Compass Knight 600E

Sunday, April 5, 2009

Chris "JustPlaneChris" Boultinghouse

Specifications:

Manufacturer: Compass Model
Distributor: Common Sense RC
Type: 600 electric aerobatic helicopter
For: intermediate to advanced pilots
Flying weight (review model): 7.9 lbs / 3.58 kg
Radio: JR X9303 transmitter, Spektrum 7000 receiver, 3 Futaba 9452 servos on cyclic, and a JR on the tail (JR 770 3D gyro)
Power system: Stock 790kv outrunner, Hobby Wing Platinum 120A-HV ESC, and CSRC 8S 3700mah battery

Background

Those of you who follow InsideHeli.com podcast probably know that I’ve been pondering the purchase of a 600mm electric helicopter for quite a while. I already have a 550mm heli (Century Swift) and the fact that it was almost as big kept me away from them for a while.

However, time goes on and after flying my nitro Compass Knight 3D for a while and feeling the goodness of 600mm blades I started looking seriously at the E-version again. Why the Knight 600E instead of the more popular Align T-Rex 600E? Several reasons:

• The Knight is (in my opinion) a better flying helicopter. Yes, I know that’s largely subjective. But I’ve flown both and simply prefer the cyclic response and feel of the Knight’s head design over the T-Rex.
• The T-Rex 600 is designed around a 6S power system. It is somewhat controversial, but I’m in the camp that says 6S is insufficient voltage for such a large helicopter. The watts required to fly it demand a lot of amps from the battery packs, which shortens their useful lifespan. Compass offers a 6S Knight (presumably for the T-Rex owner who wants to try one) but they also offer one with a motor suitable for 8S.
• I already have a Knight, so compatible spares is appealing
• The Knight looks better. (I know, that’s vanity talking. So I’m shallow.)

Once the decision was made, it was time to see about getting one. As luck would have it, a conversation on HeliFreak regarding the Compass helis put me in touch with Dick at KBDD, LLC – then the US distributor of Compass products, and also their own line of excellent tail blades, dampers and paddles. One thing led to another, and Dick offered to send me a Knight 600E (8S version) to review for InsideHeli.com! He also included a set of dampers, tail blades and paddles. More about those items later.

One thing to note is that during the course of this review, the US distributorship has changed from KBDD, LLC to Common Sense RC. This does not reflect poorly at all on KBDD, in fact they did a lot to get the Compass name out there. CSRC is simply in a better position to further the brand and get them out to the hobbyists through their substantial local hobby shop network. This also frees up KBDD to continue development of their own product line.

Since CSRC was now involved, they provided a pair of their excellent 4S 3700 mah 35c lipo packs to use in a serial configuration for this review. These packs are loafing along in this application, and run so cool it’s hard to even tell they are warmer than ambient temperature after a flight!

The Knight kit included the Compass motor, but of course I still needed a speed controller – and a high voltage one at that! That means it was time to ring up my friend Greg Alderman at HeliDirect.com and see what neat goodies they have. Greg told me about the new Platinum series from Hobby Wing, and said that the Outrage team had been flying them for a while and really were impressed. That’s a good enough endorsement for me, so Greg worked a little pricing magic for me (thanks Greg!) and soon a Hobby Wing Platinum 120A-HV arrived at my doorstep.

That just left me needing cyclic servos, gyro, and a way to power the radio. To save time (and money), I just “borrowed” the cyclic servos and gyro from my nitro Knight. To power the radio, I ordered a Medusa HV regulator from my friend Bobby Smith at RREModels.com. And while there, I just couldn’t resist a shiny new Fusono Knight canopy. (There’s that vanity thing again….)

Okay, all the bits and pieces were in hand, so I was out of excuses. Time to build this thing!

Building

The Knight comes largely pre-assembled, so this will be a rather short read. The frame is assembled, the head is assembled (only needing flybar installation) and the tail mechanism is pre-assembled as well. What I’ll do is just touch on things that I had trouble with, or that needed some clarification. Speaking of clarification, if you haven’t already seen them be sure to check out Finless Bob’s Knight 600E build video series on HeliFreak.com. Between his videos and the pictures that accompany this review, you should have no excuses when it comes to putting this thing together correctly!

First, a few words about the manual: While it’s not horrible, it’s not fantastic either. Unfortunately, this is typical of many helicopter kits. If you’ve built a few helicopters, this won’t bother you at all. And frankly, if you haven’t built a few helicopters you probably shouldn’t be building this one! The information you need is all there, but sometimes requires a bit of study and pondering before the light bulb comes on and you say “Oh, I get it!”

There is one thing that really annoyed me though: If you follow the sequence of assembly steps in the manual, you’ll be removing the motor later on in order to install the tailboom and belt assembly! Silly me, I followed the instructions and then had to remove the (already loctited) motor assembly later on. Bob didn’t have that issue in his build videos, because he followed a different assembly sequence for clarity during filming.

