robotmatrix.org

 Introduction

• Objective: When properly set up, the Thrower can throw a table-tennis ball into a cup a meter away with more than 90% success. If you ever try to throw a table tennis ball into a cup one meter away, as this robot is doing, you'll gain a greater appreciation of this little machine. Using three servos in coordinated motion, when properly adjusted this robot can hit the target 9 times out of 10.
• Parts:
  • Robix Rascal Robot Kit/Construction Set
  • Binder clips or rubber bands to hold the spoon in place;
  • Plastic cup, about 3.25" (9cm) diameter, plus coins to weight the cup.
• To learn: It is simple to build but challenging to program and ?tune?. And, when not properly tuned, the robot may throw the ball in all directions -- backward, straight up, straight down in front, or just dropped in back -- in a way reminiscent of the throws a child makes when first learning the skill.

 Step 1: Assemble and build the Thrower Robot Body and Muscle

The cup is plastic, and has some loose coins at the bottom to weight it and also to help absorb energy as the ball hits -- otherwise the ball tends to bounce out easily. A ceramic mug will not work well for the same reason: It is so hard that the ball, even when thrown well, will very often bounce right out again.

 Step 2: Thrower Robot Teaching and Macro Programming

You may have to tinker with it slightly for distance throwing. Also note on the follow-through that the spoon should not hit the table or be left pressing on it when the motion is complete, as this will change the spoon's alignment.

A common mistake that first-time tuners of the motion make is that they do not get all three servos in play for the throwing motion; typically they have one servo that hardly rotates at all, or even moves backwards somewhat while the other servos move forward.

You may also want to weight or clamp the breadboard base so that it does not hop when the ball is thrown.