Mechanical Design Concept

• Pioneer P3 DX is the mobile robot base
  • Two wheeled base allows turning on the spot
• Catapult based bean bag launch mechanism
  • Adjust amount of spring tension by adjusting the spring displacement to change velocity of bean bag
  • Adjust stopping location of catapult to change trajectory
• Bean bag reloading mechanism
  • Simple slot based mechanism to load bean bags
• Materials - EPDM Rubber belts, Aluminium Frame, PLA (3D Printed), Wood for mounting on pioneer base

The overall mechanical design is a catapult to use a spring constant for a force along with a solenoid to lock the catapult in while obtaining the force. The solenoid used is an electromagnet which allows for the base to be locked into place. The spring used in this setup is elastic bands as it can be combined together to change the spring constant. This allows for more force to be gained over a shorter period and make the overall design smaller.

The rationale for this design is that it would be an easy and compact way to design a way to throw the bean bag. The original design (see Mechanical Calculations) included using a belt design to throw the bean bag, but was found that this design would be much more complex than the catapult and need a much more powerful motor. Therefore, the catapult with its simpler design was chosen.

In order to make sure that the spring is not pulled too much back causing damage to the system as a whole, we also have a limit switch in place as an override mechanism. A loading mechanism in place actuated by two servos was used to replace the bean bags after throws in order to allow the system to load 3 bean bags. This required design requireda powerful motor so a wiper motor was used to pull the spring back.

In order to customize our launch distance for various scenarios a limit switch is placed along a slider, as well as the beam which stops the swing motion can be adjusted in multiple slots in order to change the throwing distance. A mount plate was also used to include an additional camera for the system in order to get a downwards view of the floor. This helps the teleoperator stop at the right places. Also, the components were mounted on the pioneer using a laser cut wood piece tailored to the contour of the pioneer. This allowed the overall size of the robot to be small and compact and reduce weight on the robot.

The majority of the parts on our robot is 3D printed, using PLA+ which is stronger than PLA. The rationale behind this was to make sure we can have a compact robot, with minimal needless weight. A high infill percentage in the parts was used as many of the parts are under a lot of stress.