Hermes - Photo A

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.


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


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.


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

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…


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!




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  • Graham

    More potential than Meccano, more refined than Lego 🙂

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