First FootPrints

Disclaimer: This is not an April Fool’s joke! The files for this print are available here.

As you may have guessed from last week’s post, I’ve been working to co-process motors so that prints can drive themselves off of the build plate (If you aren’t familiar with co-processing, please check out my first post here). Using last week’s lessons, I’ve switched motors and gone with a high torque full rotation servo motor, controlled by an Arduino (off the build plate) and simplified my design so that all it does is break the build plate adhesion by directly making use of the torque of the motor.

The co-processed motor breaking itself off the build plate (at 3x speed)
The co-processed motor breaking itself off the build plate (at 3x speed)

The first step of this experiment was designing to minimize build plate adhesion. There are 3 points of contact with the ground, which makes the part very easy to remove, but also can make leveling the build plate difficult, as you make have build adhesion issues. All of my previous prototypes could not get themselves off of the build plate just because they contacted the build plate too much and in non-ideal spots. The final iteration of this design reduces build adhesion and places the point of contact far away from the pivot point to increase the applied torque.

A full CAD model of the part to be printed. Note that there are only 3 points of contact with the build plate.
A full CAD model of the part to be printed. Note that there are only 3 points of contact with the build plate.
A side view of the print job. The parts are designed to increase the leverage that the motor applies to the build plate.
A side view of the print job. The parts are designed to increase the leverage that the motor applies to the build plate.

Another thing that you may notice is the hinge on the other side of the part. It consists of a hole with a disc on one side, sort of like the car wheel axle I designed, except the disc side of the hinge slightly rests on another face of the print job. Because the disc does not technically “contact” the part in my CAD file, the “foot” of the print job is free to pivot. When this prints, a small part of the disc will loosely touch the other part of the print job, and build up from there. The small contact is easily broken once the servo turns on.

A cross-section view of the hinge behind the servo. The disc is slightly separated from the lower base of the part, meaning that it can break off easily.
A cross-section view of the hinge behind the servo. The disc is slightly separated from the lower base of the part, meaning that it can break off easily.

The next design step involved being able to co-process the part easily, while still letting it be removable. The part does not fully enclose the servo, so the top brace can be easily broken to get the servo out. When the servo with the servo horn is placed in, the horn is oriented to be tangent to the top and bottom faces of the servo. When placed, the servo horn slides into its fixture and becomes fully constrained after co-processing.

A cross-section view of the spot that the servo horn slides into. This makes the co-processing job simple while constraining all components of the servo.
A cross-section view of the spot that the servo horn slides into. This makes the co-processing job simple while constraining all components of the servo.

After the co-processing step is completed, the printer will print over the servo motor because of its flat surface, which is why the shape of servos make them great for co-processing! This will secure the servo motor in place so that it is constrained to the piece it is mounted to. In future iterations, I will likely put a strip of blue painters tape on the servo so that I don’t damage the motor and so that the print sticks better.

Co-processing the servo motor during the print
Co-processing the servo motor during the print

After all that was done, the motor was plugged into an arduino and a slightly modified version of Arduino’s “Sweep” example was run, allowing the servo to break the build adhesion and release itself from the build plate.

The printed, co-processed piece hooked up to an Arduino.
The printed, co-processed piece hooked up to an Arduino.

And there we go! First successful test of co-processing a motor to get a print of the build plate is complete! You’ll see how I use this idea in a video coming next week!

The servo motor breaks the adhesion with the build plate and pulls itself up (1x speed)
The servo motor breaks the adhesion with the build plate and pulls itself up (1x speed)

-Alex

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s