on my quad, pitch,roll and throttle are working fine. When in stabilize the yaw appears to have the effect of moving along the 5oclock to 11 oclock axis, although i have to land fast before it crashes. In stabilize with simple mode enabled the quad immediately yaws after takeoff. All other inputs seem to be ok.i dont think its a compass issue. i have calibrated the compass and transmitter. The motor test in the terminal is operating as expected. The props are matched to the user guide.the frame is an x config.
Any ideas as to what is wrong?
Replies
PK, do you find that those arms vibrate in flight - i have the same ones (Cheap chinese i think) and i believe that under the weight of my quad they are vibrating and resonating to the point where the quad becomes unstable like i show in the video below.
excellent work. one can also use the other approach - add tape to shim between the motor and motor mount at the appropriate screw.
also, careful how and what you measure.
#1 rotating each prop tip to a stationary measure tape, primarily measures the perpendicularity of the prop to the motor (the prop to motor interface). This is a common problem even with high quality propellers.
#2 putting the prop perpendicular to the motor mast and measuring to the floor at each tip, primarily measures how level the motor mount is to the ship (the motor to mast interface) in the y direction (common issue with bolt-down motor mounts).
#3 putting the prop parallel to the motor mast and measuring to the floor at each tip, primarily measures how level the motor mount is to the ship (the motor to mast interface) in the x direction (an error here is not as common).
Do #1 first followed by #2 or you could end up chasing a tail.
All,
thanks for the input.I recently bought new motors and new carbon fibre props.Lets call this SETUP-A. Note the motor is mounted on an extended piece for the following Reason.
SETUP-A
After listening to Forest and Randy i now mounted the motor directly onto the fram - making sure that the screws dont extend into the motor wiring. Lets Call This SETUP-B which i tested yesterday.
SETUP-B
Now SETUP-B solves the yaw issue but there is a twitching and jumping - I think it's one or more of the motors is vibrating. So i think with the new motors, New Much Stronger props (old were APC) and the weight of the quad, that resonance is making a play here. See the following Video
So basically i think my quad is not strong enough for the weight - I was going to buy this.
What are your thoughts on the matter ? And if you have any other frame suggestions then i am open to suggestions.
A high speed camera would be useful.
Impressive. Quite the beast!
Engineering rule #1. Never add dead weight.
For example, a metal extender was added. This:
- adds weight
- requires higher rpm and vibration to lift
- weakens the copter (makes it less stiff)
- better to use nylon bolts for the motor (subtracts weight) that can be cut to the perfect length so as not to damage the motor (also eliminates the need for the redundant X motor mount.
Engineering rule #2. Stiffer is better. Holding the copter firmly to the ground, pull down on the end of a motor mast and let go. If you can make it vibrate (more than up/down/up) then it is not stiff enough. If it bends more than 6mm when normal payload weight is applied to it, it isn't stiff enough.
Engineering rule #3. Use good rotors. The plastic props shown are inefficient. What are the carbon props you just got?
Can I assume that you don't feel comfortable building your own? There are parts of your copter that are adequate and could be used on a stiffer, lighter, stronger frame you could make yourself.
I'm not familiar with the frame you are considering buying.
Forest,
These are the Carbon props.
Can I assume that you don't feel comfortable building your own? I prefer to buy.
You know i think tomorrow evening i will try to prove my theory by making the existing frame very light - i.e remove the landing gear + camera and use a smaller battery. Does this sound like a good idea - At least it will prove in theory that a stronger frame should sort the issue.
Yes, brilliant idea.
also consider removing the motor extenders and find the correct size bolts or get nylon ones (or aluminum or steel) and cut them to the correct length. You've inadvertently added a diving board. Then test.
The carbon props are plastic with carbon fiber fill. It makes the plastic stronger. Haven't tested those props. The best 11" props I've seen so far are: APC 11x5.5 C-2 or GemFan 11x4.7 AG-G.
forest, so i rebuilt on a new carbon fibre frame. it hovers at 80% throttle for about 2 minutes. yaws to the right a little bit and then drifts down. i give it 100% throttle and it still drifts down. i have tried all of my batteries.same symptoms. i am at a loss here now as to what the issue is. i have attached two short flight logs.
2014-09-11 22-47-18.log
2014-09-12 10-08-26.log
If you have 50% battery left, then it isn't your battery. It's the ship design. The ship is too heavy for the rotors or the rotors are too small for the ship.
Its the 80% throttle to hover. It needs to be 50% or less. The batteries prove it. At 80% throttle, you are pulling so many amps that the voltage of the battery drops significantly, making it think it's empty so your ship slowly falls out of the sky. When the amp load is removed, voltage immediately goes back up showing 50% left.
Remove weight or change the rotors.
First - Rebuild your copter is a must
a) hover should never take more than 50% throttle. the ship will be uncontrollable in moderate wind and take way too many amps. Thus:
... remove weight by doing a weight study and replacing parts with lighter components
... or change the rotors (motors and or propellers) so they are sized to carry the weight.
b) ensure that your ESCs are Simon K firmware (it sounds like they might be). The behavior at the end of battery life as voltage drops is the copter will slowly fall out of the sky. So you increase throttle to counter. Finally, there isn't enough % recovery left so it can't do a yaw correction without falling more out of the sky. To see this, enable CURR and track your volts and amps.
c) ensure that your battery has a high enough C. As the battery voltage drops, the ship becomes more efficient (about 1 to 2% more). So the ship will stay aloft at fewer watts. but as voltage drops this means the amps must increase, taxing the C of the battery. a chemical barrier builds up and the ability of the battery to deliver the watts drops off suddenly.
So it sounds like a typical case of going through a battery too fast.
Good news. I used some old 3000 mah batteries and i can get about 5 minutes flying time. It still hovers at about 70% which is not right. So what did i change in the last few months that could cause the issue? i remember i bought new motors and props. back then i bought these motors and these props. Now the motor spec recommends 12X45 as opposed to the 11X50 i bought. Does this explain the significant power loss? i am going to ask a separate question on the topic.
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