The TITAN robot chassis is a much larger version of the Wild Thumper chassis I designed 6 years ago. The TITAN is designed for large robotic projects such as a snow plow or fire fighting robot. The original prototype (black chassis) worked well but needed some small improvements. This post is about the TITAN MkII chassis which is bigger, stronger (I weigh 140Kg) and can use a wider range of motors.
The chassis is constructed from 3mm thick 6061 aluminium sheet that has been cut, folded and riveted. The battery bays between the wheels can hold up to six 12V @ 12Ah SLA electric bike batteries or some fairly hefty lithium batteries depending on your application.
Each wishbone section contains a brushless motor with a planetary gearbox. The chassis utilizes the same suspension system as the Wild Thumper with the center sections being a standard independent suspension while the front and rear are free floating to help keep all 6 wheel on the ground.
The wheels use are 13 inch ATV wheels. As you can see there is a big difference compared to the original Wild Thumper wheel.
Currently I am using a Spider controller to control the chassis. The Spider is essentially an Arduino Mega2560 but with a 3A switchmode power supply that allows it to run directly from the batteries (24V). The Spider controller is a good choice as it has enough IO pins and internal timers to control all 6 motors.
Each motor has 3 hall effect sensor outputs (5V) which make ideal encoder inputs. By monitoring these inputs the Spider controller can adjust the speed of each motor individually and measure speed / distance traveled if required.
TITAN fire fighting robot!
My TITAN fire fighting robot is a good example of a practical application for the TITAN robot chassis. I have take a cheap fire fighters water cannon and mounted it onto the TITAN chassis.
Making a pan/tilt mechanism for the water cannon was a bit of a challenge. In the end I decided on a simple linkage system. It is cheap and easy to maintain.
It does not have a lot of range for panning left and right but since the entire chassis can rotate the pan feature is really just a way to improve the accuracy of aim.
I used two 24V DC motors with 60:1 worm drives for the pan/tilt mechanism. Each motor shaft has a couple of small magnets and an AS5600 12bit rotary hall effect sensor (contactless potentiometer) to provide feedback on the position of the output shaft.
The pan/tilt motors are driven by a simple motor driver which I originally designed for an animatronic Chinese dancing lion. This motor driver uses two BTN7971B half bridges. The original driver (shown here) used a PTC fuse but I have since replaced it with a 10A, self resetting circuit breaker.
The problem with the PTC fuses is their "on" resistance was too high and limited the maximum current available to the motors. The circuit breakers use a bi-metal switch which has a much lower resistance.