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17 September 2017 - 9:24pm

Electric-assist torque anchors


A hub-driven electric-motor such as Bionx, Neodrive, or GoSwiss needs an anchor point that is physically fixed on the recumbent trike or bicycle, so it has something to push against. Without this anchor point, the hub would simply spin when activated with electricity.

With the anchor point, the hub can convert its spinning force or torque into forward force moving the trike forward. Every manufacturer has a unique spin (pun intended) on how this is best implemented, and each manufacturer calls the anchoring device something different. Bionx calls them "torque collars" whereas GoSwiss calls them "torque arms".

To complicate matters, Bionx has a gravity-sensitive strain-detector inside the hub. This means that the Bionx hub must be fixed in the recumbent tricycle at a particular orientation or it will not accurately sense the rider's pedaling force. Therefore, Bionx originally designed a torque collar wedged itself in place at any angle and it could be positioned differently to fit all of the plethora of different bike dropout profiles in existence.

This was a very simple and infinitely-adjustable design, and its only flaw was that removing and repositioning the torque collar required a special press tool and each shop preparing aftermarket Bionx electric-assist systems had to purchase the special tool.

After a while, Bionx redesigned the torque collar to go on and off with no special tool and it would key into a particular position with a flat edge of the torque collar fitting perfectly onto a flat edge of the motor axle. This design made it much easier to get the torque collar on and off, but it meant that a different torque collar had to made to fit each of the different dropout profiles / angles. All of a sudden, shops that used to be able to pop a torque collar off with the special tool were now required to maintain an extensive inventory of these torque collars, each holding the motor at different angles.

The standard torque collar included with a Bionx 350W electric-assist is a 27-degree torque collar. However, some recumbent trikes such as Catrike always require a different torque collar.

We recently came across a pair of these Catrikes that had Bionx systems installed without the correct torque collar. The tip-off was how much force it took to get the axle nuts off. When we pulled the wheels of each trike, we found that the unscrupulous dealer had filed away the flat keyed part of the torque collar and re-installed the torque collar with no torque anchor. To keep the axle from rotating under load, that dealer had had to tighten the axle nuts to an amazingly high torque!

GoSwiss and Neodrive electric-assists do not have the same gravity feedback as Bionx systems, so the orientation of the axle doesn't matter. Both of these European systems use a splined interface that allows the torque arm to be angle however it works best for the physical shape of the cycle frame.


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