Enable Builds a Delta Robot, Part Five: Engineering Design Madness

The main components of our Delta-bot game were complete, but it was not time for the team to rest on their laurels, for there was still work to be done.  Firstly, the Delta-bot and the spinner, both constructed from LEGO Mindstorms, would need to be attached to the Tetrix frame.  Luckily, Tetrix kits come with pieces that are designed to interact and connect with LEGO elements, so the task was not as difficult as it sounded.

With the bot and spinner bolted to the frame, it was time for Ben to test the system and make it move. First, to get the robot to respond to user-input and move to a desired position, we researched and found inverse kinematics algorithms to help us translate the motion of the motors to physical positions in space. Once we had this, we could program the joystick input using Labview.

However, in the process of testing this, we quickly discovered three problems with our bot’s design:

Problem the first: Our frame was too tall.  At its height, the optical sensor would not be able to pick up the black line on the spinning disc below.  This would make our game impossible to win, and while that may be an interesting commentary on nature of existence; metaphorical statements on the nature of competition do not make good booth-swag for the company to give away as prizes.

Solution: Remove a few pieces of Tetrix from the “legs” of the frame.  This lowers the Delta-bot by five inches, making it much closer to the spinning disc.  The bot is now much more a game and much less a statement on nihilism.

Problem the second: The gearing system that we had attached to the spinner is not as stable enough now that we have added the weight of the Plexiglas disk.  As this component is called a “spinner”, the fact that it seems like it may fly apart if it is made to spin is problematic.

Solution: Remove the gearing system.  It was too fancy, and largely unnecessary.  Having the disc connect directly to the motor will increase stability and NXT brick allows accurate control of rotational speed.

Problem the third: The Delta-bot is not connected to the frame securely.  This was discovered when Ben accidently moved his mouse before setting the motor’s limits.  This caused the arms of the bot to shoot into the up-most position, torqueing the LEGO, and causing the bot to becoming caught in the frame.  While this problem might be avoided once the bot is programmed with motor limits, the entire unit will still need to be shipped from Enable’s office in Milton, Ontario, to the NI Week conference in sunny Austin, Texas.  Flimsy construction could spell doom for our robotic creation if it is jostled or bumped in transit.

Solution: Adding two additional struts across the top of the frame.  We also bolted the LEGO elements everywhere possible to ensure that it was as strong as possible.

Our leaner, meaner Delta-bot

-by Andrew Baxter, Curriculum Developer


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