Core Electronics Forum

GPS speedo design in the making

I’m developing a new design of GPS speedo. I haven’t actually made anything yet for this particular design (awaiting access to 3D printer post lockdown). I’ve made various other GPS speedos.

I’ve done the design of the housing. Some shots of the Tinkercad design:

speedo_1

speedo_2

speedo_3

The apertures are for the various boards and other bits. I’ll be using a GPS module from Core Electronics that works well, an Arduino Pro Mini processor and a 4 digit 7 segment LED display for the speed. There will be a piezo buzzer at the rear for overspeed alert and a header for plugging in an HC-05 Bluetooth module.

It should be a neat device and I hope others make it too. Will post updates as I progress.

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Here’s some views of the general arrangement with the components. All good in theory, but I expect it will go thru a few iterations.

speedo_4
speedo_5
speedo_6

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Hi John,

It looks like a tidy assembly. We don’t have our 3D printing service up and running at the moment as we have a number of staff working remotely during COVID, but I’ve heard some libraries have 3D printing services up and running.
If you are in the Newcastle area I have heard that Newcastle library has suspended their 3D printing, however, Lake Macquarie Speers Point, and Belmont libraries are apparently still 3D printing.

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Thanks, Trent. I’m not in your part of OZ. I should have access to a makerspace shortly, after twelve months of no 3d printing.

I’m aiming to develop my skills in building designs that require few print iterations. I think most of us use the design-print-test-edit and repeat till it’s right method. So, five or six prints to get to a finished product was not unusual for me. I reckon I can spend more time and effort on the virtual object and get it pretty well right in one or two prints.

I now build virtual models of the components and fit them into the virtual object I want to print. This works well and readily shows up mistakes on-screen. For instance, when I added the component models as in my previous post, I saw that the aperture I made in the top of my housing was for the wrong GPS module. You might be able to see it’s not right. So that has to be reworked. Then I saw I haven’t got a USB socket for power connection, so I have to add that somehow. Just those two catches save me one 3d print session that I would have to reject.

I’d be interested to hear if anyone else has tips for getting it right on-screen rather than let the mistakes carry thru to the actual printed object.

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Here’s my design ready for printing tomorrow. I’m doing it in two halves so as to avoid bridges.
speedo_7

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Hi John
I have no experience with 3D printing or producing the drawings for it.

I have however done some 2D work with packages like LibreCad for the Mac and AutoSketch for Windows. When a “thing” has multiple parts I use as many layers as required and draw objects full size or the same scale. You can overlay the layers to make sure things have a fair chance of fitting. Of course this technique does not suit all circumstances but an adaption to 3D may be useful.
Cheers Bob

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Hi Bob.
That’s kind of what I do in Tinkercad. I usually don’t work in layers as it is 3D. You can group parts together and move them as one. As the object gets more involved, you either conquer the details and get everything in place, or you go nuts.
Cheers,
John.

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Hi John
Know the feeling.
Cheers Bob

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Hi John,

I did some design drafting for a hydraulics firm while I was still at University doing my engineering degree. One of the jobs I worked on, I drew up a replacement stainless steel casing for a rail clamp that was in for repair (off one of the shiploaders at the port). The old one was Missing in Action. We didn’t have any reference drawings so I had to measure it up, and we had it made up by 3rd party contractors.

Definite moment of pride when it came in and dropped straight on, all the holes lined up, and welds cleared - no angle grinders needed!

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That looks pretty neat, and something I could have used a few years ago when the speedo broke on my 1971 ACCO motorhome.

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Just completed second print. First print failed from dumb mistake – I had one half 5mm off the print bed. Anyone who 3D prints knows what you get from that.


I opted for short print time over quality of finsh. That’s my usual preference.

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Spectacular, Bob. Did the bike and car travel with the truck?
John.

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Here they are. Look a bit rough in finish close up. I’m treating this as a prototype. I’m pleased with the close match b/w the physical and virtual objects. No surprises.

The printer was Ultima2+; PLA filament; layer thickness 0.3mm; print speed 100 mm/s; 10% infill; no support.



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Yep. The bike winches up inside the back of the body, into the lounge room. The car just drives separately.

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Hi, nice design.
How are you going to enter the various speed limits and turn them ON and OFF?
You need something on the case, not a fiddly BlueTooth app while driving?

Tom… :grinning: :+1: :cup_with_straw: :australia:

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Hi Tom.
You’ve touched on an important design consideration for this device. It must not provide a distraction to the driver. The only operator control will be a push button at the rear to enable/disable the buzzer. Operating that will be no more distracting than turning on/off the car radio.

Buttons on the box to control the current speed limit would be distracting. I’ve tried a wide range of strategies and the one I’ll be using is simple but effective.

Initially the speed limit will be set at 40kph. When the speed reaches 40-42kph the alert is activated (buzzer sounds and LED display flashes); when it goes over 42 the limit is increased by 10 to 50kph and the alert is switched off. That process repeats for each speed value of 40,50,60…110kph. with a decreasing speed the limit is reset as the speed passes thru 100,90,80,70… with no alerts. I’ve been using this strategy and it works well.

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Here’s what I reckon is a “final” workable print.


Behind it are the five prints I had to do to get to this “final”. Getting there in two or three prints seems to be unachievable for something new. Each print of the entire object took about two hours.

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Hi John,

Looks very refined! It’s great to see your project actualising on the forum! Cant wait to see it done.

Liam

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Thanks, Liam. I’m endeavouring to make something that is a product of a deliberate design process rather than the outcome of tinkering. I’ve inserted the components into the box.

pic 1 – from the front
I’ve placed it alongside an RPi4 to show the scale. There will be a hood attached to the front to shade the LED display as it can’t be read in bright daylight. The hood will also make it look more finished. That’s the antenna of the GPS module showing thru the topside.

pic #2 – from the rear
Beside a normal sized mouse. The end plate holds a piezo buzzer and a switch to enable/disable the buzzer. I’d prefer a latching pushbutton to the toggle switch – a pusbuttton wud be more ergonomic for a driver to operate than a toggle. I opted to make the end plate a separate part rather than integral with the box. I can see it being modified. This way only the end plate will need to be reprinted.

pic #3 – from the underside
The pro mini just nestles inside the aperture. I attached a USB breakout for power connection.

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Hi John,

Looks smiiicho, is there any projection for the MCU? I’ve seen a few busted from stray random metal things getting around like keys, rulers, other electronics. I’d imagine it would be safe on the dash or tucked away

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