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G.E.A.R. 2

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My Goal was to come up with a design where all the speciality parts could be ordered  for under $20US.

The bill of matirels (BOM) looks like this:

2 ea 9g CR Servos

2 ea Wheels for the Servos

1 ea 4xAAA battery box with switch

1 ea SR-04 ultrasonic range sensor  

1 ea Arduino IDE compatable ATTINY85 based controller board.  Such as a Digispark, Iteaduino or any one of the similar devices. 

All the speciality parts come to just over $21 from Robotshop. depending on how much effort you want to put into shopping you could trim a few dollars off of that.

To build one you will also need:

A soldering iron and solder.

Material for the body. I used foamcore but sturdy cardboard or thin wood would also work.

Hookup wire

AAA batteries ( I use rechargeable ones because I built a controller without a voltage regulator.)

Hot glue gun and hot glue

Stick on Velcro to mount the battery box.


     I have a dislike of unused pins and overpowered processors.  So when I ran across the Digispark I had to build an inexpensive robot anyone can build.  (Programing will leave you with either a sense of accomplishment or handsfull of your own hair, or both.)

     If you need some guidance learning how to solder check out a Maker Fair or reach out to a local makerspace.  Same with hot glue.  You might burn yourself,  Solder hurts more than glue.

The Body is simple:

     I cut some holes in the vertical pieces to feed the servo wires out and tuck any excess wire in to keep it out of the way.

     You may want to mount the servos before attaching the top deck It would make it easier to get a good fit.  The body is hot glued together. The servos are also mounted with hot glue. I used poster putty to hold the sensor and Controller pcb in place.  And finally the battery box is mounted with stick on Velcro.

     I picked a sonar sensor because it is the cheapest plug-and-play sensor available.  I will work on trying to find a cheaper and easier to program sensor and will up date the page if i find one.

     The wiring is simple The Battery is connected to the Vin, the left servo to PB0 the right servo to PB1 and the signal (or both the signal and trig on the SR-04)  pin of the sonar connects to PB2.  All the +5v pins and pads are connected together and all the Gnd pins and pads and the black Battery wire are connected together. 


And now about the attached sample code:

     First a big Thanks to Adafruit for Adafruit_SoftServo.h that made it possible.  And also thanks to the people who made their SketchUp models available on the 3D warehouse for making the design graphics easier.

      The code works and is commented but unrefined.  (I was a little rushed to get it out in time for Maker Fair.) If anyone has ideas or suggestions feel free to post them.  The whole idea of this thing is so we can have a standard platform that lets us test each others code ideas.

More to follow.


update: 9-27-2016

I uploaded two sizes of drive wheels to attach to servo horns.  They use hardware store O-rings for tires.



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This is what the one i built looks like.

gear2 F

gear2 R

I switched to the smaller wheels and added a voltage regulator (like the off the shelf versions) and added 2 more AAA cells.  The Controler is a homemade clone of a digispark.


Like you, I am keen on building robots as cheaply as possible. I have collected lots of cheap parts by purchasing from Chinese vendors on Ebay. From my own experience of purchasing from many Chinese vendors, shipping parts to the UK, here are my findings:

I generally have very few problems. When problems occur (e.g. non-delivery or faulty part) then the vendors usually resolve it (e.g. refund or resend). Once I've bought a component, e.g. SR-04 ultrasonic sensor, I test it (connect to Arduino and install suitable ultrasonic tester program, usually outputting the sensor values to usb serial, and then view in the serial monitor on the IDE).

Cost achieved for various parts, on ebay.co.uk using Chinese vendors:

SR-04 sensor ~ approx £1 each ($1.30 USD)

Arduino Nano v3 CLONE ~ approx £1.80 each  ($2.50 USD)

TowerPro SG90 regular servo ~ approx £1.20 each ($1.60 USD)

Plastic battery case ~ approx £0.70 each  ($1.00 USD)

400pin Solderless Breadboard ~ approx £1.00 each ($1.30 USD)

LM7805 voltage regulator ~ £0.50 ($0.40 USD)

2k ohm SMD resistor ~ cheap (need 2 per servo)


In the case of the regular SG90 servos, if you are courageous enough, you can take them apart, modify them, add 2 SMD resistors, put them back together and have a Continuous Rotation servo which you've built yourself. There are youtube videos showing how to do that.  e.g. like this:  https://www.youtube.com/watch?v=Peppk_Ffzc4

Also, I like to repurpose CAT5, CAT6 ethernet network cable - chop it apart, use wire strippers, and you get insulated pieces of wire, that can be used for building robots or circuits (and these wires fit perfectly into the holes on solderless breadboards).


I like your 3D printed robot wheels - very tempted to make and use those myself, once I get my hands on a 3D printer. Potentially a good saving to be made there. Although again, you can get cheap ready-made wheels from China ;)

Okay, bye for now. SG


I really like the idea of something as inexpensive as possible, but with as little work required as possible too (the two often don't go together). For the frame, maybe plastic corrugated board? As for the rear, maybe 3D print some ball caster supports and use marbes at the rear?


I ended up using some furniture sliders I had laying around.

As for plastic corrugated board. When the election season ends there will be a lot of excess lawn signs about.  Perfect to make robots if you can talk the owners out of them or pull them from the trash.  (don't just take them off of lawns)  That stuff can be tricky to cut but the price is right.