Lotus Elan

Help needed to mount a Monit speed sensor

PostPost by: LarsD » Tue Feb 09, 2016 6:05 pm

Dear all

I have an Elan S3 which I use for classic rallys. I use a Monit rally computer with GPS. Due to restrictions and differencies between the GPS messurements and the local messurements from the Organizers equipment I would rather use a magnetic speed sensor which is more accurate. Normally you mount this close to the wheel bolts/studs in one of your wheels and Monit recommend this solution but I have tried to do this in many different ways with no success. Problem is that my Elan has center bolt and no rotating nuts or bolts in the wheels to use as sense points.
I have tried to find a visible part of the rotating propeller shaft as alternative for the sensor with no luck and also used the donut bolts but forgot how much the donut flex during driving.

Any help is appreciated because the season starts soon

Kind regards Lars
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PostPost by: john.p.clegg » Tue Feb 09, 2016 9:03 pm

Lars
You could mount it on the brake caliper,front or rear and castellate the required number on the disc in situ....

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PostPost by: vstibbard » Wed Feb 10, 2016 6:56 am

Never fit to rear wheels as spinning wheels etc causes accuracy discrepancies.

The four bots holding the disk on to the front hub may be the best option, you may need to modify or mount sensor in the brake dust shield if fitted

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PostPost by: 7skypilot » Wed Feb 10, 2016 9:06 am

I fitted a Monit speed sensor through the front left brake shield, set to count the disc mounting bolts.

It is robust and reliable. The cable is routed through the wing, bulkhead and to the Monit unit mounted on the glove box lid. It's been in place for about three years now with no problems.

Our rules prohibit GPS or average speed, so I have the basic Monit (Q10?) which only gives instantaneous speed information.
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PostPost by: miked » Sun Feb 14, 2016 1:57 pm

Interesting, I have been looking at this the past week as I am sick of mechanical Speedo problems over the years. The cable route is not good. Got needle bounce on an Elan and a total failure on the Plus 2 s. Not yet looked at what it is. Angle drive or Speedo.

I have come to the conclusion that I will go electronic and like the look of the front wheel bolt heads for the disc (as mentioned). Not had a look yet but it seems a tried and tested method. I have been on the ETB web site (link below) and there is some good data about sensors types and fixing etc. I am going to ring next week to see whether to go for just the bolt head or those little tiny magnets that can be mounted. I don't fancy the prop shaft thing. Looks a PITA.

http://www.etbinstruments.com/index.php ... ath=99_110

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PostPost by: patrics » Tue Feb 16, 2016 8:15 pm

Hi,
If you have no restrictions then the obvious thing to do is go gps - I was talking to somebody approx September last year and they were developing a gps conversion for the Smiths speedo but I think they wanted to concentrate on the classic Mini speedo, might go back and see how much progress they have made.

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Steve
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PostPost by: miked » Thu Feb 18, 2016 11:22 pm

Hall effect sensor mounted behind front hub. I had to run the bolt heads flat on the lathe as the 0.5mm dimple in the centre of the UNF bolt and the writing caused double detect on one bolt. Now they are flat I have tested with power and got a single LED signal over each bolts. See lit LED. Spinning the wheel by hand gave 12 pulses per second. Just need to buy my Speedo. Not bothered about originality as the car is heavily modified.
Looked at GPS and looks good but messes with my head (headaches) as does a mobile phone.
I think this will work just fine. Gap is about 2mm under sensor. Cable now protected and clipped in with slack bends and routed back to dash.

Mike :D
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PostPost by: elandoc » Tue May 03, 2016 12:55 pm

That looks great, Mike.

I use a Terratrip 303+ and couldn't figure out how to mount the probe on the front wheel (rushing to prep the car for an event), so it's mounted on a bracket on the diff, pointing to some tab washers I made up on the cv bolts. Surprisingly accurate, actually, considering it's on a back wheel. I also have a probe on the speedo cable, but the angle drive (or something, haven't looked yet) failed last rally (Targa Tasmania). The wheel probe has been wiped out a couple of times over the years, so I'll have another look at the front - yours looks to be an elegant solution!

BTW, I found you really only need an accurate trip computer on a transport stage (no wheel spin there) - I use pace notes on a rally stage.
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PostPost by: LarsD » Mon May 16, 2016 6:02 am

My new solution with a U shaped steel profile around the brake caliper on front wheel works very well together with my Monit. Last competition race gave +/- 1-3 meter or less at the secret controls and that is to blame the driver and not the Monit trip. I sanded the small caliper mounting bulges to give the magnet a better touch.

By the way in the beginning of the race one of the wheel spinners got loose so now I have learned the hard way always to start a competition by knoking on all spinners :D
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PostPost by: miked » Fri Oct 06, 2017 9:37 pm

Bumped for info.
Mike :D
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PostPost by: Foxie » Sun Oct 08, 2017 1:38 pm

In 31 years of Lotus ownership I was never happy with the amount of speedo needle bounce despite many (very awkward) cable and angle drive replacements. So a few years ago I had my mechanical Smiths speedo converted to electronic drive by Speedy Cables. I fitted their pick-up unit behind the dash at the speedo end of the cable. This worked fine, though there was still a bit of a waver, probably as a result of cable wind-up.

So when the cable broke (again) recently I chose to buy a remote pick-up unit rather than remove the engine/gearbox to fit a new cable.

I had seen various set-ups on here and elsewhere, but I wanted to avoid cable flex resulting from suspension travel or worse, combined steering and suspension travel, so I had a look under the car.

One option was the propshaft u/js, but mounting the pick-up looked complicated. Looking at the diff output shafts appeared to be a good option, so I cut a small mounting wing from some light sheet steel, and glued it to the side flange of the differential, using Weicon Flex+bond. No other modifications were necessary, the cable is solidly mounted, and it all works very well. :)

Calibration can be done by measuring wheel rolling radius and calculating pick-up impulses per mile, but I found driving a measured distance using motorway mile markers and calculating correction figures re-iteratively gave very good results. Can also be calibrated/checked using GPS.

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PostPost by: miked » Tue Oct 10, 2017 1:31 pm

Mine is still working on front hub some 5k later. Thread bumped as I had a question about it. I left small loops in the wishbone area to limit flex. Just tie wrapped a long wishbone
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