to7motor@SZ
🔌 New-ish
We’ve been closely following the community discussions around the DM02, particularly regarding the nylon gears and the shift to a 14A current limit. We appreciate the feedback, and we want to be completely transparent about our engineering choices, what happened with earlier units, and the updates we've made.
To achieve that near-silent, natural pedal assist, we used a fine-pitch (Module 1.0) polymer gear in the primary reduction stage, rather than the heavier m1.7 setup found in our DM01. It was a deliberate engineering choice because the finer m1.0 pitch provides smoother engagement, and the polymer material heavily dampens vibration, eliminating the "gear-grinding" feel you often get from larger-pitch or all-metal gears.
Pushing high current through the motor, especially at a lower pedaling cadence (30–50 RPM), puts a sustained load on the fine gear teeth. Because the m1.0 teeth are smaller to prioritize smoothness, they have less thermal mass to absorb heat. Under repeated heavy loads, heat builds up locally.
High-grade polymer doesn't snap or shatter like overloaded steel, instead, it softens as it hits its thermal limit. This softening led to deformation and faster wear over time. The issue wasn't a structural defect with nylon itself, but rather heat-driven fatigue under specific, heavy-load riding conditions.
The Design Goal Behind the DM02
The DM02 was built with a very specific ride feel in mind: lightweight, exceptionally smooth, and quiet.To achieve that near-silent, natural pedal assist, we used a fine-pitch (Module 1.0) polymer gear in the primary reduction stage, rather than the heavier m1.7 setup found in our DM01. It was a deliberate engineering choice because the finer m1.0 pitch provides smoother engagement, and the polymer material heavily dampens vibration, eliminating the "gear-grinding" feel you often get from larger-pitch or all-metal gears.
What Happened with Early Units?
In some early setups running at higher currents (16A–20A), some riders experienced premature gear wear. We looked into the root cause, and here is exactly what was happening:Pushing high current through the motor, especially at a lower pedaling cadence (30–50 RPM), puts a sustained load on the fine gear teeth. Because the m1.0 teeth are smaller to prioritize smoothness, they have less thermal mass to absorb heat. Under repeated heavy loads, heat builds up locally.
High-grade polymer doesn't snap or shatter like overloaded steel, instead, it softens as it hits its thermal limit. This softening led to deformation and faster wear over time. The issue wasn't a structural defect with nylon itself, but rather heat-driven fatigue under specific, heavy-load riding conditions.
Why 14A is the Sweet Spot
To address this, we ran extensive bench testing and real-world trials to find where the motor runs best. The data showed a clear pattern:- Thermal Stability: At 14A, the system stays within a safe, stable thermal envelope across a wide variety of riding conditions.
- Efficiency: Pushing past 14A on this specific m1.0 setup hit a wall of diminishing returns. The extra current wasn't translating into meaningful additional torque—it was mostly converting into waste heat, which was the exact cause of the gear wear.
The Updates We've Made
On the latest units and updated firmware, we haven't just adjusted the current. We've implemented several key upgrades:- Improved Thermal Management: The controller handles heat dissipation much more effectively.
- Refined Torque Ramping: The power delivery is less aggressive at low cadences, preventing sudden heat spikes.
- Upgraded Lubrication: We are now using a high-stability synthetic grease specifically formulated for MC nylon.
