RC-Expert Carbon Frame

The following is a review of the RC-Expert Carbon Fiber Frame.
Thanks to my father for this review.

Initially let's take a look at the parts ...

The rc-expert.com ccpm carbonframe set for the trex is the result of a very clever match of the custom made frames and all other parts required to complete assembly taken from the Ark X400 helicopter. The design is identical to the frame build up of an X400 with upper and lower frames connected by aluminium spacers.

The kit as received for review had no sketches or instructions so after a period of study of the parts it was decided to assemble the complete kit as received in order to ensure which parts and screws went together. There are different lengths of threaded and self tapping screws, this methodology proved to be successful as when the final build with all parts from the donor Trex was undertaken it was never necessary to disassemble parts because the wrong length or type of screw had been used.

Here is a list of the parts that are used from an X400 (and supplied) with this frame :

Mainshaft bearing blocks

Taildrive bearing blocks

Tailboom holders

Motor mount

Battery tray

Radius arm stay

Frame spacers, threaded and self tapping screws of varying lengths

You will also need a swashplate, preferably the ARK CNC swashplate as this is a perfect match to the other supplied components.

The first thing noticed with the trial fit of the frames was that the lugs on the cross members when fitted into the slots on the side frames fouled on a corner radius leaving a gap between them. This is easily remedied by removing a small amount of the radius where it fouls with a small file or sharp knife. See picture that follows:

The dry run of the frame assembly can be seen below :

The first part of the assembly is to fit the servos into the frames. This is best done before joining the frames together. The screw fixing holes for the servos are predrilled but we were not informed as to what servos they match. The first servos tried were the Align as these are probably the ones purchased with the original Trex. Unfortunately fitting into the frames required enlarging the slots or removing the screws from the servo casing and splitting the servo open in order to juggle it into the slot. The second option was used only to discover that the screw holes did not line up with the servo, but whilst holding it in the frame a trial fit of the two frames revealed that the depth of the servo was such that the frames would not fit together. It required that there was a packing piece of a minimum thickness of 2mm under the fixing screw lugs in order to fit, we did not think this a good idea. The next servo tried was a Hitec HS50 (for tail) which is considerably smaller than the Align. This fitted into the slot with ease and its depth was much less, again the screw holes did not line up with the predrilled ones but it was decided to use a high speed one for tail rotor control and the HS50 made to fit by using a rat tailed swiss file to open up the holes in the frame. At the same time the holes were pulled towards each other so that they lined up with the fixing holes in the servo and then held it in place with screws and nuts. This is a better solution than mounting the tail servo on the tail boom. The tail servo is far better protected from a blade strike when mounted within the carbon fibre frames.

The next servos tried (for cyclic control) were the MS Composite brand which once more were a problem to fit into the frame because the width was too great and once more the screw holes in the servo and frame did not match up. It occurred to me that this could become time consuming and expensive sorting out the servo match for these frames and I made the decision to fit the MS servos by filing one end of the slot and using one of the predrilled holes and drilling the second hole to line up with the fixing lug, this proved to be very successful.

Pictures of fitting the servos follow :

The next job to tackle is the mainshaft bearing holders which is pretty straight forward. Having first removed the drive gears from the mainshaft remove the two roller bearings from the shaft and push them into the bearing holders (they are not a tight fit). Put the bearings back on the shaft so that the top bearing holder (the one closest to the swashplate) has the raised circular lug facing down and the bottom bearing holder has the raised lug facing up which means the two raised lugs face each other. Fit the shaft into the frames and screw the bearing holders to the frames with supplied self tapping screws reassemble the gears to the shaft.

And now the one part of the conversion that could be the most difficult, fitting the bearing holders to the taildrive shaft will depend on what you have to hand in order to carry this out. The bottom bearing is very easy to do and again is not a tight fit but the top bearing holder is not so straight forward. The correct way is to remove the top grey drive pulley from the shaft which is a tight fit onto a straight knurl. One way to do this is to obtain a small piece of metal that will just fit under the gear (2.5mm is ideal) and cut a slot to just clear the small diameter of the pulley. See the picture below which shows how to locate the pulley in order to use a small punch to separate the shaft from the pulley.

Having fitted the second bearing holder it only remains to refit the pulley but ensure that the knurl on the inside is lined up with that on the shaft to obtain a trouble free fit. Do not hit or put side pressure on the bearings when refitting the pulley. When completed assemble to frames and screw into position with self tapping screws.

The final part of the build was very straight forward transferring the rest of the donor Trex to the new frames,the canopy required a degree of cutting to clear the front pushrods and the fit over the skid. See Pictures below.

In conclusion (for the build) there were some problems fitting the servos, which will affect almost everyone purchasing any upgrade of this type. As an example the Heliup frames are designed for HS56 servos and nothing else. The prospective purchaser is not going to ditch four servos because they don't match the frames but will set to as we have here and make them fit, it's not difficult after all we are modelers. Other than this minor issue the frames themselves are beautifully made and the completed helicopter looks very nice indeed. Forthunately these frames can be modified to fit a servo, which would not be possible with the Heliup frames.

Flight Testing

Unfortunately there has been an error by my being so keen to build these frames up that I have omitted to weigh the parts being rendered redundant and comparing them to the rc-expert.com kit. This will be a significant saving when taking into account the parts retained for transfer to the carbon fiber frames which are as follows :

canopy
skid set
complete mainshaft with bearings and gears, rotor head and mixers but not the swashplate which is replaced with the 120 degree one
taildrive assembly and bearings
tailboom assembly complete with boom supports and pitch change rod
motor and all electronic controls and servos

It may be necessary to purchase pushrods for the new position of the cyclic servos.

So how does it fly, well the answer is very good the saving in weight has improved the vertical climb, combine this with a much faster cyclic response due of course to 120 degree ccpm control and then the totally flex free frames the results speak for themselves with faster and sharper control. Unless someone can come up with something better this is about as good as it gets without spending mega bucks.
In order to convert to ccpm control you must have a transmitter with 120 degree mixer function

Overall conclusion

In conclusion these frames are an interesting idea. By drawing upon parts supplied by ARK, Rc-expert have managed to produce a nice set of frames that work very well and are backed up by a good supply of spare parts (from ARK). Rc-expert also do a set of X-400 frames and unsurprisingly they are identical to the ones reviewed here. The carbon fibre in this frames is 1.5 millimetres thick and the overall frame rigidity is superb. Considering this design is really based around the proven design of the X-400 and it's side frames there is little to criticise. The only source of frustration may be finding servos that fit without modification to the frames. As mentioned earlier it is more likely that the frames will be modified by the purchaser to allow fitting of the donor servos from the owners stock machine.

Benny from RC-Expert also wished to add the following footnote :

a. We'll provide an improved version soon with different servos control
b. We'll sell it assembled in the future
Benny also mentioned that the frames are drilled for servos they use but they will look into drilling for other more popular servos on future frames.

Performance

Number of ratings: 9

Rating: 3