Project Wave Hello (the story of getting an Android USB charger to wave his arms)

I started a project to get Andru, a cute little USB charger, to wave his arm. Check it out:

Some wise scientist once said we should publish more of our failures, so others may learn from this. Although I don’t quite consider this project a failure, it certainly didn’t come out as expected, and needs more iterations of design and testing.


I used a 100:1 gearmotor from Sparkfun and then 3D printed the arm waver (inspired by coupling rods from trains).

The end that mates with the gearmotor fits perfectly. The end that hooks the arm is slightly looser. Perhaps that’s one of the problems.

If I hold down Andru’s feet platform while running the motor, nothing actually moves. I suspect the gearmotor isn’t strong enough to torque the arm.

The gearmotor is powered by a 3V coin cell battery. Since the gearmotor’s peak performance runs at 6V, I might try upping the voltage and seeing if that provides more torque.

Maybe the overall design also needs an update.

The arm waver is actually the second iteration of the design. In the first iteration, I forgot the measure the space between Andru’s arm and his body, so the arm cylinder didn’t fit. I also didn’t account for the imprecision of 3D printing, and the hole for the shaft of the was too small.

The motor I picked was also a second iteration. I knew nothing of motors and gears before this project, and bought some toy motors and some hobby motors. Those motors spun really fast but had very little torque… not so great for me, if I didn’t want to build a gearbox. The gearbox is what allows the motor to reduce that speed and increase torque.

You can see the evolution of the arm waver and download the design on my Github.

all the components

I hope my learnings help you in your projects. I modeled all the components separately in one file, so you can just pull out pieces for your project (like the part that mates with the gearbox), if you so desire. I only ask you to also share your models and designs.

If you have any tips or suggestions for me, let me know!

  1. onel said:

    Thank you for sharing this!! You made my day with your dancing Andru actually (I laughed so hard) so it’s not a failure 😉 Is the arm attached too tightly to the body that it couldn’t move?

    • Jenny said:

      Haha, I’m so glad you liked it! 😀 The arm is indeed attached pretty tightly. I can move it myself but I might need a stronger motor. By the way, I *love* the photos on your blog!

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: