GOBAO ECVT EMTB Mid-Drive Motor

[TonTonUB]

The second motor needs to be strong enough to oppose the input torque it encounters, but that means it needs to resist a fraction of the torque of the primary motor. It runs at (potentially higher RPM and) lower torque because it spins the sun gear. The primary motor needs to spin the output ring.

Here's a diagram that shows where MG1/MG2 are connected, where you can see the smaller windings. Note how the MG1 only drives the sun gear, but MG2 drives the output, thereby requiring higher torque (yeah, it's another car pic, but there aren't any good diagrams for bike MGUs yet):

View attachment 187960

MG1 rotor on right side (MG2 rotor instead?) Typo maybe ?
Whatever, very interesting.

 

[ArmyOfEvilRobots]

MG1 rotor on right side (MG2 rotor instead?) Typo maybe ?
Whatever, very interesting.

Good catch, I didn't notice when I posted the image. Yes, the MG1 rotor is on the left, MG2 rotor on the right, and whoever made the diagram did a bad copy-pasta.

 

[jeanjean]

(yeah, it's another car pic, but there aren't any good diagrams for bike MGUs yet)

Best diagrams, to my opinion, to be found in the e2drives patent applications.

 

[emtbeast]

The second motor needs to be strong enough to oppose the input torque it encounters, but that means it needs to resist a fraction of the torque of the primary motor. It runs at (potentially higher RPM and) lower torque because it spins the sun gear. The primary motor needs to spin the output ring.

Here's a diagram that shows where MG1/MG2 are connected, where you can see the smaller windings. Note how the MG1 only drives the sun gear, but MG2 drives the output, thereby requiring higher torque (yeah, it's another car pic, but there aren't any good diagrams for bike MGUs yet):

View attachment 187960

Yes good find, this is a diagram of a coaxial drive like in the 1st to 3rd generation Toyota HSD transaxle.
The 4th and latest 5th generations are parallel layout, I think @Ndanger posted a diagram of one. The Gobao and Avinox MG are most probably parallel layout drives as those are newer and have a few advantages.

Coaxial vs. Parallel Axis Drive
Toyota shifted away from the strictly coaxial layout to save space, reduce weight, and improve mechanical efficiency:

Generations 1 through 3 (Coaxial): The gasoline engine, the smaller motor-generator (MG1), and the main traction motor (MG2) were all arranged inline on a single, long central axis. While elegant, this created a very wide transaxle that was difficult to package into smaller engine bays.

Generations 4 and 5 (Parallel Axis): Toyota completely redesigned the transaxle. They moved MG2 onto its own separate, parallel shaft adjacent to the main engine/MG1 shaft.

Reasons for the Parallel Axis Drive:

Reduced Width: Moving MG2 to a parallel axis allowed the transaxle to be significantly shorter end-to-end, making it much easier to fit. (Probably also better for ebikes to have a narrow crankset Q factor).
Less Friction: The parallel layout allowed Toyota to replace the heavy, multi-layered planetary reduction gears previously tied to MG2 with a simpler, lighter parallel reduction gear, cutting mechanical power losses.

In 2019 Toyota released approximately 23,740 patents awarded over more than 20 years of electrified vehicle technology development for free use(that is a lot of R&D). A boom of hybridization of cars in different forms in the automotive world started right after the Covid time passed.

I am pretty certain that these two ecvt drives and some of the existing ones floating on the market are scaled down ecvt drives based on fundamentals from Toyota's patents. The only main difference being is replacing the ICE with human leg input power.
That's a significant difference in power so the down scaling was the real R&D for Avinox.

When asking AI to scale down the Toyota e-cvt to emtb middrive level and substitute the ICE with human power this is what it threw out: If anyone is interested, there are some interesting other things to read...

Power Ratio Scaling:

In an eCVT car, the power ratio between MG1 and MG2 is roughly 1:2. In an eMTB, because human legs provide the entry torque and space is highly restricted, the ratio widens to about 1:4 in favor of MG2.

• MG2 (The Drive Motor): 250W to 500W rated with peaks up to 600W-900W). It provides the raw assistance power.

