Build The Robot

Your robot will be made from two sections, each connected to the TT motor at the center of mass. The motor will drive a pulley wheel that rests on the tightrope.

The chassis section will hole the battery pack and act as the mounting point for the Crickit and CPX.

The upper frame will support the robot armature and costuming parts.

Let's get building!

Make the Chassis

  • Cut a piece of corrugated cardboard from a shipping box, about 16"W x 12"H
  • Use the template below (or a Cricut or laser cutter) to cut out the four parts

Template

Download the .svg or .pdf file depending on your preferred tools. You can print either one and then use it at a template on your cardboard. You can cut out each shape, then trace around it with a pence while you hold it to the cardboard.

Then, cut out the shapes. Be careful not to cut along the purple dashed lines -- those are just to indicate where you'll fold the cardboard.

Be sure to print the template at 1:1 size, don't let your printer software scale it! You can print in tile mode to create properly scaled printouts if the image is too large for a single page on your printer.

Chassis Assembly

robotics___cnc_uni_bot_0014_2k.jpg
Note: the arms are in a low position from a previous version, the higher position on the template is correct
  • Place four nylon standoffs into the cardboard frame as shown and secure them with nuts (you can do all eight if you like, but it's overkill)
  • Screw the Crickit onto the standoffs

Battery Box Holder

Put three fresh alkaline AA batteries in your battery box before proceeding.
  • Fold the chassis at the two fold lines to form the battery holder
  • Fold the two arms at their fold lines
  • Place a brass fastener into the holes in the arms
  • Set the battery box in place
  • Secure the arms using the brass fastener

Motor Prep (for motors without wires already)

Next, we'll prepare the motor by soldering two wires to the tabs, and screwing the pulley wheel onto the shaft.

If you're using the yellow, plastic geared TT motor, you can skip this next step, as it comes with wires pre-soldered to the motor's tabs.
  • Strip the insulation from the ends of two short wires -- around 5" in length
  • Solder a wire to each tab of the motor
  • Polarity doesn't matter, since we can insert either wire into the motor terminals on the Crickit board, as well as choose forward and backward direction in software later
If you're using the yellow, plastic geared TT motor, use the provided screw that come with the pulley wheel. No need to widen the pulley wheel center hole, either!
  • Widen the center hole of the pulley wheel a little bit with a small drill or the tip of a screwdriver
  • Attach the pulley wheel to the shaft of the motor with an M3 screw

Upper Frame

The upper frame will connect to the motor and chassis in order to provide a structure from which to hang the robot.

  • Use a straight edge to crease the upper frame piece along the bend marks
  • Fold the two bends at 90° each
  • To help the cardboard hold its shape, you can add some white glue or hot melt glue to the insides of the creases, then hold it in place while the glue sets

Assemble the Parts

Now, its time to assemble the chassis, motor, and upper frame to each other. You can use two long M2.5 screws and nuts, or if you don't have those on hand, use zip ties, or even string!

Screw the battery box's red and black wires into the DC plug adapter's '+' and '-' terminals, respectively.

Connect the Chassis, Motor, and Frame

  • Use the long M2.5 screws to attach the chassis to the motor as shown
  • Attach the frame to the screws on the back-side of the motor
  • Use the two nuts to fasten
If you chose to use a yellow TT motor, you'll also need to poke out a small hole for the rear axle to poke through the upper frame.

Wire the Motor

Next, run the motor wires to the Motor 1 terminals on the Crickit board and screw them in place. You can insert either wire in either of the two terminals on the Motor 1 block -- you do not need to use the terminal marked GND.

Center of Mass

Try holding the robot with one finger under the pulley wheel -- you'll see that it balances pretty well. This is because most of the weight of the Crickit, CPX, and batteries is directly underneath the pulley, with a bit of it protruding beyond it in order to compensate for the weight of the motor itself.

This means that pulley wheel is at the the robot's center of mass (also called "center of gravity"). This is what will allow it to balance on the tightrope without tipping over.

Speaker

To give your robot some atmospheric sound capabilities (big top music, perhaps!) screw the two speaker wires into the Crickit's speaker terminals, then secure the speaker to the chassis with tape, glue, or poster putty.

Leg Armature

Next, we'll build the leg. The leg will rotate around two pivot points, the hip and knee, and connect to the pulley wheel to provide rotation of the system.

Knee Joint

  • overlap the lower and upper leg segments at the 'knee' joint
  • put a nylon screw through the knee holes
  • secure with a nut -- but not too tightly, this joint needs to rotate freely!

Hip Joint

  • Place the upper leg pivot hole over the torso's hip pivot hole
  • Gently secure it in place with a nylon screw and nut, again, making sure it can rotate freely

Ankle Joint

If you have a nylon screw that's long enough to use as an ankle pivot, go ahead and use it. If not, have no fear, we can make the ankle pivot from a toothpick!

  • Cut off 1/3 of a toothpick with some scissors
  • Insert the toothpick through the ankle pivot hole and through one of the outer holes on the pulley wheel
  • Allowing the toothpick to protrude a bit from either end of the mechanism, trim it to size
  • If you worry the toothpick pivot may fall out, you can flatten each end a bit like a makeshift rivet

You've completed the structural, electrical, and mechanical build for your robot! Next, we'll program it, and later we'll dress it up a bit!

Try hand turning the pulley wheel to see the leg go through its motion range.

This guide was first published on May 29, 2018. It was last updated on May 29, 2018. This page (Build The Robot) was last updated on Sep 23, 2019.