v2.0: The Pendulum Juggler
The new version of the juggler performing it's "first bounces". The maximal amplitude is 25° at the moment. We are working on getting it to reach 30°.
Higher Quality Video Available Here
A New Challenge
After the success of our first prototype, we wanted to create a new challenge: The Pendulum Juggler. We imagined attaching the Blind Juggler to a pendulum and letting it swing back and forth. The robot would hit the ball at one peak position of the pendulum, swing to the other peak, and hit the ball back.
It's Possible without Sensing the Ball
Our first calculations and simulations (see below) predicted that the trajectory of the ball is stable without sensing the position - just like the first prototype.
A First CAD Draft of the Pendulum Juggler
Some Control is Needed
The trajectory of the ball is stable without sensing the position. However, we would still need to measure and control the motion of the pendulum.
Why is control needed? Because like a child on a swing, the motion of the paddle pumps energy into the motion of the pendulum, causing it to swing higher and higher. To limit and control the motion of the pendulum, we attached two motors at the top of the structure (the two round bodies on top in the illustration and video).
What's next?
The amount of energy the paddle is pumping into the pendulum is quite large. With the current control design, the motors are too weak to control the pendulum for amplitudes larger than 25°. Therefore, we are not able to reach the desired amplitude of 30°.
We are currently working on getting the full amplitude range to work. Furthermore, we investigate the possibility of using only the motion of the paddle to control the pendulum. The only constraint in the paddle's motion is the hitting motions; in between, we can create an arbitrary paddle trajectory to control the motion of the pendulum.
Simulations in MATLAB
It is easy to drop a ball on the first prototype when it is running and get it to juggle. With the new prototype, however, this is much more difficult: It is almost impossible to throw the ball on the plate at the right moment, right angle and right velocity. The robot can only start to juggle by itself. It starts to juggle like the first prototype. Then, the motors start to swing the mechanism and, very slowly, increase the amplitude until the desired amplitude angle is reached. The video of the pendulum juggler is the result of such a start.
The amplitude of the pendulum is 30 degrees, which is the maximal amplitude in the design specifications. The period time of the pendulum is 1.88 seconds - that means there is an impact every 0.94 seconds and the ball reaches a height of about 1.1 meters above the impact point. The sketched mechanism which supports the motor is called a four bar linkage. If we just attached the motor directly to a regular pendulum with one bar, the paddle would not hit the ball at the right angle and the ball would fall off. We designed the mechanism to make sure the ideal impact angles are matched.
