3D-printed gauges

[ame]

Hi everyone,

I have been working on an easy way to build steam gauges. My design uses the slim Switec stepper motors found in car dashboards. It can support motors with front contacts or rear contacts, and is mostly 3D printed. There is no PCB, no exotic fasteners or other parts, and the gauge can be assembled by hand.

Attached are 3D renders of the front contact and rear contact assemblies. Currently I have made only 60mm gauges, but the technique will work for 80mm gauges.

I will publish the original OpenSCAD files on Gitlab, and STL files for immediate slicing and printing.

The Switec stepper motors are easy to interface and can be controlled by an Arduino, or just about any group of four GPIO pins on any microcontroller.

I recently bought some matte black PLA filament for my printer, and frankly, it looks awesome.
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[ame]

I'm going to document how to build a gauge with my design here, and use any feedback that I get to make a clearer guide that I will publish on my Gitlab.

First, let's look at the parts required. I will focus on the 'front connector' design, which supports the X27.589 (single) or X40.879 (dual) stepper motor. I do have a design that supports an X27.168 stepper motor with rear connectors, and the assembly is very similar.

To build a basic single-needle gauge you need these five 3D-printed parts (shown in the photo):
Bezel (top left), should be matte black, probably printed with fine layers
Spacer (top right), should be black
Stepper plate (bottom left), can be any colour
Template (bottom right), can be any colour
Indicator needle (centre), should be black with a white painted tip

The parts could be printed in any colour and then painted. It's up to you.

In addition you will need the following parts:
X27.589 stepper motor
3mm white acrylic (60 x 60mm)
2mm clear acrylic (60 x 60mm)
2x M3x14 countersunk head machine screw
2x M3x8 button/panel head machine screw
4x M3 nut
4x panel mounting screw, e.g. M4x16 machine screw
4x panel mounting nut to match screw, e.g. M4 nut
3mm white LED
LED resistor (optional)
4-pin connector
2-pin connector
6 pieces of thin wire
Decal
Needle cover 8mm vinyl disc or sticker (optional)

Note that we are building the gauge only. Driving the stepper motor and LED are completely separate issues, but will be discussed later.

The STL files can be found here:
https://gitlab.com/andrewerrington/flight-sim-gauge

The OpenSCAD file for the complete model can also be found there. Note that the STL files are quite large, so it is more efficient to download the OpenSCAD files and generate your own STL files locally.

The next step is using the template to cut the acrylic pieces.

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[ame]

The next step is to cut two pieces of acrylic. You will need a 60x60mm square of 3mm white acrylic and a 60x60mm square of 2mm clear acrylic. You can measure then cut, or you can use the outer edge of the template as a guide.

The white acrylic will be the back panel of the gauge, with the decal on it. The transparent acrylic is the window on the front of the gauge.

Each of the 3D-printed pieces has a small notch at one edge. This is to make sure all the pieces are in the correct orientation. The notch should be on the bottom edge, at the right. Use a file to make a notch on both pieces of acrylic in the right place as shown in the photo.

For the 3mm white acrylic:
Clamp the template to the acrylic and drill all the holes with a 3mm drill. I find it useful to insert an M3 screw and nut in each of the first four holes to help keep the pieces together and aligned.

When all the holes are drilled, remove the template and drill out holes 'a' to 4mm (M4 clear). Drill hole 'd' to 4mm to accept the flange of the 3mm LED. Drill hole 'c' to 6.5mm to accept the needle boss.

For the 2mm clear acrylic:
Clamp the template to the acrylic and drill only 'a' and 'b' holes with a 3mm drill. Again, I find it useful to insert an M3 screw and nut in each of the first four holes to help keep the pieces together and aligned.

When all the holes are drilled, remove the template and drill out holes 'a' to 4mm (M4 clear).

Attach the template to the rear of the clear acrylic and use four M3 screws and nuts to keep the template aligned. Now, with a sharp point, score a line in the acrylic around the inside edge of the large circle. Use a 3mm drill in hole 'd' to make a small indent in the surface of the acrylic.

Remove the M3 screws and rotate the template 90 or 180 degrees. Reinstall the screws. Now you can score the parts of the circle that were not accessible due to the centre support arms.

As this is a hand-made item all holes may need to be adjusted to suit your specific assembly.

The next step is to prepare the stepper plate.You cannot view this attachment.

[ame]

The stepper plate supports the stepper motor, wiring, LED, and connectors.

First, insert the M4 nuts in the corners. They should be a tight fit and may need to be pressed into place with pliers or a vice.

Next, insert the M3 nuts. Note that they must be pressed in from the back of the stepper plate.

Test fit the stepper motor at the back of the plate to be sure the mounting pegs fit the holes in the plate, and that the electrical pins go through the plate freely. Do not glue the motor in place yet.

Test fit the LED legs in the two holes at the top edge of the plate. The LED is mounted from the front. From the front, the long leg is on the right. From the rear, the long leg is on the left. When assembled, the top of the LED will be about 7mm above the front of the plate.

