Maker Faire demo: automated treasure chest with jrk motor controller and linear actuator

This blog post is part of a continuing series of blogs about the demos that Pololu displayed at our booth at Las Vegas Mini Maker Faire 2014. For more about the Faire and a video, see my previous blog post. This blog post will focus on our automated treasure chest demo.

Last year we brought a jrk and a linear actuator with position feedback to the Faire to show people how easy it could be to use the closed loop feedback features of the jrk. The jrk was connected to a laptop so attendees could use the slider in the configuration utility to extend and retract the actuator, and the actuator was laid out on the table beside it. While many people thought it was interesting, we also got a lot of questions about what something like that could be used for. This year we showed one possible use by putting the actuator inside a treasure chest.

In the new and improved demo, a Concentric linear actuator was mounted inside the treasure chest with a special mounting bracket that allows the actuator to rotate freely in one axis. The end of the actuator shaft was fastened to the lid of the chest with a second bracket. When its shaft extends, the actuator is forced to rotate around the bracket, causing the lid of the chest to open. The jrk 21v3 was configured for analog mode, and the signal from a potentiometer was connected to its analog input. The potentiometer is used to set the target position of the actuator. The settings used on the jrk were taken from the jrk 21v3 settings file for use with LACTxP (1k txt), which is provided in the “Using a jrk motor controller with a linear actuator with feedback” section at the bottom of all of our linear actuator product pages. Then the maximum and minimum position limits were adjusted to prevent anyone from trying to open the chest too far or accidentally close it on a hand.

The frame of the treasure chest was made of standard planks of wood from a hardware store, but the curved surface on the top of its lid was laser cut from a single sheet of 1/8" wood using a living hinge design and then laid into place. It is supported on the sides by two more laser cut pieces. Living hinge patterns like this are a great way to extend what is possible with a laser cutter and also give a cool look to the finished project. You can find out more about living hinges and how they can be used in laser cutting in this project on Make.

The treasure chest can be seen in action (and full of Pololu swag) in our video of the event around 51 seconds in. A full list of the parts used in the demo is given below:

• Pololu Jrk 21v3 USB Motor Controller with Feedback
• Concentric LACT6P-12V-20 Linear Actuator with Feedback: 6" Stroke, 12V, 0.5"/s
• Mounting Bracket for Concentric LD Linear Actuators
• Wall Power Adapter: 12VDC, 5A, 5.5×2.1mm Barrel Jack, Center-Positive
• DC Barrel Jack to 2-Pin Terminal Block Adapter
• Female Crimp Pins for 0.1" Housings 100-Pack
• 0.1" (2.54mm) Crimp Connector Housing: 1×1-Pin 25-Pack
• Custom Laser Cutting Service

Related products

	Jrk 21v3 USB Motor Controller with Feedback
	Glideforce LACT6P-12V-20 Light-Duty Linear Actuator with Feedback: 50kgf, 6" Stroke (5.9" Usable), 0.57"/s, 12V
	Mounting Bracket for Glideforce Light-Duty Linear Actuators - Aluminum
	Custom Laser Cutting Service