Wednesday, September 10, 2008

Actuator Fulcrum: the Bogey Part

Throughout the entire project up to this point, there has been one component that was our "bogey part". This is the assembly that we are calling the load cell actuator fulcrum.

Part of the reason for this being such a head-scratcher is that there are no photos of Todd's production pedals on his web site that show this part. And it doesn't exist in his DIY design.

So we had to infer not only the function of the part, but its configuration.

We spent a considerable part of the first day of the project (the design day) brainstorming different ideas for what this part should look like and how to make it. We made several sketches, and finally settled on a design and ordered the materials.

But as the project went on, each time we looked at this part, we found ourselves reconsidering its design, trying to come up with something that was going to be easier to build and yet properly effective.

In the end, this past weekend, after yet another round of reconsiderations - which included perusing a variety of specialty bolts on McMaster.com - we ended up settling on a design which was essentially the same as one of our early concepts.

Amos started cutting metal. He said it was annoying to do all the hacksawing this part required (the steel bar stock we had ordered was bigger than necessary) and he seemed to dread drilling and tapping the necessary holes.

He even fired up his laptop and looked up on the Internet to find the drill sizes for the 10-32 and 8-32 threads he had to tap. Of course, these are number drills, and naturally we found that his dad didn't have any number bits. So he had to make do with inch sizes, which was even more annoying.

But by the end of the day Amos said that the process had been incredibly fun and satisfying. And he'd produced a part that was simple, elegant, and (we hope) effective.

Isn't it pretty?

4 comments:

thren said...

Is there a reason other than good looks for the black knob?
I'm thinking of using a nylock nut
and a piece of threaded rod with a
piece of round welded to it as the
fulcrum ?

Alisonnic said...

You could use any kind of knob or nut (or even a wing nut), as long as you can use it to clamp the fulcrum to the angle iron. See the top photo on the page "The Actual Wing Nut."

If you use a different design for the fulcrum, just make sure it will not rotate horizontally when you operate the brake pedal.

We used a rectangular block for the main part of the fulcrum to prevent it from rotating. It slides through the wide slot in the flat bar attached to the load cell, so it can't rotate horizontally.

This makes adjustment very convenient. But since you don't do a lot of adjusting of this part - once it's set, you probably won't adjust it again - our design may be overkill.

Olivier said...

What kind of hardware parts did you ordered from mcmaster to make this part ?

Alex said...

if this fulcrum is a pivot point, and the load cell's bolt is the "load" point, at what point of the slotted steel bar is the force being applied to? I'm trying to measure the lever forces of the whole break so I can know how "hard" it will be on my model before constructing it.

great work by the way! :)