Pedal Design

[Jenni.]

I am working on a group design project to design the pedal box for a Formula Student car. I was just going through the anthropometric data relevant to pedal design and came across this...

"The following summarizes foot control specifications:

Brake...
...
Free play: 30mm
...
Height above accelerator: 30mm for power-assisted brakes, 91mm for unassisted foot operation."

I was concerned as our current design has the brake pedal lower vertically and set further back rotationally. What does height above accelerator mean, is it the centre of the pedal pad vertically or the top of the pedal pad vertically or should it be set forward rotationally?

Also what does "free play" refer to?

Any help would be appreciated, thanks.

[Jenni.]

I am working on a group design project to design the pedal box for a Formula Student car. I was just going through the anthropometric data relevant to pedal design and came across this...

"The following summarizes foot control specifications:

Brake...
...
Free play: 30mm
...
Height above accelerator: 30mm for power-assisted brakes, 91mm for unassisted foot operation."

I was concerned as our current design has the brake pedal lower vertically and set further back rotationally. What does height above accelerator mean, is it the centre of the pedal pad vertically or the top of the pedal pad vertically or should it be set forward rotationally?

Also what does "free play" refer to?

Any help would be appreciated, thanks.

[Mikey Antonakakis]

I'm not exactly sure what context the stuff you quoted was presented in, but generally you want your pedal bay to easily facilitate heel-toe braking, or at least to have enough clearance so shoes don't get caught on anything. I'm pretty sure "free play" means the amount the pedal displaces before the brake pads come in contact with the rotor, basically how much you have to push the pedal before the brakes actually do anything. Also, I think they may be using "height above accelerator" to refer to the rotational position of the pedal. For heel-toe, you want the brake pedal to be closer to the driver than the gas pedal (rotationally or however you want to look at it). This allows the driver to easily pronate his foot and blip the throttle to downshift. One way to test your positioning is to depress the brake pedal with a similar force you'd give for full braking, and check to see that it roughly lines up with the gas pedal. If you take a look in most any car, you'll see that the brake pedal is closer to the driver than the gas. If you don't really know anything about heel-toe braking, it's a way to use two feet to accomplish a task needing three feet: downshifting while braking. To do so smoothly, you have to put pressure on the brake pedal, depress the clutch pedal, shift, and blip the throttle, then release the clutch pedal. You use your right foot on the brake pedal, your left foot for the clutch, then roll your right foot over to the gas pedal while still maintaining pressure on the brake pedal. So that's one of the main reasons you want the brake pedal closer to the driver, as well as to avoid accidentally hitting the throttle when you go for the brakes.

Maybe a picture will help:

http://a332.g.akamai.net/f/332/936/12h/www.edmunds.com/media/advice/youngdrivers/heel.toe.downshift/heel.toe.2.500.jpg
Here's an article that explains it better than I do:
http://www.edmunds.com/advice/.../119593/article.html (http://www.edmunds.com/advice/youngdrivers/articles/119593/article.html)

[Jenni.]

Ok thanks, that's cleared it up for me. I must have got my rest position angles the wrong way round so I'll go and take a closer look at that. We're not having a clutch pedal therefore this is not crucial for us.

Just for clarity, the quote is from an anthropometrics book called "The Measure of Man & Woman" by Henry Dreyfuss Associates. It has a section on vehicle design and the quote was from a section entitled forces for hand and foot controls.

[Bazanaius]

Check the type of vehicle your reference talks about. I'd like the brake pedal in my racing car to have as little free play in it as possible.

[ffrgtm]

If you are not using a clutch pedal it is probably best to take advantage of the fact that you can now easily use left book braking. Space the pedals as they would be in an f1 car.. gas directly in line with the right heel (as it normally should be, even if you had a clutch) and the brake very slightly offset to the right of the left heel. Practice left foot braking until you develop the sensitivity that your right foot already has and you will be MUCH faster. Left foot braking is undoubtedly the fastest way to drive, and this is even more so true in an autocross style competition.

Woohoo first post!