700 New to me Trex 700L Dominator

[jcfernan51]

My new to me Trex 700L Dominator, have not seen air yet I have been going over it making some adjustments. Will take video when it does.

FBL Bavarian Demon 3SX (2 DSMX Sats)
Motor: Scorpion 4525 Ultimate 520KV
ESC Castle Edge 160 HV
Cyclic Servos BL815H High Voltage Brushless
Tail Servo BL855H High Voltage Brushless
four battery trays
Also have the original canopy

 

[Tony]

The bird looks great! Keep us posted.

 

[jcfernan51]

Took the Monster for a hover, you have to love technology, the camera came on and only recorded the first 10 sec or less . Well it need to be adjusted it is drifting right had to apply a permanent correction. Need to charge batteries and try again. will try video again.

 

[holtneil]

Hi mate sound like the swash is not level , great looking bird , I nearly got the 800 Trex , but its huge no where to keep it so got the SAB Goblin 630 comp , Cant wait to see the Video , I hope the weather is better with you ,we have rain gale force winds , sun has just come out be still to windy

 

[jcfernan51]

You are talking about nowhere to keep it right now it sits on the kitchen counter don't know for how long maybe until it get put in the trash or I get in the trash will see who goes first.. Oh, when I have to work on it it goes to the kitchen table, now how do you thing that goes. Actually, this is just man BS, what others expect to hear. My wife has not said anything, wait a minute, silent treatment, I better find a new place soon.

This is the history so far;
I got this heli Trex 700L used, I have no problem with that. The first time I took it for a hover the spooling up was good, as I increased the collective all of the sudden the tail stopped spinning, the heli never moved, so I knew the tail did not hit the ground. After inspecting I found the two front 45deg gears stripped, the drive gear was perfect no damage. Now this puzzled me because these gear's meshing is set by the gear housing nothing we can do about it. I manually spin the shaft and felt smooth. I replaced the gears, put it back together and ran it without blades, all was okay.
Tuesday took it for a hover and everything looked good other then a drift to the right . Wednesday I adjusted for the drift and went out to try to hover when again the tail gears stripped but this time was the rear two 45 deg by the blade and the two front are bad as well. The drive gear is good and same scenario as I increased the collective all of the sudden the tail stopped spinning, Heli never left the ground or moved.

Have not taken it apart again because I don't have replacement gears, received email today that they shipped. Any suggestion of what to look will be appreciated. I have been told to check the governor gain setting in the Castle EDGE HV160 if it is to high could cause this. It was set to 20 I lowered it to 14 will see what happen once I fix it.

 

[Tony]

Did you ever get this sorted out?

 

[Smoggie]

On the subject of the TT gears stripping.. Check the screws that hold the dual arm tail control yoke to the pitch slider. If these screws are a fraction too long then they nip the bush preventing it turning with the shaft. To test spin the tail by hand and make sure that the slider bush rotates with the tail shaft, rather than remaining static.

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PS.. the other thing that can knock out the TT gears is (if using governor) having the governor gain set too high... but this is very unlikely to be the cause if you were only gently spooling up.

 

[Tony]

There is a way to adjust the mesh. Usually on the vertical gear you can add or remove shims to raise or lower it. Same on the horizontal gear, you can add or remove shims from behind the gear between the gear and bearing. It's a time consuming process but it pays off with a perfect mesh. Might have to make a video showing how to do this.

 

[Smoggie]

Tony,
The Trex 700 doesn't have any shims on the vertical or horizontal gears. You could of course add them if the mesh was unacceptably loose but by design it's not meant to have any and normally it's fine without them. The TT gears are pretty strong on the 700, it's the 600 that is usually the one that strips gears.

 

[Tony]

Never had a 700 and thought they would use them. Thanks for the correction.

 

[jcfernan51]

Update, I got the gears replaced but have not finish putting it together, to many things going on and I want to add a switch to turn ON/OFF power to BD 3SX this way I can connect everything install the canopy and don't have to worry about it spooling if I by mistake hit the TH switch with throttle on while getting ready. Neither the rear or front gears have any play up or down, the meshing look good. Hope this is it because at almost $14 a set of gears adds up, I am on my third set two front and one rear.

Smoggie, I did adjusted the gain, was set to 20 in the Castle EDGE HV160 I lowered it to 14, nominal is 15 will see what happen once I put it all back together again.

 

[holtneil]

Hi Mate if your using HV servos I dont think there is a switch that can handle the amps pulled , the switches used on RC car planes etc are that strong , was going to do that on my Goblin but the switches are to low rated to take the amps needed by the system ,Ask Smoggle he will tell you not to he was they one that said it to me would not want to see your heli crash due to this switch

 

[Smoggie]

+1 on Neil's advice... Don't use a switch, standard RC receiver switches aren't man enough, and anyway it's just a potential failure point that you dont need.

How are you powering the system?... HV BEC., battery direct, or battery and voltage regulator? If it's a battery just use the Rx battery connector as your 'switch'. Also bear in mind that the power from the battery/BEC should be wired into two seperate connections on the FBL controller. A single servo type plug cant handle the potential current spikes.

