MTM 2: ‘MAGGY’ CNC Drawing Machine

MANUALLY OPERATION

Finally we operated the machine to make a demonstration of what it does.

ASS-09 [Assembly] from Fablab Sv on Vimeo.

Machine Design

CONNECT THE STEP MOTORS

For this assignment we made the two step motors work separately first out and then into their respective cardboard boxes we will use as X and Y axis. To do that, we use an Arduino UNO board and a breadboard to be able to connect all the necessary cables using one Pololu DRV8834 driver carrier for each motor. We programed the movements using Arduino IDE.

Step motor test from Fablab SV on Vimeo.

SOLVE ISSUES

The first and most important issue was not to have the necessary materials to construct the boxes. First of all we weren’t able to find plastic or pvc bushings and aluminium pipes in the local hardware store, we had to substitute the pipes for wooden round sticks causing non accurate movements in both axis.



We didn’t have the Gestalt Nodes and FabNet boards either, so we had to solve the issue using an Arduino UNO board and two Pololu drivers as H Bridge to be able to move both motors at the same time.



Second issue was fasten the two axis inside boxes, we try several methods and the one worked the best was join them with Velcro tape, but we still have problems because each time we had to split them, the Y axis box is falling apart of its top cap.



Third issue we had to solve was the X axis balance, because the motor itself is 68 oz and the X axis is upside down and it doesn’t have anything supporting it, and when the axis inside box isn’t in the middle, the entire cardboard box tends to unbalance because the motors weight, causing the marker lost contact with the sheet of paper in the other side and the drawing wasn’t as accurate as we wanted, and most of the time it didn’t draw anything. To solve this issue we decide to add a spherical caster behind the motor making the necessary support and let the axis move in both directions.



Fourth issue was the motor coupling, besides we printed them in PLA, it was difficult to keep them attached to the motors pin, and sometimes at the middle of the procedure they split apart ruining everything. To solve the issue we had to paste them with super strong glue and some masking tape.

UNDERSTAND C++ CODE AND ARDUINO IDE

As we said before, we use an Arduino Uno and Pololu Driver to move a stepper motor. Before begin programming there are three things that we need to understand:

The stepper motor function by generating a temporal magnetic field when we polarize opposite coils, this make one step, to generate a continuous movement we need to polarize and depolarize consecutive coils with certain delays; this delay defines the rotary speed of the motor and they are inversely proportional, the longer the delay, the slower the speed and vice versa.

Pololu driver make two principal functions, first it acts as a H bridge, supplies power to the motor that the control circuit can’t supply; and second is responsible of making the sequential shift of the coils by the rhythm of an external clock and controls its direction, all this with PWM and digital commands respectively.

Arduino, in this case, defines the quantity of steps that we need the stepper make and the direction we want it to go.

Knowing this, to make the program practically we need to tell Arduino: “We need you to give 1000 steps on this direction, and for every step you have to put on 5V the step pin, wait, put on 0V, wait and repeat”

On C++, it would be this:



This code lines will make that one motor give 1,000 steps. But we design our machine to move on 2 axis, so if we want to move both motors at the same time we have to tell the same to each motor, like this.



This would do that both motors turn at the same time with the same speed, the direction is independent for each one.

If we want a complete a program we need to set the IOs and the directions of movement, this code was our first sketch to test our machine and it will make a box with a diagonal in a very long method.



A very large code, and it will be larger if we want the machine to execute more movementsl, so we realized that we can sintetize it by making a function with the code that is repetitive, and this is the "for cycle".

MEASURE DISTANCE VS TIME STEP MOTORS MOVEMENTS

But first we need to measure some parameters, like the relation of the rotation and the straight line distance, and the relation of the delay with the speed.

Once we had the X and Y axis assembled and the motors connected, we made the program to draw horizontal and vertical lines using first milliseconds and measuring how many centimeters the motors ran in that specific time. Using that information, we were able to define a formula to make the motors run changing the distance instead of changing the time.

Thanks to this calculation we could define that the amount of steps it will be equal to the stright line distance we want to draw on milimeters multiplied by 250
steps = distance * 250

And the delay will be a factor of 15,000,000/(1200*6.25) divided by the linear speed on milimeters per seconds
delay = 15000000/(1200*6.25*linearSpeed)



Download this Code for Arduino
This code works as a "Baby G-Code" because we only need to specify, for example, in the command line(distance, direction, speed) and in the command diag(distance X, distance Y, direction, speed). It still has some delimitation, it can't draw diagonals lines with an angle different from 45°, and can't draw curves.

RESULTS

Here is the sequence of the test that we made





Here is a video of what does the last program that we make!!!

Week 11 - Machine Design from Ivan Lopez on Vimeo.