Prototyping the pedals (27.5 hrs)
The original brake pedals are pretty ingenious, they are light, sturdy, and as small as the designer dared making them. Better yet, I own a set of never-before-used ones already. The left one was a gift from my friend Walter, and it’s an original Brock specimen (1980’s vintage), the right one I threw together on a “slow day” using 4130 steel from my leftover pile.
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| Old and new together |
I can only imagine improving a couple of things. First, I’d like the pedals to be a tad bigger so that I can steel feel them through winter shoes, and second, I’d like to do away with the cross-tubes, this is just a nuisance to have to get over every time I’d like to stretch my legs in flight, and a newly designed pedal set could easily eliminate them.
Initial brake assembly idea
These issues alone wouldn’t justify “reinventing the wheel”, but the availability of CNC tipped the balance in favor of more R&D (research and development), and so it was that I started down another rabbit hole.
My original intention was to use a 3/4” (1.9 cm) U channel. This forced me to carve a lot of relief around the master cylinder base, or it wouldn’t be able to swing properly.
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| A lot of aluminum was trimmed to remove the interference |
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| Close up of the critical joint |
Later, when I tried to purchase a 3/4” U channel, I found that nobody carried it, so had to settle on a 1-1/4” (3.2 cm) wide extrusion. This negated the requirement for the relief, since the body of the master cylinder now easily fits within the channel.
However, I didn't want to design a new bracket since I actually liked its curvy profile, and I rationalized that it would be lighter to boost. So, since I was going to have to machine it anyway, I decided to make it even lighter (read: fancier) by incorporating a few lightening holes.
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| Why not! |
The biggest problem I faced was the length of the bracket. It was just too big for my little mill, so I decided to split the work in two zones, the “brake pedal” half, and the “master cylinder” half.
A small reference hole in the middle of the bracket would tie the two zones together. Because this hole would be the only mean to zero out the mill’s coordinates after repositioning the U channel in the vise, it would be one of the first features to get machined.
This arrangement worked fairly well, given that precision was only needed for looks, rather than fit.
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| First half done. Getting ready to machine the second half. |
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| finished bracket |
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| Spacer had to be machined on the lathe because of the wider U channel |
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| Inch reference marks |
This is how it was done
With all the cool stuff starting to come out of the garage, I thought it would be appropriate to give it a name.
I decided to call it the “EZ shop”.
What do you think?
Anyway... I decided that machining aluminum brake pedals would be too difficult for me at this stage, and that I would start out with welded steel ones, perhaps swapping them in the future.
I started out with 2 different 4130 steel tubes, the big one would become the pedal, while the smaller and thicker tube would become the hinge point, and get welded to the former.
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| 4130 chromoly steel tubing ready to become a brake pedal |
I started working on the hinge by precision cutting the small tube on the lathe, and fitting it to the bracket.
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| Pedal hinge |
Next, I drilled a hole in the big tube the same size as the small one.
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| Creating the mating hole |
The two got welded together, then the assembly went back on the mill for some more drilling on the opposite end. This time I enlarged the hole until the tube was severed, leaving the perfect notch to fit the part that my foot will actually stomp on.
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| Tubes mated and welded together (left), and top of pedal getting prepared (right) |
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| A drill with the same diameter as the tube cut it in two |
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| Tube welded to pedal hinge |
I crosshatched a pattern with the lathe on one end, then welded it in the shape of a capital T.
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| Top tube crosshatched and welded |
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| A view of the whole assembly |
The non-crosshatched side will connect to the rudder cable somehow, I haven’t figured it out yet.
The more immediate problem to solve was how to connect the pedal to the master cylinder in a way that would activate the rudder first, then the brakes.
One option I liked was the way my friend Mike did it, so I came up with a similar design of my own.
Virtual testing of the blade type pedal prototype
The advantage of this design is that the connection between the pedal and the master cylinder is retained even in the aft part of the pedal’s travel envelope, in other words the pedal does not disconnect and fall backward under the rudder’s rearward pull.
I just wasn’t too fond of the size of the “blade”, and decided to go a different route.
I’d use a smaller blade, and concentric tubes to activate rudders and brakes.
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| Smaller, yet much trickier design. |
CNC machining the small pedal tab
The only problem with my new design, as you might have guessed, was pedal retention in the aft region of travel. The tube could just slide off of the rod with nothing stopping it from happening.
The way I solved this new puzzle was to machine a slot on the slider tube and insert a set screw into the rod that stuck out about 0.070” (1.8 mm), and rode in the slot.
Positioning of the screw was critical since I didn’t want it to bear any load during brake applications.
Brake application itself does not require additional items like washers or nuts for the siding tube to press against, but occurs when the steel flange contacts the inner steel rod.
Fine adjustment for length is maintained at 1 turn intervals, by removing the set screw (or the bolt), screwing or unscrewing the steel rod, and reinserting the set screw after the desired position is achieved.
Coarse adjustment is through the 5 hole pattern drilled into the steel flange.
At this stage, rudder throw before brake activation is 2" (5 cm). Should more be required once the coarse adjustment has been decided, the slider's slot can be lengthened to provide more aft travel of the pedal. I will have to complete my wings and rudders first though, before I can confirm that.
Exciting (not!) video shot while machining the slot into the steel slider tube
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| The slot length and position are essentially the brains behind the pedal retention |
Demonstrating the rudder pedal retention mechanism
The prototype bracket served its purpose well. I now know that a shorter one is more advantageous, both in terms of cockpit space, as well as pedal mechanics.
I will redesign it down from 12" (30.5 cm) to just 9.5" (24.1 cm), and machine two new specimens soon.
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