 

[jcfernan51]

I installed the switch to the Rx battery disconnecting(opening) the ground lead. I ran a servo extension from the Rx battery to the switch then loop back to the Gyro. I used a 36" servo extension this way I only cut the black and solder it to the switch the other two red (Rx +V) and white (not used) just loop back. Now with the main battery and Rx connected and switch OFF the motor will not spool, Gyro and servos are OFF, I tried it with no blades first just in case. I will double check the amp rating of the switch. Looking at the BD3SX manual it can supply 10A max with a spike of 12 A. There are a lot of switches that can handle 10A.

 

[Smoggie]

Your heli so your call but if you really want to use a switch use one rated for bursts of 10A or more. The constant amps is very low but in short spikes large heli servos can pull a high current and if the wiring/switch isnt up to it voltage drops and you get brown-outs... This is a well documented problem.

For the same reason it's highly recommended not to have any extra connectors in the wiring and you really should use two connections into the FBL to carry the power from the battery. Each servo type plug will only take about 4A before voltage drop becomes excessive (I've done testing on this). The wires should be heavy gauge servo extensions wire at the absolute minimum, the longer the extension the heavier the wire.

There are a number of ways to prevent inadvertent spool-up. Setting a throttle cut in the Tx is one, powering up without throttle hold engauged prevents the ESC from arming so that's another option (as long as you don't use the dreaded 'normal mode')...

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Your heli so your call but if you really want to use a switch use one rated for bursts of 10A or more. The constant amps is very low but in short spikes large heli servos can pull a high current and if the wiring/switch isnt up to it voltage drops and you get brown-outs... This is a well documented problem.

For the same reason it's highly recommended not to have any extra connectors in the wiring and you really should use two connections into the FBL to carry the power from the battery. Each servo type plug will only take about 4A before voltage drop becomes excessive (I've done testing on this). The wires should be heavy gauge servo extensions wire at the absolute minimum, the longer the extension the heavier the wire.

There are a number of ways to prevent inadvertent spool-up. Setting a throttle cut in the Tx is one, powering up without throttle hold engauged prevents the ESC from arming so that's another option (as long as you don't use the dreaded 'normal mode')...

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PS... sorry for the duplication, i didn't post the answer twice, must be some bug?... and i dont seem to be allowed to edit my posts to fix the problem (no idea why i can't edit?)

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PPS.. i just looked again at your picture... You should be using the main (EC2?) connector on the battery, not the servo plug connector.. It's not rated high enough. The way I'd have done it is have two short heavy duty servo extensions soldered into a matching EC2, connected directly between battery and FBL. On/off is achieved by plugging/unplugging the battery... simple and bullet proof.

 

[jcfernan51]

Smoggie, thanks for your reply. I do use throttle hold but I also do have the normal curve starting at 0 up to second point in a 5 point curve then flat 30%. I see that I am using the wrong wires to power the Rx, thanks for the advice I was wondering why they put that big connector. My thinking was for charging purpose to be able to handle max C charging rate and the one with the servo connector was the one we should use. I did use the heavy gauge extension. To be sure you used two extension in parallel to share current load, one side with EC2 the other with a two servo connectors and use two ports in the FBL, correct?

ps: I looked in the BD 3SX manual and I only see one battery terminal input share with servo 4, the only other input is the S. Bus.

 

[Smoggie]

To be sure you used two extension in parallel to share current load, one side with EC2 the other with a two servo connectors and use two ports in the FBL, correct?

Yes, that's it exactly. On some FBL controllers it's hard to find a spare connection for the extra plug to connect to, in that case a Y lead of some type is necessary. To be honest the way you have it would probably be fine 99% of the time, but it's just that rare occasion when the servos try to pull very high current that you could have issues.

Some FBL controllers like the AR7300 and the Microbeast HD have a special high current connector for the battery/BEC to feed into that negates the need for the dual servo plugs.. it would be nice if all FBL controlles had something similar, maybe one day?

This is the AR7300 which has an EC3 connector and lead built in:

 

[jcfernan51]

After replacing the tail gears the heli had a lot of vibration, turned out the main shaft was bent, don't know how I missed it. I was able to test fly in my backyard. If I let go of the stick it has a slight forward drift but not bad.

Sorry for the sideways video

[video=youtube_share;UDcewXAAdw0]https://youtu.be/UDcewXAAdw0[/video]

 

[jcfernan51]

More of the same, went to the field and again blew the front umbrella gear on the 700L Dominator, I don't think it finished spooling, never left the ground. I guess I cannot complain much because I rather be in the ground when this happens. This time I am replacing the TT, all gears front and back and all bearings associated with the tail. When I took it apart I did not notice any play on the gears. I took the TT and the two bearing are good.

 

[Smoggie]

This is certainly not normal for a trex 700, those gears are normally pretty tough.
There is obviously a real physical problem somewhere in the system. If you are sure that the bevel gears were properly assembled and meshing correctly then it's really got to be something jamming the tail rotor or the TT and stopping it turning, or making it very stiff to turn. Have you removed the tail rotor assembly and checked that is spins freely while moving the the pitch slider into all positions along the shaft, also that the shaft isn't bent? Check that the inner bush on the slider is also free to turn within the slider body.. The bearings on the TT and the umbrella gears would be the other things to check. I can't see how it could possibly be the TT itself, it's just a shaft, as long as it's straight then it's ok.