Handbrake

 One of the things I've had in mind all the way through is the idea of an underdash handbrake. The demo HSR car had a handbrake right under the steering wheel, and while I was unsure about it being in direct range of my knees I couldn't argue with the clean look of the centre tunnel. 

The main issue is that it was still a handbrake, IE it was still the same handle and mechanism that would have been in the tunnel. This made it look odd (as well as the aforementioned knee impact). Other cars have had similar mounted handbrakes, and a quick google suggests there are much better options.

The easiest one to replicate would be the one used in some cars in the 90's. It was basically a pull rod inside a tube, attached to a cable and then on to the mechanism. 

There's a couple of things to consider though, the ratchet mechanism and the mechanical effort required to apply the brakes. 

The ratchet mechanism was achieved by having slots cut into the pull rod on one side only. To release the ratchet the handle would be twisted so the pawl no longer engaged. 

The mechanical effort needed some maths, based on the existing handbrake. The following measurements were made;

1. Distance from pivot to cable channel = 34mm.

2. Distance from pivot to handle centre = 240mm.

3. 19 clicks on the ratchet mechanism for full travel.

4. 45 degrees of travel for the handle.

The distances from the pivot means that the mechanical advantage is 240/34 or 7:1. IE the handle moves 7 times further than the cable. 

The cable travel is Pi x 68 / 8, or 26mm from stop to stop (the actual travel is less than that but I'll maintain the full travel distance for now). The same travel for the handle is Pi * 480 / 8, or 189mm. 

This means that I need to come up with a mechanism that moves 189mm on the lever, to 26mm on the cable. It shouldn't be too difficult, except that it's 'the wrong way'. The pull handle will come out towards the driver (front to back) whereas the cable needs to pull from back to front. A bowden cable would achieve this quite simply, but that would reverse the action without applying mechanical advantage. It would also add friction which would mean more effort and/or pulling distance. More than 7 inches is already a far pull distance, I wouldn't want it much longer.

I need to come up with a solution to apply the reverse in direction as well as operate the change in ratio. Time for some Fusion 360 I think!

Oh, for the ratchet mechanism, I counted 19 clicks on the ratchet. To have the same on the pull handle would mean 19 notches on the 189mm of pull, or 1 every 10mm. Not a problem. I need to have a spring loaded pawl to operate on the solid rod of the pull handle within the hollow tube of the slide. This is a little more of a problem but still not insurmountable. After all, I already have a handbrake with a pawl mechanism that I won't need anymore!