Brackets and Rods: Precise Machining Required

On October 12 Amos and I got together one more time to work on the pedal project. By the end of the day the pedals would be assembled, standing on their own two feet, ready for wiring.

The first step, though, was dismantling all three pedal units. Amos stripped them right down to the bare minimum, removing all the parts that were bolted on, and some of the parts that were riveted on as well.

He needed to do this in order to drill four very precise holes in each pedal platform. These holes needed to line up with each other, because half-inch steel rods would slide through them to hold the entire assembly together. If any of the holes didn't line up, the pieces wouldn't go together. And if there was any slop in the holes, the pedal platforms would move around when the pedals were pressed.

In addition to the three pedal platforms, there were two brackets, one on which end, to which the legs of the pedal unit would be attached. These, too, had to slide onto the half-inch steel rods.

So Amos had a lot of very precise drilling and hand reaming to do. Since the drill press on hand wasn't really accurate to get these holes dead on, he came up with the plan of carefully slotting the rear holes in each platform and bracket by hand, just enough to allow the two steel rods to go through.

Here are some photos of the completed assembly. He did it! There's no discernable play, yet the pedal platforms and brackets slide freely on the steel rods. Awesome work.

Three Fine Assemblies

With all three assemblies completed, we of course had to line them up on the mockup stand to see how they looked all in a row like soldiers.

Be sure to click on the images to see the larger 800x600 images. These show a lot more detail.

Don't these things look terrific?

The next steps will involve dismantling the pedal assemblies so we can drill half inch holes in the aluminum channel sections for the 1/2" galvanized steel rods that will support the pedal platforms.

We waited to drill these holes until we had completed the assemblies because we wanted to make sure that wherever we ran the steel rods through, they wouldn't interfere with bolt heads or rivets or anything else attached to the sides or undersides of the channel section pedal platforms.

Now that we know where everything has ended up, we can position the holes for the rods with confidence.

After that, all that will remain will be construction of the actual pedal base and installation of the load cell controller and wiring.

By the way, the day after we did this work on the pedal project, Amos totally destroyed the absolute lap record at Rocky Ridge in his stock-engined shifter kart. He won the heat race going away and was charging in the feature when a hub broke and put him out, leaving the way clear for his dad to take his own first shifter kart feature win. With one race day to go, Amos has a healthy lead in the Vermont Shifter Kart Stock 80 championship.

Way to go, Amos!

Pot Mounts and Actuators

No, this has nothing to do with either cooking or weed.

The throttle and clutch pedals work by operating a potentiometer, which is a variable resistor. Each of these will be connected by a couple of wires to the Leo Bodnar load cell controller, which has circuitry to deal with switches and pots as well as the load cell.

The little bracket that mounts the pot to the top of the pedal platform is made from a 3/4" long piece of 1" angle aluminum. The pot is the black plastic box with the little solder tabs sticking out to the left.

The pot actuator arm is made from a piece of gray square plastic rod we ordered from McMaster. The minimum was three feet and we only need about six inches to do both pedals on both my and Amos' (yet to be built) pedal sets, so we have a lot left over! Fortunately this stuff cost about a dollar.

It's also very easy to work. Which is lucky because I drilled the hole for the pot shaft a little bit oversize in the first one I made, so I had to make two more. This took about ten minutes each.

Once we'd cut some 6-32 threaded rod for the pot pushrods we were able to assemble them together with the little R/C aircraft rod ends and 4-40 screws, nuts, and washers, and figure out exactly where we wanted to mount the pot mounting brackets to make sure we got free motion throughout the range of travel of the pedals.

We were also hoping for linearity of operation of the pot, but given the geometry that's pretty much impossible. However, we think that the nonlinearity will be advantageous, with slower ratio at the beginning of the pedal travel and higher ratio at the end of travel.

I think this is wicked cool!

Throttle and Clutch Final Assemblies

While Amos was doing all his work on the brake pedal and actuator assembly, I fabricated the bracket that the front end of the throttle spring would be pressing against.

I also drilled out the rivets in the corresponding bracket for the clutch spring and cut a quarter of an inch off the bottom of the bracket to make it match the length of the new throttle spring bracket, and then riveted the little angle bracket back on.

I did this to lower the height of the front end of the pedal pushrods so the pushrods would be more nearly level. I thought this would look better, and also it fixed it so the up-stop (the large steel and rubber washers at the front of the assembly) were resting nearly flat against the front side of the spring end bracket.

