Clean voltage investigation

I find it hard to maintain stable vertical height whilst flying my quadcopter, sometimes it takes almost 100% throttle to prevent touchdown and even after a short time at a stable altitude the quad either rises rapidly or starts to drop. This is all with stabilise mode on, asking the APM do do alt hold or position hold is no better, but as the guides say, I should get stable working first then look at the other modes.

I built the quad from parts from HobbyKing (ESCs, motors and batteries) which having read more of this forum was perhaps a mistake.

The behaviour makes me think that perhaps the motors are not getting constant clean voltage, pointing to either a problem with the battery or the ESCs. I have a couple of batteries and some are better than others but none are as good as I think it should be. This makes me suspect the batteries.

Flying today the quad would get itself into a spin requiring full anticlockwise lock to hold straight. This makes me suspect at least one of the ESCs.

Is there a way to test an ESC to see if it is providing a clean voltage, do the flight logs include the voltage level of the 5V rail to see if the battery could be dropping voltage sporadically?

If in a worst case the ESCs, batteries and motors are just not reliable for stable flight then I can justify replacing them with more branded components. If this is the case, the what are the best/recommended brands for motors, batteries and ESCs?

Sorry this is a bit ramble-y, I can't think how to describe the issues I am experiencing better. I can post logs or on board video if it would help anyone help me diagnose the problem.

Many thanks,
Tony

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3D RoboticsPermalink Reply by Chris Anderson on January 5, 2013 at 1:35pm

If you're using APM 2.5, the best thing is to get the Power Module, which will not only provide clean power but will also let you datalog the battery voltage and current. 

Permalink Reply by Tony Coupland on January 6, 2013 at 6:15am
I think I have the 2.0 rather than 2.5, will check. Does the power module work on both?

3D RoboticsPermalink Reply by Chris Anderson on January 6, 2013 at 9:48am

No, it just works on 2.5

Permalink Reply by Boston UAV on January 5, 2013 at 2:52pm

Are you saying that it sometime takes 100% throttle to hover? This would indicate that your quad doesn't have enough thrust.  Could you please list out your motors, ESC, and battery info?

While I highly recommend the 3DR power module or a dedicated BEC for powering the APM, I really don't think that is your problem.

Permalink Reply by Tony Coupland on January 6, 2013 at 6:33am
I don't think the problem is insufficient thrust since the copter is capable of vertical acceleration and when it feels like it quite resposnsive agile behaviour!

I have 2200mah 45-90c batteries, 1100kv motors and 30a ESCs all from HobbyKing (components list is available here http://blog.coupland.me/?p=707 ) my copter weighs 1.4kg now with camera and batteries.

Do you think that is sufficient?
Permalink Reply by Tony Coupland on January 6, 2013 at 6:40am
I have been trying to think how to describe my copters flight characteristics and realised something that might be helpful in diagnosing a problem (the problem could of course be the human element!)

I can maintain vertical position roughly if I only use the throttle control and move between 10 and 70% once airborne. However, if I use any of the other controls, rotation or strafing the when I release them the copter shoots upwards requiring counter action on the throttle.

This again points me towards suspect batteries to being able to deliver the power consistently. What rating and brand batteries would be recommended for a craft of this size, 1.4kg with 4x 1100kv motors with 8x4.5 props?

Thanks again
Permalink Reply by Tim McPherson on January 6, 2013 at 11:21am

Does it help if you lower your roll/pitch/yaw P and I gain parameter values some?

Permalink Reply by Boston UAV on January 6, 2013 at 8:09pm

I agree, seems like the PIDs just need some tuning.

Permalink Reply by Boston UAV on January 6, 2013 at 8:15pm

Tony: You should probably post what version of arducopter you are using and the PID values you have set.

Permalink Reply by Tony Coupland on January 7, 2013 at 1:50am

I reduced the PIDs significantly when I first built it which made the copter much more stable, but I am happy to make further changes if any one can recommend some.

I have an APM 2.0 and the following screenshot should show my PID configuration.


ModeratorPermalink Reply by Carl Campbell on January 8, 2013 at 12:23pm

Hey Tony,  I am running a pretty simalar setup with the same weight.  Turnigy Motors esc's etc.  I am also using 9 inch turnigy slow fly propellers as the 8's would not give me enough lift.  I have a set of 10's but I like the motor esc temps with the 9's better.  

A 2200 mAh pack will give me 5 minutes before my low voltage alarm starts squaking.  a 4000 goes almost 10.  that is regular flying.  Hovering around I get about 15 minutes on a 4000mAh pack or 7ish on the 2200  

Your pids look like mine too. I am running a .090 on the angular rate control. 

If I did not have the LVA alarm I would loosing altitude as the soft cut outs on the ESC's kicked in.  

Oh and moving threadto flying tuning Multicopters for greater exposure.

Permalink Reply by Tony Coupland on January 9, 2013 at 1:55am

That's interesting that you found the 8's did not have enough lift, I guess I need to get some different props and see how that changes things.

I have a LVA on mine too but the variable power problem seems to manifest way before the alarms start going.

I think I might pick up a 4000mah battery too and a good charger, what brand batteries do you run with?  From what I've read Turnigy Nanotech batteries are not as frowed upon as much as their other components, but perhaps having something other than HK parts would help diagnosing?

I've also just added a gimbal to my copter and the beginning of this short video show the problem I am experiencing with inconsistent thrust.  Don't know if it helps with understanding what component might be failing?

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