eCVT e-bike hub motor - Cedric's Substack

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eCVT e-bike hub motor<br>Jun 20, 2026

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This is about the development of an eCVT regen e-bike hub motor. eCVT stands for electric continuously variable transmission. E-bike motors with this technology can maintain a pedal cadence regardless of the riding speed. They do this with a clever combination of an electric motor and gears. This eliminates the need for shifting mechanisms like a derailleur, and it’s compatible with belt drives, which are clean and low maintenance. My mountain bike drivetrain invention (Supre Drive) cuts derailleurs in half, and my idea for an eCVT hub motor eliminates derailleurs, so you could say I have a complicated relationship with derailleurs.<br>There are commercially available eCVT e-bike motors that are mid-drive, but as of this writing, none are hub motors (where all the magic is contained in the hub). In addition to the eCVT aspect, my hub motor idea has a new regen technology from the inventor Alon Goldman which enables regenerative braking controlled with a conventional mechanical brake. There are lots of fascinating concepts in this hub motor. Rather than dive straight into a technical explanation of the hub motor itself, I’ll share the story behind it.<br>This idea originated shortly after I learned about the regen technology from Alon Goldman through a Youtube video from Grin Technologies (they refer to it as Freegen). Alon came up with a novel idea for regenerative braking with the same intuitive user experience as conventional brakes on bicycles. Regenerative braking, or simply regen, is where the e-bike’s motor acts as a generator so that braking power charges the battery instead of being wasted as heat. There are no brake levers on the market that control regen braking electronically while providing the same physical user experience of a conventional brake lever. Alon’s idea enables the control of regen braking with a conventional mechanical brake, and it does this in a fascinating way.<br>Electric motors like to spin a lot faster than bike wheels or cranks, so e-bike motors often have a gearset for reducing the speed of the electric motor down to the speed of the wheel or crank. This gearset often includes a planetary gearset. Planetary gearsets have an inner sun gear, an outer ring gear, and a few planet gears between them with these planet gears supported by a planet carrier. Typically, the planet carrier is fixed, and there’s a fixed reduction ratio between the sun gear that spins fast and the ring gear that spins slow. If instead the planet carrier is allowed to rotate, the gearset has a total of three inputs and outputs (in other words, it has two degrees of freedom).

Alon’s idea is to attach the brake rotor to the planet carrier. This enables the mechanical braking force to control the amount of regen braking power. When the rider brakes, the system has a target rotation speed of the brake rotor and therefore the planet carrier. Braking forces slow the planet carrier down below the target speed. To get the speed back up, the motor needs to apply regen torque at the sun gear to counter the braking torque at the planet carrier. The extreme of this is that the rider brakes so hard that the brake rotor stops, which makes the sun gear spin fast with the motor applying a maximum of regen torque. This Freegen idea allows the rider to communicate to the motor how much regen braking they want using a conventional mechanical brake1. In other words, it’s mechanically-modulated regen braking.<br>When I learned about Freegen in the summer of 2024, I was also aware of another interesting mechanical concept which is the gearset in the TQ HPR50 e-bike mid-drive motor. Their gearset has two cycloidal gears connected with an eccentric gear that is double-sided, each side meshing with either the inner cycloidal gear or the outer cycloidal gear. The eccentric gear has the same function as the pin ring of a conventional cycloidal drive — in fact, in TQ’s gearset, the teeth of the eccentric gear have the same geometry as a series of round pins, just like the pins in a conventional cycloidal gearset. To learn about how conventional cycloidal gearsets work, check out this video. TQ’s gearset has two cycloidal gears and two pin rings, unlike a conventional cycloidal gearset that has a single cycloidal gear and an output shaft with pins that wobble around in holes in the cycloidal gear. TQ’s gearset has half the reduction ratio of a typical cycloidal gearset, but on the other hand, it’s very compact. The following animation shows the motion of the apsion gearset with cycloidal gears in the TQ HPR50 motor (excerpt of this video).

As a side note, TQ calls their gearset a “harmonic pin ring”, which implies that it’s a type of harmonic gearset, but harmonic gearsets, also known as strain wave gearsets, are a completely different thing that involves a flexing gear. TQ’s motor does not have a flexing gear. You could...