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speedo sensor calibration
grahamgg - 7/4/09 at 10:55 AM

I have a new set of smiths telemetrix clocks to fit, I didn't fancy fitting magnets to the prop flange so i plan to drive the sensor from the original cable drive.

It is a manta 1.8 gearbox and I have used the rear part of the speedo and replaced the cogs with a round plastic disk that will hold the magnet.

Question is do you think I need one magnet or two. And what problems do you see in calibrating with this set up.

thanks Graham

speedo drive
speedo drive

02GF74 - 7/4/09 at 11:02 AM

quote:
Originally posted by grahamgg

Question is do you think I need one magnet or two. And what problems do you see in calibrating with this set up.


I see no reason why that won't work.

Number of magnets? Dunno since you do not give any info. about the programming for the speedo.

Quick rule of thumb - mechanical speedos run at around 1,000 turns per mile.

You can use this info to see whereabouts in the range for your smiths gauage it falls and adjust the number of magnets accordingly.

I would say any number between 1 and 6 would be in the range.

Another thing to bear in mind is to fit the magnets in such a way to keep the small wheel balance i.e. diametraically opposite if fitting pairs although it probablywon;t make that big a difference, unless your magnets are huge.

maybe drill a hole and fit magent in there?

BenB - 7/4/09 at 11:10 AM

Very much depends how many pulses the dial wants. The Racetech one I've used required ridiculous amounts of pulses so I ended up having about 32 pulses per wheel revolution (any less and it wouldn't work).... I would have though you'ld need minimum 2 but ultimately it's a case of trying and seeing!!! Are you using the standard sensor with your magnet / speedo combo? Some speedos are very choosy re sensors as well!!!

hicost blade - 7/4/09 at 04:24 PM

Hello. I fear you have over complicated this a bit too much. You do not use magnets with this type of sender as it is a field effect sensor. This type picks up on bolt heads and needs four pulses per revolution. The pulses can be checked by powering the unit up without connecting it to a gauge (brown 12V+ and blue 0v) as every time the unit pulses the built in LED on the back will light up. You can just pick up on the bolt heads on the prop shaft quite easily without modifying it at all. The end of the sensor needs to be within 2mm of the bolt heads to work.

I hope this helps

Dave

grahamgg - 7/4/09 at 07:50 PM

quote:
Originally posted by hicost blade
Hello. I fear you have over complicated this a bit too much. You do not use magnets with this type of sender as it is a field effect sensor. This type picks up on bolt heads and needs four pulses per revolution. The pulses can be checked by powering the unit up without connecting it to a gauge (brown 12V+ and blue 0v) as every time the unit pulses the built in LED on the back will light up. You can just pick up on the bolt heads on the prop shaft quite easily without modifying it at all. The end of the sensor needs to be within 2mm of the bolt heads to work.

I hope this helps

Dave


cheers Dave, no need to hunt out the magnets I bought about a year ago. Just tested the sensor and it picks up on bolt heads, I,m staying with the speedo drive, dont fancy pulling the tunnel off and fabricating a bracket.

graham