Build: Spec Miata "Replica" with VR and Tactile

AS noted in several threads, I have a real racecar. Its a 1990 Miata converted into a Spec Miata (SM) and I race with the National Auto Sports Association (NASA), and the Sports Car Club of America (SCCA). For a couple different reasons, my race season in 2020 and probably 2021 has been/will be non-existent. So, I've turned to iRacing and the MX-5 Cup car (mostly) as continue training. To that end, I want my rig to reflect the ergonomics of my actual cockpit as much as practical.

cockpit_sideview.jpg
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The wheel (not pictured) is a Momo 78. The seat is a 16" Ultrashield VS Road Race Halo (20 deg layback). Note, the above pics were taken mid-rebuild after a rather serious wreck....hence the shattered windshield, and wires hanging loose.

Besides wanting to replicate my SM controls, my other constraint is space. I don't have a place for a dedicated rig, and I use my computer for working from home these days. So, the rig needs to be portable, and compact...and reasonably cosmetically pleasing when not in use. To that end I opted for VR (Rift S) rather than a triple setup, and a coffin style overall design, DIY out of wood. The general idea is that it can be folded inside itself when not in use and become a "bench" or coffee table.
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The idea is that all the parts that protrude beyond the boundaries of the "box" can be removed, and tucked inside or fold into it on hinges of some kind.

I've used scale drawings of Fanatec parts for proof of concepts, because a friend was going to sell me his CSW 2.5+V3 pedals+shifter setup when he upgraded to SC2/Quaife/Heusinkveld. Now that he's building a racecar, too...I'm guessing his money priorities have shifted. So, I'll probably replace with Accuforce V2, and a TBD H-pattern. I have an old Logitech Momo that I bought ages and ages ago.

For the pedals, I have a spare set of miata pedals: Clutch, Throttle, and brake. I'm mid build in converting those into a load-cell brake, and linear pot based clutch/throttle. The pedals will be mounted in a box which will hang off the end, and slide inside when not in use.

The seat I plan to use is an expired FIA Sparco Circuit Pro. Its not the same seat as the race car, but its also a halo seat, but I've found that the tactile Exciters work quite a bit better on the composite material than they did on the aluminum. I was going to use it in the car, but it won't fit in around the roll-cage. So, its been sitting on the shop collecting dust and spiders.

I started a separate thread on the Button Box, yesterday. That's here.

For tactile, I'm still very early stages in planning that. But, I currently have 4 DAEX32P-4, and have another 4 on order. I also scored a BK-LFE yesterday for less than half-price.

Anyway....that's a start at this build thread.
 
Wouldn’t you need to do the same to get left and right to also not close the push circuit? This is a great solution. I’m gonna try it myself.

Yes, absolutely. I was just keeping the example above to the simplest case....showing how it works for two buttons. You just need more diodes in series with each button.

The caveat to this approach is that the transient behavior may be a bit undefined...depending on how the Alps makes/breaks connections internally as you push or release. So, there could be some "bounce" or extra PUSH presses as the switch transitions to/from each position. That should be solvable in the button controller. If not you could always use a simple RC debounce.
 
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Its pretty amazing what's possible and affordable today. I started designing products almost 30 years ago. I designed my first professional electronics product back in 1993---a VetMed thermocouple based thermometer. Back then it took a month to get prototype PCBs turned and about $500 / 5 pcs, IIRC.

Today? I placed an order 3 days ago...for the 3 different PCBs for this project. $10 total for 5 pieces of each board. DHL Shipping cost more than the PCBs at $15. $25 total to my door. And....I get real-time updates as my board progress through the process stages:

pcbs_inprocess.png


I've starting printing the final parts, in a color scheme that matches the real car. The mango colored PLA prints REALLY nicely, across a wide range of settings. I had a little under-extrusion in the front plate after I switched to the orange. I've had that happen a couple of times after changing filaments. I don't know if marlin gets confused or what.

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plate_sideview.jpg
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Since KiCAD and FreeCAD can integrate to model the PCBs...for giggles I decided to print a fully loaded set of PCBs.

