Trex 700 heli shaking

ArduCopter Traditional Helicopter
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It’s registering a little higher vibration now with the mount tied down. But nothing drastic and no clipping at all. Definite improvement in the position controller. Looks like it tracked the GPS course pretty much dead on this time.

Are you gonna plug in that radio and try it again?

It was actually at ~10kts, not 20. But it looks like the turn from 2 to 3 is pretty sharp. And it must be only about 200 feet from 3 to 4. Due to the way the nav controller works it might not get going much faster than that so it can make the corners within the accel limits. You’d have to give it bit more room like maybe 400-500 feet to see if it gets to 20kts in auto. But as weak as the battery is in that helicopter that might not be a good idea because it doesn’t look like it’s going to go very far until you put bigger fuel tanks on it.

Yeah, servo1 is still bouncing around but bounces opposite servo 2 when everything is fairly static as far as attitude

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And now, can actually see what the frame is doing. You have slightly higher vibes in Y-axis than X

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But the y-axis is a bit excessive and that is the axis that rotor balance and tracking issues show up on. Checking the blade pitch static on the bench for tracking is a good setup practice. But they rarely fly that way when they’re producing lift. Seeing that knife edge on the rotor disc in static hover is good but doesn’t always yield the best vibration characteristics. This is where the DynaVibe comes in handy. We’ll some track the rotor on Jet Rangers so one blade is sometimes flying higher than the other to get lowest vibration in static hover. Then take it out and cruise it at 100kts and see what we get. Sometimes have to adjust the pitch links for cruise to lower the vibration in cruise flight after adjusting it in static hover. But the DynaVibe has a strobe and the blades are numbered so we know exactly which blade is causing the problem.

Your RC heli is no different. And the controller has a sort of DynaVibe built into it with the IMU vibration measurement. You were hiding this from yourself with that jello plate. Now you can see it. So what I do when I can’t wangle the DynaVibe is mark one blade holder with a marker so you always adjust the same one. Hover it and look in your ground station at the vibe messages. Land it and turn the pitch link on that marked blade one way or the other. Re-hover it and observe the disc tracking visually, as well as what it says on the GCS. If it gets worse, turn the pitch link the other way and try it again. Before I found out we could use the DynaVibe on RC heli’s I have spent 6 hours before tuning and tracking the rotor on my RC heli’s to get both x and y below 8-10.

Another source is the transmission gears. Check the backlash all the way around on the main gear and see how much radial and axial runout it has. Align is horrible for this because of the way that gear mounts on their very poor autorotation clutch. So sometimes it’s just about impossible to get rid of that geartrain vibration in an Align without replacing all the parts from a higher-quality helicopter that has a brass bushed over-running clutch.

Sure, you can try to filter it all out and adjust the tuning to match. But fixing it mechanically yields the best results. Keep in mind these things are mass-produced for 3D pilots who crash 'em and rebuild 'em several times a season. So the quality is “good enough”.

As far as the servos, the controller only sends a signal to it. The servo has an internal pot or hall effect that tells the servo’s controller what the position of the output shaft is. So that dancing on servo1 is not from the servo, it’s because the frame is shaking side to side.

Doesn’t that helicopter have a FBL unit tray in the front? Why didn’t you put the controller on that? IMO that would be a better location for it.

Edit: This is the plot of the x and y vibes with that jello plate in there. It doesn’t tell you anything about what the frame is doing. It would be like let’s mount the DynaVibe transducers on the Jet Ranger with some rubber pads and see if we can still balance the rotor. Fly it, cyclic shakes, all the needles in the panel shake, your passengers in the back got their coffee vibrated right out on their lap, but the DynaVibe says it’s all good.

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This is what you want to get your vibration plot to look like. This is from one of my piston machines flying a survey flight. This machine has a perfectly balanced and tracked rotor using the DynaVibe to tune it. Notice the amplitude of the vibration peaks on y-axis. The higher amplitude on x is due to the engine and the vibration from the acceleration of the piston and crankcase and what gets transferred to the frame. When the mix in the cylinder lights and the piston goes down, the crankcase goes the other way. It is balanced with reciprocating weight in the piston and rod, as well as the counterweights on the crank. But it still vibrates.

