Pavlovian Device – Dog Biscuit Chucker

Written by: admin@makezilla

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A while back when I first discovered Make Magazine, (which eventually led me to instructables) they featured a project where a pug got his own treat by pressing on a paddle.  The makers design was awesome, but was much more complex.  I was thinking how could I do this in a more simple manner... The idea faded to the back of my head until several years later when...

I was at a thrift store in town and found one of those old golf machines, the kind you use as a putting target. You shoot the ball at the target; if it goes in correctly the ball would trigger a switch, which in turn energizes a solenoid. The solenoid would pop the ball out and the switch would automatically reset, simple. This is truly when inspiration struck for this build, I thought this would be simplest method of ejecting a dog biscuit. Not only is the design utterly simple, it makes a satisfying sort of noise upon activation “ka-chunk-brazzzat”.This noise acts as a Pavlovian training aid, as it has quite a distinguishable sound. I have always had an interest in Ivan Petrovich Pavlov's experiments.  So much so that so, that one of my paintings is based them. He was one of the first to perform experiments involving conditioning. Kinda like Mad scientist brainwashing to a degree – yikes! One of his classic experiments involves feeding a dog while a bell rings. The dog has all its life been conditioned to associate the ringing of the bell with his food. Later the dog is given food without the bell ringing and the dog can not or will not eat. Another time the bell is rung without any food given, and the dog salivates like crazy. – “Little know fact, this is the main reason the experiment was performed. To measure the amount of given saliva or psychic secretions” produced in relation to the digestive system for dogs, and later for children. Some of his other experiments were a little too freaky for me, as at the time scientists gave little thought to animal suffering.”

Here is a link to good ol' Pavlov -

Of course the thought behind this is not so I have my dog Maximus drooling all over the place, but rather to provide a fun means where he can help himself to his own treat – furthering my degree in laziness, or to quote ToneLoc from the movie Fern Gully,  “an un-necessary expenditure of calories” . 

NOTE 1: 
Before you begin, this involves using dangerous power tools and electricity - be careful!  If you don't feel comfortable with some of the wiring steps or power tool usage, get a friend who can do it for you, or show you how.
Also very important, If your dog is a glutton, and is susceptible to various doggy complications from potentially becoming overweight, meter out how much access your dog has to this device.  My dog is a dachshund, they are prone to hip degeneration if they gain too much weight.  Suffice to say, this isn't left out all the time.


NOTE 2:  As you may have noticed, the dog used in the video looks a little, well... off.  My own dog Max refuses to perform for camera.  As soon as he sees a camera he forgets all of his Pavlovian conditioning and runs straight for the camera for snuggles.  So, i built my own artificial Max, Maximus 2.0

NOTE 3:  It has been brought to my attention that this instructable would be ill advised to be just left out, as it could lead to a form of OCD in dogs.  Basically imagine your dog has been trained to use the Pavlovian device.  Then you either forget to fill it or perhaps leave it unplugged, and your happy dog goes to use the now defunct unit = The dog becomes frustrated.  So perhaps if you have a dog prone to loopy behaviour this should be used as a supervised item only.  This may also be beneficial if you your dog is a glutton as his access will be limited.

Step 1: Tools and supplies

Picture of Tools and supplies


  • Project box – your choice of finish, doesn’t have to be metal, and you could always make it yourself
  • 110v solenoid – mine was pulled from an auto golf putt return machine
  • 110v house plug and cable – mine was recycled from the golf machine
  • U-channel about 6 inches worth – sized to your dog biscuit shape
  • Legs, if you like that sort of thing
  • Momentary switch – must be very easy to activate
  • Metal tube to act as a dog biscuit holder - sized to your dog biscuit shape
  • Piece of plate metal or wood – sized to your project box – mine was about 4”x5”
  • Hinge – must move with little to no resistance
  • Various connectors – screws and bolts
  • The odd chunk of plywood – sized to the inside bottom of your box
  • Epoxy glue (5 minute or faster, cause who has time to wait!)
  • Hot glue sticks
  • And of course some dog biscuits – these really will determine the design“form follows function”


Tools used

  • Angle grinder with various zip-cuts and grinding wheels “flap disc” is king
  • Drill or better yet drill press
  • Glue Gun
  • Various hand tools

