There must be a list somewhere of the 10 most common projects undertaken by noobies when starting out in robotics. I’d wager building a two-wheeled, obstacle avoidance bot is up there in the top 4; right after blinking LEDs and using potentiometers to control servos.
I wanted to get my wheeled rover up and running with minimal fuss. I could cobble together something from the bits and pieces I have round the house but time is scarce and I’m more interested in the programming part than in the build.
After searching for a while I decided to try Pololu’s 5″ chassis and micro geared motors. (Did you know the plural of chassis is chassis? I didn’t) They seemed reasonably priced and there are lots of accessories, like encoders, spacers and such that all work together.
As it is with all hobbies, items seem reasonably priced, even cheap, until they start adding up. Particularly when you decide to buy two of everything so that you can, later on, build two autonomous but interacting bots, which is one of the things in robotics I’m most interested in.
My stash of parts finally arrived:
Pololu did a great job of packaging. Everything was of good quality.
Here are all the parts needed for the two wheel chassis:
I meant to order the clear plastic chassis but it turns out I ordered the white ones. Bah! There are two 100:1 geared motors, the chassis, two motor mounting brackets, two mourning spacers, two wheels and a small metal ball caster (the third wheel).
Soldering wires on to the motors was tough as the terminal flanges where teensy:
I put a capacitor across the motor terminals but I noticed that motors I have from my helicopter days have three capacitors configured. I need to figure out why. [Adding a cap across the terminals and a cap from each terminal to the motor casing does the best job of minimizing electrical noise form the brushes. Use non-polarissed cap with low internal resistance. Suggested capacitance is 0.1uF]
I couldn’t believe how small the motors are.
I guess when they say micro, they mean micro. The clear plastic I’m holding with my thumb is a spacer. It’s subbing for an encoder you can purchase for the kit. I will probably get some in the future so my autonomous bots can more precisely track their movements.
Assembling the motors onto the chassis with the brackets and the spacers was surprisingly fiddlely. Also pushing the wheels onto the motor shafts was nerve-racking. The fit on one of the wheels was super tight and I was worried I’d damage the motor’s internals with all the force I had to apply.
Nevertheless I got it all together:
My next problem was to figure out how to mount the Arduino and batteries. I ended up using the second chassis, meant for the second bot, as a raised platform.
This way I can mount the batteries – 9V for the Arduino and 4xAA for the motors – on the bottom section and the electronics on the top. A nice feature of the chassis is the opening you can see on the right side, where you can place downward facing sensors.
Next is to add the electronics and figure out how to drive the motors.