Building a Robotic Arm — Part 2

Building the mechanical assembly

In the first part of this series I listed the parts required to build the mechanical assembly for a robotic arm. You might remember my delight is discovering that no instructions were included! Yes, I’m one of those silly people who assemble IKEA furniture and then look at the instructions to see if I did it correctly. (Surely having parts left over just means I have assembled it more efficiently, right…) Realising that most people won’t want to spend an hour staring at a pixelated image of the assembled arm on the amazon product page to determine the best order in which to assemble it I decided to create some instructions.

Assembled robotic arm

There’s a few ways you can put these arms together. I opted to copy how the arm was assembled according to the pictures on the amazon product page.

A quick note on fasteners

Before we begin there are 4 types of fasteners used in this robot arm kit. To avoid any confusion in this guide I will refer to them by a number as shown in the image below.

Nuts and bolts
  • Machine screw #1 is used to attach the metal servo horn to the servo and also to attach the servo horn to the metal parts of the robotic arm. These screws came with the metal servo horns and were not part of the robotic arm kit. Some equivalent screws were included with the arm kit but I decided not to use them as they were shorter.
  • Bolt and nut #2 are used to connect all the non-moving metal parts together.
  • Bolt and nut #3 are used with a bearing (not pictured) to connect the 4 main moving joints of the robotic arm.
  • Bolt and nut #4 are used to attach the body of the servos to the robotic arm.

#1, #2, and #3 all have the same thread which I believe is an M2 thread. #4 appears to have an M4 thread.

Right, with that out of the way let’s get going! Read More

Bluetooth controlled LED flashing Frisbee

A few friends and I decided it would be a good idea to make a light-up Frisbee so we could continue playing with it after it became dark. The first version featured 8 LEDs located around the edge of the Frisbee. Each LED was connected in parallel via a resistor to a small LiPo battery. This worked well and looked really good in the dark.

I decided to make a second version using a microcontroller so that the LEDs could be flashed in various patterns. Since I had several BLE112 Bluetooth Low Energy (BLE) modules left over from a previous project, I decided to make a Bluetooth controlled flashing Frisbee! Why…? because “Everything is better with Bluetooth” (Sheldon Cooper).

The BLE112 modules include a 8051 microcontroller which can be programmed using a propitiatory scripting language called BGScript. BGScript was created by Bluegiga, the manufactures of the BLE112 modules. BGScript works great for simple applications, so it was perfect for this project.

As part of a previous project I had designed a small PCB to breakout the pins on the BLE112 module to through hole 0.1” headers. The PCB was 1.3” x 1.6” and manufactured by OSH Park. In the interest of hacking the Frisbee together quickly I decided to reuse this PCB as well.

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