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How to simulate 600lbs — Parallax Forums

How to simulate 600lbs

T ChapT Chap Posts: 4,198
edited 2017-02-26 13:34 in General Discussion
I want to test a method to move an object up and down that weighs 600lb. This includes not only getting the motor and drive train right but also a method to hold it at any point with a brake. I am looking for options to simulate the object (I don't have the object) without having to stack up gym weights. I only need a few inches travel to test the concept. Any ideas on this ? A spring would be ideal but a spring does not have constant pressure over a distance.

As I finished this the idea of a fulcrum came to mind where a lower weight could be used out on a boom so I could maybe get by with 100lb of weights.
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Comments

  • T ChapT Chap Posts: 4,198
    This is a lot better than use 600lbs of weights. Maybe there are other idea.
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  • MikeDYurMikeDYur Posts: 2,176
    edited 2017-02-26 16:09
    Water would be the easiest way to come up with the weight. But it would have to be in a closed tank with no air gap. Or the weight will shift on you.

    I remember bringing a 500lbs safe home in the back of my pickup, and having to get it in my basement by myself. A ramp from the bed to the basement floor, sliding the safe down on blankets with come alongs. 600 pounds is a lot of weight, be carefull.

    EDIT: A scale connected to an immovable object would be even easier.

    Do you have a job to do, or are you proving mechanical advantage?
  • localrogerlocalroger Posts: 3,451
    You can sometimes find used 55 gallon drums cheap or free for the hauling; filled with water they come to around 450 lb and won't shift if you fill them completely.
  • ercoerco Posts: 20,250
    edited 2017-02-26 16:25
    Three and a half lawyers in a duffle bag is about 600 lbs.

    And a good start.
  • MikeDYurMikeDYur Posts: 2,176
    Three lawyer's sitting on an empty politician works out about the same.
  • DigitalBobDigitalBob Posts: 1,486
    I didn't know what your application is but you could always use a hydraulic press with a load cell. A small press at Harbor Freight is cheap if it fits your budget. You can pump it in small increments to get the pounds you want and hold it
  • Dave HeinDave Hein Posts: 6,347
    I think using a lever would be the easiest way. Put 100 lbs at one end of a 6-foot 2x4, and hinge the 2x4 at the other end. If you lift the 2x4 at a point one foot from the hinge it will require 600 lbs of force to lift it. Note, there will be 500 lbs of force on the hinge, so that needs to be strong enough to handle it. I think a 2x4 can handle the force, but you may need something with a little more strength.
  • ercoerco Posts: 20,250
    If there a gorilla in the room that no one is talking about...
  • SeairthSeairth Posts: 2,474
    erco wrote: »
    If there a gorilla in the room that no one is talking about...

    Or a spherical cow.
  • ercoerco Posts: 20,250
    Or a 600 foot lever and a pound of sugar...
  • T ChapT Chap Posts: 4,198
    edited 2017-02-27 15:49
    I love the idea of hydraulic but I'm not sure how you would maintain a constant pressure to test the system moving up and down several inches. I'm liking the idea of a fulcrum. I have no idea about a gorilla
  • T ChapT Chap Posts: 4,198
    The motor is pushing the object up and down with a ballscrew. I'm just looking for ways to simulate the weight that it has to push up and down
  • kwinnkwinn Posts: 8,697
    T Chap wrote: »
    The motor is pushing the object up and down with a ballscrew. I'm just looking for ways to simulate the weight that it has to push up and down

    If the distance is relatively small you may be able to use a pneumatic system for testing. A 4-6 foot pipe with a piston could provide several inches of travel with only a small change of the load. For instance a 4" id pipe would require ~ 50PSI of pressure to produce 600 lbs of force.
  • T ChapT Chap Posts: 4,198
    edited 2017-02-27 16:30
    Interesting. So I'd need an air compressor and a piston and a pipe. I never thought about multiplying the force like that. Sure seems like over unity! Put in 50 get out 600. Is that how 40psi in my tires supports 4000lb truck. I'll look for such a piston and cylinder.
  • kwinnkwinn Posts: 8,697
    T Chap wrote: »
    Interesting. So I'd need an air compressor and a piston and a pipe. I never thought about multiplying the force like that. Sure seems like over unity! Put in 50 get out 600. Is that how 40psi in my tires supports 4000lb truck. I'll look for such a piston and cylinder.

