Accelerator Pedal Sensors

Technical discussion on converting internal combustion to electric
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Johny
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Accelerator Pedal Sensors

Post by Johny » Tue, 09 Sep 2008, 21:20

Has anyone investigated stock standard fly-by-wire accelerator pedals for use with EVs? Many modern cards now use electric throttles.
These Ford F250 pedals are inexpensive on eBay but I do not know anything about resistance etc.
Ford pedal with sensor

Edit: Replaced link
Last edited by Johny on Fri, 01 May 2009, 12:06, edited 1 time in total.

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Accelerator Pedal Sensors

Post by Benonymous » Tue, 09 Sep 2008, 21:27

Looks like a Hall Effect sensor to me. Cheap enough to get one and pull it apart.

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Post by Johny » Wed, 10 Sep 2008, 18:16

acmotor is using an industrial conductive plastic position sensor.
I inquired around for prices and they are generally pretty expensive however this one lands for just less than AU$200.
It's got a 50mm travel and is equivalent to a 5K pot.

        Dear John,

        price for CLP 13-50 R5K or 10K is Euro 79,40 /pcs,
        delivery: CLP 13-50 R5K is available in week 42
                     CLP 13-50 R10K is on our stock (subject to prior sale)

   shipping charge to Melbourne:   UPS Expedited Euro 135,45
                                   Airpost Parcel    Euro 29.05

        best regards
        Regina Eiglsperger
       
MEGATRON ELEKTRONIK AG & CO.
INDUSTRIESENSORIK
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Tel.       ++49 89 460 94 116
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Accelerator Pedal Sensors

Post by Johny » Wed, 14 Jan 2009, 01:41

I'm still procrastinating on accelerator sensors.
Does anyone have experience with an off the shelf petrol engine throttle sensor like this one?
eBay Throttle sensor

Like, can you mechanically interface it with an accelerator arm (mine is not a cable) and what does it output.
Last edited by Johny on Tue, 13 Jan 2009, 14:42, edited 1 time in total.

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Accelerator Pedal Sensors

Post by Electrocycle » Wed, 14 Jan 2009, 06:13

usually a throttle position sensor for an engine is a 5 or 10k pot which gets a bit under 90° travel from the throttle cable / pulley.
Generally they mount on the end of the throttle shaft.

Most of them have some sort of simple coupling that mates up to a slot in the end of the throttle shaft or a small arm.
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Accelerator Pedal Sensors

Post by Nevilleh » Thu, 12 Feb 2009, 15:12

If you want to make a cheap - and nasty! - sensor, you can buy a 5K wire wound pot from Dick Smith for $9.00! Don't know how long it would last, but if you greased the bushing it might be OK.
Thinking about it, the shaft travel is 270 deg, so you'd probably want a 10K one and just set it up to use half the travel. Should be able to get 135 deg without too much trouble.
I wonder how hard it might be to use a fet as a variable resistor?

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Post by Electrocycle » Thu, 12 Feb 2009, 15:51

you can do that, but you still need to drive it from a variable source (like a pot!)

On the bike I have a hall effect throttle, which gives 0-5v output, but I needed a 0-5k input to the controller (it's actually 0-5v but has an internal pullup to 12v so it works with a 5k pot)

I made a little transistor circuit to translate between the two.
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Post by Johny » Thu, 12 Feb 2009, 17:06

Since my original post the ongoing search for a long life solution has unearthed this device:

Linear Motion Control

It only has 13mm travel but a bit of mechanical work should adapt that to most accelerator systems.
Rated at 1 million full cycles and 5 million dither cycles.
At under $30 AU it is easily the lowest cost of the conductive plastic sensors that I've found. Comes in 1K, 5K and 10K.

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Post by evric » Thu, 12 Feb 2009, 17:19

Looks good, but zero stock in Australia...
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Post by Johny » Thu, 12 Feb 2009, 17:39

Yes, but a few months ago I ordered a current sensor which wasn't stocked in Australia and it still only took about 5 days to arrive - so they're pretty good as long as there is stock somewhere.

