R22 - Reconfigurable Robot Chassis for the Raspberry Pi.

R22 Reconfigurable Robot Chassis for Raspberry Pi 2,3,4

For many years we had one of those Tamiya 70100 track sets as well as the universal plate set.

Our plans were to one day use the track set and universal plate to make a tracked robot. Because we planned to experiment with different configurations and sensors, we wanted to make it into a reconfigurable platform. However, every time we tried to create a durable and versatile platform, we were never really happy with the results. So, the kit sat unused and mostly forgotten. However, over the years some wonderful developments occurred, such as the advent of the Raspberry Pi, the availability of inexpensive yet full-featured PCB CAD programs such as Eagle and KiCad, and the introduction of relatively low-cost CNC routers. These factors made it easier and quicker for us to finally design and craft a robotic platform that we're truly happy with and proud of. Not only that, but we finally have a platform that allows us to expand upon and explore more options, like using wheels, instead of tracks as the drive mechanism. We finally dusted off that Tamiya 70100 track set, but instead of using the Tamiya universal plate set, we designed our own custom skid plate to work with it. The skid plate you see below is machined from 1/4" thick acrylic and it has threaded holes, so it doesn't require too much hardware to fasten together. We wanted something reconfigurable, but also quick to reconfigure.

There are two versions of the Tamiya gearbox. The first is the 70097, known as the "Twin gear box" and the second is the 70168, known as the "Double gear box". Both gearboxes can be assembled with different gear ratios to achieve different values of torque versus speed. The 70097 twin gearbox offers two gear ratios, while the 70168 double gearbox offers four. Here is a picture of the 70097 box, which shows that the the gearbox can be assembled to have a 58:1 or a 203:1 gear ratio.

And shown below is the box for the 70168, which shows the four possible gear ratios of: 12.7:1, 38.2:1, 114.7:1, and 344.2:1, which are labeled "Type A", "Type B", "Type C", and "Type D", respectively.

We designed our skid plate to be able to mount either gear box, however we prefer the 70168, due to its wider range of gear ratio offerings. After some experimentation, we found that the configuration type D suited our needs best and thus the R22B was born!

Watch this thing in action!

We control our robots remotely through a dedicated WIFI router and we'll describe the setup, code, and other details in later posts. We were pleased with the speed, torque, and runtime for this configuration. It works really well on smooth surfaces like hardwood flooring. So, we decided to push this new creation to its limits and move it onto the outside driveway. The driveway is mostly comprised of lumpy asphalt, which wreaked havoc on the tank treads and pulled them off of the sprockets. This was a problem, but fortunately there was an answer: Wheels! We designed motor mounting rails to connect to the chassis. The wheels and motors now offered a 4WD drive configuration that now glided over the lumpy asphalt surface with ease. And if we ever needed to switch back to the tracked configuration, we can do so quickly and easily.

When it came to powering the robot we wanted to keep our options open, so we designed a pocket that can house a 6-AA battery holder or a 9.6V rechargeable NiMH battery pack. Again, the goal was quick reconfigurability.

Here's the R22 with the included 6-AA battery holder installed:

Here's the same R22 chassis with a 9.6V rechargeable battery pack (9.6V rechargeable battery pack not include in kit):

Here's a video showing the process for swapping battery types:

The enclosure protects the Raspberry Pi, but still allows access to the USB and ethernet ports in the back.

The ventilation cover can also be removed to access the HDMI, audio, and power connectors.

Here's a photo showing a monitor, wireless keyboard and wireless mouse connected to the robot, while it's powered on for development and debugging. We typically run our robots headless, but if we wanted to, we could just plug right in and check email!

Here's a view with the lid off. The Raspberry Pi fits inside with enough room for a HAT board. In this picture, we're using our own internally developed GPIO board (the purple board) to interface between the Raspberry Pi and the motor driver PCB. Our GPIO board also has an onboard voltage regulator that can accept a battery voltage as high as 24 volts and convert it down to 5 volts, which can power the Raspberry Pi through the 5-volt header pins. Our GPIO board is not yet available for sale and is not included in the R22 robot chassis kit, but there are similar GPIO boards available on the market that can be used. The R22 chassis is designed to be open and flexible, so you are encouraged to find a GPIO board that works for your application.

We really wanted to be able to explore with this platform, so we gave it a 5MP camera with an IR-cut filter. There are two InfraRed, (IR) fill LEDs on both sides of the camera lens that automatically turn on when the lights are turned off. In other words, the camera is equipped with night vision!

We're using Gstreamer to stream first-person video from the robot back to our base station.

Shown below is a screen capture with the lights on.

Two minutes later, the lights are switched off and the IR-fill LEDs automatically turn on. The camera, which has no IR filter allows IR light to pass on through, thus enabling vision in total darkness. We would include an image from a normal camera without night vision for comparison, but it would just be a black rectangle.

R22 Robot Chassis configured as a 4WD robot using the included motors and wheels.

R22 Robot Chassis configured as a tracked robot using the Tamiya 70168 gearbox and the 70100 track and wheel set. (Tamiya 70168 gearbox and 70100 track and wheel set are not included in the R22 Robot Chassis kit and need to be purchased separately.)

Both of these configurations are best suited for smooth surfaces. The 4WD configuration performs better on carpet, concrete, and asphalt, than does the tracked one. The Raspberry Pi and remote control code are scalable, so we'll be busy developing larger platforms that can handle rougher terrain.

We are proud to introduce the R22 Reconfigurable Robot Chassis kit to the robotics community. This kit offers unique features and loads of value and we are eager to see how it can help you on your journey of robotics exploration and experimentation. We will definitely be using it on ours. Until next time, go Learn, Apply, and Solve!