10 replies to this topic

[MarkWill]

Looking at the article on the fly-by-wire brakes, I see they use potentiometers. Any idea who makes them? Given the inherent releiability issues with certain designs, I would have thought this was rather risky, but I guess history proves me wrong, but I am really curious.

[GrumpyYoungMan]

IMO, As fly by wire throttles have been around years on cars now and have proven pretty reliable, I would actually say they are a pretty reliable system so can't see why it won't work just as well on the brakes.

 

I dont know who would make the potentiometers.

Edited by GrumpyYoungMan, 21 February 2014 - 15:26.

[sblick]

Most hybrids are close to using fly by wire for brakes with push through capabilities. If there is a failure of the electrical systems you can "push through" and get a more traditional stop. Albeit not with any boost.

[Magoo]

Fly-by-throttle pots generally use multiple levels of redundancy -- triple is common. Suppliers are the customary bunch of automotive electrical manufacturers.

 

Personally, brakes don't scare me so much. Steering rattles me a bit. 

[MarkWill]

We have had issues with the wipers on potentiometers generating debris, or else scratching the mating surface to a point where they lose accuracy over time.The ones we use are only guaranteed for about 8000 cycles (although they will continue to give readings way beyond that). In vibration up to 20KHz we always see them skip but, again, I suppose it depends on what sort of accuracy you need and for how long you can live with degrading accuracy. Triple redundancy is used  - you take the two most consistent readings. So are you saying that the F1 cars use "off-the-shelf" pots?

[NotAPineapple]

Looking at the article on the fly-by-wire brakes, I see they use potentiometers. Any idea who makes them? Given the inherent releiability issues with certain designs, I would have thought this was rather risky, but I guess history proves me wrong, but I am really curious.

 

From reading the article, I didn't get the impression that they use potentiometers. Thats was the description of the throttle-by-wire system which has been in place for years.

 

I'd be surprised if they use pots for th brake by wire since brakes are a force operated system not a position one. My guess is that the would use either master cylinder pressure, brake pedal strain measurement or a combination of both to give redundancy.

 

Measuring brake demand using pedal position is the wrong way to go IMO. The position vs torque relationship changes as the pads wear so the same displacement will give different braking torques (on the purely hyrdraulic front axe) at different points in the race. Other effects which stuff up your pedal position vs brake torque relationship are: volume changes due to temperature, deflection in the pads, discs and upright, and air in the system and deflection in the hydrauli lines.

Edited by NotAPineapple, 21 February 2014 - 23:24.

[kevins]

I think I've read somewhere that McLaren Electronics supply a lot of this type of stuff to the F1 grid. I found this page.

 

 

[MarkWill]

Hey, thanks for the link. I will look into them.

[scarbs]

Try this link on the increasingly popular non contact sensor for Fly by Wire throttles.  http://www.gillsenso...formula-1-team/

 

Obviously the brake by wire doesnt use potentiometers, as explained in the text.

[Catalina Park]

I'd be surprised if they use pots for th brake by wire since brakes are a force operated system not a position one. My guess is that the would use either master cylinder pressure, brake pedal strain measurement or a combination of both to give redundancy.
 
Measuring brake demand using pedal position is the wrong way to go IMO. The position vs torque relationship changes as the pads wear so the same displacement will give different braking torques (on the purely hyrdraulic front axe) at different points in the race. Other effects which stuff up your pedal position vs brake torque relationship are: volume changes due to temperature, deflection in the pads, discs and upright, and air in the system and deflection in the hydrauli lines.

Air brakes on trucks are a position based system and not a force operated system. You get used to after you headbutt the windscreen a couple of times.

[scolbourne]

For racing simulations it is common to use pressure sensitive pedals rather than those using potentiometers for best results. I can see no reason why these could not be used in real car applications.

Another alternative to potentiometers is to use optical wheels like used in a computer mouse.

For high end joysticks magnetic field sensors (Hall effect)  have been used.

Edited by scolbourne, 24 February 2014 - 10:59.