Finally insert the 2-pin and 4-pin KF-2510 connectors from the back of the plate, with their flaps closest to the bottom edge, and glue them in place with cyanoacrylate (super glue). The 2-pin connector is a tight fit against the flat on the body of the motor. For a single needle motor install the 4-pin connector to the right of the 2-pin connector (away from the alignment notch).

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Now all of the electrical parts are mounted and need to be wired up.

We will adopt the convention that pins 1-4 of the stepper motor will be wired to pins 1-4 of the 4-pin connector in that order. Pins 1-2 of the 2-pin connector will be power and ground respectively for the LED. Looking at the back of the plate, pin 1 is on the left.

On the front of the plate, solder four pieces of thin wire (e.g. wire-wrapping wire) between the visible tips of the motor pins and 4-pin connector. Do not apply too much heat to the motor pins or you will melt the motor housing or damage the internal connections.

Solder two wires from the LED legs to the 2-pin connector. Install a resistor if necessary for your preferred cockpit lighting circuit. For example, if you have a 12V lighting supply you should probably install a 470R resistor in series with the LED. The positive supply pin connects to the long LED lead. The final position of the LED will be set during final assembly, so ensure the LED can move a little, or be prepared to de-solder and re-solder the connections.

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The next step is to attach the decal and assemble the gauge.

[ame]

Now the parts are all prepared they can be assembled.

Place the 3mm white acrylic plate onto the front of the stepper plate. Use the alignment notch to make sure it is the right way round. Insert the two M3x8mm screws into the upper right and lower left holes and tighten them up against the M3 nuts that were inserted into the stepper plate.

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Cut the decal to size. It should be a little larger than the 51mm diameter viewing area. Punch out the centre hole and glue the decal to the white acrylic plate.

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Install the needle. Ensure the stepper motor is rotated fully anticlockwise and that the needle is pointing at its reset position. At this point the gauge can be tested if required as all the wiring and mechanical parts are complete.

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Place the spacer on top of the white acrylic plate.

Place the 2mm clear acrylic plate on top of the spacer. Ensure the side with the scored circle is downwards (which should be that case if the alignment notch is in the right place).

Place the bezel on top of the 2mm clear acrylic.

Insert the two M3x14mm screws into the upper left and lower right holes and tighten them up against the M3 nuts that were inserted into the stepper plate.

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Ensure the LED is pushed forward into the housing as far as possible. It will be touching the back face of the clear acrylic, into the indent that was drilled there.

Congratulations! You have built a gauge.

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To mount the gauge in a panel, use dimensions for a 2-1/4" (2.25") instrument. I used a 57mm hole saw. The mounting hole centres are on a 47x47mm square, drilled out M4 clear. You can drill two holes on either diagonal, or drill all four holes. The gauge is placed behind the panel. The mounting screws go through the panel and through the body of the gauge and attach to the M4 nuts in the stepper plate.

[KyleH]

Just a placeholder that I can come back and edit with the final assembly instructions.

What...you mean you don't want someone to come in here and post in the middle of you instructions???

[ame]

Just a placeholder that I can come back and edit with the final assembly instructions.

What...you mean you don't want someone to come in here and post in the middle of you instructions???

Yup.

[Trevor Hale]

Well Done,  Thank you for this..

Great tutorial.

You can attach your stl files too if you like.

Trev

[ame]

Well Done,  Thank you for this..

Great tutorial.

You can attach your stl files too if you like.

Trev

Thanks Trev.

The STL files are rather large. Plus, if I update them I will put the update on Gitlab, so the files here will be stale.

I'll think about it, but probably won't do it.

Andrew

[Trevor Hale]

Then at least post the link to where you are going to host them please.

[ame]

Then at least post the link to where you are going to host them please.

I already did. In the second message:
https://gitlab.com/andrewerrington/flight-sim-gauge

[ame]

Thanks to the magic of technology I have already made the first change to the repository. I have made the stepper plate 0.4mm thicker because I didn't allow for the rear-contact stepper to have a slightly different length needle to the front contact stepper. In general it won't matter due to tolerances in all the layers, however, with an additional 0.4mm the tolerance requirements can be relaxed a little.

[ame]

And lastly, a video.

The gauge is being controlled by a simple test program.

• Run the motor anticlockwise for a full revolution. This will cause the motor to hit the leftmost stop, so we know it is in the correct starting position. On many gauges this will be the 0 position, but I have seen pictures of this specific gauge on a real plane with the pointer sitting around 10 o'clock.
• Next, I have measured the number of steps from the leftmost stop to the 0% (UP) position. The test software moves the pointer to this position.
• Now the software moves the pointer up (clockwise) to key points on the dial, 20%, 40%, 60%, 80% and 100% (DOWN).
• In the "Takeoff and Approach" zone the pointer moves slowly back and forth.
• After hitting 100% (DOWN) the software moves the pointer down (anti-clockwise) to each 10% position from 100% to 0%.
• Finally, I turned off the light so we can see the backlight working. The camera takes a short time to adjust to the new light levels, and it looks better in real life.

Thanks for watching.

[ame]

The same design can be used to build a dual concentric-needle gauge. This uses an X40.879 stepper motor.

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I'd like to make a twin needle gauge next. Only the stepper plate and drilling template will change.

[ame]

Well... that was easy. 
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