Bike PTO design – work in progress

The hardware design phase of Cider Year Five is only 48 hours or so from complete (or at least, that’s when parts start arriving) and the major remaining design task is to figure out the coupling of a bicycle to the dual-stage hydraulic pump that has been ordered.


The bike PTO that we use for the apple grinder is dirt simple – we remove the chain from the front chainring and ziptie it out of the way, then install a new, longer chain that runs forward and up to a jackshaft with a standard freewheel attached to it.  The front wheel is removed and the front fork attached to a wooden stanchion on the grinder frame, fixing the bike more or less in place but allowing the rear wheel to swing right and left.  This swinging is used to tension the chain, as there is no derailleur in play, and by this means it’s possible to adjust through 2 or 3 gearings before the chain starts scraping too badly on the front fork.

This setup is nice in that it is very quick to engage and disengage the bike, and because the operator gets a nice view of the apple-grinding action.  But it’s already in use for grinding apples, and if we need to build another bike PTO anyway, it might as well be a more universally adaptable design, and one that takes better advantage of the existing bike drive system.  I toyed with ideas that used an actual bike rear wheel, perhaps inflated with cement instead of air to provide a substantial flywheel.  But if we are destined for a higher speed shaft anyway, that’s where the flywheel belongs, and it’s hard to see fitting the freewheel, PTO sprocket(s), AND a standard wheel in between the rear dropouts of an unmodified bike in any case.

Anyway, here are my design requirements:

  • Can use most bikes as a power source
  • Utilizes existing front and rear derailleurs; allows shifting through the usual range of gearing
  • Has a freewheel to decouple pedaling from load
  • Enables driving a variety of rotary  loads including hydraulic pump via standard bike chain
  • Compact, stable platform, can be set up on any flat surface
  • Sets up and breaks down easily
  • Incorporates flywheel?

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