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Driving a compact can crusher- stepper motor or gear motor?

  1. Mar 8, 2011 #1


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    Greetings everyone, i'm in the process of designing a compact can crushing device for use on my college campus to crush aluminum beverage cans.

    The device consists of a 6ft tall x 5'' diameter steel tube mounted vertically to the inside corner of a residential style wheeled dumpster. The dumpster is to be used to collect the crushed aluminum cans. The can crushing mechanism is designed to fit entirely within the tube and powered by electricity. I envision the crushing chamber as a section cut out of the front side of the steel tube with a revolving acrylic window for safety reasons. I also expect the motor driving the revolving door to be mounted above the door, on the upper section of the tube and the crushing mechanism to be enclosed in the bottom section of the tube. I envision the plunger crushing the can as it rises up through the crushing chamber. The can would be crushed against the triangular shaped ceiling of the crushing chamber to aid can collapse. The crushed can will then be ejected into the dumpster by a small solenoid.

    My challenge is to fit the crushing plunger and control mechanism into a steel tube 5'' in diameter and about 4.5 feet long. Plunger travel distance is about 8 inches. Time between crushing cans needs to be about 4 seconds. The device also needs to be near silent as they will go in the hallways of my university. The driving mechanism and control device needs to cost under ~$150. attached is an image I found online of something similar. Though I cant find a distributor.
    Possible driving mechanisms are the following:

    1. Geared motor driving a home-made linear actuator (lead screw with threaded plunger). This would be a good option as the gears would provide the torque, but the required RPM to drive 8 inches in ~2 seconds is higher than anything I've found within my budget
    2. Stepper motor driving a home-made linear actuator (lead screw with threaded plunger). cost of stepper motor and its driving electronics seems to made this a difficult option. this seems the best option of these 4.
    3. pneumatic cylinder driving a plunger powered by a small air compressor and tank. This seems impractical as the compressor and tank would take up too much volume and be far too noisy in operation and take too long to 'recharge'
    4. linear motors- would be perfect, but are far too expensive and too complex to purchase or construct in our simple machine shop.
    5. linear stepper motors- are these practical? http://www.motioncontrolproducts.co.uk/sections/3/Linear%20Stepper%20Motors/" [Broken]

    My difficulty in this project is finding a suitable drive for my crushing mechanism. I'm seeking advice regarding reasonable lead screw threads per inch versus in/oz torque levels of the motor. I want to crush these cans nice and flat.

    Thoughts or comments would be appreciated


    Attached Files:

    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Mar 8, 2011 #2
    First, I'm not being rude, but I think your concept is too complicated, probably too expensive and people would stop using it after the novelty wore off. If you have to stop walking to wait for the machine, then you're not going to bother.

    Stepper motors are a bit of a fantasy for students because they seem so wonderful not needing gears and feedback. But they have disadvantages like missing steps, cost, size, speed, expensive power transistors, etc.

    I once made a press thing, with pretty amazing force, by using an electric drill. The leadscrew was just a hand operated spring compressor tool for removing car suspension springs. Using consumer products can massively cut costs. Try finding an industrial gear motor with the same power as an electric drill for $20! Reliability is the problem here tho.

    Screw force - torque releationship is pretty easy. You can find it in plenty of machine design text books. Just some basic trig and you need to know the friction coefficient, which again you can get from the library. If you need to grease it to increase the lifetime (or save power)then you should work out the pressure at which the grease will be squeezed out of the contact areas to make sure that doesn't happen.

    I don't like the rotating window. What if someone puts their finger in it while it's closing?What if they block it with rubbish? Does keep trying to close all day? Does it time out and open again? You might actually need a computer just to control the door! A hand operated window would be less frustrating to use and avoid so many extra complications.

    I've used a public can crusher that looked like a vending machine. You open a metal door by hand, put the can in the cradle (inside of the door), close it by hand, and it crushes with some wirring sounds.

    Further, having the crusher mechanism below the can means any other rubbish, liquids (somebody will put a full can in), etc. could upset the mechanism, or at least get stuck. If you have the plunger coming down from above, then the underneath of the platform can be a free space leading directly into the bin. In fact the crushed can itself could fall off the platform and down the inside of the tube so you don't need an ejector solenoid.
  4. Mar 9, 2011 #3
    What about a cylindrical mass that drops down the tube and crushes the can? The crushing surfaces can be coated in rubber to make it quieter. It seems much simpler (and cheaper) than steppers motors and the like.
  5. Mar 9, 2011 #4
    Even simpler idea, tho I doubt how well you could control the noise without a whole lot of acoustic design.