Step 2: Harvest the parts

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  • To harvest the solenoid, simply remove the retaining clips from the bottom. I used my handy dandy Instructable Leatherman, but I suppose you could still do it with some lesser tool of sorts…
  • The bottom plate just kinda falls out after. Now reach in and pluck out the solenoid, its just wedged with nothing special holding it in place. Make sure to watch that the spring or the solenoids push rod doesn’t sproing out to be lost in some crack somewhere
  • You will also get a rather homemade looking switch that looks kinda like the trembler switch one of the bad guys use in the movie “the rock”. Set it aside to use in the future one day
  • There will also be a standard plug and cord, might as well re-use it, plus its a delightful golf green.

Step 3: Build the base

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The key to any build is to have a solid base. I had an old electrical project box that I was saving for just such a build. The only problem with it being that it is made of aluminum. I try to stay away from aluminum in my builds when I can, merely for the fact that I am not equipped to weld it. Usually my builds are steel as it is so much more forgiving, oh well. I had to figure out how I was going to attach things to the box as all though it is fairly easy to machine, it has its downfalls.

  • Drilling and threading holes in the aluminum is easy, but with repeated movement & vibrations, the threads tend to wear down an loosen up
  • Brazing? I’m not sure how well that would work with my sloppy joints
  • Adhesives? Maybe, but you need a fair bit of surface prep

I decided to skip on the brazing and go with mechanical and a medley of adhesives as outline below and on the next couple of pages

  1. First I drilled/cut my hole in the lid for the dog biscuit hopper tube. Now I say “cut” because I discovered the spade bit I was using was bent a little.Suffice to say it caused a wobble and the center guide hole was now misshapen. I finished off the hole with a jig-saw and fine metal saw.
  2. If you haven’t removed the lid, do so now. It’s simply screwed on.
  3. Next I cut a piece of plywood to serve as a base within the project box. It would allow an easier method of attaching items whether mechanically or when using adhesives. The plywood was cut slightly small then the bottom of the box. Their were all ready 4 holes in the bottom of the box, so I used these to attach the plywood. I simple screwed in a deck screw through the bottom of each hole into the plywood, locking it in place.
  4. Next I attached the 3 legs. (why 3 legs instead of 4? = 3 legs are inherently more stable then 4)The legs I was using were taken from an old drill press, they had a nice meaty feel. The bonus, the tips of the legs were all ready threaded. So I drew a circle on the bottom of the box and roughly spaced out where I would drill the 3 holes. Drill the holes at about 70 degrees, this lets the legs splay out nicely. Drill all the way through the aluminum into the plywood. Fill the holes with epoxy 1/3 of the way and screw in the legs. Wipe off the excess glue and allow to dry – or rather cure. - The curing process is a chemical reaction in which the epoxide groups in epoxy resin reacts with a curing agent (hardener) to form a highly crosslinked, three-dimensional network. In order to convert epoxy resins into a hard, infusible, and rigid material, it is necessary to cure the resin with hardener. Epoxy resins cure quickly and easily at practically any temperature from 5-150oC depending on the choice of curing agent.

Step 4: Build the feed tube - HOPPER

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  1. Insert your tube into the hole and center it the best you can. Grip the tube and while pressing down rotate it back in forth. The act of the downward pressure and rotating will burnish the plywood underneath it slightly, marking exactly where the tube will land.
  2. Take a sharpie and mark where you are planning on placing your solenoid and where the ejection chute will be.
  3. Pull out your tube and stand it up on a level surface, place the solenoid beside as you would in the box and mark off the top of the solenoid plunger
  4. Drill out this mark, ensure it is just large enough for the plunger to clear
  5. Notch out the bottom of the hole
  6. On the reverse side cut a T into the pipe, when you unfold the metal it should be large enough for your biscuit to slide through easily. - See pictures
  7. At this point you can if you so choose add the hoppers PEEP holes.  I just chucked it in a vise and used my drill press.  The holes are spaced about 1 1/2" apart, this is horrible to admit but I didn't measure it, just drilled the holes free-hand.  I am my own worst enemy sometimes...
  8. Slide the tube through the bottom of the hole on the lid. Put the lid back on the box. Run a bead of hot glue around the tube where it comes out of the box, allow and to cool.
  9. Carefully remove the lid with the tube locked in place.
  10. Flip it over and now slather on some epoxy, make sure where ever you plan on applying your epoxy that you have roughened up the metal to give the glue some tooth to grab. Allow to cure.
  11. Once cured, peel off the hot glue. The epoxy will now be holding it in place.

