Comment by beAbU | Hacker News Reader

Comment by beAbU | Hacker News Reader

Parent Full thread

So initially I thought it was just a drum brake that applied the braking force on the face of the drum in stead of on the circumference. But it seems the key invention here is some camming system that automatically increased the braking force as speed increased. So this system supposedly did not require a brake booster as part of the hydraulics.

I wonder what prevented this camming innovation from being transferred to the more conventional drum brake of the time?

I'm not an engineer, but I do have some wrenching hours under my belt. I see a flaw in the design: The two halves of the drum are held together by machine screws/bolts. The braking pressure from the pads is applied directly to these screws. If they are not properly fastened, or if they are loosening over time, then braking force will be directly impacted. A failure could result in a total loss of braking ability. A conventional drum or disk brake is kind of fail safe in that regard: The mechanical pressure from the brake pads is not transferred through any fasteners. I see this design less resistant to poor maintenance practice. Maybe they somehow accounted for this and the article failed to mention it.

The mechanism reads a lot like an admittedly more sophisticated version of what existed in early mountainbiking as the "self energizing" Pedersen brake. More braking for less force, but terrible at dosing. I'd be surprised if this mechanism did not suffer from the same problems.

Leading shoes on drum brakes were self-energizing like the old Pedersen mountain bike brakes. With a leading shoe the pivot point is after the braking surface, so the friction tends to push the shoe harder against the drum. Most drum brakes had one leading and one trailing shoe.

Some motorcycles even twin leading shoes on the front (maybe even four leading shoes with two sided drum brakes). These had issues with modulation like the Pederson brakes. You also had twin trailing shoes when backing up, so you had to squeeze the brakes extra hard then.

> A conventional drum or disk brake is kind of fail safe in that regard: The mechanical pressure from the brake pads is not transferred through any fasteners.

A slight nitpick, the torque applied to the caliper from the disc, through the pads, does travel through the caliper mounting bolts. It's a lateral force rather then a axial one but it does go through fasteners.

On most, no, little to no braking force is taken up by the fasteners themselves. For most designs the calipers sit inside a frame that takes the braking force, and the fasteners simply hold the caliper in alignment within that frame.

This wikipedia photo happens to be from an AMC pacer, but it does show the frame that takes the braking torque load (https://en.wikipedia.org/wiki/File:Detail_of_-_AMC_Pacer_-_r...). The frame is the lighter metal object at the top above the top edge of one of the pads.

I go to pains to not mention torque, because I'm not talking about that. I'm talking about the physical pressure exerted by the pads on to the surrounding structure. The forces involved even when the vehicle is not moving.

Reply on news.ycombinator.com