OK well, I've had my fill of complete drones and I have sitting on my desk (for the last five years) a true open source drone, so time now to be a real nerd and get it all running. So there is lots of confusing terminology here, but basically a complete drone has two (and sometimes three different subsystems at the same time):

1. Flight controller hardware. This is the low level ARM controller that runs things. Pixhawk is one of the largest standards here. They have open source designs in Pixhawk 2 and 3 and their latest is closed source Pixhawk 4. You can think of them like Raspberry Pi which uses a proprietary Broadcom System on Chip and then the rest is open source.
2. Flight controller software. On top of this runs the low level flight control and there are two flavors Ardupilot and Dronecode's PX4 and many arguments about which is better. For the purposes of this post, we will focus on Ardupilot.
3. Remote control transmitter. OK, this is a little confusing, but there is a separate protocol just for joystick control. This is very low level and typically, these days it is running at 2.4GHz so works in the same spectrum of WiFi 2.4. It does frequency hopping and so forth. You basically buy a thingy with a joystick and the fancy ones require that you buy our own battery system and also you can put different transmitter modules at different frequencies with 433 Mhz and 900 Mhz for the US being common. This is a point-to-point protocol so you want lots of frequencies and the ability to hop.
4. Remote control reciever in the the drone. Because there are a bunch of frequencies, the typical DYI has you buying this module separately.
5. Telemetry in the drone. OK, this is also a little confusing, but there is another layer of control that is computer control. This uses a different frequency from the RC control. It was originally just for telemetry (that is digital facts about the drone that was one way from drone to a ground station, but is now two way). So this can also run at 900 Mhz or 2.4GHz. So you get to select that as well. This is also a point to point protocol.
6. Video downlink. OK, if you are flying First Person or you have a DJI Mavic drone, then they will also transmitt video down. This also can be done at 2.4GHz or the WiFi5 5GHz band (it uses the same frequeniceis but divides them dffferently, so depending on how many FPV links you can 4-6 videos at most
7. Companion computer. You can also have attached a full computer that talks to the flight controller over a serial port using the Dronecode Mavlink protocol. This is completely separate and can have its own networking. Typically, it might have a WiFi 2.4GHz or 5GHz connection. And this is multipoint protocol since obviously with WiFi you can have lots of stations connected to an access point.

## Making the Radio Frequency Decisions:

So, net, net, when you get a drone you have four different signal decisions to make so to give some examples of drones:

Arksey Pixhawk 2/Ardupilot. This was our first effort at this and it flies with

1. 900Mhz telemetry so it can talk with the Ardupilot computer-control software on 900 Mhz
2. 2.4GHz RC. You can also control it manually with a FrSky Taranis QX9 Plus over 2.4GHZ
4. No companion computer networking

Arksey Pixhawk 4/PX4. This is our second effort which swaps in a new flight controller and we use the Dronecode stack

1. 900Mhz Telemetry. So a computer running Dronecode Mission Control can fly
2. 2.4GHz RC. Same manual control
4. No companion computer networking

Holybro PX4 Vision (PX4 documentation) is one that Dronecode has on their site, but you can see how 2.4GHz is going to get crowded if you are flying just one of these, it will be really complicated if you are flying 10 as the first three are all point to point protocols:

1. 2.4GHz Telemetry to run Mission Control
2. 2.4GHz for the FrSky Taranis QX9 Plus or QX7s to fly manually
4. 2.4GHz for Intel Atom Companion computer WiFi.

Well, PX4 recommends the FrSky Taranis X9D-Plus and there is the lower spec Taranis QX7S both of which have 2.4GHz Remote control built-in. The main things are:

1. Batteries are not typically included with these setups, so for instance you can get the ZOP Power 7.4V 3000mAh 2S 10C for $15 at Bangood from China arriving in six weeks. 2. They come with typically a base 2.4GHz transmitter but you can buy a separate one if you have specific needs. The internal one has 16 channels if you use a ACCST D16 receiver in your drone or 24 with ACCESS receivers. The Taranis Q X7S is a nice bundle at$159 because it includes a 2000mAH NiMH battery pack (now it says it uses two 18650 LiPo and a 2S LiPo or NiMH charger and a carrying case. Note that, unlike the Taranis X9D, you do have to unplug the pack to charge it. It does have Bluetooth inside of it as well, so you can connect the controller to a software trainer to practice with their Frsky Telemetry App which lets you record all the moves you make manual control. And it works with the latest ACCESS (see below receivers).

If you do the Q X7S, you also need 18650 battery chargers. These are also useful for professional Li-Ion flashlights, so asking Bikecologyla (not very useful) and 1Lumen.com, here is what we get, but the best chargers here are the ones that don't need it, so you might just get a 18650 with its own micro USB charging cable. But, the Opus BT C3100 I've had versions of and it definitely works.

If you want to splurge then for $280, you can get the X9D Plus SE 2019 for$280 from Asia via Banggood