Your electric in its current configuration is not as smooth as my piston gasser.

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My y axis has always been a lot higher from the the other 2. I never asked which one is was which I guessed y was like a yaw vibration. Wrong.
Ya I’m charging the batteries again. To do a fliggt with the radio. But with the battery on the radio frozen and no warnings. I’m scared to go to far. I messed with the heli on as in servos and controller for 40 min before I flew it. I know it said 25.1 volt but think that was ghost voltage. It normally goes down evenly not a huge drop like that. I have more battery showing up today with a dual charger. So I don’t have to plan battery charges days in advance. Current charger takes 3 hours per batt.
Now if they are getting weaker if I put the new batterys in parallel should I put diodes in to make sure their is no canabilism. Or will they “use up” evenly. I only have the 25 volt sensor. I was looking at buying the 50 volt sensor for the series.

Looking at weather it might have had 10 mph tail and head wind. So forward could have been faster than return. I never found spec on ground speed in log. Only in tlog. But no tlog this time.

Another question. My motor has 3 wires but under it are 2 tiny wires they were connected to something on The original 3gx or a some thing. Those wires could not be producing an rf wave somehow causing problems?

Thinking of running longer wires on the radio and putting it on the tail. For a test after I run it again normally.
In the crash my ESC to a mild hit and broke the plastic off the ESC and a piece of the nose. Glad I had controller where it is.

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More info came to my brain. When hooking up the craft and theory cable for telemetry I hooked it to serial port 4/5 and followed wiki. It did not work I think I had to set the setting to 6 to get it to work. Don’t know if that would have caused the delay I can look toniggt yo see what I actually set the param at.

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Y is side to side, X is front and back, Z is up and down. A tail vibration can definitely cause high Y-axis vibration.

Parallel batteries will discharge together and remain even on voltage. You can even put two different sized ones in parallel, the smaller one will deliver less current than the larger one. If they are in series, then they both have to be matched because the same current will flow in both batteries, regardless of their size, it will over-discharge the smaller one (or one with less capacity) and damage it.

Look in the GPS tab in the log. It shows the GPS speed, which is usually pretty accurate.

I doubt it as radio frequency interference from a 10 pole motor would be somewhere in the AM radio broadcast band and cause an annoying alternator whine in your AM radio. What would those wires be for? Maybe rpm telemetry or a governor? If in doubt, and they’re not being used, twist them into a tight twisted pair and terminate them properly so they don’t short out on anything.

IMO the FBL unit tray is the best location. But I think I have seen photos where some people that have put their controller on the top of the plastic tail mount too. It appears you have yours in the battery bay, which is where the batteries should be. The Z-axis CG of the helicopter should be somewhere around the main transmission gear and I think they design the location of the FBL unit tray so it is approximately inline with that Z-axis CG for proper roll sensing.

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The plan what to hang batteries on the landing gear for easier changes and more batteries. I didn’t know if I’d need 6 batteries for a 20 min flight. 2series 3 parallel. I hung the copter by a string centered on the main shaft. To see what the cg was. As long as it is all vertical weight and I’m not doing eratic flying couldn’t see the harm. Might make heli react slower but under the belly is gonna be the gimbal I am designing for my odd shaped sensor we spoke of before.
Me being a noon and everyone saying its gonna crash. And as the motor cycle saying goes it’s not if but when. So I put it in the battery hold to protect it. I ran all high voltage to the nose I nfrong of the motor to get away from rf. I put radios on the back and below to get distance from rf. Had to plan on the worst case because I had no clue how sensitive a these sensors were.

On another note. Iv had 3 close calls and 1 crash due to battery voltage telemetry. I know the yaapu has lots of neat features. I think the auto rotate rpm would be cool I bought an align hall effect sensor. But looks like I need to buy the gas suite to make it work. Also the last GPS coordinates for a crashed heli. But on a battery machine battery knowledge is king. If I can’t figure that out I’m going to have to get a Bluetooth ear bud to listen to the computer warnings since radio will be in my hand but way behind

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I’ve had a set of 500mw radios before and they caused havoc with my servos. I could make the tail servo go nuts by moving the antenna around.

