Hi.

Anyone have a program for the empeg that could be adapted to output vechicle speed?

The reason i ask is i am changing my gearbox for one out of a car that uses the abs sensor on the diff for its speed signal, where as my car normaly uses a sensor on the gearbox.

My diff generates 97 pulses per minute and i run 245/40/18's

any help would be good.

Thanks

C.

should have said pulses per rev on the wheels.

C.

I dunno, but if your empeg crashed while you were driving...... you'd be rolling at 60 mph with your speedometer reading 0 mph so (just guessing here) the car cuts the gas because it thinks your stopped etc etc etc.

Or, if you could tweak the pulse speed on the empeg itself WHILE driving. Crank it up a notch to tell the car you're going faster and need more gas so you can get a boost......... or something. I know nothing about cars, haha.

Yeah. Making your empeg an integral part of the car system like this isn't a good idea. A better idea than using the empeg would just be to use a PIC/AVR/whatever to do the conversion.

Forget the empeg get a cycle computer

Strip the magnet out of the bit that fits to wheel spoke and stick it inside your wheel. then mount the sensor somewhere so it can pick up on the magnet.

Then extend the cable which is a bit tricky then mount the cycle computer in the car set the wheel diameter and there you go

You running 18,s should cause no problems as this is a common thing in caterhams and we run 13's.

the other solution is to get a small gps with serial out and it should be able to squirt speed out down a cable to the empeg.

Or use my solution borrow a GPS and go out and work out what revs in what gears are what speeds. the you just use the rev counter.

You running 18,s should cause no problems as this is a common thing in caterhams and we run 13's.


That is surprising to me.

In my experience, I have found that cycle computer pickup sensors start skipping at speeds above 45-50 mph.

This is not because the computer can't digest the information quickly enough. It is a matter of the linear velocity of the magnet as it passes the sensor. On my bikes, I move the magnet as close to the wheel hub as possible, thus slowing the speed of the magnet to where the sensor will read it reliably.

If the magnet is mounted out near the rim, it passes the sensor so quickly that at 50 MPH (coasting down a steep hill -- I'm not that fast a pedaler!) the speed shown on the computer fluctuates wildly.

Hmmm... 13" wheels on a Caterham, figure total wheel diameter including tire to be about 20". If (hypothetically, of course) the magnet were mounted on the tread of the tire, at 50 MPH the magnet would be traveling at (are you ready for this?) 50 MPH as it passed the sensor, or 73 feet per second. Since the magnet is not going to be mounted at the 20" diameter part of the wheel, but more realistically at about a 12" diameter point, the linear velocity of the magnet would be 12/20 of 73 fps, or about 44 feet per second.

On a bicycle wheel, with the magnet mounted out near the rim, we are looking at about a 26" diameter magnet placement, out of the total 28" wheel diameter including the tire. So at 50 MPH on the bike, the magnet would be traveling at 68 fps, and I know from experience that at that velocity things get dicey.

It would seem that perhaps 60 fps is about as fast as the magnet can travel and still be picked up reliably by the sensor.

That would translate to abour 70 MPH on the Caterham, assuming of course that you are indeed placing the magnet on the outer part of the rim, and not down closer to the hub.

Do you indeed get reliable results at high speeds? If so, where are you placing the magnet?

tanstaafl.

some bike computers cope others don't. i don't run this i have a blob on the rev counter that is 70mph but even that varies as rear tyres i have are anything from a 185/70r13 to a 175/50r13

You can probably have your speedometer reprogrammed to adjust. Or since it's computer speed control related, for many cars there are companies that will reprogram your car computer to accomodate for changes.

Hi.

Yes i have a chap building a pic that can do it, but i need something quick until thats done.

I don't expect the car to do much over 170mph with the new box

I realy don't think the cycle computer would do it for me.

Thanks
C.

Quicker to wait for the PIC. I doubt anyone on here will have the time to write a program to do it for you.