The reverse transmission efficiency (also known as back drive efficiency) of a harmonic reducer refers to the efficiency when torque is applied to the output end (such as a robot joint) to drive the input end (such as a motor shaft) to rotate. Compared with forward drive, the reverse efficiency of harmonic reducers is usually lower and greatly affected by reduction ratio, temperature, and lubrication conditions.
Is the Reverse Efficiency Always 80%?
Under certain ideal operating conditions, the reverse efficiency may approach 80%, but this is not absolute. In practical applications, the reverse transmission characteristics mainly depend on the reduction ratio.
Low reduction ratio (such as 1:30, 1:50): The reverse efficiency under this reduction ratio is relatively high, and the output end is easily rotated by external forces, with good "backdrivability".
High reduction ratio (such as 1:100, 1:120 and above): The reverse efficiency drops sharply at this reduction ratio. Due to the increased friction caused by internal gear meshing, high reduction ratio models are difficult to reverse drive, and in some cases even have a self-locking tendency (i.e. cannot rotate the input end through the output end).
Starting Torque: More important than just "efficiency percentage" is the "reverse starting torque". Due to the presence of preload force in harmonic reducers, static friction must be overcome before they can start rotating.
Why Does This Matter?
Understanding reverse efficiency is crucial for applications such as:
Collaborative Robots (Cobots): For "teach modes" where a human guides the robot arm, low resistance (good backdrivability) is essential.
Safety: Knowing if a load will hold its position or backdrive when power is lost.
Conclusion
For most Hansheng harmonic reducers, you can expect reliable performance, but for applications requiring specific backdriving capabilities, we suggest that you review the drawings of our harmonic drive, from which you can obtain more information, or you can also contact our engineers.