# Home made pot box



## etischer (Jun 16, 2008)

$90 bucks is worth the peace of mind knowing you are using reliable hardware. If you insist on making something yourself, you will want a pot rated for the duty cycle, and you probably want 0 to full scale to be over 90 degrees like a typical throttle. Also keep in mind what will happen if the pot were to fail, faulty contact, dirty contact, broken return spring, loose coupling... Throttle pot is just as important as brakes in my mind, not a place I would want to cobb things together to save money.


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## Tesseract (Sep 27, 2008)

BHall said:


> ... what kind of rotary pot? Wire wound or carbon?...


The best for this application is a conductive plastic element; Cermet is the worst (has very low rotational life - often less than 500 turns!); carbon can be good if done well - check the rotational life; wirewound also has poor rotational life, a tendency for the wiper to "skip" over the wires leading to a very jumpy driving experience and/or triggering throttle input faults, and the benefits of a high pulse-power rating and low tempco are totally wasted in this application 

Rather than cobble together something out of parts why not buy an actual throttle assembly from a junkyard and reuse the TPS if not the whole assembly?


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## Woodsmith (Jun 5, 2008)

Tesseract said:


> Rather than cobble together something out of parts why not buy an actual throttle assembly from a junkyard and reuse the TPS if not the whole assembly?


Something like this?
http://cgi.ebay.co.uk/TOYOTA-MR2-RE...arts_Vehicles_CarParts_SM?hash=item3a558a5cd9


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## Tesseract (Sep 27, 2008)

Woodsmith said:


> Something like this?
> http://cgi.ebay.co.uk/TOYOTA-MR2-RE...arts_Vehicles_CarParts_SM?hash=item3a558a5cd9



Hmmm... maybe... The TPS on that one has 4 terminals.. I'd try to pick one that has 3 terminals.

Also, pulling one yourself from a car in the junkyard (or breakers, as I think you folks in the UK call them) allows you to snag the all important mating connector, and perhaps even pre-identify the wires (though if it's a pot, as it usually is, then identifying the wires isn't too difficult  )


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## Woodsmith (Jun 5, 2008)

Thanks Tesseract,

That is the one I have off my donor car. It measures 6k across two of the pins, with one other being the wiper. The 4th pin gives a reading that seems unrelated to the pot.
I do still have the rest of the engine wiring to get the plug from.

Hopefully this will help others in the same boat.


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## PhantomPholly (Aug 20, 2008)

You do know that the title of this thread just cries out for some off-topic humor?


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## vpoppv (Jul 27, 2009)

Woodsmith said:


> Something like this?
> http://cgi.ebay.co.uk/TOYOTA-MR2-RE...arts_Vehicles_CarParts_SM?hash=item3a558a5cd9


 Naw, something more like THIS:

http://cgi.ebay.com/ebaymotors/85-8...r_Truck_Parts_Accessories?hash=item414b3caa91


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## Woodsmith (Jun 5, 2008)

vpoppv said:


> Naw, something more like THIS:
> 
> http://cgi.ebay.com/ebaymotors/85-8...r_Truck_Parts_Accessories?hash=item414b3caa91


Yebut look at the price!


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## vpoppv (Jul 27, 2009)

Woodsmith said:


> Yebut look at the price!


 But it's purdeee.....
Yeah, I wasn't looking at the price, the whole point of the thread, but it would be plug and play for a Fiero, and solve the mechanical aspect of the whole operation. Of course, the TPS needs to be 0-5K. Mine is SUPPOSED to be 0-5K, but ends up closer to 200-2K....


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## Woodsmith (Jun 5, 2008)

Yes, the MR2 one works out at 6k so it is close enough and is also plug and play for MR2 converters.

I think jackbauer is using the one that was standard on his BMW too.

It becomes a good reason to double check the parts on the ICE before getting rid of it.


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## Stunt Driver (May 14, 2009)

2 cheap options for you guys:

1 - rip pot box out of forklift. It has safely switches for open/close pedal, and standard potentiometer that can be swapped for correct value. Thing is built to last. I bit large, but durable. It is on the picture.