Here is a video of the hopper being loaded


Step 5: Build the ejection chute

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  1. The chute is simply a piece of u shaped channel that is just wide enough for the biscuit to travel through easily as it is kicked out by the solenoid. I angled both sides as shown in the pictures, but for different reasons.Originally I had plans to have the lid open and close with the use of the hinge. This proved to problematic trying to get everything to line up just right. This is why the angle exists on that section of the chute, to accommodate the angle change as the tube would be pivoted up at an angle. You can simply keep this side square. The other end that sticks out of the box itself was angled for mostly aesthetical reasons. Also, the harsh square angle of the chute sticking out seems a little poky to canine eyes.So I angled it and smoothed all the sharp corners to a fine rounded radius.
  2. Next I cut out a square in the side of the box to squeeze the chute through.Make sure it is nice and snug and you can minimize the use of extra fasteners.
  3. I counter sunk one single screw into the bottom of the chute and drilled it home. Make sure to use a wood type screw to keep it all nice and flush

Step 6: Fit the switch and snout paddle

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The switch

  1. How you fit the switch will really be dependent on what kind of switch you choose to use. I had a roller arm switch that was very easy to actuate so it fit the bill. However you may have a push button type, this would work as well. Either way it must be able to spring back relatively easy and actuate easily also.
  2. I cut and bent a scrap piece of steel into an L shaped braked, screwed the switch to it and mounted it in the box. I took advantage of the pre-existing knock outs and had the roller arm protrude through this. You may need to drill a hole.


The paddle

  1. The paddle was just a piece of aluminum diamond plate cut to fit. Being aluminum its fairly stiff yet light weight.
  2. I used a chunk of piano hinge for the movement. Simply drill through the box an possibly the hinge and use a nut and bolt as a fastener.
  3. The spring in my switch wasn’t quite strong enough to return the door to a firing position so I bolted on a small spring to the side of the box, under the paddle. This also took part of the stress off of the switch.

Step 7: Line up the solenoid

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Disclaimer - Ok, from the pictures you may notice the tube isn’t attached to the lid… This is one of those do as I say, not do what I have done.Initially when I attached the tube to the lid I neglected to roughen the surface, so half way through the build it snapped off. This happened to be when I was fitting the solenoid.


That aside, fitting the solenoid is simple

  1. First drill your hole where you plan on running your power cord.
  2. Next, you should wire it up, see the attached schematic for this. Make sure before you hook up all your wires that you feed the power cord through the bottom of the base, and knot it inside the box.
  3. Now join up the wires and tape, use shrink tube, marretes or insulators of choice!
  4. Lower your solenoid in the place where you think it should be then mark the location with a pencil.
  5. Put a biscuit in front of the solenoid, plug the cord into the wall and while holding the solenoid in place hit the switch. If all went well, a loud ka-chunk-brazzzat sound was heard and the biscuit bounced down your work surface out of the ejection chute. Or, your electrical skills suck and you are doing the not so happy dance as 110volts courses through your body – oh joy…
  6. If all went well, prepare to glue the solenoid in place, first things first though, unplug it!
  7. If it didn’t go so well, you’re probably still alive, but not in a very good mood – take 5 and enjoy the fact your still alive, I hope “insert nervous laughter here”
  8. Moving on… I used epoxy to fasten the solenoid in place. Basically make up a crap load and bathe the solenoid in it – carefully! You want to pour the epoxy over the center of the solenoid, encapsulating it and having a solid bead of the stuff drip down and soak into the plywood. You need to be careful however that it doesn’t drip into the center tube at all and gum up the works.
  9. Now I tend to go a little overboard at times, in addition to the silicon I basically potted the solenoid and plug cord with hot glue – couldn’t hurt.
  10. Once everything has dried/cooled down, verify all your wires are insulated and not touching any of the metal bits - no electrocution of snoopy here.

