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Compass 7HV 'Ultimate' build thread

Old 02-01-2014, 06:33 PM
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JetPlaneFlyer
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Default Compass 7HV 'Ultimate' build thread

Hi,

I picked up a 7HV Ultimate kit on eBay recently. The kit was un-started with the parts still sealed in the box. This was the version of the kit that included blades and a motor and I got it for a great price

It was an impulse buy and possibly a bit ambitious for me as I've only been flying helis for a year, but what the heck!

The 7HV is a 700 size electric heli, here are the stats:
  • Length: 1372mm
  • Height: 403mm
  • Rotor diameter: 1560mm
  • Motor pinion: 13T
  • Gear ratio: 13T: 10.46:1:4.8
  • Take off weight: ca. 4.3 - 5.1kg
  • Motor type: SZ-5926 510kv
  • Battery size: LiPo 12S (2 x 6S) 4000-6000mAh
  • Rotor blade size: 690-710mm

Here's the photos from the eBay listing:





More to follow....
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Old 02-01-2014, 08:26 PM
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Here is the equipment that's going to go into this build. Bear in mind I'm trying to keep the cost down, so the aim is good performance without breaking the bank:
  • Motor: Compass' own SZ4926 510Kv motor that came with the kit (this has proved a slight problem, see details below)
  • ESC: Hobbyking YEP 120HV
  • Cyclic Servos: RJX FS-0521HV
  • Tail servo: RJX FS-0521THV (more problems)
  • BEC: Castle Pro BEC (or maybe direct 2s LiPo?)
  • FBL controller: Align 3GX (v4.0), or V-Bar clone
  • Battery: 2 x Turnigy 6s 5000mAh 40c


The SZ-4926 motor is an absolute beast, rated for 200A burst which will be about 9000W of power!. Unfortunately when I was checking it over I noticed that it had a loose magnet, this was worrying on a motor that had never been run.
I re-glued the magnet and it seemed ok but on researching found that this was a common issue with the early versions of the Compass motor and that Compass had recalled and replaced with a 'version 2' motor that had different magnet design.
The UK dealers weren't very helpful as I couldn't show where the kit was originally purchased. Luckily for me I came across a Guy called Jason O'Connel who owns ProStarHobby.com in the US. Jason amazingly offered to send me a new rotor with the new magnet design totally free of charge. Words fail me to express what a great guy Jason is, all I can do is put a big plug in for him and say that if you want a new heli or heli parts have a look at ProStarHobby.com. You know that the service you get will be outstanding with a guy like Jason at the helm, he ships international.

Here is a pic off the net of the 'old' and 'new' rotors:


The servos have been a bit of a problem too. To keep costs down I ordered then from flying-hobby.com in Hong Kong and they came in super quick time, but the tail servo was faulty, it just twitched. This is of course the risk you take when 'buying cheap' from China. Flying-Hobby seem to be willing to replace it, but that does mean sending it back, which is a pain. In the meantime and anticipating a drawn out RMA process I ordered another RJX servo from Hobbyking along with the YEP 120HV ESC. I'm still awaiting arrival, Chinese new year seems to be slowing things up.

On the good side these RJX servos do seem to be top quality, so I'm sure I just got unlucky with the faulty one.

Normally these delays would be frustrating but the weather has been terrible, so I'm not missing out on flying which makes the delay easier to accept.
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Old 02-14-2014, 12:58 AM
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Sorry but i was too impatient to take any photos during assembly, but there was nothing much to see to be honest. it was a nice straightforward build. Here's a few photos including one of the new Compass 700 with my Trex 600 and 500

Maiden flight tomorrow, weather permitting!
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Old 02-14-2014, 09:42 AM
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Looks very nice Steve! Very clean install.

I almost bought a 600(?) size Compass when they first came out with an electric but went with a Raptor instead. Some of the local guys around here really like the Compass.

Do the packs fit in between the frames?

Are those digital servos? I havent heard anything about that brand yet.

I'll bet you like it. As Im sure you know, the bigger they are the smoother they fly
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Old 02-14-2014, 02:25 PM
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Thanks Larry,

Yes there is a 600 size one too, it looks like a nice heli.

