Brake over travel switch

[Gupta]

I was thinking of using brake fluid level indicator for the BOT switch. The brake fails when the fluid level drops below a certain level. So i will make the switch actuate when the fluid drops below that level rather than the pedal over-travelling. Is my thinking right? Will it work for sure??

[Gupta]

I was thinking of using brake fluid level indicator for the BOT switch. The brake fails when the fluid level drops below a certain level. So i will make the switch actuate when the fluid drops below that level rather than the pedal over-travelling. Is my thinking right? Will it work for sure??

[TMichaels]

Read the rules. It's not allowed. How should it be tested at scrutineering?

Regards,

Tobi

[A Richards]

HAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA. Good luck with that one. Brakes can fail for more reasons then them just running out of fluid man, come on. READ THE RULES.........................

[Gupta]

Thanks people..i knew someone will find it funny but we are participating for the first time..i will actuate the switch only when brake pedal over-travels

[A Richards]

Well its about time you read the rules for the first time yeah. They will answer most of your concerns and queries.

[Steve O]

To offer a post slightly more productive than just bashing, something like the system you had posted above would be much more complicated to make and more prone to failure. Being a first time team, complication and failure are already abundant, so why add more headaches? Also as it has already been noted, the rules do specify a break over travel switch not a low break fluid switch. Just mount a limit switch on your break pedal assembly and use relay logic, or mount a toggle switch for a slightly less neat but equally effective switch.

Steve

[Geoffct]

Ideally the BOT switch should kill the engine under any brake failure mode. Accounting for all modes of failure is not possible, but activating the switch on the pedal is standards and accepted. Activating on low fluid is NOT accepted.

Given some of the pedal designs I have seen I would also activate above the pivot in case the bias bar or pedal fails.

[Gupta]

Okay..now i just want to confirm one thing..according to latest rules of 2008 will it be ok to use a push-pull switch in front of the brake pedal and connecting it in series with the dash ignition switch. In this the switch will be actuated only when the brake pushes the switch and there is no scope for the driver to pull the switch..so will it pass tech easily??

[A Richards]

I cant see why not

[Gupta]

Actually I just spoke to some guy who suggested me to cut the igntion line coming from the ECU itself..cutting off the dash ignition switch at high speed n rpm may damage the ignition switch

[Steve O]

I'm not sure I follow that...

He may be referring to inductive slap back which should not be a problem in this instance at all.

Either way, I would not run anything all the way to the front of the car carrying current that is powering the car, it is dangerous and a waste of energy to travel through all the wires. For all switches up front you should only have low current battery power. Use a relay and use the switching connections on that to allow or not allow power to the rest of the car. I recommend this relay being connected to the switching wire for the rest of the relays. That means power going through this relay turns on the other relays allowing power from the battery to turn on the fuel pump, ecu, etc. When you stop current flowing through the relay it shuts off the fuel pump and cuts ignition as the rule book requests.

This can be done through positive logic or negative logic. The simplest way would be positive logic where you hook up the negative switch terminal from the relay to the BOT switch to a NC terminal with ground. That then completes the switching loop and turns on the relay. However, if the wire going to your BOT switch gets damaged and is shorting out, your BOT switch will not work. For this instance you can use a negative logic setup, where you use two relays to create a feedback loop that keep each other on. You tap off the feedback loop and run that up to your BOT switch NO with ground. Now when you push the switch it grounds out and kills the feedback loop killing power to everything. If the wire was to short out before the BOT switch, the safety would still kick in and shut the car off. For this setup you could run a momentary switch at the pedal and another momentary switch outside the drivers reach that "primes" the relay feedback.


Steve

[vandit]

@ gupta

since you have already understood your porblem, i thought i should share my team experience about BOT in the competition to give you insight as to what all types of brake failures are there...

in australia'06, our team , on the very first attempt at braking event broke the pivot mounts of brake pedal and the brake pedal went and killed the engine through BOT....now if we would have used a fluid level indicator switch as suggested by you , the Engine would not have been cut off, and it could have been disastrous...

so please whatever you do with your car, do it with the intentions of making your driver safe and dont do just for conforming the rules....you drivers life is in your hands...

a simple tic-tic switch from RC cars or any electronic toy can be used, or even you can use industrial push-pull switches use to switch off anything...

[Renato]

steve

could you send me a diagram of this system??

i didn´t understand well how it works.

thanks

[Steve O]

I'll draw one up within the next couple days and post it. Remind me in a PM if you don't see it up by the end of the week.

Steve