I really liked the look of Pololu’s Zumo Bot and ended up purchasing the kit a while back. I have some plans for this bot but I’ll write more on that in a future post. For now I thought I’d just document some aspects of the build.
The kit comes with the following:
It is basically a compact track-based chassis that houses a motor for each track, 4 AA batteries and has a circuit board on top that effectively makes the chassis an Arduino shield. On the board is a motor controller, compass and an assortment of buttons and LEDS, a buzzer and an on/off switch. It also has a convenient battery charger connection. It is primarily meant as a sumobot.
I decided to build mine using Pololu’s optical encoders. These are specially designed for Pololu’s extended shaft micro gear motors. I settled on the 100:1 Micro Metal Gearmotor HP (with Extended Motor Shaft).
Going with the encoders presented three fairly big problems:
First, they are tiny:
Soldering them on to the motors and then soldering their 6 wires each was the hardest job to date I’ve undertaken with a soldering iron.
[UPDATE: Pololu now have magnetic shaft encoders that much easier to setup and use: Magnetic Encoder Pair Kit for Micro Metal Gearmotors. However, I have not tried to use them and they have a slightly higher profile than the optical ones so might require more finessing]
I had to hot-glue them on first otherwise there was no way I could solder and keep them straight. Even hot glueing them was tricky and it took a few attempts to get them level on the motor casing. After that soldering the motor leads was easy.
The really hard part was soldering the wires. Positioning them was a challenge:
But the actual soldering was nerve-racking. I was convinced I’d ruin both devices before I was through but in the end it worked out fine:
The next hurdle was routing the wiring from the motor housing to the Zumo shield on top. I ended up making small slits for the wire to come through on the underneath of the housing:
Used a sharp tool to mark and the Dremel to make the cuts.
Had already worked out that the wiring would easily be able to go from the under the chassis up to the shield, even with the sumo blade and the reflectance sensor array attached.
Also had to change the way the motor leads connect to the shield but that was simple enough:
Also added female headers to the outer most pins of Zumo shield. A nice feature of the outer pins is that they are spaced out correctly for use with a perfboard, which I plan to use to create a mounting platform for other devices.
After that it was all plain sailing.
One issue still remains with the encoders:
As you can see from the image, the encoders (the rainbow ribbons) are not connected to anything. Unfortunately they only provide analog output so I still need to build a circuit to make the signals digital. I’m hoping to use the back area of the shield to host the converter.
In the meantime I need to start on some coding. I purchased the reflectance sensor array so a simple line following bot will be a good starting point.
Read: Zumo – Part II
Ended up not having to build a circuit for the encoders. For my setup the analog signals were good enough that they could be connect directly as digital inputs. So far I’ve not had any issues.