Probot Sample Lessons

Sample mechanics lesson

The parts on a wheel shaft and the order they go on

How a wheel turns

  • The motor turns the small gear
  • Their teeth mesh, so the small gear turns the big one
  • The big gear is on the wheel's shaft, and the wheel turns with it
  • Today, the parts on this shaft

Profile, the robot's frame

  • The robot's frame is aluminum bars with holes, called Structure profiles
  • The big holes are where the shaft goes through
  • One face is open, the inside is hollow, it is light
  • Two profiles hold the wheel shaft, an inner one and an outer one

Shaft

  • Drag with the left button, and the part turns
  • The mouse wheel zooms in and out
  • Drag with the right button, and the part moves
  • If it gets lost, Reset view at the top of the box

Bearing

  • The outer ring sits in the profile's big hole
  • The inner ring turns with the shaft, and the balls in between reduce friction
  • The flange is the thin edge that sticks out on one face
  • One bearing at each end of the shaft

Spacer

  • A short tube that slides onto the shaft
  • It fills the gap between two parts, so the distance always stays the same
  • The parts do not slide along the shaft
  • On this shaft, an 8 mm, a 21 mm and four thin 3 mm spacers

40-tooth gear

  • The hole in the middle is hexagonal, so the gear turns together with the shaft
  • The four holes around it are for attaching the wheel
  • The small gear on the motor turns it

Wheel

  • The rubber surface grips the ground and drives the robot
  • The hole in the middle is round, so it does not grip the shaft
  • It is attached to the gear with four bolts and turns with the gear

Shaft collar

  • Two halves, tightened onto the shaft with two bolts
  • Once it is tightened, the parts inside cannot slide outward
  • It rests against the end of the 21 mm spacer

Order of assembly, from the inside out

  • The parts go on from the inner profile outward
  • The shaft goes in through the bearing in the inner profile
  • The shaft collar is the last part, the one that locks the assembly
  • The outer bearing and the outer profile close the assembly

Step 1. Inner profile

The long glowing part is the inner profile. The shaft will go through one of its big holes.

Step 2. Inner bearing, the shaft will go through it

The glowing ring is the bearing, and it will sit in the big hole of the inner profile. Its thin edge is the flange.

Step 3. The shaft goes in through the inner bearing

The glowing hexagonal bar is the shaft. It will go through the middle of the inner bearing.

Step 4. 8 mm spacer, next to the bearing

The short glowing tube is the 8 mm spacer. It will go onto the shaft right next to the bearing.

Step 5. 40-tooth gear, on the side near the profile

The glowing gear is the 40-tooth gear. It will go next to the 8 mm spacer, on the side near the inner profile.

Step 6. 3 mm spacers, between the gear and the wheel

The four thin, flat 3 mm spacers glowing next to the gear.

Step 7. Wheel, the wheel assembly is complete

The big glowing rubber wheel will go on the outer side of the 3 mm spacers.

Step 8. 21 mm spacer, goes through the wheel's hole

The long glowing tube is the 21 mm spacer. It will go into the center hole of the wheel from the outer side.

Step 9. Shaft collar, locks the assembly

The glowing shaft collar. It will rest against the outer end of the 21 mm spacer.

Step 10. Outer bearing

The second glowing bearing, at the outer end of the shaft.

Step 11. The outer profile closes the assembly

The glowing outer profile. The outer bearing will sit in its hole, and the wheel is between the two profiles.

Count outward from the profile

Turn the assembly and count the parts from the inner profile outward. Count the four thin spacers as one.

Common mistakes

  • If a spacer is forgotten, the wheel slides and the gears slip away from each other
  • If the collar is not tightened, or there is no spacer in front of it, the assembly slides
  • If the gear goes on the outer side of the wheel, the gears do not mesh

Without the bearing

We forgot to put in the bearing, and the shaft went straight through the big hole of the profile. What happens when the shaft turns?
Your turn

Put the order together

ActivityThe order of the shaft assembly

Put the 11 parts of the shaft assembly in the order they go on, starting from the inner profile. Hold a part and drag it up or down, or move it with the arrows.

Homework

  • Another shaft, the omni wheel's shaft
  • In picture B, write the parts in order from the profile outward
  • Next to each part, add its job