    Yep. Good thing about a pneumatic system like that is that you can move the piston a few inches and the load only increases a small amount.
  • Heater.Heater. Posts: 21,230
    edited 2017-02-27 16:42
    No over unity magic there.

    A piston in a 4 inch pipe about a 12.6 inch surface area across the pipe. 50 pounds of air pressure on each square inch of piston is a total of 628 pounds.

    Given your truck weighs 4000 pounds and the tire pressure is 40psi I we can estimate the area of the contact patches between tire and road. 100 square inches.

    The "over unity" thing can happen if you have that piston in your pipe pushing on a 1 inch square area "piston rod". That piston rod can now exert 628 pounds pressure on a square inch!

  • xanaduxanadu Posts: 3,347
    What if the 600lbs was static, and you used a crane scale? Anchor the scale to something, and if you get a reading over 600lbs you know it can hold or lift 600lbs. Here's one on eBay - http://www.ebay.com/itm/like/281579348372 You could probably resell it when done if you don't need it anymore.
  • T ChapT Chap Posts: 4,198
    edited 2017-02-27 16:58
    Heater. wrote: »
    No over unity magic there.

    The "over unity" thing can happen if you have that piston in your pipe pushing on a 1 inch square area "piston rod". That piston rod can now exert 628 pounds pressure on a square inch!

    Yes that is what I meant.

    https://www.mcmaster.com/#6491k431/=16jdwmw

    4.5 bore @50psi = 795 force!

    I need to make some estimates on the range of force over a certain distance that is easy. Thanks for the idea.

    The fulcrum seems to give the most consistent load but due to the lever length, it's working travel at the load will be restricted. So I will have to compare the consistent load of air versus lever and find what gives the most travel for testing purposes.

    The scale idea is good but allows for no travel at a near consistent load.
  • SeairthSeairth Posts: 2,474
    xanadu wrote: »
    What if the 600lbs was static, and you used a crane scale? Anchor the scale to something, and if you get a reading over 600lbs you know it can hold or lift 600lbs. Here's one on eBay - http://www.ebay.com/itm/like/281579348372 You could probably resell it when done if you don't need it anymore.

    Excellent idea! Actually, you could probably go even cheaper. It look like there are some 200lb hanging scales for less than $50. Combine that with your class 3 lever above (the load arm can be shorter).
  • T ChapT Chap Posts: 4,198
    I should clarify that I am not just checking to see if it will hold 600lb, but I need to test the braking at several points at that load. The points can be an inch apart minimum just to test motion + braking at different points. In the real world the object will move 5' up and down.
  • T ChapT Chap Posts: 4,198
    edited 2017-02-27 17:24
    Using an air compressor directly connected to the cylinder, I would assume that the larger the air compressor tank = the least amount of affect on the pressure at the piston over a distance.
  • Heater.Heater. Posts: 21,230
    That is right.

  • kwinnkwinn Posts: 8,697
    If this is a "one off" situation you might be able to rent a pneumatic cylinder/ram and compressor. If it will be needed on a regular basis you may want to build your own test jig.
  • T ChapT Chap Posts: 4,198
    Seems I recall some type of pulley block with multiple ropes that can multiply power.
  • SeairthSeairth Posts: 2,474
    Pulleys only exchange speed for torque, I believe.
  • Heater.Heater. Posts: 21,230
    Pulleys do the same as levers. Ignoring frictional losses. Small force big speed at one end, big force slow speed at the other. Or vice versa.

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    A block-and-tackle arrangement would certainly be a good candidate:

    https://en.wikipedia.org/wiki/Block_and_tackle

    -Phil
  • DigitalBobDigitalBob Posts: 1,486
    Now that you've shed some light on the application I agree that the hydraulic cylinder is the best bet. These cylinders are fairly cheap if you buy it from northern Tool etc. You would need too fill it with oil and have two adjustable relief valves (one for each direction) The relief pressure would determine the force and this would be a static system. Adding a pump would increase the cost. The air doesn't work well on hydraulic cylinders because the O-ring drags. They have cylinders made for just air but air tends to be spongy.
    And don't forget the load cell to measure the force. (S-beam type)
  • kwinnkwinn Posts: 8,697
    T Chap wrote: »
    Seems I recall some type of pulley block with multiple ropes that can multiply power.

    That would be a block and tackle. Two blocks of pulleys connected by a rope looped through the high and low pulleys to multiply the force.
  • kwinnkwinn Posts: 8,697
    There is also the differential pulley system using a chain that is able to provide high force multipliers. Simpler than blocks with many pulleys.
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