- Currently a FT Guinea Pig airframe
- Eventually capable of lifting several pounds of avionics to an elevation of several thousand feet AGL.
- Live on-board video feed
- Long range (70cm UHF link) control and 5.8GHz live video / telemetry (OSD)
A foam airplane made to lift a payload to 1,000'+ AGL for parachute testing in a rocketry project
In the RC forums you'll find mostly incorrect information about mixing batteries in parallel. You'll here that you shouldn't run battery packs in parallel, shouldn't mix capacities, and shouldn't mix C ratings.
I'll go over the basics of how to determine safe operation of mixed capacity/C rating batteries.
LiPi batteries will usually have a published cell count, capacity, constant C rating and burst C rating.
Cell count tells you how many individual LiPo cells there are, and hence the voltage. Fully charged each cell is 4.2V, and the battery pack follows the convention of "3S" or "4S". A 3S battery at full charge will be 12.6V.
Capacity is listed in mAh, or Ah. Pretty self explanatory.
C rating is a number that tells you at what rate the battery can be discharged at without damage (or fire hazard). A 5,200mAh 10C battery can discharge constantly at 52A without damage.
My plane has two 30A ESCs, and I have a 5.2Ah 10C 3S battery pack and a 2,250mAh 75C battery pack I want to fly in parallel. Is it safe?
Once both packs are fully charged to 12.6V, they are connected in parallel. Total capacity is now 7.45Ah, but what about the C rating?
Current will drain from both batteries at a ratio defined by their capacity. So for every 74.5mA drained, 52mA will come from the 5.2Ah battery and 22.5mA will come from from 2.25Ah battery.
So even though the 2,250mAh battery has a 75C rating, it is limited to the 10C rating of the 5.2Ah battery, and if we pull more than this from our parallel pack we run the risk of damaging the lower C rating battery.
But just because we are limited to 10C, doesn't mean we can only pull 52A. The 10C rating now applies to the whole parallel pack.
So 10C of 7.45Ah is 74.5A constant current without hurting the lower rated battery.
74.5A is plenty of current for my system, so all is good.
When combining multiple LiPo battery packs in parallel:
For example using two equal batteries, let's say two 1Ah 10C batteries, the parallel battery capacity is now 2Ah, and the C rating is still 10C, but now the highest discharge rate has doubled to 20A because the discharge rate is determined by C rating AND total capacity.
Alright, so in this post I'll be going over some of my incremental testing of my new UHF transmitter.
RSSI is the Receive Signal Strength Indicator value, and it comes from the onboard UHF receiver on the aircraft. This data is brought back to my ground station over the on screen display. The lower the RSSI value, the worse the control signal quality is to the aircraft, so it is important that we understand how it works with incremental testing of the system.
For the first couple minutes of this flight, I have taken the OSD data and graphed it. You can see I took the aircraft to 500m, and then out to 700m. The Orange line at the top is the RSSI value, and you can see when the aircraft gets close to the transmitter.
I believe I may need to alter the calibration on the RSSI curve a little bit to get a more consistent linear response. I also need to see where control dropout starts to occur.
Here are the videos! The first in HD with no OSD, the second is what I saw while flying (minus the skipping, which I believed is caused by a lower quality SD card in my DVR).
I'm going to be flying a UAS system capable of lifting several pounds to over a couple thousand feet, so I did some testing of range of both the on-board telemetry/video feed and my transmitter itself.
Overall the test was successful, but I will be needing to do a few things now to maintain legality and to further the design.
Here's a video of my recent test, which validates data paths to and from the aircraft at medium range. The next round of testing will use the long range electronics, capable of the distances necessary.
Since I live near the coast, there is almost always significant wind. In this case 15-17 knots from the west (the ocean). It certainly makes landing a bit more interesting.
My mid size cargo plane was built to teach me advanced flight with flaperons and differential thrust. My full size plane will be about 150% of this 58" wingspan with a more utilitarian body style.