• MG1 (The Control Motor/Generator): 60W ta 150W rated. It does not propel the bike directly, instead it's main purpose is applying "reaction torque" to the planetary gearset to infinitely vary the gear ratio.

The Lever Analogy & Torque Split Math:
To understand how the eCVT controller commands MG1. we have to look at the torque split mathematics and the control loops governing the planetary gearset.
In a planetary gear system, torque cannot be applied to one component without a reaction torque balancing it on the others. The system behaves like a mechanical lever where the Planet Carrier (your legs) acts as the main fulcrum in the middle, balancing the Sun Gear (MG1) on one side and the Ring Gear (MG2/front chainring) on the other.

The Fundamental Torque Equation
The physical constraint of a planetary gearset dictates that torque splits based on the number of teeth on the Ring Gear(R) and the Sun Gear(S). In a compact bicycle gearbox, R should have about twice as many teeth as S. The static torque distribution should look something like this: MG1 always experiences cca 1/3 of your leg torque, while the Ring Gear (output) receives cca 2/3 of vour leg torque. This relationship is fixed by the metal gears(teeth number) and cannot be changed by software.

The Controller's Computational Logic:
The eMTBs controller processor checks sensor data (cadence, rider torque, wheel speed, and incline) to decide how to run MG1.

Scenario A: Simulating a Low Gear (Climbing a Steep Hill):
You hit a steep wall on a trail. Your leg cadence drops to a sluggish, knee-straining 40 RPM, but you want to spin comfortably at 80 RPM. To allow your legs to spin faster while the wheel is moving slower, the controller commands(this depends on the mode you are using Auto, Manual Shift,....) the internal inverter to spin MG1 forward in the same direction as your legs.

The Result: MG1 acts as a motor, consuming electricity. This relieves the resistance on the planet carrier, acting like a tiny mechanical lever that lets your legs spin up to an effortless 80 RPM while the bike crawls up the hill.

Scenario B: Simulating a High Gear (Decent speed on flat ground or flying down a fire road):

The wheel speed is high, and your legs are spinning out at 100 RPM and you want to feel more resistance so you can push the bike faster. To reduce the cadence relative to a very fast-spinning wheel the inverter applies an electrical load(regen) to slow MG1 down or actively spin it backward.

The Result: MG1 resists the movement and acts as a generator. It absorbs the excess kinetic energy from your legs, turns it into electricity and either shunts that power directly into MG2 to help push the wheel, or sends it back ta charge the battery. Your pedals stiffen up mimicking a hard, high-speed gear.

The "Dead Battery" Dilemma:
In Toyota's system, if MG1 has no power, the car cannot drive because the engine's power just spins the unresisted sun gear into infinity. On an eMTB, a dead battery means MG1 cannot provide reaction torque. Without a mechanical lock-out clutch to freeze MG1 when the battery dies, the rider would pedal completely in a void, unable to move the bike at all.

The Mechanical Safeguards for a Dead Battery situation:

To prevent riders from being stranded deep on a trail, engineers can use different mechanical failsafes:

The Electromagnetic Fail-Safe Lockout (Brake):
A small, spring-loaded electromagnetic brake is held open by the battery's residual power. The moment electrical power drops below a safety threshold, the magnet de-energizes. Strong mechanical springs slam a locking pin or clutch into MG1 (the sun gear), forcing it to freeze solid.

The "Default Fixed Gear" Mode:
With MG1 locked to the housing, the planetary gearset stops acting like a CVT and locks into a single, permanent mechanical gear ratio (usually a low, easy-to-pedal climbing ratio). Your feet are now directly, mechanically linked to the rear wheel, converting the eMTB into a heavy, single- speed analog mountain bike.

The BMS Buffer:
Modern Battery Management Systems (BMS) never let an e-bike drain to a literal 0%. When your display screen reads "0%", the system has shut down the power- hungry traction motor (MG2) to save a hidden 3-5% buffer. This remaining juice keeps the controller awake and keeps MG1 locked or positioned so you can limp back home safely.