The new ART4 quadcopter on TBS is almost finalized. So far, in my mind there was one unfinished element in this quadcopter.

Modem. Yes, with Raspberry PI3 I had problems with my Huawei E3276s modem. Sometimes the modem did not work and sometimes stopped. On the other hand, I did not have any problems with the E3372h.

At first, I thought it might be a "modem manager" problem or a Linux compatibility problem.
Because the second E3372h modem worked perfectly with both PI3 and PI0w, I decided to change the Huawei E3276s also to the hi-link version. Now both modems are hi-links and do not require the launch of the modem manager, but this change did not solve my problems.

E3276s does not work well with PI3. I think this problem may be related to currents on Raspberry USB ports. PI3 is not powerful enough to power this model.

But this modem works very well with Pi0w, where all the current is available on one USB port, not like in PI3. After all these tests and modifications, the two modems are re-connected and the final modems work as follows:

• Huawei E3276s - works with ART3 (with integrated PI0w). It is also a Hi-Link modem.
• Huawei E3372h - ART4 with the PI3 mainboard.