Rally speed probe?

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Rally speed probe?

Postby Joose on Sun Apr 24, 2011 2:36 pm

Hi All,

does anyone know how to wire up one of these?

Image

its a rally probe (apparently) speed sensor. Its seems to be a hall-effect sensor which uses magnets to work out the speed. The problem is, I dont know how far the sensor should be from the magnets, how many magnets I should attach to the driveshaft, how much space to leave between magnets or even how to attach the magnets to the driveshaft (epoxy? something else?). Has anyone seen or installed one of these before?

Also, I dont know which wire is for what. I got no wiring diagram or instructions with this, but I have a blue wire, a red wire and a green wire. Does anyone have any ideas which are for what?

Thanks in advance!

Gary
Building: 4AGE 20v Locost SA
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Re: Rally speed probe?

Postby muller on Mon Apr 25, 2011 9:18 am

Most people mount 2 magnets, 180 degs apart from each other with epoxy glue.

You want the sensor as close as possible without touching the magnets, so pick a location free of obstruction where you make a solid mount for the probe.

The 3 wires are
Power
Earth
Signal

I'd guess Red is power, but you will have to try out the other 2 and swap them around to see which works.
(I would go with green = earth and blue = signal for a first attempt)
Anton

Race car 1: Birkin IRS 4AGE 20v (TLR class B - B10)
Race car 2: Birkin IRS 4AGE 20v (TLR Class B for SO - B20)
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Re: Rally speed probe?

Postby Joose on Tue Apr 26, 2011 12:23 pm

thanks for the reply muller! Another question though with the magnets: There seem to be three lots of them, arranged as follows:

Image

There is what appears to be a backplate with double sided tape on it with two small round magnets on attached to it. These two small magnets can be separated from the backplate and they have a black surface on the underside, like this:

Image

Do you have any idea why the backplates have double-sided tape on them? I would think that I just need to attach the two small round magnets to the driveshaft, but then why have they included four backplates with SIX(!!?) little magnets on them? :?
Building: 4AGE 20v Locost SA
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Re: Rally speed probe?

Postby muller on Tue Apr 26, 2011 4:23 pm

You will need to calibrate the speedo in any event so you could theoretically use any number of magnets. I would guess that more magnets might give you a stabler speed reading but dont have any real idea.
Anton

Race car 1: Birkin IRS 4AGE 20v (TLR class B - B10)
Race car 2: Birkin IRS 4AGE 20v (TLR Class B for SO - B20)
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Re: Rally speed probe?

Postby craigsez on Sat Apr 30, 2011 10:21 am

Hi,

My two cents,

I used three neodymium magnets from old magnetic personnel name badges, stuck them onto the lobro joint at the diff on one of the drive shafts (IRS Locost) Used the standard 5min Pratley epoxy that you mix from two components, made a bracket and set the pick up to be approx 3-5mm away from the 'highest' of the three(hard to glue them all exactly same height :wink: ) The gap was a bit of trial and error, if you wave the magnets over the connected pick up you can get an idea of how close they need to be to give a 'signal',closer is better but you dont want to risk them fouling.

As far as the manual for my unit is concerned there needs to be at least two magnets and a maximum of 6, I would guess that in practical terms 2 or 3 is best (obviously equal distances apart from each other)

On my dash unit (Koso RX2N) you can set the number of pick up magnets that you have attached and input the diameter of the rotating component that they are attached to....end result is accurate speedo pick up (reads 5km/h under the 'actual' on GPS) and has been rock solid for two years now.

Hope that helps? :wink:

Craig
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Re: Rally speed probe?

Postby Joose on Mon Jun 04, 2012 11:44 am

Okay, so after playing with this sender for a while now, I cant seem to get anything out of it. I have tried all different combinations of power, earth and signal from the 3 wires and nothing - no movement from the gauge in any of the combinations. Does anyone know where I can get another sender that will actually work :P I have a VDO electronic speedometer and when I phone CAI (control instruments automotive), they told me they could only supply me with a gearbox drive and that they dont do the magnetic pickup type. Where did you all get your senders?
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Re: Rally speed probe?

Postby ross on Tue Jun 05, 2012 1:36 pm

I've got a sender, that doesn't need magnets, I used the cap heads on the bolts of the inboard Lobros joint. The reason I have it is because I put it away in a safe place and then when I needed it couldn't remember what I had done with it, :oops: so I bought another one; and then, of course I found the original one. :roll: It has three wires and I have the wiring and set up instructions. Btw' the spacing doesn't matter it counts and you just tell the speedo how many counts per rev. I think the little flat plates you have were intended to be wrapped around the propshaft.
Locost chassis with Toyota 20 valve blacktop and T50 box.
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Re: Rally speed probe?

Postby Joose on Tue Jun 05, 2012 2:04 pm

ross wrote:I've got a sender, that doesn't need magnets, I used the cap heads on the bolts of the inboard Lobros joint. The reason I have it is because I put it away in a safe place and then when I needed it couldn't remember what I had done with it, :oops: so I bought another one; and then, of course I found the original one. :roll: It has three wires and I have the wiring and set up instructions. Btw' the spacing doesn't matter it counts and you just tell the speedo how many counts per rev. I think the little flat plates you have were intended to be wrapped around the propshaft.



Thanks a million Ross, that sounds like just the thing! Could I buy it off you? I presume it will work with a VDO speedometer?
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Re: Rally speed probe?

Postby ross on Tue Jun 05, 2012 4:12 pm

Pretty sure it will work, I'll dig it out and have a look at the instructions to see what it says. I can always ask the guys that I bought it from about it's compatibility with VDO instruments.
Locost chassis with Toyota 20 valve blacktop and T50 box.
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