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Post by Thalass » Fri, 13 Feb 2009, 08:58

I was thinking about this sort of thing, back when I wanted to convert a bike (not practical, though). I was going to scavenge a slotted wheel and photo interrupter from a mouse, with an up/down counter and DAC to put out a reasonably smooth variable dc voltage. My thinking was that the last thing you want when you're going 80 on a bike is that throttle pot to get noisy and start getting jittery on you! It'd be like a bucking bronco haha.

Seeing as I'm going to convert a car now, it's less of an issue. It was probably too junkyard-warsy to work out, though.
I'll drive an electric vehicle one day.

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Accelerator Pedal Sensors

Post by Nevilleh » Fri, 13 Feb 2009, 14:24

Just out of interest, I pulled an EVT scooter controller apart to see how they do it. The throttle cable disappears into the cast Al housing. If you pull it right out you see a 6 mm steel pin with a slot for the end of the cable and it is pulled back in by a fairly powerful spring.
Dismantling the thing shows an infra-red led pointing at a phototransistor and sliding back and forth in the gap is an aluminium wedge connected to the throttle cable pin/spring. So as you open the throttle, the wedge lets more and more light across the gap. Pretty basic, but it works very smoothly. The steel pin supports the wedge and slides back and forth in a brass bush. It has a bit of grease on it and a rubber boot covers the whole thing from the outside.
I would think the phototransistor could simply be connected to the pot terminals on the controller - there must be a pull-up resistor inside - collector to + and emitter to gnd and it should work easy as.

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Post by Electrocycle » Fri, 13 Feb 2009, 15:55

My twist grip throttles cost $10 from Oatley electronics, and give a 0-5v output.
They're weather proof and have a hall effect sensor and magnet in them.
Doesn't get much simpler!
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Accelerator Pedal Sensors

Post by EVLearner » Sat, 14 Feb 2009, 18:08

I must admit the first thing that came to my mind was a noisy (carbon)pot, and the second thing wasa conductive plastic pot, which I used in several projects, but.... they are more expensive. The photo conductive resistor sounds good and the moving parts are minimised, as does the Hall effect resistor/resistor.

Something like http://www.vishay.com/docs/57001/9701036.pdf could be a good starting point.

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Post by Tritium_James » Mon, 09 Mar 2009, 17:07

We've used an electronic throttle pedal assembly from a late model Honda Civic in the Porsche conversion. It's sealed, robust and has dual redundant outputs on it.

You supply each section with 5V, and section A puts out 0.5 to 2.0V, and section B puts out 1.0 to 4.0V. B always = 2*A. This way you can cross check that you've got a working throttle, and that no wires are shorted to ground, 5V or each other. I made a little adapter board (micro + DAC) that takes the pedal input and puts out a 0 to 4.5V DC that the ACP motor controller requires - this bit is obviously no longer redundant.

The pedal wasn't that cheap, I think we paid about $200 from the wreckers (make sure you also take 6" of the wiring harness, it's got a weird connector!). Honda wanted $400 for a new one, and won't sell you the connector without buying a complete under-dash harness subassembly. On the other hand, it's bulletproof. I'm sure some of the pedals from other manufacturers would be cheaper.

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Post by acmotor » Mon, 09 Mar 2009, 19:57

Great information there TJ.
Do Honda use the dual sensors for fault detection or redundancy ? The former makes most sense to me.

If you are accepting both inputs to a micro then in software you made the 2:1 check (plus a few others like read back DAC analogue and cross check) then run WDT to reset including output disable to zero with a status line to ACP controller then it would be fairly secure. For safety your are looking for self diagnostic cross check not redundancy ?

Sorry, just thinking aloud. You've probably got all that covered. Image
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Post by Tritium_James » Mon, 09 Mar 2009, 21:10

acmotor wrote: Great information there TJ.
Do Honda use the dual sensors for fault detection or redundancy ? The former makes most sense to me.

