STEM Trifecta 2018 TEACHER TRAINING RESOURCE ROBOTIC ASSEMBLY

STEM Trifecta: 2018 TEACHER TRAINING RESOURCE: ROBOTIC ASSEMBLY

Step 1: Building a basic chassis: Install the servos with the shaft end closest to the front of the robot chassis. From the inside of the chassis, align the servo with the hole and push into the hole. The servo should be installed from the inside while screws run from the outside – in. Fastener Chart - Fastener Basics Chart Utilize 6/32 X ½ Inch screws. It would be good to use a lock washer when putting these together as they often work loose due to vibration. Push the screw through the hole from the OUTSIDE so the head of the screw is seen from the outside. Because of the tight space, its often good to hold the nut still on the inside with a pair of pliers while you turn the screw from the outside to tighten.

Step 2: Plan a rear wheel or skid A few options are: A “Castor” is a good rear wheel attachment as it is easy to mount and generally swivels as needed. Be sure to allow clearance for the wheel to swivel 360 degrees otherwise, when backing up, the wheel will impede travel. Be sure it is mounted so the bot is level. A “skid” is also a good universal fix on the arena. The skid just slides over the wood or flat surface and keeps the robot level. Two to three screws are generally all you need to attach a skid as long as the screws are tight.

Step 3: Battery pack mounting: The battery pack should be strategically placed on the chassis to be stable. Since power plugs must be connected to it on one end, be sure the end is open enough to connect/disconnect the wires as necessary. The length of the USB cable is also a factor in placement since it must reach the power port on the Pi. Options for mounting: Velcro 3 D strap or sticky back Velcro - easiest printed bracket – most difficult, but very efficient with a good design. Vex strips across battery – A little time consuming but pretty basic Velcro pic Velcro Strap Maker bot bracket Vex strips

Step 4: Raspberry Pi mounting: It is recommended that the raspberry pi be mounted on top of the robot since constant connections to the pi may be necessary such as the HDMI adaptor, Keyboard, Mouse, Hat Board and power connections. Options are: 3 D printed holder – student designed – (Most difficult) White board or Wood base – easy (Use spacers under each screw to avoid issues) Direct bolt on – time consuming and tricky to lay out White board base Bolt on pic 3 D holder pic

Step 5: Design and layout: Plan around “your” design Although the basic forms of attachment are the same, the location and arrangement of the Pi do matter. Things to consider; Where will you place your arm/gripper and or other attachments? Will the placement of the arm make the parts universally accessible? Will the placement of the Pi allow connector access or will the arm interfere? Will the placement allow “fast” access

Step 6: Arm / ball striker design: An arm/gripper will be necessary to meet the demands of the challenge. As a general rule, servo motors are used as source of rotation for an arm, gripper and or striker. Servos have a very small amount of torque: (43 in oz) and as a result, careful design must be implemented. Things to consider: Length of arm from the center of rotation – the farther away, the more difficult for the servo to lift. Weight of striker – Strikers must be exceptionally light unless care is taken to counterbalance the striker to reduce the load on the servo when lifting. Gripper must generally be simple and very light since a servo motor is often attached to the end of the arm with the gripper mechanism. 3 D printed objects are good for this task due to light weight and structural strength.

Gripper Ideas:

The gas caps used in the event that must be picked up will require a “special” grabber. Things to consider: The caps will need retrieval from the container and the gripper will need to be able to “Pick” one among the group. The arm will need to lift slightly above the container and still grab and “Place” the caps in the appropriate location. Due to the shape of the caps, it might be difficult to grab a single cap easily. Will your gripper or scoop drop the cap directly down or will you have to be careful to literally place the cap on the spot before slowly opening the gripper and moving away? ( a scoop design might pick the cap and hold it well, but may be more difficult to drop in a specific location) (Design of grippers or scoops will matter!)

How to make a bucket scoop easily!

Questions…. . How can we help guide you and your team to success?