Work in progress

Since my last update, I’ve made up a new base, and made a start on the new roller..

The base was made by gluing up and shaping a stack of MDF. I’d had an issue with the previous version, in that the front bolts for the pillow block bearings overlapped with the position of the bolt for attaching the base to the rest of the trainer (if keeping the original geometry between trainer arms and roller position). To avoid this, I’ve tilted the whole assembly forward by 30 degrees.


I’ve also started machining the roller from 50mm EN1A leaded steel. So far, the ends have been turned down to 25.4mm for the bearings. Next job is to get on with machining the tapers and threads for attaching the flywheel and brake assemblies.



2 thoughts on “Work in progress

  1. Tony

    Hi Jon,
    I was thinking about your comment regarding the thickness of the disc, and thought someone must have done a calculation for this, so I had a look online and found these links. I figure it is best to waste a few minutes doing math to deduce possible prototype thicknesses, than waste valuable material building coasters.
    Apologies if you already know of these equations, I hope I’m being helpfull, if not just let me know and I’l go stand on the naughty step!
    The Calculation relating to disc thickness to give generated braking torque is in the link below (section 2 eddy current braking equation 3.):-

    You may need some additional formulae, listed below, to provide required input values.

    the angular velocity of the disc required in the main formula can be found by converting from rpm using formula below:-
    Angular Velocity = rpm x (2pi)/60
    (an online calculator is also at site:’’)

    to find magnitude of magnetic field for your electromagnets, see online calculator here:-

    You will need to look up the specific resistivity/permeability of your disc material. (Aluminium approx. 1.000022)

    Once you have these values you can use these as fixed values for the main formula and just change the value of the disc thickness to calculate an appropiate disc thickness for your setup.
    Hopefully this will save you milling too many prototype sample discs and help remove any guesswork.

    1. jescombe Post author

      Hi, definitely helpful – thanks!

      I think I’ve stumbled across that first link already, but will check them all out..


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