    I don't think the contact of the weight with the can would make much noise if the weight doesn't stop moving. It's more likely the can itself would generate a bang as all its walls suddenly change shape.

    A rubber coated surface would also require more weight. The maximum force is needed at the start to initiate buckling, after that it can keep crushing with a fairly low force. Except maybe at the end, depending on how flat it needs to be. But rubber will reduce the force at the first contact, which is precisely where it needs to be a maximum.
  6. Mar 11, 2011 #5


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    Regarding the collapse of the can, the collapse should be encouraged by the crushing platform being wedge shaped, causing the base or top of the can to buckle and initiate collapse of the walls.

    I also agree that simply dropping a weight would be too noisy. There would be quite a bit of shock though the system, causing the whole device to shake every time the mass is dropped.

    Another possibility for a drive mechanism that seems promising is using a motor with a gear mounted to the axle which drives a linear gear (a gear unrolled on a flat surface...I don't remember what it's called) The crushing mechanism would be attached to the 'linear gear' and the motor would simply drive the motion of the piston/ plunger.

    Does anybody remember what I refer to as a 'linear gear' is actually called?
    Also, would it be reasonable to use such gears in this fashion and still achieve adequate force to crush the can?

    Thanks everyone
  7. Mar 11, 2011 #6
    A rack and pinion gear.
  8. Apr 17, 2011 #7
    so, did u managed to make the thing works?
    becoz i also doing a project of can crusher with rack and pinion. I need some advise and info on the motor u used. can u share with me?
  9. Apr 18, 2011 #8


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    Hi Billyam, Unfortunately I have not constructed a can crusher yet. Regarding the crushing mechanism, i'm still trying to figure out whither or not a rack and pinion or driving a plunger with a lead screw is best. The Rack and pinion's issue is that it needs a motor with sufficient RPM and high torque (at low cost) that would be sufficient to crush a 8'' tall [energy drink] can. The linear actuator using a plunger and lead screw would require a lead screw with a very low pitch and with a driving motor of relatively high RPM and torque.

    I would be glad to share my plans with you once they are put down on paper.
    Regarding which motors to use, I would recommend going over electronics surplus websites and eBay listings. Specific motors for sale that i'm considering are found on the following links:

    1 HP Motor Treadmill Duty
    40291 COPIER MOTOR
    http://www.electronicsurplus.com/It...N - Motor_ DC_ Supply_ 90VDC_ - 303 Magnapak/
    http://www.electronicsurplus.com/It... DC_ 12-24VDC 200mA-no load - 852-048025-001/
    http://www.cgco.com/default.aspx?page=item detail&itemcode=2GB18KA

    I also found this can crusher on Amazon.com that has promise

    I will post again once I have more progress. Sorry I couldn't be of more help...
    Last edited by a moderator: May 5, 2017
  10. Apr 18, 2011 #9
    Well, honestly, i had to study more on the mechanism as i only have the rough idea & sketch on paper. my idea was to made something like tis:
    but that product use only man power and my aim was tried to make it become electrical powered. thanks for the info!! i really appreciate that..:approve:
    Last edited by a moderator: May 5, 2017
  11. May 18, 2012 #10
    well i spent some time thinking about this before it occurred to me that this is a rather old post, and the semester is over so you probably already turned in a design. but i'm going to give my sentiment regardless because i am bored at work. i think that if you were deadset (or required) to use a cylindrical tube, it would definitely be ideal that the crushing piston come from the top. furthermore, i would impose a rather weighty end on the crushing piston to take advantage of gravity and create less work for the motor. compressed air is certainly out. you could eliminate the noise issue by locating the compressor away from the actual device in an insulated room, but the cost of all that makes it a useless option for you. if i was designing this for the real world, i would hope to have a budget that would allow me to use hydraulics, but i'd basically just be making a modern day trash compactor. in interest of sticking to the project, i would go with a rack and pinion design because it would 1) be fast 2) be strong. the tricky part then becomes ejecting the can afterward. this thought partly led to the idea i am about to mention. it also occurred to me that you could make the machine faster if you crushed the can from the side rather than the top. that's about 3 or 4 inches to accommodate all cans rather than 8 inches, and the can should have less rigidity from that direction as well. obviously, this would not work in a cylindrical crushing chamber, which led me to envision a box style crushing chamber instead, in which a piston comes in from the side rather than the top, still using a rack and pinion driven shaft. there is still the issue of expelling the can, which i resolved by creating a rectangular slit below the point where the can would be completely flattened, so, the piston having completed the crush, upon moving back into it's starting position, will release the can allowing it to fall straight through the opening and into the awaiting recycling bin below. this design would be well within your budget and operate quickly and simply. oh, and as for the access door, i'd go with a hinging design that would also act as a ground interrupt (completing the circuit only when closed) to prevent the piston from operating with the door open for maximum safety. the attachment is an illustration of what i am talking about.

