Less than 6 months is reasonable if you have the right background in soldering/assembly, Arducopter, Python scripting and Linux
The first major hurdle you will encounter is that there are only 4x motor PWM outputs from the solo Mainboard (since that is all they need for Solo). So to get the other two for a Hex, I believe you will have to remove (and possible dismantle) the Pixhawk2, find where the other outputs come from (see if you can find the pinout of the 80 pin connector between the Pixhawk 2 and the Mainoboard), and solder additional outputs for them. I hope you have SMD-level soldering skills and a very fine soldering tip!
Obvious things you will have to reconfigure in software:
- Frame type,
- IMU and compass orienation
- Flight PIDs
- Tuning in general - you will have to re-tune every relevant flight parameter for your Hex from the ground up, but if you have used a Pixhawk or Ardupilot before then you will be familiar with this process
Less obvious things you may have to reconfigure/consider, depending on how deeply you want to jump into this:
- All of your flight parameters tuning must be done manually in Mission Planner or similar connected over WIFI. Never use the "tortoise/hare" slider in Solo App for tuning another aircraft. This slider changes a host of different parameters in the Pixhawk that are fused together in a way that is optimized for Solo only, and may produce quite different behavior in other aircraft. Keep in mind that using the autotune feature is available, but there are no auxiliary switches available from the Solo controller, so you will need a computer/tablet connected over WIFI to initial the tuning sequence through Mission Planner (I think Tower can do it too).
- If you plan to use any other type of gimbal other than Solos gimbal, or camera other than the GoPro, then you have a lot of work ahead modifying the Arducopter gimbal parameters, python scripts in the companion computer and getting gstreamer to work. The gimbal stuff isn't too bad, but I don't know how to even start with gstreamer. If you have had lots of experience in Linux environments then this may not be too hard for you though.
- If you plan to use a different battery from the Solo Battery (I assume with a 900 size frame that you will need more juice) then there is also a bit of work to be done. If you want to use a conventional 'dumb' LiPo, you can either try to tap into the analog input pin as per the extra 2x motor PWMs I described earlier (this pin is not expressed anywhere on the Solo mainboard unfortunately), or try to make a custom script that runs off of an Arduino that speaks in I2C to the autopilot. I have used a 5S battery with Solo guts, and I think it can handle up to 6S too. I would be very careful about more than 6S however - I think some of the regulators may only be rated to 26V. Also if you are using regenerative ESCs at 6S be particularly careful as they may pump in way more than 26V in braking conditions. Needless to say, the Arducopter parameters that relate to the battery management system must be modified to reflect the characteristics of whatever battery you choose.
The only other big thing I can think of is to be
very careful with applying Solo updates - they can change the Arducopter parameters, which could drastically affect the way your aircraft flies (
or crashes).
Hope this helps, best of luck