6 replies to this topic

[Peter_NottinghamS]

I've posted on a separate thread about speedos issues and I'm considering a digital replacement (although my wallet is not happy about this!) but I can't find the information I'm looking for.

 

How do they work?  As a digital alternative, does this remove the need to for a speedo cable? 

 

I've searched for photos of the rear of the digital device but this is all I can come up with:

 

 

I got the image from this site.

 

So how is it connected?  Magic? No speedo cable? (which would suit me).

I've found the Instructions for Electronic Mini Speedometer on the Smiths website and I've found this in the Smiths Website:

 

 

What’s the best way to pick up a speed signal from my electronic speedometer?

 

There are several ways of picking up a speed signal, but some are definitely better than others, our recommendation, in order of preference would be:-

• If your engine is of recent manufacture with electronic management then you can collect a very clean, precise signal from the electronic control unit of the engine management system, and you also avoid the need to buy and fit a sensor.
• If you engine was originally fitted with a speedometer, then you will have a mechanical take-off for the speedometer cable. Here you could fit a hall effect device, which uses the mechanical take off to generate an electronic signal, or you can use a magnetic sensor kit as described below.
• If you engine came with neither a speedometer cable take off, nor an electronic engine management system, then you will have to use a magnetic sensor, to count the revolutions of the prop shaft or the revolutions of the road wheels. CAI offers a magnetic sensor kit which can be ordered when you purchase your speedometer.
• we can also supply GPS devices that will provide a pulsed input into your speedometer, you will need to check whether this is an accepted method of speed measurement in your country

Detailed fitting instructions are available for the sensor kit

 

 

Apparently I need a "Hall effect device" and I've started to go down the rabbit hole of 'hall effect devices' and I'm totally baffled.

Does anyone have an idiots guide (assume I'm the idiot) to successfully fitting a digital speedometer.

 

Thanks in advance.

 

Peter 

 

[Ethel]

https://www.minispar...o-drive-adapter

 

https://youtu.be/jANN9snyyRE

 

 

 

If your speedo cables have been tortured to death, a right angle adapter might be a cheaper option.

[stoneface]

What engine do you have, as you could use this.

https://www.minispar...o-drive-adapter

 

 

[Peter_NottinghamS]

https://www.minispar...o-drive-adapter

 

https://youtu.be/jANN9snyyRE

 

Ha ha!  

Thanks @Ethel.  I'd gone so far down the rabbit hole I was stuck! 

 

This is awesome.  And so easy.

 

The bad news is my wallet is even more unhappy! 

 

Thank you! 

[Peter_NottinghamS]

What engine do you have, as you could use this.

https://www.minispar...o-drive-adapter

 

Thank you.  @Ethel beat you by a minute to answering the question.

 

I've been well and truly schooled.

 

  Peter 

[DeadSquare]

In the 1970s, when Crop spraying with helicopters, the Air Speed Indicator could not be relied on for ground speed when flying up and down a field, into and against the wind.

 

From the yachting world, I found and (without telling the Civil Aviation Authority) fitted an american Doppler Speedometer, (A police mobile speed gun in reverse),

 

It was ideal;  I wanted to fly at 40 Knots = 46 MPH and it read 0 to 50 MPH, digitally, and the display colour changed from green to red at a predetermined speed.  24 volts, $35.00 plus import duty plus 8%vat.

 

Killed by GPS on a mobile phone.

[Spider]

I've been running an Electronic Smiths Speedo for near on 15 years now. I've also set a few up for others. This is some of the stuff I've learned along the way.

If you are not changing final drive ratios or sticking with the same tyre / wheel sizes, it maybe cheaper to sort through your mechanical speedo, if you see yourself changing these, this is where electronic speedos really pay off. For me, it was the likely hood of tyres and also I like a dead accurate, in particular for navigation (though GPS mapping has taken that need away now).

Dead easy to hook up, but you do need to get a good speed sensor. There are a few on the market, I've tried quite a few but didn't find any successful over time. The Speedo needs an electric 'pulse' to sense speed, this can be done in several ways, some better than others. The more pulses per rev, the better the speedo will work and will work to lower speeds.

There's a few types available here;-

Inductive,
Hall Effect
Satellite (sometimes referred to as a GPS type)

Inductive types are simpler to hook up, but don't register low speeds (roughly less than 10 mph). I didn't like this one one bit.

Hall Effect types have an extra wire to connect and you need to be careful about polarities of wires, so also need a 'Pull Up Resistor' but don't be put off by that. These can in they register down to 0.0001 mph, but in reality, there's other factors that come in to play, but there's no reason why you can't get them down to reading / showing 0.5 mph. Many of the cheaper sensors will only last a short time and only provide 1 to 4 pulses per rev on the sensor shaft. I've found for a Mini or a Moke, you need a minimum of 6 pulses per rev and if you have a final drive ratio of about 3.2 or taller you need 8 r even 10 pulses. For what ever it's worth, I run a final drive that gives 17 mph per 1000 engine rpm and I have a 6 pulse sender. The cheaper units too seem to have a 'floating' shaft & magnet as in they have no bearings or bushes in the unit at all and rely of the speedo drive to keep them running 'true', the issue here is that most are a sloppy fit, so the shaft runs in all kinds of orbits inside the sensor and eventually leads to their early failure.

Satellite types are easy to set up and use, but have limitations in that around trees, buildings and on cloudy days where there patchy or limited line of sight to the sky, they are slow to up date data to the speedo, they also don't work in tunnels or any covered spaces. In Australia, they are not legal to use because of these limitations, though some of the more expensive speedos can use 2 inputs and will favour 1, so you could use say a hall effect as a back up and a Satellite for a primary signal. The other aspect to consider, probably now more than ever is that these use GPS Satellites which are owned and controlled by the US. In times of conflict, they can (and do) switch these off or make them unavailable for certain areas (and not just confined to the area of conflict) or 'dial in an error' to them.

A few years back, after scourering what was commercially available the short of that was I couldn't find a decent sensor and made my own 8 pulse Hall Effect type, it's done around 20,000 miles since and has been faultless. Since this time though, there have been a few others that have popped up and look much better in many aspects than what was around.

In regards to Speedos, there are those that while digital, still display by analogue means, eg, the Smiths range and also some like Aps for your phone that give a Number. You'll find the Analogue types better (and I think what's legally required) as your brain doesn't need to read and register what a number is, where as glancing at a needle is faster for the brain to process simply by the angle of it.