I recommend this set:

Or if you really need the longer range:
http://store.jdrones.com/jD_RD900Plus_Telemetry_Bundle_p/rf900set02.htm

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It looks like the battery failsafe went off at 22.9 volts, which is 3.8VPC with a 6-cell battery? And that’s under load.

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I am certainly not well-versed in setting up this battery stuff, but is that what people use? I thought 3.85VPC at rest is storage voltage, and about 50% capacity for LiPo batteries?

So when you shut down it looks like it immediately recovered to 23.5V, which is 3.91VPC, which is only very lightly discharged (I think). Are you sure you have this battery stuff set up right?

Seems to me back when I flew electric helicopters if they came in at 3.5 VPC after a flight and they had rested for awhile, I was not too concerned about it, and they seemed to last about 200 cycles. Although some of them would develop a bad cell after only 60-70 cycles and that’s what I didn’t like about the expense of flying electric aircraft.

I think I had the low battery cutoff at 3.0VPC in the ESC, which would be 18.0V for a 6-cell. If it got to 36 volts (12S power) then it would cut the power and start cycling it and had to autorotate the heli (although still under power). But even those recovered back to at least maybe 3.2VPC if I ran them to the limit. Which was not good for the battery, but I only did that a few times. I never set any failsafes on the battery because if it was still running and not home yet I would fly it and ruin the battery before I’d lose power and have to autorotate it.

Maybe somebody that knows more about these batteries can point you in the right direction on that. I only tried electric one year after I seized up my O.S. 105HZ nitro engine for the third time and didn’t have time to put another sleeve and piston it because I had flights to fly. So I bought a Trex 600 electric and flew that, it seemed to work pretty good. Then I bought a Synergy 626 electric and flew that for a year. The care and feeding of those batteries was more than I wanted to deal with. Nitro fuel was $35/gallon. $150 bucks a crack for piston, sleeve and bearings in the 105 and overhaul that every 50-60 hours. Carey Shurley developed the piston gas conversion for the Synergy 766, I’ve never looked back. Just dump gas in it and fly it 10 hours a day and it comes back for more. 411.7 hours on the first one and the engine has never been out of the frame since new. Only problem I’ve had with those is the fuel pump. I put the new stainless steel fuel pump diaphragm from Walbro in them, even that’s not a problem anymore.

So, unfortunately, I forgot most of what I learned about electrics. But I do know I ran the batteries a lot more aggressive than you are.

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I have disabled the cut-off on the ESC on mines. I’d rather ruin the battery.
Lipos can be run down to 3.3v/cell. Hit 3.0v/cell and you start doing real damage. 3.8v/cell is ~50% full.

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Jacob there is these new settings for sag compensated voltage, etc… I don’t know much about that, or how it works. Alan is not measuring current so I don’t think he can use that anyway. But doesn’t experience flying it, and then see what the battery recovers to after it rests, tell you what the voltage sag is under load anyway? Are those figures you gave under load? Or after the battery rests and recovers?

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Sorry, yes…apart from the 3.8v/cell = 50%, the numbers are under load.

Huh, so there is
Sory, http://ardupilot.org/copter/docs/parameters.html#batt-fs-voltsrc-failsafe-voltage-source

I cannot find how it calculates the sag?.
Sag will vary greatly depending on battery type and load.

I set up my failsafes based on under load values. If you go below 3.3v/cell, under load, you will wear down the cell quickly, below 3v/cell, you can kill it.

First few flights, I rarely use more than 50% of estimated usuable capacity. I then go home, look at the discharge curve, vs expected and then go 75% next flight.

As a general rule of thumb, I expect usable capacity to be ~80% of rated capacity. Some batteries, like the Multistars, you were lucky to get 50%, even if you stayed well under the batteries claimed C-rating. (The “cheaper” tattus weren’t much better).

