You Reply: I've purchased quite a few of your DSS-M15S servos and other DRFROBOT products before for use in RC based Robotics applications at our Mind Labs STEM education center and we have previously been quite satisfied. Just received two newly purchased DSS-M15S Servos (this time sold by Amazon Prime) that seem to be very defectively manufactured. Both servos exhibited exactly the same defects. They both were grossly non-linear and very jerky in exactly the same way when sweeping them with a smoothly and relatively slowly increasing and decreasing PWM servo test signal. These servos would never have passed any sort of useful final test so my guess is that none was performed. Certainly such defectively manufactured servos should never have been shipped to a customer. If you are unaware of this problem I believe you should recall these defective servos immediately before they significantly negatively impact customer perception of DFROBOT's products.