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  1. logbook

    best permanent magnet core materials

    ...on a 12 inch lever. Measuring and scaling from the photo it seems that the magnet gap is at about 2.8 inch radius from the axle. I therefore get 40*(12/2.8) = 171 lbf maximum shear force for the 18 magnet pairs = 9.5 lbf/magnet pair. And I predicted 8lbf/magnet pair I’m a genius [bowleft]...
  2. logbook

    best permanent magnet core materials

    MagBen, the uncertainty I have put down is x3 in either direction from a very dodgy starting point. I used the K & J magnet calculator to get the pull force between two magnets with steel backings. I have simply said the maximum transverse force will be somewhere near that value. I have made...
  3. logbook

    best permanent magnet core materials

    ok GM, I'm going to put my money where my mouth is, apart from there being no money involved for me [bigsmile] I am going to predict the peak static shear force on your jig as being nominally 8 lbf/magnet pair. Because of my uncertainty I need limits from 2.4 lbf/magnet pair to 24 lbf/magnet...
  4. logbook

    best permanent magnet core materials

    Design info for permanent magnets K & J N42 curve Taking each magnet assembly as a complete magnetic circuit we have 2 off 1/4" magnets and a 1/16" inch air gap. That makes 1/2" of magnet per 1/16" inch of air. I get a permeance coefficient of 8 to draw on the N42 curve, giving an impressive...
  5. logbook

    best permanent magnet core materials

    GM, without wishing to deflate your “inspired” state, what you would measure with your setup is not representative of your actual task by quite a bit. If you had two magnets on top and two underneath, with iron backing for each pair, then that would be more representative. At the moment you have...
  6. logbook

    best permanent magnet core materials

    Ahh! Yes. Now we agree.[flowerface]
  7. logbook

    best permanent magnet core materials

    I'm curious why you think that. The force is directed straight down onto the scales so there is no "lever arm" to create a torque. (It is probable that you haven't fully understood the setup just from the pictures, which is easy to understand as they are mostly from one weird angle. It was hard...
  8. logbook

    best permanent magnet core materials

    I was annoyed that I couldn't figure out how to calculate the shear force on the magnetic coupling so I thought I'd have a go at measuring the shear force on magnets that I do have. Youtube video of lateral separation force on neo magnets It was actually pretty hard. I'm not happy with the...
  9. logbook

    best permanent magnet core materials

    Thanks. No, the magnetisation is from one large flat face to the other.
  10. logbook

    Stepper mo

    I have another thought for the low cost end of the market. [idea] Use the highest reduction ratio gear box you can find, regardless of backlash, and put a mechanical brake on the driven shaft. The backlash in the gearbox will be irrelevant as the brake will hold the load until forced to move...
  11. logbook

    Stepper mo

    The gearboxes you are looking at are rubbish for your application. 18 arc minute low-backlash gearboxes The last thing you want to do is step once every 24 seconds. The motor needs to run continuously or it will wobble the load on every step. I would use a high ratio gearbox. The RGP60 at 320...
  12. logbook

    Lenz's Law pictorial

    I think you are overcomplicating things involving Lenz's law. Increased load slows anything down. Try running with a marine on your back, that will slow you down! Ever had a car? Try letting the clutch out without pressing the accelerator (gas peddle for USA). The engine slows. (Of course...
  13. logbook

    Stepper mo

    converter 48 kg.cm = 4.7 N.m Why are you tracking the sun? If it is to optimise power output from a solar panel, for example, this is massive overkill. The backlash is wobble. If you are not driving the gearbox the wind load on the system can make it wobble. 1.5° seems a ridiculously large...
  14. logbook

    best permanent magnet core materials

    Those things looks really difficult to handle now.[bomb] I’m guessing you have done the easy part so far. The axles and hubs those things connect to need to be really strong as you only have zero radial force when the two parts are exactly coaxial. If one is able to move slightly the...
  15. logbook

    how can I have a plate that magnetically attracts a beam

    That wiki article was far too complicated. Try this video instead electromagnet video The forces you are talking about are massive. If you look for electromagnets used for lifting cars in scrap yards you will see how big they can get. >I want the attraction to be made in only one direction...
  16. logbook

    Distressed Nerd - How to increase Motor RPM

    The attached tutorial file may help. Skip over the first section on establishing the cooling requirements, but the rest is all relevant.http://files.engineering.com/getfile.aspx?folder=12cd4043-14ea-414a-b730-f0960a5f3126&file=Comair_Tutorial_EstablishingCoolingRequirements.pdf
  17. logbook

    best permanent magnet core materials

    Thanks [thumbsup2]
  18. logbook

    best permanent magnet core materials

    I thought I'd post a link to my recently uploaded "rival" Eddy Current Braking video just for completeness. YouTube short eddy current braking video
  19. logbook

    Duty Cycle

    The more that was promised ...http://files.engineering.com/getfile.aspx?folder=ad2b4d95-00fb-4cff-b042-4675ef184cb7&file=winch.pdf
  20. logbook

    Duty Cycle

    I googled the OP’s winch. First hit tells it all. winch data It also has a pdf data sheet (owner’s manual). It is for a car. It uses a 12V supply. By interpolation a 250lb load draws 20A and runs at 12 feet per minute. 132A x 12V= 1584W. 20A x 12V = 240W. (although when the manufacturer says...

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