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Arduino Project: Hermes

Speed! Cunning! Moving freely between the worlds of the mortal and divine!

Picture of the Greek messenger Hermes
Hermes – A speedy dude.

Okay, not the kind of language that leaps to mind when we’re talking about Arduino and homemade robots, but I had to choose a cool name for my Arduino-powered vehicle. The Greek gods had awesome names, and of all the gods that I know of, Hermes was the most…movey.

Not long after playing around with the parts included in the Osooyoo UNO kit I began to ponder how I could make something that could roam the house and pester my wife and daughter, so naturally motors and wheels became the order of the day.

MOTORS & SHIELDS

The Arduino team have produced something called a Motor Shield. A “shield” is an add-on board that sits squarely above an Arduino board and passes through all of the digital and analog headers while providing additional functionality. By adding the Motor Shield to my UNO, I was able to easily attach the two 3V motors included with a Tamiya Double Gearbox which can be controlled via software.

Left: The Arduino Motor Shield. Right: The Tamiya Double Gearbox
Left: The Arduino Motor Shield. Right: The Tamiya Double Gearbox

SLEEP IS FOR BABIES. GAMERS PLAY ALL NIGHT.

After a night of messing around soldering wires to the microscopic tabs on the 3V motors, and getting to grips with the ins and outs of the motor controller, I finally created Hermes Mk1, a tiny car that drives around in circles. Progress!
Check the video I recorded at a groggy 3:00AM below.

Not bad for a first try. More problems came later on, when I tried to add a separate battery pack for powering the motors discretely. The added weight slowed the whole car to a crawl, and the motors emitted sounds and smells that would make your mother blush.

Y’KNOW WHAT REALLY GRINDS MY GEARS?

After some head-scratching I figured out that what I needed was more torque. The motors are 3V motors and I was running them from a 5-6V battery pack, so current wasn’t an issue. This prompted me to look at the gearbox, which I’d absent-mindedly built and configured for maximum RPM in my race (so punny) to create a speed machine. In my defence, the instructions don’t really help you to relate torque to anything, so I ended up just picking one configuration – 12.7 : 1 – and going for it. This landed me a speedy 1039 RPM and a paltry 94 gf/cm of torque. Somewhere, an amateur RC car hobbyist is laughing at me. I can HEAR THEM.

Picture of the Tamiya gearbox specifications
NUMBERS. NUMBERS EVERYWHERE.

After rebuilding the gearbox twice, once in 38.2 : 1 ratio, and again in 114.7 : 1, I finally decided on 114.7 to 1. The resulting torque was 809 gf/cm (gram-force per centimeter – I had to check too) and 115 rpm, which for my needs is adequate. Firing up the motors at maximum power still sends poor Hermes slamming into a wall, and he can now carry considerably more weight. He no longer sounds like Steven Hawking passing a kidney stone either. Always a plus.

Until this point I had been attaching everything to one 160mm x 60mm board, but I was running out of space for the battery packs, so I bought one more Universal Plate kit from Tamiya and attached a second layer above the Arduino and Motor Shield. Then I attached the two battery packs to the second layer and had more space available to use for add-on components. Speak of the devil…

CLOAKED BY THE THUNDERS OF THE NORTH WIND

It was time to upgrade Hermes and instil him with some sense of direction in life. Sounds like a job for… the Octopus 3-Axis Digital Compass Sensor! By equipping the Arduino with a digital compass, it would be possible for Hermes to point himself in specific directions and turn in (hopefully) near-perfect 45 or 90 degree increments. This would allow him to draw things on the ground or “dance” in preset patterns. At least that’s my theory up to this point. I also added a 4-digit LED display for readouts of its current bearing. The digital compass and display are mounted on top with nylon stand-off screw post thingies – that’s the technical term for them.

I will update soon when I add more functionality. Thank you for reading, and I appreciate any feedback or comments you can share. Take it easy, and enjoy the gallery below!

Ben

 

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