How to avoing descent wobble/oscillation???

[Old Man]

Whoa, slow down! First thing in trouble shooting is to do one thing, and one thing only at a time to gauge the impacts of the effort. A 770mm craft is not "too large" by any means and both a WKM or Naza M will fly it just fine once dialed in. Reducing prop size to reduce thrust below max efficiency is counter productive. Consider an earlier post where adding a battery to add a little weight was suggested. Redundant batteries is, IMO, always better than a single battery where if the one fails you hit the dirt for certain.

Re-run your thrust/power calcs again or better still perform your own thrust test to know absolutely what you have. You only need to do one. Find out how long your battery will do what it needs to do while you're at it. Verify that your ESC/motor/battery association is correct. Verify you are already using the mfg suggested propeller diameter and pitch for the motor/ESC/voltage combination. Verify you are lifting off at close to 50% throttle and not actually a lot more, or a lot less. Most of all, don't try to rush through the process for disaster awaits if you do. You'll overlook something simple in haste and berate yourself badly for it later, or become discouraged and trash the project when success was only moments away.

It may be things are just too light. It may be the amount of throttle required to hover is too much or too little. Either of those will create some level of control problems, with one being twitchy and the other leaving little "head room" for attitude compensation if the wind blows. It may just be PID settings, which generally is a trial and error thing anyway. Systematically work your way through it, exhausting one item before moving on to another.

A 5100 mAH 4s battery seems a little "under gunned" to me for a 770mm multirotor but that's what your motors are rated at.

 

[Old Man]

Looking at the T-Motor site your motor-prop-voltage combination is rated at 580 g.thrust/motor at 50% throttle. Load the copter up to 2300 grams and see if it lifts off at a true 50% throttle and note how it acts.

 

[PCMAerial]

Looking at the T-Motor site your motor-prop-voltage combination is rated at 580 g.thrust/motor at 50% throttle. Load the copter up to 2300 grams and see if it lifts off at a true 50% throttle and note how it acts.

Thanks alot for the help my friend. At times I want to move TOO quick to diagnose, and know I need to just slow down and look at things. I definitely did my math wrong on the motor-prop-voltage combo, yours is looking right. I was reading and saw they recommend a quadcopter with 4kg takeoff weight. Not sure if that needs 11 or 12in props. But. Sounds a bit more realistic

As far as 4s goes, I'm really torn between picking up another 5100 and running parallel. Or just one big 8000-10000mAh. I definitely like the idea of the redundancy of a second battery running, just never considered running two. Have always been strict to running one battery. But I can change if need be

I'll have to pick up a scale soon, because I can't weigh anything at the moment. Can only add up the product weight(s) and calculate an approximate value. I'll try to get as much weight as I can and see what happens.

 

[SJBrit]

I would definitely run 2 batteries. The weight difference isn't significant between 1 and 2 ( 2 being slightly heavier but not much) and having some redundancy is always a great thing for flying machines.

 

[PCMAerial]

I would definitely run 2 batteries. The weight difference isn't significant between 1 and 2 ( 2 being slightly heavier but not much) and having some redundancy is always a great thing for flying machines.

Thank you sir. I definitely NEED more weight so I guess that would be no problem. I have one 4s which is 700g, can get another which brings me to 1400g on batteries alone. Seems high for me but that will result in (hopefully) much more flight time. Although I have never ran two at once so will have to research and learn on how to parallel

 

[SJBrit]

You can either buy a Y adapter to run batteries in parallel or make one yourself. Here's a great tutorial on soldering heavy gauge wire: https://www.youtube.com/watch?v=7t9nT3Hn9b0. What kind of connectors are you using on your batteries?

 

[PCMAerial]

You can either buy a Y adapter to run batteries in parallel or make one yourself. Here's a great tutorial on soldering heavy gauge wire: https://www.youtube.com/watch?v=7t9nT3Hn9b0. What kind of connectors are you using on your batteries?

Right now XT60 connectors. So I'm thinking of trying to find a premade Y adapter to fit. And then I would assume it's as simple as mounting both batteries to the COG and plugging them into the adapter, change a bit of voltage settings.

