10. Mechanical and Machine design¶
For this assignment, we thought of something fun and were inspired by the Willy and the Coyote cartoons: a Dingo chasing Bip-Bip the speedy ostrich all over the canyon.
So we tried to reproduce those scenes by designing a cannon that could move both on the XY axis and on the Z axis.
Joints and structural modules CAD and CAM¶
Unfortunately I had messed up my Fusion educational licence so at the moment I do not have access to the actual Fusion files of my design.
I had designed a series of elements needed for the machine structure:
- a cannon body, presenting and opening for the servo motor trigger, and a connection to the pillar block it was attached to
- a rotatory joint that would allow the cannon to basculate, changing it’s angle with the changing of the Z axis
- a pillow block connector that would run along the cannon body to allow for aforementioned basculating movement
- a piston to be pulled from inside the cannon, this is the actuale projectile movement, it is allowed by a hidden spring
- a spacer used to align different pulley wheels
All these parts were mounted using the assembly function on Fusion 360. The original file also included the models of electronic components (as offered by online vendors), so to better include all parts in our design.
Enventually, we settled to focus on how to move 2 axis only, the vertical one, that would determine the cannon inclination, and the rotatory one.
In order to rotate the machine contiously by 360°, we wanted to use a potentiometer connected to the board with it’s CNC shield, going to a NEMA 17 motor. this motor would be connected to a belt drive, the motor connected to the bigger cog, coupled with a smaller one (attached to the rotating shaft), with a ratio of 1:3.
So, the first thing was to understand how many steps would the motor take for a full revolution:
- 200, without enabling microstepping
- 3200, with microstepping engaged
The rotational speed was determined by the delay between each step, this can be done in sketch just like the steps count
The by defining the two pins for the rotary encoder, we have one single click of the rotary encoder corresponding to 1 step of the motor, in each direction.
A very similar approach can be taken for the vertical axis, the difference being that the rotatory axis could turn endlessly in each direction, while the veritcal one has to have limits on each side.
In this sense I thought it would have made sense to have a potentiometre to control this movement, as it has a value limit. The harder part for this approach was to correctly link each potentiometre value increment to the correct number of steps, so that the minimum value on the potentiometre would equate to the lowest possible position of the vertical axis, and so would be the maximum value with the highest position.
More on Machine and mechanical design¶
More on what we’ve done for this week on Raji‘s website.
Joints and structural modules: