Limb prototype v2.0

I got new parts from pololu.com and decided to go right ahead and create the second prototype limb for my robot. Thanks to the mounting brackets and wheels, making this prototype was a breeze!

Here are the steps:

I cut two 30 + 3 cm tubes like last time.

I flattened the end of the Femur with pliers.

I found some screws that would sit in plastic, and a drillbit that was "just too small".

I eyeballed the mounting bracket for where to drill.

Applying the pliers ensured that the tube stayed flat while tightening the screws.

Two screws in place.

All screws in place.


Motor fastened to mounting bracket.

Eyeballing where to drill holes for wheel in Tibia.

The screws don't fit, but I just force them through the aluminum.

Screws in place.


Wheel mounted on Tibia.

Knee joint complete!

Different angle.


Unboxing new motors from pololu.com

Since my last prototype, I figured out that I needed 3 things:
  • More torque.
  • A way to establish motor location.
  • A better way to mount the motor and shaft.
Therefore I decided to get some new gear. This time I picked up some 131:1 gearmotors from pololu.com that had a built in 64 step rotary encoder.

I also picked up matching mounting brackets and shaft mounting wheels.

Here is the unboxing:

The unopened box.

One of the three motors in its box.


One 131:1 12VDC gear motor with encoder.

Wheels and mounting brackets.


Closeup of wheel.

Motor with wheel and bracket mounted.

The CPR 64 encoder closeup.

Limb prototype v1.0

OK, I finally have the stuff i need to create the first prototype of a limb for my robot. My expectations are:
  1. Quick to build
  2. Won't work 
  3. Learn a lot

The process is documented thoroughly with images for every step below. But before we get to that, I would like to summarize what I learned:

  • Making prototypes is really fun!
  • The motor needs more torque to be useful for limbs of 30cm.
  • I still need to find a way to determine the position of the limbs.
  • The wood block broke (surprise)!
Now for the details:
I measured up two lengths of 30 + 3cm plastic tube, one for the tibia and one for Femur (thigh) and one for Tibia (shin).

I wanted the hinge to be at exactly 30cm so i left 3cm of extra length.

First i work on the Femur near the knee joint.

I flattened the end with some pliers.

On both sides of the 30cm mark.

I eyeballed what to cut.
I cut out the part that got in the way of the motor with my new dremel tool. 

Cutting complete.

I measured the motor screws to find the perfect drill bit.

First attempt at holes.

I had to widen one of the holes.

Motor securely fastened to Femur.

Now I need to fasten the Tibia to the shaft somehow.

A small block of wood to the rescue.

I divide it to get the right thickness.

Sawing parallel to the fibers is slow.

Sawing complete.

Now a hole for the shaft.

Shaft fit perfectly.

I found a screw to fasten the shaft.

The block was to long for the screw to reach all the way in to the shaft.

There, now it's perfect.

I drilled the hole for the screw perpendicular to the shaft hole.


The block is now firmly attached to the motor shaft with the screw.

Holes for mounting the Tibia to the block.

Screws through the block.

screws on their way into the limb tube.

Tibia prepared for mounting on block.

Block securely fastened to Tibia.

Knee joint complete.