2 - used myself, discussed above, less pretty but compact - TPS from scrapped ICE. For mine, wiper used to measure from 1k to 6k, so I had to file off some restricting plastic, so wiper can go further. Now it is 0k to 5.5k appr, enough for Alltrax to avoid High/low pedal disable feature not to kick in. I will not post picture of mine, because it turned out ugly but TPS is built to last in ICE, where heat, dirt, oil and vibration are essential. I am not expecting it to fail. Also reused mating connector


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## Dave Koller (Nov 15, 2008)

Ok so here's what I am doing as we speak - ( I have a pb6 installed) BUT :

Conductive plastic element (right on Tesseract  ), sealed ( Mouser - I think even Digi-Key) 5 K pot. 270 degree pot ( give or take some degrees) figure the circumference (minus the lost degrees) needed for your throttle distance. Let's say 2 inches full on to full off on pedal. 

Make three disks about 1 inch in diameter. And two about 7/8 ths. (I can't draw on this old computer - so bear with me) put them together so you get two side by side pulleys.. one holds a wire wound one direction ( wire to a spring ) the other holds the throttle cable.. put it on the shaft of the pot and set screw it to the shaft... ( I know hard to see) err like a tape measure. pull one side (throttle) and it unrolls - the other side rolls up the spring. It is just a poor mans version of a pot called a "string" pot.. 



It rolls about 2 inches for 270 degrees of turn and springs back just like a lever but slicker - and easy to build -- I will post it on my thread when I can build it to show! If this makes no sense then ignore it! 


P.S. sorry this is the best I can do on this computer - PAINT pic... will shoot pics later (we are in middle of storm!)


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## etischer (Jun 16, 2008)

You can buy a pulley instead of making one. I would go with a larger pulley diameter than 1" though. The small bending radius will fatigue the throttle cable. I've gone though a few throttle cables to know. You will probably need bearings unless the pot is rated to have a large side load. With a 270 degree pot, you'll only be getting a 0-2 volt signal instead of 0-10v. I think there are better ways to get a throttle signal. 

This is what my Passat uses.










This would eliminate the throttle cable entirely, and you don't have to worry about return springs, cable clamps, bearings.... You won't even have to have anything under the hood! just buy the entire pedal assembly. The best part is, it is used on millions of cars and proven safe!

I get 2-8 volts out of the pot, this allows me to check if there is a wire break.



Dave Koller said:


> Make three disks about 1 inch in diameter. And two about 7/8 ths. (I can't draw on this old computer - so bear with me) put them together so you get two side by side pulleys.. one holds a wire wound one direction ( wire to a spring ) the other holds the throttle cable..


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## Dave Koller (Nov 15, 2008)

etischer said:


> You can buy a pulley instead of making one. I would go with a larger pulley diameter than 1" though. The small bending radius will fatigue the throttle cable. I've gone though a few throttle cables to know. You will probably need bearings unless the pot is rated to have a large side load. With a 270 degree pot, you'll only be getting a 0-2 volt signal instead of 0-10v. I think there are better ways to get a throttle signal.
> 
> This is what my Passat uses
> 
> ...


That looks great.. my pulley is aluminum and there is a bearing in the box the 2" throw of my throttle needs the small diameter anything larger would be a longer turn for the 270 degrees - as to the cable my old TPS on my truck rolled about the same way - but I will see how much it wears - I may just set it out farther and use a small length of another cable -- same thing but no flex on the actual throttle cable.. my mock up works smooth but it is of wood !!. Large pulley - less flex but then I get 90 degree turn of pot.... err 20k pot lol....

Edit: I was not reading your post Duh... I get full voltage swing as I get *full *270 degree with small pulley.. But as you say the pedal is nice...


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## BHall (Aug 1, 2007)

Thank you all for the replies! Tesseract, thanks for the conductive plastic info too. Several great ideas, but I really like the idea of the ICE throttle body w/ TPS. That is one of those "duh, why didn't I think of that" things. Now the decision is to cannibalize my current ICE throttle body ass'y or find one on eBay.

Once again thanks!

Brian


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