    p.s., if the piston retracted too fast it might sometimes result in the can flopping over inside of the chamber rather than falling straight out. i believe this problem could be avoided however by a combination of the rate at which the piston retracted and the size of the opening which the can is supposed to fall through. you might even consider turning it on it's side so the can is lying down and thus less top heavy and less likely to topple over.

    Attached Files:

    Last edited: May 18, 2012
  12. May 19, 2012 #11
    why you need high rpm,
    its must expensive if you find a driving motor with high RPM and torque,
    its not worth,
    which I think is that you simply have a high torque
    an used driving motor photocopy/xerox its my suggestion.but the dimensions are the same as for cans.
  13. May 20, 2012 #12


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    What's wrong with a simple old auger smashing the metal through a spout, sort of like an extrusion die? (I have no idea of what a "residential dumpster" is; we use garbage cans for residences and expensive dumpsters for commercial operations.)
  14. Jun 1, 2012 #13


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    9-ton electric can crusher in a 3.25'' tube at 0.5''/ sec.

    Hey Guys, sorry for the delay
    I've made a bunch of progress on my can crusher design.
    i've settled with a design that uses a 2HP permanent magnet variable speed tredmill motor by Image I got from a friend. It rotates at a rated ~3200 RPM (@130vdc) with a calculated torque of about 66 in-lb and operates off rectified 120vac mains. The motor shaft is then coupled to two "Currie Planetary drive- 75mm Planetary Gear" for a Scooter" which I got for $25 a piece on eBay, each with a 4.5:1 ratio. Hooked up in a step-down configuration, they should reduce the speed to ~160 rpm. The gear-reduced drive shaft is then connected to a ball screw of 3/4'' dia. The input torque attached to the lead screw which has a 0.25'' lead
    has a calculated linear (crushing) force of 17,973.65 pounds*
    or ~9 tons.,
    traveling a 0.5 inches per second :eek::approve: Resulting in a can with a crushed thickness of between 2-4 mm.

    The whole design has a footprint of a 6'' dia. The motor is enclosed in the 6'' steel tube and acts as a weighted pedestal with the motor axis pointing vertically. After about 14 inches, the 6'' tube is then reduced to a 3.25'' dia. steel tube which is also oriented vertically. I would rather have my can crusher be tall than take up more floor space. The 3'' dia. planetary gear drives are mounted to the tube wall via machined mounting hardware. The ball screw shaft is then coupled to the appropriate part of the nearest planetary gear. The nut on the ball screw is attached to a steel plunger which crushes the can upwards. There is a 8.5'' tall slot cut in the side of the 3.25'' dia steel tube where the user inserts the aluminum can.
    Above the crushing chamber which I just described is near the top of the 3.25'' dia. tube and is equipped with a simple motorized door driven by a servo. To prevent the acrylic door from crushing fingers, the shaft connected to the door is spring loaded using a RC car "servo saver". Of course its equipped with a tachometer, micro switch, red and green leds, power switch, fan, etc.. all enclosed in the 3.25'' dia tube.

    The 3.25'' dia carbon steel tube has a wall thickness of 1/16 inch. My friend says it should withstand the tensile force... Lets hope.

    all told i've spent
    56$ for the gears
    40$ for the motor
    20$ for the steel tubes
    0$ for the machined mounting hardware (Scrap)
    0$ for the Basic Stamp microcontroller (in house)
    15$ for the "cans crushed" counter, tungsten contacts relay, thermal sensor and connectors.
    and 0$ for 8 industrial garbage bags full of uncrushed aluminum cans from the university I attend. Unfortunately WA State doesn't pay hardly jack for aluminum. 0.25$ per lb.
    Oh... and 7 months of designing.

    Right now i'm working on a way to disengage only one of the planetary drives for 7 of the 8 inches of travel so I can reduce the crushing cycle time. Taking out one reduction gear would increase the speed to about 2''/ second. Currently however, it's going to take about 32 sec/ can. Which is pretty slow... I would like to reduce that to about 8 seconds or less.

    i've modeled most of it in solidworks and will post images as soon as I can.
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