I've put together a test stand for my 450 class quadcopter running APM 2.6/Arducopter 3.2. After a recent crash where my quad suddenly fell out of the sky, I want to run some tests on the stand, keeping most variables the same as if it were in flight. I'm pretty sure the crash was due to battery cell failure but I want to run some tests on the stand using the same battery (which still balance charges okay).
My quad is zip tied solidly to the stand, i.e. it cannot move. This presents an apparent problem because the motors won't all run at the same speed in Stabilize flight mode. How can I achieve this kind of test? Do I need to attach the ship to a rod on a ball joint? I've seen a couple of videos on YouTube where people did this, but I would rather have my ship solidly mounted. Have any of you done this?
thanks
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Jim Frantz has given me details on a test stand that he's used quite extensively. (I wish he had posted it here) but I'm building my own version right now. Its kind of like a stripper pole for my quad, lol.
If it works as planned, my quad will be able to roll and pitch as well as do 360 yaw moves on the stand. I'll post pics soon.
Yes do please post pics as this concept seems interesting. I'm picturing it in my head but missing the pitch/roll limiting design.
What type of ESCs are you using?
Have you checked their temp during the testing?
Are the ESCs rated for the type of motors you are using?
I'm using what comes with a stock QAV400 - Lumenier 30A ESCs with SimonK firmware and 1100kv motors. So this is a very well tested combination. I am checking temps as well. I want to get all of the motors running at the same speed on the test stand first.
I used bunji cords to attach mine between two trees. When attached to the bow and stern, this allows it to roll freely, allows some play up and down and a little fore and aft. All the motors spin. I use this to tune it in the roll direction.
Then I remount it sideways and so it can pitch up and down freely and tune that direction. This should be usable for what you want to do.
Make sure you have VERY strong and well-attached bunji cords, and PLENTY of clearance. At full power, these birds can pull a LOT. Also make sure ALL your motors have their snap-rings on their shafts. If you use full power on a brushless motor and the bird is anchored like this, the motor bell housing and prop can fly off. Trust me on this. Really. I learned that the hard way.
I would try the bunji cords if I was doing this outdoors for tuning PIDs. And YES, its amazing how much thrust these things produce! Also, good point about the snap rings. They were checked! (I had replaced some bearings recently)
The main purpose of my stand is to test motor power vs. current draw and to test the C rating of the batteries. I want to simulate a flight where I'm putting a full load on the battery. I know there are many others ways I could test battery capacity alone, but I want to test everything at once, with the props spinning, the motors, ESCs, and flight controller all doing their thing.
You probably realize this, but remember that if you are running full power, in real life, the craft will be moving and thus there may be more cooling of your ESCs, depending on where they are mounted. I wouldn't want them to overheat. And I wonder if their tempurature will affect their efficiency?
I use a Hobbywing 4-in-1 which mounts centrally, and so when the quad is not moving, there is very little airflow. I've had temp issues with it, even when flying, and in fact, I just had to replace it, probably due to the stress.
I guess, in your case, "full power" might mean that you have it flying as fast as it will go, i.e. full throttle, constant altitude.
In my previous test where my quad was firmly mounted, I was watching current draw and I was also using an IR temperature gun to read the temps of the motors and ESCs. I've considered that temperature might be a problem.
The way i've decided to handle this is real world. Run each test after the motor has reached temp at 50% throttle (about where one hovers). This can be done with a temp gauge of some sort or with time (run for 5 minutes and then test). Then run the tests for the same time duration.
We have been using this for years:
Hang the copter's CG from the ceiling (to eliminate ground effect).
Tie the copter to a jug of water on the floor, weighted so it can barely lift at full throttle. Loosen the jug's rope however much free movement you want, say 6 inches.
If you think you might go crazy, like a reversed motor, you can temporally tie safety ropes to the sides and jug. In the old days we used bungee cords on a big x brace.
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