Hi,
I’m a programmer, and I totally new to electronics. The only thing I know in electronics is how to reheat food in the microwave.
I want to build a quadrocopter.
Can any one explain me (or may be put a pictures) how should i supply power to raspberry pi 2, Navio+ and to four motors?
I made a similar journey six months ago. As already suggested you should do reading but here are the main points:
Battery+ESC+Motor are the critical combination you need to have in balance…
The battery “C rating” is significant, multiply this number (30C in your example) by the amp hours (3.3*30) to get the maximum load possible, 99 in your case. That must be enough for all devices, e.g. four motors maybe at 10A * 4/quad = 40C then add a few amps more for the controller board and FPV equipment. The only other significant devices would be LED strips and stuff like that. Too low and nasty things will happen (flames in the sky). Too high is okay but then you probably paid too much money and had less choice, maybe even heavier then. Perhaps a 20C would be enough at this capacity, or a lower capacity to reduce weight.
There is also a burst C rating which is an extreme draw together with a number of seconds it can withstand it. That may be touched upon when doing tricks and crazy things with your quadcopter, depending how close to the normal C rating your specification was in the first place.
Motors are the main cause of load and so their maximum amps tells you which ESCs you need, at least the same plus 20% to prevent nasty surprises (flames in the sky again). Sometimes it is not clear and that is not worth the risk so hit the forums to search for independent motor test results. For example the Hobby King “Baby Beast v2” is a nice motor which should only draw about 10A but some people have recorded up to 16A when using 6 inch props and a greater pitch. For this motor a 12A ESC would be the minimum, maybe even 20A to be safe but then you need a battery like you already chose with a lot higher C rating.
The ESCs constantly draw the amps even if you are not using them, so a 20A ESC when you only need 12A will result in shorter battery life. With the Baby Beast v2 and 20A I was only getting about six and a half minutes with a fully loaded 0.75kg quad (full Pixhawk with FPV gear and APM telemetry). The same quad with 12A ESCs runs well over seven minutes and the ESCs did not burn out yet.
The thrust of the motor is required to lift the quad of course and you should be hovering at “half stick” (neutral/middle position). It’s measured in grams so it’s easy to calculate by taking the total weight of the quad, doubling it (so half is neutral), then dividing by the number of motors (4 of course on a quad). Most mini/FPV quads are about half a kilogram to 750kg including the battery, so you’ll need 400-500g of thrust unless you built a real lightweight. Many mini-quad motors only spec around 300g thrust. The trick is to use 6045 props and three blade props if you are building something at the heavier end, with the Baby Beast v2 you can get over 600g of thrust then! I found that on the forum tests and verified it myself to be true by purchasing a thrust stand. Actually you don’t need that because if you’ve under-spec’ed it won’t get off the ground or won’t hover at half-stick so be hard to fly and drain the battery quickly. That was a lucky choice for me then, so unless you specifically want the Baby Beast v2 with 6045 props too, I’d recommend using a different motor running near manufacturer specification!.
Flight time is of course provided by battery power so the next question is normally how heavy can the battery be (because more capacity means more weight). The rule of thumb (I found on various forums) is no heavier than the weight of the quad without the battery. But in my experience it’s a lot less, say 35-40% percent. For example 2200mAh 3 cell batteries give me 7 minutes, but 4000mAh only10-12 minutes (not double/14 minutes like the capacity almost is). That’s unfortunately the limit because the heavier the quad is the greater work the motors do which means more draw on the same battery, so we quickly get to a point where we cannot add more flight time without re-designing the multi-copter with more motors or just making it bigger overall (motors/propellers/battery cells and frame).
3 cell batteries are common but 4 cells will give more extreme power to the motors (check the ESCs, PDB and motors can handle it) and if you have 12v FPV cameras and transmitters (common) may be necessary to deliver at least 12v all the time. 3 cell batteries which use BECs to produce 12v may only provide 11 volts for much of the flight time, so your video feed could drop-out halfway through! There are many good 5v FPV cameras (e.g. Mobius) and also 5v FPV transmitters. But luckily by choosing Navio you have the possibility to eliminate the FPV gear altogether (use a RasPi Camera with Wifi), so 3 cell will be fine in this case. It’s something you need to check though; the voltage supply “operating range” for all devices you plan to install must be satisfied.
The best way to learn all this and remember it is to go watch the FliteTest YouTube videos. They have hundreds so look for the playlists relating to getting started with RC models and some others on your first flights with a quadcopter. They explain it very simply with visual demonstrations and humour so it’s also entertaining. The stuff I learnt from there saved me a lot of trouble and expense buying the wrong parts, as I learnt later I made a pretty good pick to start with.
