Some of us have been behind the scenes for a while, dealing with the latest issue found on the LPF family...
At mid October a Polish AFOL found one potential problem with the new PF V2 Receiver (released with the 9398, 4x4 Crawler) when there are two PF M-motors connected to one of its outputs.
The issue can be put shortly like this - When two or more Medium motors are connected to a single output of the V2 Receiver (no matter which one), they often make a squeaking sound instead of starting, and only start after some time, or if forced by hand. Even after they finally start and then stop, the problem occurs again.
Today after having concluded their own investigations, the Technology Platform Team came-up with one official statement about this issue, signed by Gaute Munch as usual.
LEGO Power Functions V2 RC Receiver
There has been some confusion regarding the new LEGO Power Functions V2 RC Receiver that is released in the Technic 9398 4X4 Crawler. This component is currently only available through the 9398 set, but was not made exclusively for this product.
The V2 RC Receiver is updated with a CMOS motor driver giving less power loss. This is done to improve the user experience with longer battery lifetime and better motor performance. Unfortunately it has the drawback that it is not able to start 2 or more LPF Medium motors at the same output. As I will explain below this is not a problem with the motor driver, but a known issue with the LPF Medium motor.
The raw motor currently used in the LPF Medium motor internally contains a relatively large capacitor (1 uF) across each of the 3 motor coils. This is done by the motor manufacturer for noise reduction.
We knew that this would be an issue with the new CMOS motor driver (DRV8833). Since it can source a very high inrush current the over current protection will kick in sooner (typically after 2,25 us with a current exceeding 3,3 A). At start up the motor driver will first charge the input capacitance. With 2 or more LPF Medium motors at the same output this can trigger the over current protection. It will repeatedly try to start the motors and you will only hear a singing noise.
For many reasons we have been searching for a higher quality solution for the LPF Medium motor and we now have an approved new raw motor. It has better quality commutation and only 1nF across the terminal. An updated LPF Medium motor will be released during 2013.
Backwards compatibility is of very high importance when we choose new solutions. In this case our decision was that the advantages of the new motor driver together with the fact that we would update the LPF Medium motor would compensate for the inconvenience with the current LPF Medium motor.
We hope this is not causing too many limitations to your model creativity.
The LEGO Group
We guess the Tech Platform team has been frantically searching for a replacement for the raw Medium motor, in the last weeks.
Although the problem has been identified a the solution as well, we will remain with a legacy of 'not so compatible PF elements'. At this point and thinking on the possible remedy, I can only wish TLG will make the new version of the PF M-motor easily distinguishable from the original version actually in the market.
We had already two versions of the PF IR Receiver (with firmware differences only) and two versions of the large Technic Linear Actuator, which are inconvenient enough to distinguish...