Motor Control

At the moment our system… sort of works. Our last working easy driver fried in the early morning hours before the deadline which meant we were only get the system working with three motors running at once. For our final presentation we decided to sacrifice control over the pen grabber, but for the future we’d like to have full system running with four motors. Due to limited analog pins on the myRIO, this could require using two myRIOs communicating over shared variables.

Mechanical Improvements

There are currently a couple of mechanical issues that need to be sorted out. We came up with some makeshift solutions to get it up and running, but with some simple fixes we believe we could have the robot operating smoothly.

‘Down Drifting’

One issue we ran into was that the pen plate gradually drifting down despite being sent the same number of steps for each direction. We’re still not entirely sure what’s causing this, but the drift seems to be consistent so it might be possible to calibrate the number of steps it goes up in order to account for it.

‘X’ slippage

Right now the motion in X direction isn’t perfect. It runs to issues where there’s too much friction on the rack, so it occasionally slips as it does steps. There are a couple things we could try in order to fix this.

For a quick fix we could flip the direction that the system paints the face. The Y direction seems to be more consistent, so having it do the repeated motion of going back and forth all the time would make X direction slippage less of an issue.

It’s possible that this is caused by gears not being perfectly mated with the rack. We could do some more gear math and recut them to be more accurate.

The gear opposite the motor tilts weirdly because it doesn’t have a support for the axis. This would be easy to fix by 3D printing a new part.

Four gears might just be too much friction for the system in general. Using a linear bearing and rod similarly to the ‘Y’ axis could solve this issue.

Improving the Gripper Mechanism

Even when actually operating the gripper mechanism isn’t perfect. It relies on holding torque and friction to keep the pen from slipping and the grabber has to approach the pen at exactly the right position for it to correctly grab.To fix these issues we could add mechanical stops on the pen to keep it from slipping and we could mess with the geometry of the grabbers more to make it easier for them to consistently grab.