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This instructable will walk through how to build the Length mechanism from our Americas Greatest Makers.. It is a bit of a long sequence of steps but in the end you will have a way to change the length of something and control many of these devices with only 3 wires from your Arduino and 3D print yourself or purchase most parts from your local hardware store.

Step 1: Mechanical Parts List

You will need the following parts for the mechanical system
  • 2 8-32 Nylon Lock Nuts
  • 1 2" 8-32 threaded rod
  • 1 1/2" Aluminum Threaded Spacer
  • 2 6-32 set screw
  • 1 #8 lock washer
  • 2 #8 Nylon washer
  • 2 L-Brackets they are about 1/2 on each side
  • 8-32 Square Nut
  • 2 1/2" 6-32 bolts
  • 3 3/8" 6-32 bolts
  • 2 6-32 Nylon Lock Nuts
  • 2 #6 Nylon Washer
  • 10K ohm pot
  • Micro Gearmotor 170-270 RPM
  • The parts from thingiverse 3D Printed
  • 6-32 Tap (to thread aluminum spacer and 3D printed parts)

You can print as many staves as you want to make the length longer. As you add those staves the ability to move will be muted.

The only part that seems hard to find on other sites like McMaster-Carr is the L bracket. But this is the common L bracket that is about 1/2" on each side. One of the holes is a bit longer than the other.

Step 2: Assembly

This can be a bit of a challenge.

We use the word Stave for the pieces of the mechanism that make up the scissor lift like mechanism. There are three flavors of these staves. There are two special ones that connect to the potentiomenter. There are two that are bolted together with 6-32 bolts. Finally there are two which snap together and need no other hardware.

I use the following process to assemble just the mechanical parts into the length changing mechanism.

  1. Prop the Aluminum Spacer in a way that you can safely drill through the spacer with a drill bit that will allow you to thread the hole when you are done.
  2. Add the two 6-32 set screws to both sides of the hole. These will be tightened onto the the shaft of the motor.
  3. I put the Nylon lock nut on the end of the 2" threaded rod. You might use a 2" 8-32 bolt just as well as both the lock nut and threaded rod.
  4. Mount the 6-32 bolts through the bottom of the L-Brackets.
  5. Add a #6 Nylon washer under the L-Bracket.
  6. Run the 6-32 bolt through the both staves.
  7. Put a 6-32 nylon lock nut on the other side.
  8. Drop the 8-32 Square nut into the 3D printed piece that holds it against the L-Bracket.
  9. Push an L-Bracket into the same 3D Printed piece.
  10. Run the threaded rod through the block with the square nut and L bracket. You should have about 1 inch on the other sided of the block to go to the next step.
  11. Put a Nylon lock nut on the other end of the rod and tighten until there is about 3/4" on the other side. This really not how you are supposed to use a lock nut but it is simpler for our purpose.
  12. Slide on a #8 Nylon Washer, the L-Bracket, and another #8 Nylon Washer.
  13. Then spin on the 8-32 nut that presses up against the nylon washer.
  14. Then put on the #8 split lock washer and the tighten into the spacer.
  15. Push the spacer onto the motor end and adjust the lock nut, nut and spacer until you have it moving smoothly.
  16. Then tighten the 6-32 set screws to connect the motor to the screw drive.
  17. Put the remaining 6-32 bolt to hold together the rest of the scissor lift

Step 3: Our Pride and Joy

It tool many revisions to get to a design for the staves that requires no additional hardware. If you watched the show you can see we started out with much more hardware for each section. This added to the weight and to the cost of the length mechanism.

These are fun to just print and play with honestly. We will show how connecting these together in interesting ways to get interesting movements in the clothing.

Step 4: Electronics Parts

For this you need three parts

Step 5: Theory of the Length Control

When the motor is run in one direction the stave pieces are driven together or apart. The change in that angle is measured by the potentiomenter. The code is simply meant to take requests for lengths from the I^2C wires on the Arduino Pro Mini and then run the motor in the correct direction to get to that position. In fact this code is borrowed from our DARPA Robotics Challenge robot Cog-Burn.

The code is changed just a bit to run for the much smaller motor and cute little motor control.

Step 6: What Is Next

Later this week we will post how to test the component you just made. Then our last Instructable for Control will show you how to use a Finte State Machine to control the dress or scarf in a very intuitive way. This technique can be applied to many different situations and is fundamental to many computer tools like compilers and network protocols.

Step 7: Feedback Welcome

If you build this, or attempt to build this please provide feedback on how to make it cleaner, cheaper or easier to understand.

About This Instructable

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Bio: I am an Assistant Professor of Computer Science at Colorado Mesa University, I recently lead a DARPA DRC Team, and I am one of Americas ... More »
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