13. X, Y and a pen

It starts to look like what it is meant to be: a 2D plotter.

I just need to add a pen, which is achieved with nice linear shafts on the vertical axis. Yet no command to lift the pen at this time: it draws a continuous line for now.

It allows to make a simple test to check how precisely it closes a rectangle or write over the same lines several times. Here it is in motion:


Precision-wise, I'm not so happy: around 2 mm while I was targeting around 0.5 mm. I still have a bit of a way.

12. X and Y

One more axis.

I left my 2D plotter away for some time. Back with the 2nd axis: Y

For this Y-axis, I use 2 stepper motors, hence 2 servos, one for Y and the other one for A, configured to duplicate Y. I added two jumpers as shown here:

Initially, both stepper motors were turning in the same direction, which considering their position on the board is wrong. I needed one of the to turn in the opposite direction: easy, it's just a matter of inverting its connection on the CNC shield. Note the wires: black, green, red, blue on the left-inside (A) and opposite on the right in-side (Y).

I also created a wood box to hold electronic parts together.

Closed, the PC sits on the top and I have an emergency stop on the left in-side that works !

And now the result in motion:

Note just for the record: few useful G-code commands

• ! = Hold
• ~ = Start cycle
• ?  = Current Position/Status
• $$ = Current Settings

11. Not yet lost in translation

Got there. It's not perfect but it's a good progress.

I managed to built the gantry over which some kind of a cart can move, controlled by one axis of the CNC shield + Arduino.

Here it is in action:

Looks ok so far.

Yet I was surprised that the belt vibrates so much. Also the stepper motor is quite nosy, especially as the whole aluminum structure resonates.

Apparently the quality of piloting the stepper motor depends on the drivers I am using: I bought another set of drivers and I will check one of these days if it makes any difference.

10. Well it's complicated... :-)

Well I feel more comfortable with software, a little less with electronics. I am not really into mechanics, so I need to learn everything from scratch.

How to properly cut to get everything squared and aligned. How to drill a hole that fits my design, with the right position, angle...

All sorts of little details that seem so obvious until you do it.

I bought quite a few tools for that, such as a vertical drilling machine, a tap and die set,... and parts.

I also purchased wheels and belt for the transmission and drilled a hole for its axis: this is exactly when I discovered that it was not that easy... :-)

09. Designing the mechanics

Now stepping into mechanical design: after reviewing plenty videos and websites looking for the kind of cheap mechanical parts I can buy, I took my pencil, an eraser, my old wood board and found back some yellowish Canson paper I had bought last century.

Here is how my design look so far.

Front view

View from above

Two versions of a device to adjust belt tension

08. Into mechanics

So the basics for the Arduino + CNC shield + G-code are under control to get the stepper motor moving. I now need some mechanical thing to move.

The following video is good source of inspiration:



Quite smart. Yet my constrains are different from a CNC: the axis should move faster and they don't need as much strength. Still the linear guidance could be the same...

After browsing the Internet for almost a whole week end, I end up with the following ideas:

1. Linear guidance: 
1. Use an aluminum T profil + 624vv bearing on one side
2. Plain bearings as wheel on the other side
2. Linear motion: use toothed belts by the meter + pulley + clamps

Suppliers found:

• Bearings; on ebay for around 0.50 EUR per bearing
• Toothed belt & co: http://www.tridistribution.fr/fr : it's way more expensive and I still need to get some details sorted out to choose the right features.

07. Plug my stepper motor and test it

Now it's time to plug my stepper motor onthe CNC shield.

I read this tip: "Do NOT connect or disconnect a motor while the driver is energized. This will cause permanent damage."  -- Sparkfun

As per the specification of my 42BYGH47401A stepper motor, the wiring of the 4 leads are ordered as:

• RED Phase: A
• BLUE Phase: A Return
• GREEN Phase: B
• BLACK Phase: B Return

Not fully explicit to me as my CNC shield shows A1, A2, B1 and B2 for each

As per http://www.selene.co/Articles/WiringConfigurations.aspx, "Bipolar motors are the simplest of the configurations presented here. Bipolar motors have 4 leads and two windings. Only one configuration is possible with a bipolar motor, as shown to the right. What is important for a bipolar motor configuration is the polarity of each winding. The windings must be symmetric (A+ and B+ winding leads must be connected to the same end of the winding."

So I decided to wire it as

• B2: black wire
• B1: green wire
• A1: red wire
• A2: blue wire

This is how it looks:

So I am now ready for my first test:

1. Switch on the main alim
2. Plug in the USB cable into the Arduino

Here is my stepup:

In the Arduino IDE, I open a serial monitor (under Tools / Serial monitor):

1. I type in $$ + send, to check that I am properly connected: I get my default parameter setup
2. Now I can type in my first G-Code command:

It means "move x-axis by 4 mm at a feed rate of 25 mm per minute". And it works !!

Now the same in video: yeah !! :-)

---

As a recap, this video is also a pretty good introduction by John to getting started with Arduino CNC Shield.