At this point I was ready to assemble the spring end brackets and their diagonal braces to the clutch and throttle platforms. After a bunch of drilling and riveting, the job was done and the throttle and clutch pedal assemblies were complete.

Brake Pedal Final Assembly

More progress! In fact, at this point it feels like we're nearly done.

On Saturday we spent a long day completing and assembling each of the three pedal assemblies.

This day felt different from the previous days, however. At this point we are so far along that there was very little time spent dithering and making decisions, then reconsidering and deciding agaian, as we'd been doing most of the previous days of this project.

Instead, we found that things were falling into place. Both of us simply kept working: measuring, drilling, cutting, filing, riveting, and bolting together. It was a rewarding day!

Amos spent most of the day working on the most complex assembly, the brake. He drilled the pivot holes in the u-bracket that mounts the load cell actuator and then spent some time tinkering with the alignment to try to get the actuator perfectly square with the tongue he'd fabricated earlier and mounted on the load cell.

He also determined where he wanted the u-bracket to sit on the pedal platform, and drilled the holes for that.

Along the way he decided to put a shim under the rear end of the load cell, and then during the alignment process he also made a shim to go between the u-bracket and the pedal platform.

It also took some tweaking to get the spring situated so it didn't flex sideways and hang up on the nut on the threaded pushrod inside it as the pedal is actuated.

By late afternoon the complicated brake pedal assembly - the part of the project that had required the most design work and the largest amount of precision fabrication - was complete.

Didn't Amos do a fantastic job on this?

Hot Shoes

And now, at last, we get to see the pedals in action (sort of).

Here are some shots of the clutch and brake pedal assemblies sitting on top of the mockup floor stand. Don't they look cool?

We haven't got a throttle assembly yet. I know I said we did in an earlier post, but actually that was the clutch assembly masquerading as the throttle assembly so we could gauge the relationship of the throttle pedal to the floor.

In reality, the throttle and clutch assemblies will be identical except that the throttle will have a longer pedal pad to facilitate heel and toeing.

But in our case, the first pedal shaft and platform assembly Amos made has a little bit of play in the pivot between the two, because Amos was learning how to deal with a slightly bent chuck in his dad's drill press. This makes the drill bit wobble and makes it difficult to produce holes that are precisely the right size and in precisely the right place.

By the time he made the second and third pedal shafts, Amos had mastered a technique that allowed him to drill extremely precise holes despite the defective chuck. Since a small amount of side to side wobble is less critical in the clutch than it will be in the throttle and brake (again, for heeling and toeing we want them to be stable laterally) we've decided to use the first assembly for the clutch and use the more precise later assemblies - which have no play at all - for throttle and brake.

Anyway, in these shots you can see how the assemblies will look when finally mounted on the finished pedal stand (which we haven't started building yet).

Amos kindly contributed his shoes so that we could demonstrate the operation of the pedals. The shoes are having a rather hard time heeling and toeing, though, because of the absence of the missing throttle pedal.

The Actual Load Cell

Finally we were able to assemble the actual load cell to the aluminum channel section part that I'm calling the pedal platform, and set all the load cell actuation pieces in place.

The right-hand end of the load cell in these photos is bolted to the pedal platform by two metric bolts that go through holes from the bottom side and into the load cell, which is tapped with metric threads from the factory.

To the other end of the load cell we've bolted a part we made. This is just a flat piece of steel bar stock that is slotted to accept the load cell actuator fulcrum.

The fulcrum projects upwards and the plastic knob, whose stud screws into the fulcrum, clamps the fulcrum to the horizontal section of the load cell actuator. So when you push on the pedal, the pushrod will move to the left (in these photos), rotating the actuator counter-clockwise, and putting upward pressure on the fulcrum.

This will lift the left end of the load cell, which will cry uncle and send a resistence change through its wires to the load cell controller (which has yet to make an appearance in this blog). The controller will notice this change and produce numbers which will, in turn, be sent via USB to the racing sim to let it know you are pressing on the brake - and precisely how hard.

We still need to drill the holes in the steel U-bracket that will accept the actuator's pivot bolt, and also we need to drill holes in the U-bracket and the aluminum channel that will allow us to bolt the two together.

We put these off till last because the size of the fulcrum and load cell and the actuator all dictate where the pivot holes have to be.

At the moment we're debating whether to cut down the top of the fulcrum a little, which will allow us to lower the actuator so the pushrod will end up being more nearly parallel to the top surface of the pedal platform. (See the top photo in this post for the actual position of the actuator and fulcrum once everything's assembled.)

This is just a question of aesthetics, but, hey, aesthetics are important, right?