Sunday afternoon robot

I had nothing to do today so I copied hubbens creation from the Swedish electronics forum. It is a two wheeled radio controled vehicle based on just two servos.

For wheels I used two wheels from an old Lego Technics truck I got for christmas almost 20 years ago (The best christmas gift I’ve ever got BTW). The wheels were bolted to servo horns from two HXT900 servos.

Lego wheel
Lego Wheel
Servo Horn
Servo horn bolted on lego wheel
Servos
The servos are glued together and self adhesive velcro is glued to both sides

These servos are modified for continous rotation according to this guide.

Pretty simple:

  1. Open servo and remove the gears and potentiometer.
  2. Connect to your receiver and set your output to center. (or use another way to generate a 1.5 ms pulse every 20 ms)
  3. Adjust the potentiometer to the center until the motor stops and solder it so it can’t rotate any more.
  4. Remove the stop pins on the output gear with a sharp knife
  5. Sand the top of the potentiometer axis so the top gear spin easy on the axis.
  6. Re-assemble the servo

The servos are then glued back to back and some self adhesive velcro are mounted on both sides and the wheels are mounted.

The ideal would be to run both the receiver and the servos of a 2S LiPo but I only have 3S at home so I needed to use a Turnigy 8 V – 10 V 5A SBEC to power the servos and the receiver. Together with the DC/DC converter the über cheap Hobby King 2.4Ghz 6Ch receiver was mounted on the top of the servos.

Top
Top of the vehicle, the Turnigy SBEC to the left and Hobbyking receiver to the right.

On the bottom I have a Turnigy 1000mAh 3S 20C Lipo which is a little to large for this project but it was the smallest one I had.

Battery
Turnigy 3S 1000 mAh LiPo

I used channel 1 and 2 and mixed them 100% with each other. Since the servos are mirrored they need to rotate in the same direction for a turn and in oposite directions to move forwards och backwards.

This is what it looked like when it was ready.

Front
Front
Back
Back

My next order from HobbyKing will include a smaller 2S battery. And maybe I’ll put together a small controller board for this to make it autonomous.

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