If you are accepting both inputs to a micro then in software you made the 2:1 check (plus a few others like read back DAC analogue and cross check) then run WDT to reset including output disable to zero with a status line to ACP controller then it would be fairly secure. For safety your are looking for self diagnostic cross check not redundancy ?

Sorry, just thinking aloud. You've probably got all that covered. Image


Well I'm not sure what Honda's intentions are, but I'm guessing fault detection. The car throws a fault code if it's not plugged in when you try to start it. I don't think you would continue to drive if you detect a discrepancy while moving - which of the pair of sensors do you assume is the correct one? The only option is to start coasting.

The problem with the AC Propulsion motor controller system in the Porsche (this won't be a problem with our controllers) is that 0V on the throttle input = full regen. So, even if I detect a fault in the throttle, I can't tell it to go to zero, you might be doing 120km/h on the freeway at the time and getting unexpected full regen is a bit too exciting! Unfortunately, 'zero' is around a 1/3 of pedal travel, but it moves around a bit depending on speed. My little micro board has no way to know where 'zero' actually is. So in that car, I'm ignoring any errors. It's still more reliable than the bodgy linear pot arrangement that was in there before.

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Post by acmotor » Mon, 09 Mar 2009, 21:16

As you say, probably historical now, but does the ACP controller have a simple disable line you can pull on with your micro rather than trying to find zero torque ? OOps, maybe asking too much ?
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Post by Tritium_James » Mon, 09 Mar 2009, 21:54

Yes, it does, but it's on a different connector and it was too hard to get at. The system is a mess.

I'm currently waiting for my thermal testing to stabilise for the waterblock on our new controller, so I've got plenty of time to make posts on here :)

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Post by Johny » Wed, 22 Apr 2009, 16:41

Electrocycle wrote: My twist grip throttles cost $10 from Oatley electronics, and give a 0-5v output.
They're weather proof and have a hall effect sensor and magnet in them.
Doesn't get much simpler!
Have you ever pulled one apart?
Do you think it could be adapted to use in a Car?

Sorry if this is a "do this for me" question but I haven't seen one and my current sub-project is to get an accelerator solution that is:
1. Reliable
2. Cheap
My bias up to now has been toward a Ford style pedal and sensor system (first post on this thread) but the boss has told me that she doesn't like the pivot-from-top accelerator pedals. I agree but I figured I could adapt... Nope - I'll keeping looking.

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Post by Electrocycle » Wed, 22 Apr 2009, 17:45

yep, it has a magnet mounted on an angle next to a hall effect sensor, so as the grip rotates the magnet gets closer to the sensor.
It'd be easy enough to modify one to be driven by a throttle cable, or build a similar setup with some ICE throttle parts (although then you could just use an ICE throttle position sensor as well)
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Post by Johny » Wed, 22 Apr 2009, 17:59

My donor is from 1965 so the existing throttle didn't take sensors into account.

Basically I either replace the whole pedal or keep it and mount something equivalent to a potbox on the engine side of the firewall.

I have about 30-40mm of linear "push-pull" from the existing setup.

This uses a rod going east-west across the firewall which turns through about 90 degrees. This rod/shaft has a fixed arm on the firewall side near the carby about 50mm long. This connects to an adjustable linkage about 100mm long that connects to an extension of the throttle shaft on the carby - the carby throttle runs north-south. It's typical Hillman style. Similar to Cortina 1960s but no ball joints.
I should just photograph all this...

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Post by Electrocycle » Wed, 22 Apr 2009, 19:19

You should be able to put some sort of pot on the 90° linkage just behind the pedal, otherwise it'd be easy enough to convert it to a cable setup and use a normal potbox or buy a second hand throttle body from an EFI engine.
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Post by Taffy » Wed, 22 Apr 2009, 20:42

Have a look at what this guy did on DIY EV:
http://www.diyelectriccar.com/forums/sh ... 568p2.html

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Post by Johny » Wed, 22 Apr 2009, 21:29

Yes, that looks interesting. Food for thought. Thanks Taffy.

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