OT(?): Detecting nuts from a nut dispenser... Lateral thinkers apply within

[Mathew Newton]

Let me explain... (and no, an angle grinder won't do)

Based on the operation of my automated cat feeder

I've been asked to develop a similar device for dispensing nuts to birds. The existing design will be modified slightly to reduce the amount of nuts dispensed in any one 'serving' however its basic principle will remain the same: a motor will slowly turn a paddle and provide six servings per revolution.

What I want to do is be able to do is trigger only a single serving and, given the somewhat inexact method by which this paddle delivery method operates, I have decided that my best bet is to somehow detect the ejection of a bunch of nuts (there'll be less than 10 per serving i.e. per section of the paddle) once they have left the dispenser. This detection can then stop the motor turning and await the trigger for another serving.

I've been experimenting with a break beam detector (a Velleman MK120 hobby-type kit consisting of an IR transmitter/receiver) and whilst the detector functionally works and is great for detecting even a finger quickly passing through the 'beam' I am not having quite so much success with the smaller, and I guess faster, burst of nuts going through. I have yet to try focussing the falling nuts via some waste pipe or similar but I'm beginning to think even that might not help much.

I was wondering if anyone here could think of an alternative, and hopefully better, way of detecting what is essentially a small amount of nuts falling out of the dispenser? Perhaps something like a gate type arrangement attached to a lightweight microswitch that the nuts fall through activating in the process...? I want to keep things simple, not only to ensure reliability but also because the budget is finite and there's a inevitable skillset limitation too!

Does all make sense? Any thoughts would be greatly appreciated and I'm keeping my fingers crossed that there's a genius idea out there that I've overlooked...

Mathew

[Jules Richardson]

Hmm, it should be possible - I've used grain counters before and they're very reliable despite the smaller size of the grains. They held the grains on a vibrating chute which had a *very* slight slope to it - the frequency could be tweaked, but too high and grains would pour through too quick and give false results much like you're getting.

Alternately, are the nuts of uniform enough size that you could use a slotted wheel to pick one - but never two - up from a hopper and deliver it past the beam at a "slow enough" speed?

cheers

Jules

[Andy Dingley]

I'd use a stepper motor. it has the advantage of good torque from a standstill, not requiring a gearbox, and it's also easy to make it run for a precise number of angular steps, rather than for a time. To control it you could use an AVR processor (withh minimal bootloader you can make a low-cost Arduino), a PIC or even an IQ3 from MUTR (cheap and very simple, if your needs are equally simple)

[dennis]

????

What's wrong with a simple micro switch that stops the motor when the paddle blade is there. A momentary operating switch then bypasses the micro switch to start the paddle turning. The micro switch closes when the paddle blade moves and opens again when the next paddle blade pushes it.

[newshound]

I did my share of hacking electronics when I was working in a research lab, but I'm a mechanical engineer at heart. Assuming you are using the same sort of three flap dispenser, I'd be inclined to control it electromechanically with the logical equivalent of cams, microswitches, relays so that it just does a third of a turn per demand. You could implement this in all sorts of ways using linkages, gears, chains, etc.

Loved the cat-feeder and site, though!

[Owain]

Would it be possible to preload the nuts into individual service portions?

Then you could have eg a large rotating wheel (bit like a waterwheel) in a case, with an opening at the top and bottom. Insert x nuts per compartment into the top, and rotate the wheel x degrees, with each part rotation it moves on one compartment and the portion of nuts fall out the bottom hole.

Another thought is some form of compressed air system that will blow one nut at a time.

Owain

[Tabby]

I'm not convinced what you propse is the best option, but it should work. Check out any pinball machine, looking for a flap where the ball goes through it, producing a score.

NT

[Mathew Newton]

I've been asked to develop a similar

I should've mentioned already, the decision to re-use the cat feeder design principle has already been made on the grounds of limited time for (re)development, parts availability and the proven concept. If the endless protoyping and trialing taught me once thing it's that there designing this sort of thing in theory is once thing but turning that theory into practice unearths all sorts of issues that weren't immediately obvious! The most common problem is nuts getting trapped (matron) and this design has proven itself to be completely immune from that issue. Also, for what it's worth, whilst I called it a bird 'feeder' it's actually going to be used as part of a semi-automated bird-training programme (action-reward type of thing).

The suggestions based upon paddle position detection (e.g. stepper motors, flap detectors, shaft angle detection etc) have been considered but discounted based on the way the dispenser works in practice. There is a fair amount of paddle distortion to accommodate the random fall, size and position of feed and the point at which the food is dispensed really does vary continuously. It's really quite amazing how such a slow moving paddle (4RPM) can seemingly hold on to the nuts and so what would've dropped in one position may repeat quite the same next time. It might be worth further experimentation however.

I've found some microswitches with a 0.078N operating force which might be low enough to be able to detect the dropping of the nuts (there I go again) and so might grab a couple of them to see if they're of any use. Alternatively, they might serve well with a cam approach should that idea seem like a goer.

Mathew

[Mathew Newton]

You could well be right, but there may be a certain amount of 'better the devil you know' at play here!

Yes, that's an idea...

Mathew

[geoff]

In message , Mathew Newton writes

Just adapt one of these

[geoff]

In message , Owain writes

A system that blows your nuts AND feeds the birds (twopence a bag) at the same time

Hmmm ... Julie Andrews anyone ?

[Mathew Newton]

Wow.... That is quite possible the most impressive thing I've ever seen (made out of Lego at least...!)

Can I get away with claiming that manipulating non-symmetrical and irregularly-shaped nuts is more difficult that smooth plastic balls...? No, thought not...

Mathew

[Rupert Bear]

e to do is trigger only a single serving

Awe,, Fantastic,,!

They should have it drawin the lotto..

............................................

[John Rumm]

One trick they have used there with the Ferris wheel style pick-up would seem to lend itself to a measured dispenser solution. I.e. the wheel would need small "buckets" capable of holding a few nuts, and they automatically get filled simply by being dragged through a hopper of them. Add stepper motor control to save needing much in way of complex sensors (one optical or hall effect device to provide a once per rev "index" pulse might be handy for error detection).

[MuddyMike]

Biggest hammer then, or duct tape...

Mike

[Huge]

When I worked for United Biscuits (who own(ed?) KP) I have some brief exposure to the problems involved in packing mixed nuts and raisins(*). We only counted brazil nuts, since they were large and expensive - IIRC peanuts were packed by volume, since they are of reasonably constant size.

(* My real job was weighing flying crisps. Or persuading PDP11s and crisp bagging machines to do it. This was some time ago, so my knowledge of the technology is a tiny bit out of date.)

[Gary]

How about having a weighing machine of some type under the bowls and trigger the stop when the correct weight has been reached.

either mod a electronic scale or make your own pressure sensor.

[brass monkey]

How about some form of clock escapement idea ?

[root]

I've been asked to develop a similar

Just to be clear: this is intended ONLY for indoor use?

I'd consider an acoustic detector. Either an electret microphone or a piezo insert. Have that attached to the thing the nuts will fall onto and detect the noise they make. It wouldn't have to be hi-fi, just an op-amp and a high-pass filter.

[Mathew Newton]

It'll be outdoor. Suitably weatherproofed of course.

I did consider something at the delivery end but was concerned about (un)intentional interference from the birds, particularly if they start pecking at the dish in anticipation of the nuts as this might scupper both weight and acoustic detection.

Mathew