Today I finished my Floppy Disc Robot with mecanum wheels. This robot is a homage to the floppy disc beams the floppy disc into the new century. Actual the robot is powered by four DC motors and a Raspberry Pi 3. A single L298N H-Bridge is used as motor driver. This is the reason why the robot could not strafe – moving from side to side yet. But when I got the ZeroBorg motor driver I will replace the L298N H-Bridge by the ZeroBorg. With the ZeroBorg motor driver it is possible to control up to four DC motors separately. This is perfect for my mecanum wheeled robot.
ZeroBorg on Kickstarter: ZeroBorg
Maybe I will also replace the Raspberry Pi 3 with a Raspberry Pi Zero to show the power of the small Zero in action by controlling my robot. The Raspberry Pi Zero is incredible powerful for the money you have to pay for it.
The picture below shows the robot.
I implemented a web interface to control the robot via keyboard and to see what the robot sees. I am using mjpg-streamer to stream the live video out of the robot. This works very well and very fast. With the live video stream it is easy to drive around without visual contact to the robot.
With the mecanum wheels it is possible to drive omnidirectional driving manoeuvres with the robot. It looks really funny to strafe with the robot. I was asked where I bought the mecanum wheels.
I ordered my wheels from NoDNA an online shop next to my home town in Germany.
The mecanum wheels I bought are from NEXUS robot.
Website: NEXUS robot
The NEXUS mecanum wheels are very stable and easy to mount with the mounting hubs you need to buy together with the wheels. Otherwise you may have a problem to mount the wheels on the axis of your DC motors.
You always need a pair of Right /Bearing Rollers and Left /Bearing Rollers on each side of your robot. Otherwise the wheels do not make sense and the robot is not able to drive omnidirectional.
The picture below shows the mecanum wheels and on top of each wheel the mounting hub.
I searched for a nice and easy to build chassis for my robot. I found an old disc box on a junkyard and decided to give it a try. It took a few mounth to get all the parts together and to find DC motors which fit into the plastic box.
After drilling a bunch of holes into the plastic box for the DC motors. I was able to screw the four 12V DC motors into the box. With the gearbox the DC motors are very strong. The box is pretty stable and easy to work on. With the cover I am now able to drive around outside in the garden.
I bought the following four DC motors for my robot. They are cheap, not too big and they have enough torque for my little robot and the mecanum wheels.
Rated voltage: 12V DC
Voltage range: 3V-18V
Voltage 3V, there is still considerable torque, can not handle with hand
No-load speed: 70 rev / min
No-load current: <=0.1 A
Resist twisting: 7 kg / cm
Reduction ratio: 1:90
Stall torque: 7 kg/cm
Stall current: 1.2 A
Length (excluding shaft): 52mm
Shaft length: 21mm
Total length: 73mm
Shaft diameter: 6mm
I am using two 7.2V rc accus connected in series to get 14.2V and the robot on track. The picture below shows the four DC motors mounted into the plastic box.
Then I had to mount the mecanum wheels with the mounting hub onto the axis of each DC motor. This was done very fast and at the end I got a very nice robot which is one of the coolest I ever build.
The picture below shows the finished robot with all electronic components form the right side.
The next picture shows the robot from the front. You see the Raspberry Pi camera in the middle of the chassis. The red LED is indicating that the live video stream is active.
Now it was time for the robot to drive around in my apartment. The wheels and DC motors are a little bit noisy.
Floppy Disc Robot in action:
The video below shows the first test run with the mecanum wheels.
Raspberry Pi Zero – USB Hub
When I got the ZeroBorg motor driver I will replace the Raspberry Pi 3 by the Raspberry Pi Zero. To do so I need two USB-Plugs. One for the webcam and one for the USB WiFi dongle. I opened a mini USB-Hub and replaced the normal USB-cable with a micro-USB cable to directly connect the USB-Hub too the Raspberry Pi Zero.
The picture below shows the mini USB Hub, the web cam and the USB-WIFI dongle.