The robot driver is normally a motor, which is mostly servo-controlled enabling better control using speed and position feedback and encoders. In simple terms, the robotic arm is rendered mobile by these robotic drives. In a normal robot, every axis has a drive to move it to the right placement. The accuracy of these drives offers industrial robots accurate repeatability. The drive system of the robot can be categorized into hydraulic drive, pneumatic drive and electric drive.
A good robot driver must enable the following features:
- High top speed
- Pull/push ability
- Obstacle handling
- Ease of control
PyroElectro.com demonstrates the type of control required over the motors involved. The following video emphasizes the speed and direction of motor control:
Building A Robot: Motor Control
Different types of drive trains are:
- Two wheels – These are fast and easy turning, high-speed spin-outs are possible, and more weight is applied on non-powered wheels.
- Four wheels – These drives are slightly slower and less maneuverable, have more traction and can be controlled more easily. The most common configuration is a gear box in the middle with chains to each wheel.
The next video demonstrates the functioning capabilities of a four-wheel drive/ omni-wheel learning platform by CustoBots:
4WD Omni Wheel Learning Platform - by CustoBots
- Six wheels – The six wheel drive has high traction with good maneuverability. The middle wheels are usually lowered to a specific height to enable turning.
- Omnidirectional – These drives include different types of mobility systems with the ability to move sideways. These drives can be maneuvered easily; however, this is prone to failure and complex to build.
Common drive train elements include the following:
- The motor provides rotational motion. It should not be overworked or may result in excess heat. Different motors have different characteristics hence must be selected based on the specific application.
- A gearbox changes the speed to torque ratio of the motor output. It offers an opportunity to combine motor outputs. It is significant for mounting the drivetrain to the chassis. It must be designed accurately, fabricated and assembled.
- Wheels are the actual interaction point with the field and when there are more contact points it has a better grip. If better turning capabilities are needed then one can opt for less contact points.
Rich LeGrand in 2004 designed two closed-loop drive train designs for mobile robots. Motor selection is the most significant factor while designing the drive train: more torque and less speed due to gear reduction and less torque and more speed due to less gear reduction. Modified RC servomotors that are used in robot drive trains have large gear reductions resulting in low speed and high torque.
Baek S.S et al (2009) designed a resonant drive to bring down average battery power consumption for flapping wing robots that are driven by DC motors. Considering battery and motor resistance, a non-dimensionalized analysis of a motor-driven slider crank was derived. This analysis was used to prove the advantages of effective resonant drive on a flapping wing robot weighing 5.8g and by combining a tuned compliant element, experiments showed a 30% average power reduction.
The drive trains are suitable for a wide range of robotics and automation applications that include the following:
- Simple multi-axis control
- Fully functional semiautonomous robots
- Pipe and silo inspection systems
- Linear stages
- Military and police bomb inspection units
- Automated robotic production modules
- Unmanned micro robots and surgical robotic devices.
Today there are a large number of new kinds of robots emerging. Robots find applications in unheard of places and will soon become a part of our daily lives. With advancements in robots, researchers are looking to design higher performance drives that can enable the robot to move rapidly and perform high-precision tasks. With the advent of robots that can climb stairs, move underwater, fly and crawl, the robotic drive is also highly sophisticated.
The stairBOT, for instance, maneuvers with a differential driver. Furthermore, it has the capability to change its length with linear guide mechanism with a spindle-drive. This mechanism enables the stairBOT with its omni-wheels and brake system to reliably climb up and down stair with a regular size as is demonstrated in the video below:
stairbot: approach, 1 step up
Sources and Further Reading