Onward! Everything goes together very well, and I had very few issues. I did need to shorten two of the link rods by about 2mm on each end to allow the links to thread on further, but that may or may not happen when you build yours. Link length is a very individual thing, and may vary slightly due to differences in servo arm geometry, etc.

Servo installation is straightforward, though there is a trick to getting the upper left servo into the frame. See the online photo album for a sequence of pictures showing how to work it into the frame without having to take the frame apart.

I did find aligning the flybar control arms to be frustrating at first, but then I realized it was much easier if I pivoted the arm all the way against the seesaw, snugged it down, then did the other one the same way. This assures they are parallel with each other, then you can simply adjust the paddles to align with the arms. Neat!

One other noteworthy item: The spindle bolts are not loctited, and this is clearly pointed out in an addendum to the instructions. I just want to be sure and point it out again for safety’s sake!

Other interesting or important things to note:

• The frame has alignment / guide holes to help you get the bellcranks in the proper alignment during setup.
• The tail case has a molded boss to install an anti-rotation bolt.
• The mainshaft locking collar goes under the top bearing, and above the elevator A-arm assembly.
• There is no gear lash adjustment for the pinion-to-spur gear. It is what it is (and it’s correct).

That’s really about all there is to the assembly. Please browse through the online album for plenty of pictures taken during the assembly.

Power System

As mentioned, the motor was included with the kit. It is a Compass-sourced outrunner of unknown manufacture. There is a sticker on the side that lists it as 760KV, and the headspeed measurements show that to be reasonably accurate. Note that it’s 8 pole, not 16 pole as written on the label in the photos. The motor has a 10 tooth pinion factory installed, and nice gold bullet-connectors are soldered onto the leads.

The ESC is the Hobby Wing Platinum as mentioned in the introduction. This is a large unit, with a beefy heat sink. I like the mounting bracket, as it allows one to bolt it to the frame. I had to slightly enlongate one of the mounting bracket holes for alignment, but the location is just perfect for nice wire routing. Programming was done with the “stick and beep” method since the programmer box was out of stock at the time of this review.

The BEC / voltage regulator is a Medusa Potencia 3.5A 5/6volt unit. While this may seem a bit on the low side, it has proven itself quite capable of handling the power needs of a 50 size helicopter by many owners.

Cyclic servos are Futaba 9452, while tail duties are handled by a JR 7703D paired with the JR 8900G.

And finally, power to the whole thing is supplied by a pair of 4S 3700mah 35C CSRC packs, connected in series. This is very easy to do since I use Anderson Powerpole connectors. Charging is typically done in parallel, since this equalizes voltage across the packs automatically. These batteries are beasts, and the 35C rating is actually overkill for a HV power system like the Knight. However, overhead is a nice thing to have since it keeps everything cool and un-stressed.

Flying

Be honest, you skipped right to this section didn’t you? Don’t feel bad, I do it to. Just be sure and eventually go back and read the rest of it, ok?

If you’ve listened to the podcast, you have no doubt heard James and me ramble on and on about how incredibly well the Knight 3D flies, so take all that and apply it to the Knight 600E – minus the engine noise and smoke trail. With the headspeed dialed in at 1950, the cyclic and collective response is (not surprisingly) just the same as my nitro-powered Knight 3D at the same headspeed. Flight times on the 3700 mah pack are a comfortable 6 minutes, without breaking the “80% rule” of the battery capacity.

Due to the design of the battery mounting area, you can run much larger packs if you so desire and get longer flights. Simply shift them fore / aft to get the CG where you want and strap ‘em down. In fact, I recommend larger batteries just because they will work less and last longer!

But wait Chris, only 1950 rpm you say? Not enough for you, Mr. Headspeed Junkie? No problem! Just dial up the throttle curve a little and go nuts! My initial spoolup with an 80% transmitter setting in governor mode netted a scary 2550 rpm! While that’s certainly not necessary (or recommended!) it’s good to know the power system has the guts to really crank those big 600mm sticks.

Conclusion

The Compass Knight 600E is a fantastic machine! In the right hands it is capable of the most hardcore smackdown 3D imaginable. Not my hands, of course. But even for my more sedate flying style, it’s a very enjoyable machine. I can honestly say I’ve never flown any other helicopter that has this same seductive mix of power, stability, and agility. Every flight brings a perma-grin to my face, and that’s what this hobby is all about. If you are in the market for a 600mm e-bird, do yourself a favor and find someone who has a Knight 600E and check it out. I think you’ll be impressed.

Videos, Podcasts, and Photos

I took quite a few pictures during the assembly, and you can find them all in this online photo album along with a couple of Eagle Tree data logs from the first couple of flights. We discussed the Knight in three episodes of InsideHeli Podcast. Here are direct links to all three shows (mp3 files):

Episode 51
Episode 52
Episode 53

This is the walkaround video:



Here's a video of the 2nd flight, with the stock plastic canopy and one of my "trademark" dayglow paint jobs.



And finally here's a video with some more aggressive flying (not me!), and shows the Fusono canopy: