RC India

I will be building the Compass Model Atom 500 electric heli over the next week. It comes 80% assembled from the factory, so it shouldn't need more than a few hours but I'm a meticulous (prefer that term to "lazy") builder. The build will be documented here with pictures.

This is the G10 frame version with 60A HobbyWing Platinum ESC included. Two pinions are included in the kit. The 8T one is for beginners who don't need the power needed for 3D flight, but rather would have a longer flight.

Manual, parts list. You can also see the ESC package.

Contents laid out.

Tail fin attachment and screws.

Main gear, auto rotation hub and hardened main shaft.

All bags have a sticker to associate them with the build step in the manual. You only need to open the bag for the step you are on. Do not open all the bags at the same time, it is easy to mix up screws and wonder later what goes where.

Metal tail case. The tail mechanism is a great design with zero slop unlike other helis I have seen.

Metal Head, blade grips, flybar carrier. This beauty will be unwrapped later in the build.

Metal swash plate, flybar paddle and washout assembly.

The links are already assembled  {:)} Though they are already sized close to the required length, some adjustments may be needed depending on the servo you use. The ball links are tight, will need to be reamed.

A ball link reamer is included in the kit  {:)} That is a nice touch, haven't seen any other manufacturer doing that.

There is already one pinion installed on the motor. This is the second one. The 9T is used for higher performance, but this will use more power and hence flight will be shorter. Unless you are into 3D, use the 8T pinion, this will give you a longer flight. Beginners might also want to remove the spacers in the swash to tame down the heli. Experienced fliers would prefer the crisp response of the stock setup.

Servo horns, link balls etc

G10 frame and motor. It is a hefty motor capable of much more power than needed. Overdesign is good here, I don't like overheating motors, the NdFeB magnets in brushless motors don't like heat much.

Note to myself: Remember to remove the sticker from the motor before the test flight.

All bearing blocks are metal in this heli, absolutely no need to upgrade. The bearing seems to be greased already.

Again stock part is metal, no need to upgrade. Also they have bearings unlike some other helis.

Painted fibreglass canopy. Looks much better than plastic canopies. This one looks great. Frankly I hate the canopy designs on other helis from Compass, they need to hire a better designer.

That's all for today.

These servos and gyro are getting good reviews so thought I'll try them out.

Cyclic: DS510
Tail: DS520
gyro: GP750

The other servo options are Futaba 9650, Inolab HG-D260HB, JR Z3650, MKS DS9660 etc. For the gyro you could use Futaba GY401 on the lower end or spartan DS760 on the other.

Go over the frame with a file lightly to dull the sharp edges of the frame. Otherwise the sharp edges can cut into the wiring over time. You could also use sleeving or fuel tube to protect the wires.

There are two sets of servo horn included in the kit. One for futaba and other for JR. Align servos has the same splines as Futaba, so I'll be using them. These horns are quite a bit beefier than the horns that comes with the servo, no chance of flexing under load. They are a tight fit on to the servo, so there is no slop at all.

There are markings on the horn to identify them as "FU" and "JR" type.

The servos are mounted from inside the frame. I found it easiest to get the servo in through the slots for main gear and then position them.

There are 3 lengths of screws provided for servo installation. The longest one is for use with a standard size tail servo. The middle one is for elevator servo and smallest for the aileron ones.

I used the grommet that came with the servos for the aileron servos. The eyelets are too small for the screws, so I left them out. The manual recommends installation without using them. The mounting holes on the servo is oversized for the screws, so I thought there might be some play if installed without the grommets. However later I was forced to mount the elevator servo without them and it seems to be fixed solidly. Later in the build I'll remove the grommets if that gives me better alignment.

Notice the elevator servo is installed with spacers. This is required to align it with the swash elevator input.

For the tail servo, there are two slots provided on either side of the frame. One is for a standard sized servo and the other for a mini servo. I'm using DS250, so mounted it on the mini servo slot.

The aluminum tubes are a tight fit on the landing gear struts. I decided against reaming them, but soon started regretting it. It is really tight, I'll be reaming it next time I have to do this. This was unlike Knight 3d landing gear which was a breeze to fix. Compass model heli's use ball links as holders for antenna tube. So if you need one for a quick fix at the field, you know where to get one  :)

I usually dab a bit of epoxy glue on the skid caps. They seem to be nice fit already, but this was something I learned to do with other brands where the skid caps fall off soon and carried over the procedure as extra insurance.

Good going   {:)}

BTW, I found that sand paper worked a bit better than a file while trying to remove the sharp edges from CF frame plates.

I didn't have sand paper handy. The needle file worked out really well. But I can see how the rounded corners can be easier done with sand paper.

nice build log  :)

Thank you Sahil.

There are a few of things that came to my mind that I forgot to mention earlier.

Pinions: There is also a 10T pinion for the 3D maniacs. This will trade even more power for a shorter flying time.

It was probably not clear in the pictures, the servos are fixed by self tapping screws that thread on to the frame itself. There is no servo nut like in knight 3d. The standard size tail servo is the only one that uses plastic servo nuts. The mini tail servo does not use them. As with any self tapping screw installation, it is important not to over tighten the screw and strip the threads in the frame. If you do manage to do that somehow, you could replace with a bolt and nylock nut.

The overtightening thing applies to all heli assemblies irrespective of brand and also for bolts/machine screws. Don't be a gorilla tightening them. They are manufactured for a max torque specification, if you force them beyond that, there is a possibility that the bolt head will shear off. I learned this the hard way, but fortunately on the bench, not during a flight. The screws are not supposed to held by the tightness, but they should be snugged just enough and should be held in place by using thread lock. Make sure the threads are cleaned with any alcohol to remove oil residues before using thread lock. In short, always use thread lock when installing screws onto metal parts. You don't need to use a lot of thread lock, it just makes them more difficult to remove. You just need enough to wet 4 or 5 threads. I'm a bit more generous on parts that vibrate more like engine mounts. My bolt head shearing incident was due to over tightening and overuse of thread lock. It just wouldn't budge when I tried to remove it and finally the head just sheared off. However this incident convinced me that thread lock is doing its job very well. I use the blue one from anabond. The thread lock attacks some types of plastics, makes them brittle and ends in a slow failure, so never use them on plastic.

Neat one RotorZone, nice build log, pics and details. All the best Rajesh!

Tail assembly out of the bag. The metal tail case is standard and is open for easy inspection. There are two shims provided in the bag. These are for taking out any play on the shaft. Mine didn't have any play, so I did not use them.

Warning on the tail belt not to crimp it while passing it through the tail boom. Crimping it could lead to premature failure.

The tail assembly is fixed on to the boom by the two M2 bolts you see on the side. The boom should be fully pressed in while fixing the bolts. The manual asks you not to drill the boom and let the bolts make its own holes. I was apprehensive that this might deform the boom. Anyway I thought I'll respect the wisdom of the designers and screwed in the bolt slowly. It did work perfectly. I kept pressure pushing in the boom while threading it, this also should have helped the boom retain its shape.

Tail assembly shots showing lever and slider mechanism. There is absolutely no slop in this mechanism. Another feature that is not seen here is that there is a thrust bearing and radial bearing inside he blade grips. They are lubed already from the factory.

You need to take out one of the bolts to fix the vertical fin. So fix the tail fin before applying loctite to the bolts.

At this time the tail rod guides are also slid onto the boom. The guides are split ring and there is a screw to tighten it over the boom. If you forget to put in the guides at this stage, don't fret, they are quite flexible and you can snap it over the boom without removing the tail boom later.

Compass model helis have a little longer vertical fin, this gives the tail blades more clearance from the ground and saves the blades in case of a hard landing.

The main gear and auto rotation hub comes already assembled. I pulled out the hub to check if the one way bearing was lubed and indeed it was.

The gear has a recess that hold the hex nylock nut for the jesus bolt. In case you are not aware, it is called the jesus bolt because all the weight of the heli is supported by this one M2 (M3 in the 50 size helis) bolt. Just this one bolt coming off will detach the main rotor from the heli frame. Imagine the stress the bolt has to take when the 3D pros are flinging the heli around  :o. Some of you are going to be squirming a bit when you are around a screaming heli next time I guess ;D

Keep checking this bolt often and change it after every crash. I have seen it backing off over time in other helis. Also it is very important not to overtighten this bolt that could result in bolt shearing as I explained in an earlier post. Since there is plastic gear over which the bolt tightens in this case, the deformation of the gear is the more likely result of overtightening than shear.

There are two holes on the main shaft. The end with the hole nearer to the end is where the head goes.

There is a collar on the main shaft that should be snugged under the top bearing. There is a ridge on one side of the collar, this is the one that should go on the bearing side. This will ensure the collar is snug against the inner race of the bearing and the outer race and shield can rotate freely. I donn't tighten the collar bolt at this stage, it will be done as one of the last steps. Make sure there is no up and down play on the shaft when the collar is tightened. Also don't forget to use loctite on the screw. You might wonder if the collar will slip, but that has not happened yet for me on knight 3D for with much higher loads.

The motor mount is held by two screws. Loosening the screws allows you move the motor mount to adjust the gear mesh. I will cover the gear mesh adjustment later. Also don't forget to loctite the motor mount screws after final adjustment.

Will cover the setup later. Just the pictures for now. Everything in the head, washout assembly and swash is metal.

More pics

Metal swash plate and wash out assembly.

There is just one phasing pin in the washout assembly unlike in bigger helis.