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Unread 5 July 11, 00:01   #1
conticreative's Avatar
Join Date: Jul 2008
Default Load cell goes out of calibration

I have a set of inverted G27 pedals with a load cell brake from AP Electric.

While the load cell has certainly been an improvement I have had ongoing problems with it and I was wondering what you guys think.

1) Loss of calibration: Over time, sometimes during a single race but certainly over a few days, the load cell takes more and more pressure to achieve the same degree of braking.
Often, in order to "restore" the calibration I have to snap the brake by pressing it all the way and then let it go suddenly. Sometimes it works better than other times but it works. Then it starts again.

2) I use the bodnar calibration software and when the cell was new the brake would calibrate between 12/700 (more or less). Now it is calibrating between 10/50. I am not sure what the numbers mean but it can't be good.

3) I was driving the Vette at SPA on iRacing and after struggling to calibrate the brakes I was still locking them up all the time. So I started looking at the iRacing calibration tool and the brake indicator.

It looks to me like the brake works fine between 0% and 75% of the travel, but after 75% there is no gradual approach to 100% or full brake, or at least the amount of pressure needed to go from 2/3 brake top full brake is minimal and therefore it makes locking up very easy.

So, this is the problem. What can the solution be? Do I need a new load cell? Could the circuitry be the culprit?

Can I buy a new sensor and rig it on the ap Electric pedal?

Thank you for your help
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Unread 5 July 11, 08:21   #2
Join Date: Feb 2009
Location: UK
Age: 39

I've had similar problems with my AP Electric mod in the past. Over the course of a race it would lose calibration, requiring more and more pressure to achieve 100% braking and only unplugging the pedals and plugging them in again would restore it to the original values.
I bought a standalone pedal controller from Leo Bodnar and, once calibrated, the problem went away:

After about a year though, the pedal response started to get worse in a similar way that you've described. I ended up buying a set of Fanatec pedals, but before I did so I was considering getting a replacement load cell from here, as I've read that they do wear out after a while:
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Unread 5 July 11, 20:18   #3
conticreative's Avatar
Join Date: Jul 2008

Thank you John, I never came across the Simshop before (amazing considering the searches I have done so far. maybe they should work on their SEO a bit) but that looks to m,e like a great lead. Incidentally, I already have the bodnar box (cable really, it hasn't been a box in a while) so that part is taken care of.

Incidentally, anotehr thing my pedals do that could partly the cause for the failure is that in the calibration software I can see all three colored bars "spyke" when I press any of the pedals.

For instance, if I press the accelerator pedal, the brake indicator will move 3 to 10% on average. Lately even pressing the clutch made the brake and the gas move a bit.

Plus, at times the gas pedal will fluctuate between 100% and 90% or so when fully pressed. I remember a Lemans race where this was a huge factor when it started happening in the middle of the race, robbing my car of at least 20mph on the Mulsanne straight.

Incidentally, I read someplace that WD40 helped this a bit and indeed it did. Also, after posting yesterday I simply unplugged and plugged the cables back in and the problem diminished considerably.

I would love to be able to rewire the whole thing with better quality wiring, but I am unsure on how to handle the USB plug part of it. The rest should be easy enough but the plug I have no idea how to approach.

Anyway, I'd love to buy some fanatec pedals and the cost would not be out of the question. Is going to be harder to try to run the purchase through my wife

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Unread 11 July 11, 00:12   #4
Join Date: Jul 2008

Just to inform: The Sim Shop sells a replacement load SENSOR (or a strain gage) not a load CELL.
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Unread 16 July 11, 18:50   #5
epicname's Avatar
Join Date: Sep 2007
Location: Scotland
Age: 37

maybe the brake fluid is getting too hot
happens for real...brake fade!
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