The two 6s, 5000mAh packs strap to a tray which slides on rails in-between the frames. Quite a few of the bigger size helis use a similar arrangement, it seems to work pretty good.

Yes, the servos are high voltage (8.4v max) digital, metal gear, coreless. They are actually real nice servos, I'm very impressed with them. I run them unregulated off the 2s LiPo you can see in the photo.
The tail servo is a 760us 'narrow band' which caused me a lot of confusion at first. If you plug it into a standard Rx or a servo tester it doesn't work at all. I actually returned the first one because I thought it faulty (and got refunded). Turns out it will only work when plugged into the rudder output on the gyro/FBL controller and the controller is set to 760us. Once that's done it works like a champ, it's lightening fast.

I went out flying today, i had one good flight, no problems at all, then on the second flight the governor in the ESC seems to throw in the towel and the head speed kept surging wildly up and down. No damage done fortunately, but i need to play with the ESC programming to see if i can figure what's going on. If all else fails i have a 'plan B' because the Caste Creations Edge 120HV ESC I ordered before Christmas and which I had put down as lost in the post turned up today!
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Old 02-14-2014, 09:24 PM
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No flight videos but i did get a video to show the ESC struggling, and failing badly, to maintain it's governed head speed:


I ended up trying out just about all the different programming options, nothing helped. Seems that on the first power up it often runs ok, but after shutting down and re-starting it just wont run stable on the governor.

So I switched to 'plan b' and installed the Castle. All seems to be fine now, but the weather has gone pear shaped so who knows when I'll get chance to test fly again
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Old 02-14-2014, 09:29 PM
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PS, here are some photos taken at the field, you dont get an impression of scale from the photos, but take my word, she's a big beast.
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Old 02-15-2014, 07:15 AM
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Oh boy, you sure couldnt fly it with that governor! Did you try the old fashioned way - throttle curves

It may not look big in those pics, but I bet you sure know you're standing next to a monster when it powers up!

I never did get really comfortable flying mine close in. Pumping a few kW into some 700mm head chopper-offer carbon blades is just purely frightening when your in close
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Old 03-02-2014, 08:27 PM
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The Castle Edge ESC is working flawlessly, even pulling 150A out of a 120A ESC (in very short bursts) and nudging over 6000watts doesn't seem to cause any problems.

I've got the flybarless controller set up just about nailed too. First few flights i was getting a side to side shaking when running head speed in the 1700-1800RPM range. The cause turned out not to be blade imbalance as i first thought, but to be a combination of too high cyclic gain in the FBL controller, plus running the standard hard grade dampers in the head, which are really optimised for hardcore 3D use at 2000RPM plus. Softer dampers has got the heli flying smooth as silk as my 'sports' headspeeds.

The shear size is a little intimidating even after flying a 600. The 700 uses noticeably more sky and just feels 'bigger' all round, so I tend to be more cautious with the 7HV, but that's just a matter of getting more flights under my belt.

Not having a lot of luck getting a video. I've had a couple of goes but for some reason the files got corrupted. Strange that I seem to be able to video my other helis without issue but three attempts and three fails with the 7HV.. Just coincidence obviously but annoying!
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Old 03-03-2014, 12:50 AM
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It sure is a nice feeling when you get a new bird and new tech dialed in - congrats!
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Old 03-09-2014, 07:03 PM
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At long last I got my video camera to play the game. Here's a flight of the 7HV from earlier today, nothing too spectacular as I'm still felling my way with it. These big helis are actually much easier to fly than the small ones but also a lot more intimidating, plus there were a few people at the field putting up nets for football games, so I had to keep a check on where I was flying.

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Old 03-10-2014, 09:25 PM
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Great weather today, I got a couple of more flights in, tried some brief inverted!
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Old 03-10-2014, 09:34 PM
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Nice! A very smooth flyer
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Old 10-05-2014, 06:02 PM
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I'm getting a bit more confident with inverted these days. The 7Hv makes it relatively easy because it's so incredibly stable:
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Old 01-27-2015, 11:22 PM
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Some more flying this weekend with the 7HV.. This is running slightly lower headspeed (about 1700RPM) but even at this RPM there is more performance than i need for my skill level:
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Old 01-28-2015, 12:53 PM
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Nice Compass videos
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