You also have to anticipate that as voltage goes down, current goes up and the battery will discharge faster.

I now run li-ion, so my values are quite different, but as a starting rule for lipo, I would have 3.7v/cell as my first failsafe (RTL if you don’t trust the telemetry!). and 3.4v as Land.
Then adjust as needed.

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Cool, thanks. That sounds about right. I probably over-worked my batteries when I flew electric because I remember when I hooked them to the charger if it said 3.5V on all the cells I was pretty happy. When a cell went bad I’d start finding one at 3.3, and as it got worse one day that battery would come with the cell at 2.9. And then the charger would refuse to charge it. So I “cheated” by setting the charger for lead-acid and boost that cell above 3, then switch to LiPo and it would charge it. Then I marked that battery as “bad” and used it for short flights.

I did NOT enjoy dealing with batteries. Some of these guys got elaborate balance boards and stuff to mass-charge batteries, and they’re running Honda generators at the RC field to charge their batteries. It’s like dude, just put the gas in the helicopter instead of the generator and get rid of all that :neutral_face:

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Well, as you know I’m leaning heavily that direction (Gas), however the li-ion pack has proven quite practical so far. I’m still running it conservatively, but I still gain more flight time than I did with a similar weight Lipo. It’s got an onboard BMS, that I can plug into a PC and check the heath and charging is just plugging it in and forget about it. (Well, you wont forget, as the fan on the charger sounds like a jet engine, but anyways).

However, due to the severe voltage sag, li-ion will be limited to low-to-medium power operations. S, perfect for surveys.

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I’m not a fan of batteries but what I can afford to play with for now and crash! I looked into li- ion batteries cannot find a dealer in USA. I suppose I could make my own if i bought spot welding equipment. Iv been looking at 2170 batteries. From Tesla cars or Samsung. The more I have troubles, some of my own doing, and some cuz I don’t know enough yet. Buying a ready built and TUNED heli is looking like I might mortgage the house and get a heli that flies good so I know what that looks like lol.

Early in this thread I posted a log that had hard auto in the title. During that flight. Batteries reached 22.5 volts and dropped straight down below 18 volts. The heli looked sluggish. I had soft cut off on the ice 2. I was 50 ft up. I said here comes my first auto rotate. I dropped collective. I let it come down to 10 ft flared way to early. I watched the blades dam near stop and it dropped 8 ft. Good thing I just put my tall landing gear on cuz it bent and took the blow. So that the reason for the voltage Failsafe’s. When I went into the tree. Voltage was at 22.9 and I was trying to auto it in. Not what the ESC did that time. But heli blades were slow and unresponsive.

I have looked at Milwaukee batteries but voltages are to low for amps unless I could run 60 volt instead of 50 max charge.

We are buying cheap lipo’s. Floureon they seem to work but I don’t know anything about adjusting the kV on the motor for more efficiency or if running the ESC at 70 percent is efficient. We only pull 20 amp at 12 s and max I have seen is 30 amp. My idea was if I put a few more in parallel that will lower the amp draw per battery and be able to run them longer

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Yeah, I built my own li-ion pack. It still costs a fair bit and I only did it after I had the heli working as intended on lipos.

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The ESC’s are more efficient if you can run them at 90 or above. What many people do is adjust the voltage by running like 8S or 10S instead of 12S, then run higher throttle. I did do this with the 626. It was originally 12S but the motor and ESC got really hot. I dropped it to 10S and it ran much cooler, and less heat means better efficiency.

When I went to 10S I used a 5000 6S 45C in series with a 10000 4S MultiStar. Those MultiStars don’t have anywhere close to the capacity they claim they do unless they are discharged at like 5 amps. That combination actually worked and all 10 cells came in at about the same voltage after a flight with fully charged batteries.

I got close to an hour with that helicopter with 4 6S 5000’s at 12S with two stick packs in parallel. But it got really hot and the ESC burnt the paint on the canopy. So then I stuck a canopy on it with a hole in the front and a muffin fan on the ESC. But it still got hot.

