Friday, September 5, 2008

Building a Set of Load Cell Pedals

I've always wanted a better sim racing brake pedal setup than anything I've ever tried on standard and even high end pedals. Using a spring and a potentiometer just doesn't cut it, expecially if you want to heel and toe. When resisted by a spring, but with enough range to operate a pot, a sim racing brake pedal simply moves too far. (Unless it's got a really stiff spring and some fiendishly complex linkage that translates tiny pedal movements into major pot traversal. Translation: big bucks.)

With conventional sim racing brake pedals, by the time you've got some braking, the pedal is so far down compared to the throttle that you haven't a hope of getting your heel on the throttle for that nice blip that makes a smooth downshift.

Enter my nephew Amos (above, hard at work in his dad's garage shop). Amos is a champion shifter kart racer who is hoping to move up to racing full size cars soon. He wants to use iRacing to practice his heeling and toeing. With the standard Logitech G25 pedals we are both using at the moment, this is just about impossible due to its long-travel, squishy potentiometer-driven brake pedal.

I'd read about Todd Cannon's CST pedals in the RSC forums. It seemed that a lot of people were extremely happy with them, and I learned that some real-world hotshoes like Dale Jr. were using them with iRacing.

These pedals are not only gorgeous, with a very elegant design, but they incorporate a load cell for the brake instead of a pot. And Todd sells a nice Do-It-Yourself manual so you can build a set of them yourself. Sounded like the way to go!

In early July of this year I talked this over with Amos and we decided to build two sets of Todd's pedals, one for each of us. Mine would be the prototype.

I ordered Todd's DIY manual and we spent quite a while poring over it, as well as the photos of pedals on Todd's web site. There were beautiful photos of his production pedals, and also a number of shots by people who built the DIY version.

We decided to build a design that was a hybrid of Todd's original DIY version and his new, more sophisticated (and more difficult to build) production version. This meant doing a lot more design work than if we'd just built the DIY version straight from the manual. But it would give us the advantage of more adjustability, particularly in terms of lateral pedal spacing and also in the area of brake pedal effort.

The first day we got together, Amos and I spent almost all day just going over the manual and the photos, making sketches, and creating parts lists in a Google spreadsheet.

Some of the design changes we were making were fairly straightforward, but others required a significant amount of thought, particularly because we were constrained by my chemical sensitivities; I didn't want anything with fresh paint on it in my apartment when we were done, so that ruled out welding.

Todd's production pedals have a number of weldments, so we had to come up with ways to make parts with the same functions but without any welds. Fascinating. And brain-teasing.

Finally we reached a point where I felt ready to start ordering materials and parts. A big order went off to McMaster-Carr for aluminum channel, angle, and bar stock, some steel bar, and assorted hardware. Another order went to China for a load cell, another to California for tiny R/C rod ends, and others to spring and electronics companies. And I spent a good part of an afternoon haunting the nuts and bolts section of a couple of local hardware stores.

In late July we met again at Amos' shop, which is actually the home garage/shop of my brother Nate. This is the same garage where Nate and I built my Cobra in back in the summer of 2000. Nate and his friend John Spain operated a Spec Miata out of this shop for several years. For the last year this is where Nate has been building and developing his hairy TDI Special, a former SCCA Spec Renault that now has a highly over-boosted diesel engine from a VW New Beetle and goes like stink. So to speak.

Anyway, Amos and I got together and finally started cutting metal. Or rather, Amos started cutting metal while I crashed on an air mattress he set up for me because I have this damnable illness that limits my capacity for normal activity to about five minutes an hour.

By the end of the first day, Amos had fabricated and assembled the first pedal assembly, which will be the clutch.

While Amos made the drill press sing, I'd happily assembled the springs, rod ends, nuts, washers, and other bits onto the threaded rods that will be used for all three pedals. The products of our combined efforts are evident in this photo.


msheets said...

Hello? is anyone still out there? How well did the work once they were all dialed in?

Nome: Rui Fernandes said...

Hi, i'm considering/planing to do a set of pedals based on the CST, can you please tell me what is that " white thing" that is between the spring and the "spring stopper!?", is it just a piece of pipe, looks like it? Can you also tell me what type of springs and what type of store's should i search for, i'm not from USA, so names of stores probably don't help much :D

Thanks for some good reading and pictures in this blog :D


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