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Author Topic: Spy Hunter gas pedal Pot  (Read 556 times)

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spisi

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Spy Hunter gas pedal Pot
« on: December 02, 2020, 06:42:19 pm »
Hey guys, I've been using a micro switch gas pedal to play Spy Hunter in MAME.  I realize that it is supposed to be played using a pot gas pedal.  I'm going to try to add a pot to my existing pedal so it can be used both ways.  There is a 1/4" diameter shaft that rotates when you depress the pedal, but it only turns about 45 degrees.  Will that be enough rotation for the pot?  I should be able to calibrate it in windows to get it to function properly I think.  Also, I assume I need a 5k pot.  Any thoughts would be appreciated.  Thanks.

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Re: Spy Hunter gas pedal Pot
« Reply #1 on: December 02, 2020, 07:15:07 pm »
I'm going to try to add a pot to my existing pedal so it can be used both ways.  There is a 1/4" diameter shaft that rotates when you depress the pedal, but it only turns about 45 degrees.  Will that be enough rotation for the pot?
If you want a hybrid pot + microswitch pedal, it seems like it would be easier to add a microswitch to a pot pedal than to add a pot to a microswitch pedal.

Also, I assume I need a 5k pot.
Assuming you use a three wire potentiometer (voltage divider) wiring setup, any decent-quality linear pot from 5k to 100k should work fine.
- Some people have observed slightly more jitter with 5k pots than 100k pots.
- You only need to match the resistance value with a two wire (variable resistor) setup.


Scott

spisi

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Re: Spy Hunter gas pedal Pot
« Reply #2 on: December 02, 2020, 07:45:34 pm »
Thanks Scott for the quick reply!  :D   I'm not quite sure what you mean "You only need to match the resistance value with a two wire (variable resistor) setup."

So a 100k would be better then?  What does that mean 5k or 100k?  What about my 45 degree rotation?

« Last Edit: December 02, 2020, 07:48:00 pm by spisi »

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Re: Spy Hunter gas pedal Pot
« Reply #3 on: December 02, 2020, 09:51:23 pm »
I'm not quite sure what you mean "You only need to match the resistance value with a two wire (variable resistor) setup."
With a 2-wire setup like the Atari 2600 paddles, the encoder is reading the resistance between the center tab (purple wire) and an outer tab (yellow wire) to determine the position.
- Because it reads the resistance, you couldn't substitute a 5k (5,000 Ohm) pot for the 1M (1,000,000 Ohm) pot  in the Atari paddle because it would only cover 0.5% of the range.


With a 3-wire setup, the encoder is reading the voltage on the center tab. (wiper)
- The pot is acting as a voltage divider with 5v on one outer tab, ground on the other outer tab, and a voltage on the center tab determined by where it makes contact with the resistive element.
- If you turn the pot so the wiper makes contact with the center of the resistive element, you'll get 2.5v (green line) regardless of whether it's a 5k or 100k pot.  Half of the voltage drops between 5v and wiper and the other half drops between wiper and ground.
- If you turn the pot so the wiper makes contact 90% of the way from ground to 5v, you'll get 4.5v (blue line) regardless of whether it's a 5k or 100k pot.  10% of the voltage drops between 5v and wiper and the remaining 90% drops between wiper and ground.

http://wiki.arcadecontrols.com/index.php/Analog_Encoders#How_a_potentiometer_provides_the_voltage_for_an_analog_encoder_to_measure



What does that mean 5k or 100k?
That's the resistance in Ohms measured from tab 1 to tab 3. (outer tabs)

What about my 45 degree rotation?
Different pots have different ranges of rotation.

Pots used in analog joysticks and pedals often have a lower range of rotation.
- This is another excellent reason to start with analog pedals so you don't have to fumble your way through the harder parts of the mechanical and electrical engineering.

You can reduce the range of rotation like Le Chuck did in his SW Micro build, but that's not an easy mod.   >:D
- Open the pot case, use conductive ink to bypass part of the resistive element, properly reassemble the pot, and don't turn the pot too far or you'll scrape off the conductive ink.


Scott

spisi

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Re: Spy Hunter gas pedal Pot
« Reply #4 on: December 03, 2020, 09:31:30 am »
Thank you Scott, very informative.  I ordered a few pots from Amazon, then I realized expected delivery is Jan. 8th...DOH! I'll update when they arrive.  Thanks again, very helpful as usual!  :applaud:

spisi

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Re: Spy Hunter gas pedal Pot
« Reply #5 on: December 06, 2020, 12:32:05 pm »
Upon further review, it seems as the gas pedal that I have was built to be used for either microswitch and/or pot.  It has a gear that's not being used, and a hole in the chassis for the pot!  Now, I need to know the pitch of said gear so I can get the small gear that would then be attached to the pot.  Is there a standard pitch?  If not, how do I figure it out?

BadMouth

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Re: Spy Hunter gas pedal Pot
« Reply #6 on: December 06, 2020, 02:52:49 pm »
https://na.suzohapp.com/products/driving_controls/50-2978-00

You might be able to glean enough information from the replacement parts listed at the bottom.  All these Happ pedals use the same parts as far as I know.
« Last Edit: December 07, 2020, 06:06:25 am by BadMouth »

spisi

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Re: Spy Hunter gas pedal Pot
« Reply #7 on: December 07, 2020, 09:18:12 am »
Thanks man!

spisi

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Re: Spy Hunter gas pedal Pot
« Reply #8 on: December 25, 2020, 01:29:57 pm »
Merry Christmas everybody!!!

Update: The gear and 100k pot is in!  After a few hours calibrating (Windows and in game) it's working perfect!  It's working so good that I put up a new hi score (after a few games  ;))

I'd like to thank everybody that has helped me the past few months!  My cabinet is complete!  I've got a full size stand-up with two sets of joysticks with six buttons each and a trackball in the middle. Three interchangeable panels that connect in less than 3 minutes. One for 720, one for driving games (two steering wheels), and last but not least Spy Hunter!

Thanks again (especially Scott)!!!

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Re: Spy Hunter gas pedal Pot
« Reply #9 on: December 25, 2020, 04:40:05 pm »
Glad you got everything working.   :cheers:


Scott