I have a newer 3dr iris+ and recently had a flight where the Mission stated an altitude of 200meters. It flew most of the way at the correct altitude, but towards the end it started to get low, to around 50 meters. I was watching and I switched it into loiter mode and put the throttle high up and it had no problem gaining altitude.The battery voltage was fine as well, as it was a short mission.What could cause this? I was using the droidplanner2 android software....I can provide logs if needed....Thanks in advance for your help!
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I didn't answer your last question, no raising the C rating does not change motor speed** It is possible that the Higher C rated battery might have a lower drop in voltage which would result in higher sustained RPM, however there is no free lunch here as a higher C battery of the same voltage and capacity will be heavier resulting in higher thrust required to maintain a given attitude.
Doing a quick search of the forums I found a few posts you will be interested in concerning IRIS+ with a Gimbal and GoPro. It appears that a number of people have had similar experiences to yours and have come to the conclusion that the IRIS+ when flown in this configuration is underpowered. For the most part the solution appears to have been replacing the 3S with 4S power. Or at least that seems to be the recommendation that has been suggested. I would advise that if you do decide to go this route, be sure to provide a regulated power source to your Gimbal as feeding 14.8v to the Tarot 2D Gimbal would not be good!
I fly with 4S on my 3DR Y6B with a Tarot 2D Gimbal and GoPro and it does very well.
******One big caviat here, do your homework if you plan on using 4S, I can't find any information on 3DR's website about what motor the IRIS+ uses. The only thing I see is that it's a 920kv motor and uses T-Motor 9,5"x4.5" props. I suspect that they might be MN2212 v2.0 920kv T-Motors. If that's true then they don't accept 4S power.******
Nathaniel Caner > Nathaniel CanerDecember 29, 2014 at 12:02pm
From the IRIS+ Operators Manual
IRIS is compatible with 3S lithium polymer batteries only.
Using a 4S battery can cause permanent damage to the gimbal
electronics and will void the warranty.
As stated in a previous post you can get around the limitations of powering the Tarot 2D Gimbal by providing 12v regulated power using something like this, the added advantage being that you can also power the GoPro with 5v, meaning you don't need to worry about the GoPro battery going flat during the flight and shutting down.
I don't know this for a fact but I suspect the IRIS+ uses the same ESC as my 3Dr Y6B, in which case it can handle 4S power. So the only remaining question would be the motors. If you can confirm the motor manufacturer and the model, we can determine if it would support 4S power.
If you do end up going to 4S power you will likely need to tune some of the IRIS+ parameters yourself to compensate for the response caused by the increased RPM, you may also need to change prop size.
Yes, from the most basic standpoint you are correct. In forward flight, the faster you go the more thrust is required to maintain a given altitude. So slowing down in theory would assist in maintaining altitude. The fundamental problem as I see it, and hopefully Rob or someone else will either be able to confirm or correct this, is that you don't have adequate thrust overall to support practical flight. By practical I mean that it shouldn't require nearly as much power just to maintain hover. Your THR_MID parameter is set at 700 which means it takes 70% throttle to maintain a stable hover. This only leaves 30% reserve for forward flight, and more importantly recovery from unusual attitudes. The maximum recommended value for this setting is 70%, IMHO it's too high. So what can be done about it, simply stated we need to reduce the weight or increase the thrust and get that number down closer to 50%. Ideally I think you want to see that number in the 40-60% range. Without looking at the specs for the motor, I don't know if it can handle a larger prop size or a higher pitch, but that would be one way to increase thrust. If the motor can handle it, going to 4S instead of 3S is another way, by increasing max RPM you will increase the overall thrust.
Not knowing the IRIS+ and it's capabilities, I can't comment on what you can/can't do. I'll look further and see if I can come up with some more options. Do you know what the all up weight is with battery? Also do you know the diameter/pitch of the props you are using, and the kv/rpm of the motor on the IRIS+?
I did PM Rob and ask him to take a look at your logs, hopefully he'll have the time to do so and can shed some light on what's going on.
It is interesting that it states here what you mentioned regarding DAlt not holding if it is unable to... I just don't know why it couldn't hold the altitude. Too much speed?