 

[SJBrit]

They are easy to find. Here's one at Hobby King in the US East warehouse: http://bit.ly/Y808kc. Either mount two batteries together at the CofG or spread them apart so they are balanced. Just whichever works for your rig. You don't have to change the voltage - when you run batteries in parallel the voltage stays the same and they just have the ability to deliver twice as much current. So, just buy the Y adapter, strap them on and fly - easy!

 

[PCMAerial]

They are easy to find. Here's one at Hobby King in the US East warehouse: http://bit.ly/Y808kc. Either mount two batteries together at the CofG or spread them apart so they are balanced. Just whichever works for your rig. You don't have to change the voltage - when you run batteries in parallel the voltage stays the same and they just have the ability to deliver twice as much current. So, just buy the Y adapter, strap them on and fly - easy!

Thanks alot man. Just purchased that adaptor and another battery

So I did the math and my 4s batteries are actually only 490g each. So close to 1000g on batteries, less than I wanted. But atleast more weight is on the way!

 

[min0nim]

Hey, just double check you got a parallel, not a serial adaptor.

You probably know this already, but just making sure you're clear about the suggestions!

 

[Old Man]

Good call on the adapter check!!!

Funny thing about batteries. It's easy to have one too small or limited in duration. It's easy to have one or more that end up too haevy even though they provide tremendous capacities. The secret is in finding the balance between maximum permissible weight for the amount of flight time provided. As an example one might be using a 4000mAh battery and getting 10 minute flight times. The relationship of all the working components is great so you upgrade to a 6000mAh battery and gain 8 minutes more flight time. OTH one might upgrade to a 12000mAh battery and only gain 3 minutes of flight time because the larger battery caused the system to consume more amps to carry the additional weight.

It's trial and error, but I agree dual batteries is far, far better than a single. Max out what the system will effectively carry for battery sizes versus flight time with the intended payload. No, it's not easy but some of the best things we ever do never are.

 

[PCMAerial]

Good call on the adapter check!!!

Funny thing about batteries. It's easy to have one too small or limited in duration. It's easy to have one or more that end up too haevy even though they provide tremendous capacities. The secret is in finding the balance between maximum permissible weight for the amount of flight time provided. As an example one might be using a 4000mAh battery and getting 10 minute flight times. The relationship of all the working components is great so you upgrade to a 6000mAh battery and gain 8 minutes more flight time. OTH one might upgrade to a 12000mAh battery and only gain 3 minutes of flight time because the larger battery caused the system to consume more amps to carry the additional weight.

It's trial and error, but I agree dual batteries is far, far better than a single. Max out what the system will effectively carry for battery sizes versus flight time with the intended payload. No, it's not easy but some of the best things we ever do never are.

Couldn't have done this without the valuable info in this thread. I'm definitely going with everyone's advice on Parallel vs one huge lipo. So I got the adapter for a parallel, and another 5100mAh same brand and everything

Calculating weight with the new battery I'm still only at 2.1kg:upset::upset:

With a recommended weight of 4kg I'm not sure if this is still too far underweight or not. Either way I'll be testing it with the new battery this weekend to work on gains and see what happens. At-least its SOME extra weight. Really had no idea these motors asked for so much power. Wanted a perfect GoPro/Zen lifter but now I'm almost wondering if a bigger camera is needed....

 

[Old Man]

I built a very large heavy lift not too long ago that I knew was going to be too light without a payload under it. With a pair of 10,000 mAh 6s batteries I added a 5.5kG ballast weight under the bottom deck plate before the first flight. Glad I did because at 27.5lbs it lifted off right at 50% throttle. It's design intent was to be a 55lb max auw aircraft.

It's easy to add weight but a real pain to remove it if you started out too heavy. Larger batteries are weight gains that add benefit when things are too light So add some ballast weight and see how she flies and what she draws. Find a red brick somewhere and strap it on if the frame permits it. That's what custom birds are all about; having it your way, not how some brand name maker wants you to have it.