lots of hot glue to really support the motor all the way around the bottom, left and right of the opening in the side of the mouse case. I used pliers to shape the hot glue. After the glue dries, it is easy to pick the glue bits off of the metal pliers.
Tip for handling hot glue:
You can reuse the same blob of glue when you reposition the motors by using the hot shaft of your soldering iron to reheat and reshape the glue that is stuck to your mouse case. If you have a temperature dial for your soldering iron, set it to low. I found that the soldering iron helped me shape the blob of glue into a wedge shape that would support the 60 degree angle that I wanted for my motors. Safety: Ventilation is important for your health and use a wet rag to remove the excess glue from your soldering iron. The glue fumes are not toxic, but they can still cause headaches and stink up the house. I also blame the fumes for some of my less effective design decisions (keep reading).
3. Tips for Wiring:
I used 24 gage stranded wire for everything except for the eye stalks. The thin, bendy wire put less strain on the solder joints and allowed me to move stuff around while I was soldering in small spaces. I used shrink tubing to cover many of the solder joints and prevent shorts. I used electrical tape to cover some of the larger solder joints, fearing that I would need to re-solder them frequently in the final stages of development.
In my photos, you can see that the wires inside the case are longer than they need to be. I followed Gareth’s original instructions which suggested long 3” or 4” wires for many of the steps. Now that I am done, and I can see exactly where all the components fit in my mouse, I could go back and shorten all the wires. Shorter wires means easier to close the case. The photos on the Instructrabls site show much shorter wires than in the original Make Magazine project.
One of the comments from another builder on Instructabls shows that he used a prototyping board to make the circuits really compact and reliable. Sure, it’s always possible to redesign and Build a Better Mousey! At this moment, I’m not inspired to rewire anything. I learned a lot about my tools, my abilities, and about junkbots from this project. I am not fixated on perfecting this robotic toy.
The one place where I used solid core 24 gage wire was on the eye stalks. The red wires from the eye stalks get attached to the LED and the resistor. These are nice thick connections. However the black wires from the eye stalks get soldered to pins on the OpAmp Integrated Circuit (IC) chip. These little IC pins are fragile. When I closed the mouse case by squishing the top and bottom together, the force of the solid core wire pulled so hard on the solder joint to the IC pin, that it snapped a leg off! Only a tiny bit of metal pin is still attached to the IC. I blinded Mousey in one eye! The poor thing just drove in circles.
4. Use IC Sockets
I had to completely replace my IC chip at a cost of $2.31, and find a way to put less strain on the pins from the stiff eye stalk wires.
The solution is an 8-pin IC Socket for 95 cents! The socket lets you solder your wires to the stronger pins of the socket, then plug your more expensive IC chip into the socket. Your IC won’t have to experience the heat and stress of soldering! Later, when you put this project on a shelf, you can pull the IC out of the socket for use in another project! Win – Win – Win! Now Mousey doesn’t just drive in circles. She follows light and rams into furniture like she’s supposed to.
5. Making the bump switch (how not to use super glue)
The tiny switch that I salvaged from inside the mouse (which was the “clicker” button), has just a tiny red surface for clicking. The design by Gareth Branwyn suggests using a piece of plastic, like a 2.5” x 0.5” piece of an old credit card and sticking it somehow to that switch. There are two options here. First, stick the plastic directly to that tiny red button. The second is to affix the plastic to a front corner of your mouse case so that the plastic hovers in front of the clicker until it bumps into something. I tried option 1 and it failed miserably. I thought it would be a cool shortcut. Wrong! This poor decisions was made when I was tired and I wanted to finish before going to bed.
Read on to enjoy laughing at my failed “short cuts” for the front bumper. I tried double sided sticky tape, but it wasn’t sticky enough to keep the plastic on after ramming into a wall. The fast mousy hits with force! The tape wasn’t sticky enough, so why not use something extremely sticky, like Super Glue! Super Glue is very thin and can easily seep under the button which essentially glued the button in a permanently unclicked position. I ruined that button. Good thing my mouse had two buttons! Another reason not to use a Mac mouse. Finally I went to bed and later I moved the clicker button to be flush with the front of the mouse case and then attached the bumper according to Gareth’s instructions.
Although I encourage mods, my attempt at modding the bumper failed. Overall this project was a fantastic learning experience on a minimal budget.