PCB_models.jpg
 
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Basically you can diode-OR the Up/Down/Left/Right together to drive the base of an NPN transistor. In the diagram below, the RED text represents the switch connections of the Alps, and the Com terminal. The GREEN push-out becomes the demuxed push button output.

View attachment 459400

Hi there,

I very much like your design. I’m however slightly confused at the “wire” from the transistor arriving before the push button. How would that work in practice? Aren’t all the switches internal on the Alps device? Would you need to open it up to solder the wire inside?
 
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Hi there,

I very much like your design. I’m however slightly confused at the “wire” from the transistor arriving before the push button. How would that work in practice? Aren’t all the switches internal on the Alps device? Would you need to open it up to solder the wire inside?

No. But, I agree its a bit confusing. The terminals are shown below. ABCD are the up/down/left/right terminals. Push is the central connection between the two switches, and comes out to a terminal on the package. COM is the is the "path to ground" for all switches. So, in the circuit above the PUSH terminal is what connects to the Emitter of the Transistor.


alps.png


I labeled these terminals in RED in the first simulation schematic. When any of ABCD are closed, PUSH closes also. When Only PUSH pressed, only the PUSH switch is closed.

inactive.png
 
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No. But, I agree its a bit confusing. The terminals are shown below. ABCD are the up/down/left/right terminals. Push is the central connection between the two switches, and comes out to a terminal on the package. COM is the is the "path to ground" for all switches. So, in the circuit above the PUSH terminal is what connects to the Emitter of the Transistor.
I should have first went to the datasheet… Thank you for explaining it so well. I’m slightly confused at how the internals would look but admittedly that’s of little practical concern. I’ve been struggling with making those Alps multi-control devices work for some time and your message was providential. Would
this S9014 transistor work? Looking at your circuit it seems the low emitter-base breakdown voltage wouldn’t matter and the rest seems fitting (and it’s available for cheap at my location).
 
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Do you plan on reinforcing the wheel 70mm pattern spokes with aluminum/steel threaded spacers? I've found that PLA/ABS is strong enough for up to 20 Nm of torque, but people always swear it's going to rip into pieces so I reinforce my custom made wheels using metallic spacers.

Sorry, didn't see this question earlier.

Kinda. The hub bolts do pass through the entire assembly. So, a lot of the torque/sheer will be converted into bolt tension/PLA compression. But, I didn't really do it for strength, as I'm sure the PLA is plenty strong enough for it. I mostly did it just for ease of assembly.

In addition, all the center hub parts are printed using a "mechanical parts" profile: 200% line width, 1.6mm walls, floors, and ceilings, ~8% over-extrusion, at 230C.


hub_bolts.png
 
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Wouldn’t you need to do the same to get left and right to also not close the push circuit? This is a great solution. I’m gonna try it myself.

Just to follow up.

I built up the first board. As it turns out the BlueHID does not have internal pull-up resistors on its inputs---probably a more accurate statement is that they are VERY high impedence (eg, well over 1 Mohm). So...the 108K pullup resistor above, on the collector of the BJT is needed. 108K isn't specific. I just used another 10K as that what I had within easy reach. With that pull-up added, the circuit works as advertised.


PCB_stuffed.jpg
 
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I spent the week troubleshooting two inputs on the BlueHID. Nothing I did would get them to be recognized as buttons. I was afraid I'd fried them or something. But, every configuration except "button" input seemed to work (VCC, GND, and Analog options all worked). As a last ditch effort I emailed Andy at Ultimarc. He responded within 24 hours that I had an old FW version, and included the newer version as an attachment.

After a little jigging around to work around Windows BT security, I got the device flashed,....and voila! I have an up-shift paddle to match the downshift. So, I've test fit the wheel to the Simplicity. I'm still playing with some ideas on the buttons. The unpopulated locations can be filled with either another Knitter push-button, or a up-down toggle switch such as a Knitter MTA106G. I've left them open until I make up my mind.

I also haven't wired up the wheel buttons, yet. I got excited once I finally resolved the BlueHID issues. So, now I need to screw down the Simplicity and give 'er a whirl!!! Maybe tomorrow.

wheel_tesetfit.jpg



The SW20v3 comes with a bolt on mount. Not ideal. So, I'm working on a quick-release mount using a Bicycle seat post clamp.

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