It would only fly for a half hour on the 10S. So I bought it in on a survey flight to change batteries and then sent it back out to finish the flight.

I even tried 696 blades on it once. But those took more power than the 626 configuration and it wouldn’t fly as long and had poor tail authority. I lowered the throttle setting to run the bigger blades at 400 fps, same speed as the 626 blades at higher rpm. And then it was back to overheating the ESC again.

In the end I came to the conclusion that electric is great for 7-8 minute 3D flights for a lightweight, quite powerful machine in a short burst. And for 600 class and smaller where gas engines aren’t really all that practical because of their weight. I don’t remember exactly what the engine weighs, but I know it’s heavier than a couple 6S 5000’s and an electric motor. The upside with piston power is that it can produce full rated output continuous. Electric can’t because the batteries can’t take it. And energy density of the fuel + conversion efficiency to shaft power far outweighs the energy density of batteries at the conversion efficiency to shaft power with electric if the helicopter needs long legs and high continuous power output.

There’s likely a reason you don’t see electric Bell 47’s flying around with a bunch of LiPo’s in it. It’s not practical. And the bigger they get, the less practical it becomes. :grinning:

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I just bought a motor suitable for running 12S at non-3D headspeeds :).

https://www.scorpionsystem.com/catalog/helicopter/motors_4/hkiv-40/HKIV_4035_330/

330kv rather than the usual ~500kv. Geared it down as low as I could. Gives me 2200rpm at max voltage. (626 blades)

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I bought one of those too! Mine is a 300. It will fit in a 626 with a E7 tail boom and 696 blades with the help of custom water-jet cut aluminum frames, custom machined motor mount, and a custom-built clutch shaft.

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I bought some new batteries for that helicopter and gave it to Kayla to use for a trainer. She said it only flies for 17-18 minutes and then it takes two hours to charge up the batteries. I told her I’ll fix that.

Alan might be interested in knowing that Trex 700 short flight times are also repairable:

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We have been talking about that but I have never seen one for this old turd. The pictures on that link are for the 700N. The swash and head don’t look like mine. Don’t know if that matters. But heard I need some N parts if I want to use a straight E heli. Then again. I’m learning more every say about how to tune these wild machines. I have seen the 766 kits with gas frame conversions for 1400$ but knowing what parts cost blades and radios and motors and electronics unless I canabilize the trex. I’ll have 6 grand in one before I know it and still have to work months tuning it. Trying to still talk partners into splitting cost and buying one bulit.

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1 hour flight time with 3 pound payload and gimbal to aim straight down at 20 kts is the goal. In the wind at 400 feet. Gas is the best bet. But will take a lot of weekend surveys to pay it off. The current drone hexa copter is not the ticket. But is working so far. As long as not much wind. Ground Speed below 14 mph. 4 battery changes a gen to charge battery’s. 5 sets of 6 lipo battery’s. And at least 4 hours on site min. But I am not currently flying it if I was I’d done bought a gas heli. That’s the reason for a trainer to prove concept. But struggling with this thing sets it back a bit.

If I can get 40 min out of this heli it will be a huge advantage over the hexa drone.

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Well Alan, you have several things you can look at that have been suggested sources of problems, including that it looks like you are not working your battery hard enough. It appears you did get a successful auto flight out of it where it flew fairly decent. But still not 100% certain about what caused the first really bad one.

Still not sure why your RC telemetry is delayed.

Starting out with helicopters is very difficult. They are not beginner-friendly machines. But you are making some progress.

Edit: also wanted to mention something about your two somewhat rough autorotation landings. You cannot autorotate a helicopter with ArduPilot in anything but stabilize or acro. Any of the altitude modes - Alt Hold, Loiter, Pos Hold, Auto, will stall the main rotor. You might already be aware of this, but have your flight modes set up so one click of a switch gets you into one of those modes if it quits in flight. Stabilize is probably the best because after the flare you just have let the cyclic go and it will push the nose over and level the helicopter by itself and all you have to do is manage the collective.

If you try to autorotate it in any of the altitude modes you won’t have enough collective control to make it work.