Proving some rotation

[Jim K..]

Although you only want it to show when it has slowed/stopped rotating, not how fast it's going when all is well...

[Harry Bloomfield]

Its that time of year again...

My tractor mower, sometimes suffers from the cutter blades coming to a stop due to becoming completely choked with grass. When that happens, it slips the drive clutch, but from the driving seat, there is no noticeable change in the noise and I carry on driving with no cutting taking place and damaging the clutch.

I don't use a grass collector on the rear and because it tends to be another cause of it choking up, but I can look back and see grass cuttings being blown out the back when all is well. The drive clutch and its pulley output to the cutting deck, is under the engine.

Ideally, I could do with a better way to be sure at a glance, that the clutch isn't slipping and the deck is being driven round. One idea I have is a magnet fixed to the edge of a pulley, rotating past a coil powering an LED mounted on the tractors dash. Has anyone any other suggestions?

[Andrew Mawson]

Rear view mirror?

Andrew

[newshound]

That seems a pretty neat idea to me. My analogous problem is a 100 litre electric sprayer that sits in the back of my all terrain vehicle, recognising when the spray stops for any reason. I have tried a little wireless TV camera with a monitor on the dashboard but it wasn't really effective.

[Harry Bloomfield]

Andrew Mawson brought next idea :

I have already discounted that idea, because there is no place one could be sensibly mounted, where it would allow sight of the grass cuttings being blown out. Thanks..

[ss]

Thats what Kirby vacuums use a magnet on the roller brush and it rotates past the coil lighting an LED, they use it to show if the brush stops rotating ie the belt has snapped.

[Rob Morley]

Fit a flow meter and monitor it with a microprocessor that can flash LEDs at you.

[Rob Morley]

Bicycle computers use a magnet and a reed switch to measure rotation, but your mower will probably be going too fast for it to cope. An Arduino with a Hall sensor could count your spinning magnet revolutions, and is obviously a lot more configurable but with the overhead of having to build the system from scratch.

[Brian Gaff]

Hall effect devices tend to be more reliable than mechanical things for this purpose. I replaced a dodgy read switch in an old cassette deck autostop with one some years back it outlasted the tape deck. Brian

[Brian Gaff]

Tee hee. No the magnet and hall effect sensor work well, but it would be much cleverer to somehow link the on off pulses so that if they were not present it cut the power. Brian

[Mark]

Wrong

[Steve Walker]

Mine certainly does.

SteveW

[alan_m]

A hall effect switch or reed switch could still give a false reading if the blade stops exactly in the position where the magnet is next to the hall effect or reed switch.

The coil would only react to changes so if the magnet doesn't move there will be no output from the coil irrespective of where the magnet ends up in the blade stalled position. However what is the on/off ratio going to be? Unless the magnet energises the coil (or switch) for a substantial time then the LED may only have a just perceivable flicker which cannot be seen in daylight. You probably need some simple circuit, say, where the output from the coil charges up a capacitor which in turn allows the LED to remain on long enough to be seen at full brightness.

[The Natural Philosopher]

a failing in physics understnanding, Teh avearge poutoput will be te same capacioter or not and teh peak brightness will be higher if left pulsing,

Most blades are close to the motor's speed anyway = appx 3000RPM or 50Hz.

[Harry Bloomfield]

All the pulleys are approximately the same size, so yes the blades will rotate at engine speed.

The PTO clutch is rather weird - just a metal plate trapped between disks by spring pressure.

[Harry Bloomfield]

Brian Gaff explained on 18/04/2019 :

That would involve much more complexity than it needs. It would require some means to override it, to enable the engine to be started.

My first attempt at an indicator was a simple hinged flap on the output of the duct. Air blown out by the cutter fan, lifted the flap, but it was impossible to see the flap whilst driving. No air flow, meant the deck was choked. I suppose I could fit a magnet on a flap, operating a reed switch to turn on an LED.

[The Natural Philosopher]

I think that is overblown.

All you need is something like a guitar pickup. Lots of turns round a magnet close to where the blades are. Should be enough power to light a LED

[Thomas Prufer]

As does mine -- wired computer, uses a reed switch and magnet.

Max speed 199 km/h or mph is usual, and wheel circumferences down to ~1200 mm (16"). Cunning adjustment of miles/kilometers and wheel circumference might allow it to show rpm...

Thomas Prufer

[Harry Bloomfield]

The Natural Philosopher explained :

Well I tried it and although the blown flap was able to operate a micro-switch quite easily, the flap slowed the exit air flow and quickly choked it up.

I'm not going to try attaching anything to the blades, I have in mind a magnet on blade pulley, above the deck. It should be fairly easy to then make a bracket to mount a coil.

[tabbypurr]

easier would be a strip of polythene. When the blades turn it'll blow & flap busily. You'll notice if it's not behind you.

NT