At this point you can decide if you want to take it further, I like all metal industrial look. Others not so much, I don't recommend painting with regular paints though. Once great surface treatment is to use faux anodizing paint on it. Basically its a highly translucent varnish of sorts in spray bomb. You can build it up in layers to deepen the colour. I have used a method similiar to this where I take floor varnish and gently stir in very small quantities of paint tint. Not as translucent as the commercial stuff, but close.

Step 8: Give the dog a bone

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One thing I found was that My dog didn't really like the feel of the metal paddle so my quick fix was also decorative.

  1. First draw a bone shape, or maybe a paw onto some wood.  Really the shape doesn't matter, just something pleasing to the eye.  Of course you could do away with the metal plate all together and make the whole paddle out of wood, its up to you.
  2. Cut out with a jigsaw or coping saw and sand it smooth
  3. I wanted it a little darker so decided to stain it a bit.  Rather then use some toxic stain I used an old trick, dip it in olive oil.  I just used a zip lock bag with a little oil in it, add the bone and massage it in.
  4. shake off the oil and wipe it dry.
  5. Drill a couple holes in the bone first, then hold it against the paddle and insert the drill bit into the hole to mark the paddle.
  6. Remove the bone and drill your holes
  7. Put the bone back, insert your bolt and tighten the nut down on the other side.
  8. I used some lock washers as well, probably not really needed, but I had them so why not.

Oh, my camera appears to be doing something funky again.... curses!





Step 9: Practice, practice, practise

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I would love to say that my dog loved this device right off the bat, he did not.  The Pavlovian aspect behind this though really did work.  When I first put the machine down, he ran up an sniffed it, smelling the treats inside.  When I activated it though, the sound made him jump back.  Of course once he saw the treat scooting across the ground he overcame his fear and chased after it.  But, from then on he stayed clear of the machine.  Every time he was in the kitchen begging for scraps I would dramatically walk over to the machine, bend down and push the paddle with my hand. ka-chunk-brazzzat - and his treat would skitter across the floor.  It wasn't until several days later in the middle of the night I was woken to the repeated sound of the machine going off downstairs.  When I snuck downstairs, their was Maximus laying down surrounded by a pile of treats, wagging his tail like crazy and giving me a rather proud little look.  Of course would he do this for the camera? of course not - oh the frustration...  You see, Max has always been that way with cameras, anytime one is pointed in his direction he runs up to you and flips on his back to have his belly stroked.  The pictures I did get of him for this instructable had to be pre-arranged with with my wife doing a little subtle distraction.  Maybe I should do another instructable, the first "dachshund camera blind"





Step 10: MAXIMUS 2.0

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As you might have guessed, My dog Max wasn’t very compliant on this project.  Sure he would use the Pavlovian Device, that part was a success. But, oddly enough he doesn’t like to do it in front of people.  Many times I will hear it go off, especially in the middle of the night, only to find my dog coming around the corner, wagging his tail and happily crunching down on his treat. Of course none of this makes for very good footage though, so we staged the video on step one. 

This isn’t really a step per say, but one could easily follow enough along to build their own Maximus 2.0 or maybe a nice Mr. Pickles 2.0 “This would be one of our cats”

  1. Take a side profile picture of your pet – this is actually much trickier then it seems.
  2. Print it out to scale – twice
  3. From one print out cut out just the body, rounding off where any head or other appendage may have been, amputee style.
  4. From your second body, cut out the head and appendages leaving a large chunk attached.  The chunk attached should be the muscle mass that makes the appendage move for real.  Will kinda look like the thigh on a chicken leg.  See the pics.
  5. Glue these down to some stiff cardboard, or if you lack patience like me use double sided tape.
  6. Cut everything out and reassemble laying flat.
  7. Drill or poke holes where you think things should move.  If I were to do this again I would have also made the mouth open and close.  Use nut and bolts or those little brass bendy tacks you used in kindergarten class – do they even make those anymore?
  8. I used a large section of thin tubing for my dog on a stick as it is what I had. I then added a long piece of thin rod connected to a shorter piece of rod to make the head bob up and down.  See the pics.