Replies
Adam,
I didn't answer your last question, no raising the C rating does not change motor speed** It is possible that the Higher C rated battery might have a lower drop in voltage which would result in higher sustained RPM, however there is no free lunch here as a higher C battery of the same voltage and capacity will be heavier resulting in higher thrust required to maintain a given attitude.
Doing a quick search of the forums I found a few posts you will be interested in concerning IRIS+ with a Gimbal and GoPro. It appears that a number of people have had similar experiences to yours and have come to the conclusion that the IRIS+ when flown in this configuration is underpowered. For the most part the solution appears to have been replacing the 3S with 4S power. Or at least that seems to be the recommendation that has been suggested. I would advise that if you do decide to go this route, be sure to provide a regulated power source to your Gimbal as feeding 14.8v to the Tarot 2D Gimbal would not be good!
I fly with 4S on my 3DR Y6B with a Tarot 2D Gimbal and GoPro and it does very well.
******One big caviat here, do your homework if you plan on using 4S, I can't find any information on 3DR's website about what motor the IRIS+ uses. The only thing I see is that it's a 920kv motor and uses T-Motor 9,5"x4.5" props. I suspect that they might be MN2212 v2.0 920kv T-Motors. If that's true then they don't accept 4S power.******
Anyway here are the links:
http://diydrones.com/profiles/blog/show?id=705844%3ABlogPost%3A1827...
http://diydrones.com/group/iris/forum/topics/iris-with-gimbal-and-t...
http://diydrones.com/group/iris/forum/topics/alternative-props-for-...
Regards,
Nathaniel ~KD2DEY
From the IRIS+ Operators Manual
Hey Adam,
Yes, from the most basic standpoint you are correct. In forward flight, the faster you go the more thrust is required to maintain a given altitude. So slowing down in theory would assist in maintaining altitude. The fundamental problem as I see it, and hopefully Rob or someone else will either be able to confirm or correct this, is that you don't have adequate thrust overall to support practical flight. By practical I mean that it shouldn't require nearly as much power just to maintain hover. Your THR_MID parameter is set at 700 which means it takes 70% throttle to maintain a stable hover. This only leaves 30% reserve for forward flight, and more importantly recovery from unusual attitudes. The maximum recommended value for this setting is 70%, IMHO it's too high. So what can be done about it, simply stated we need to reduce the weight or increase the thrust and get that number down closer to 50%. Ideally I think you want to see that number in the 40-60% range. Without looking at the specs for the motor, I don't know if it can handle a larger prop size or a higher pitch, but that would be one way to increase thrust. If the motor can handle it, going to 4S instead of 3S is another way, by increasing max RPM you will increase the overall thrust.
Not knowing the IRIS+ and it's capabilities, I can't comment on what you can/can't do. I'll look further and see if I can come up with some more options. Do you know what the all up weight is with battery? Also do you know the diameter/pitch of the props you are using, and the kv/rpm of the motor on the IRIS+?
I did PM Rob and ask him to take a look at your logs, hopefully he'll have the time to do so and can shed some light on what's going on.
Regards,
Nathaniel ~KD2DEY
Hi Nathaniel,
Attached is the log from the controller itself. I tried to plot it on google earth but wasn't able to.
I had the altitude set to hold at each waypoint at 200m, but it kept losing altitude.
Could part of the problem be the 8c is not enough juice to fly at the speed I was going at AND keep the altitude?
14-12-25_12-26-14.bin
Another thought, have you tried recalibrating the escs? Maybe you aren't getting full power from them.
Stu
Hi Stu,
Yes I did recalibrate following this video:
https://www.youtube.com/watch?v=sKBVadRDcEw
I also recalibrated the compass, accelerometer, and the remote as well.
It is interesting that it states here what you mentioned regarding DAlt not holding if it is unable to... I just don't know why it couldn't hold the altitude. Too much speed?
I think that this issue was fixed in 3.2
Rob Lefebvre's comment here suggests that this is the expected behavior for DAlt when altitude can't be maintained.
I'm going to shoot him a PM and ask him if he can take a look at this.
Regards,
Nathaniel ~KD2DEY
I have all my parameters in APM planner to match the values 3DR support told me to put...
https://github.com/diydrones/ardupilot/blob/master/Tools/Frame_para...
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