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| The following is a review of the MicroHeli Carbon Fiber Frame. MicroHeli have a standard and a Pro version, this
frame is the Advanced Pro version. The frame has undergone some revisions
and several components have been updated to new stronger materials. Let's look at the build initially.... |
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| The MicroHeli frame comes in a small box with all the parts nicely packaged
into separate bags. Also included is a printed set of instructions for
assembly. Later in the review I include a link to download these instructions. Following the instructions the first part of the build is the upper CNC frame. This is simply installing the main mast bearing tube and the tail boom clamps and gyro platform. |
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| Following the assembly of the upper CNC frame the instructions direct you to assemble the upper server amount and anti-rotation guide. Remember to use loctite on all screws for the above assembly and the following assembly steps below. The instructions do make this very clear. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| The instructions now direct the installation of the servos, however, as I wanted to build up the frames without the servos in order to take some pictures I skipped this step and moved on to the main frames assembly. I would not advise others to do this as it makes installing the servos harder later. A point to note with these frames is that they are made from 1.5 millimetres carbon sheet, I'm very pleased that MicroHeli did not use one millimetre carbon as this would have allowed some flex, where as this thicker carbon used in the frame is much more rigid. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| The last remaining step in order to complete the basic frame is to mount the top CNC frame onto the lower carbon frame. Below I have catalogued a number of photographs showing the bare layout of the frame before mounting any radio gear or servos. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| here are the MicroHeli build instructions ---> build instructions. These are extremely good build instructions and the first I have seen from MicroHeli. They have done a good job in producing these very comprehensive instructions and some recognition is in order. The carbon fiber parts in the frame are all nicely cut with no rough edges or issues that I could identify. The CNC parts of the frame (of which there are many) are a mixture of 6061 grade aluminium and 7075 aluminium. This is partly due to weight considerations as 7075 is a heavier grade of aluminium and only needs to be used where durability is absolutely required. The first job was to install the rear tail pulley for driving the tail belt. According to the instructions the stock pre-assembled unit (tail pulley, bearings and drive gear) needs to be disassembled. At least it needs the top grey plastic pinion removing. I used a pinion puller to achieve this. Once the plastic pinion is removed the pulley assembly can be inserted into the frames and the pinion replaced and some CA used to glue it back onto the shaft. This installation step can be seen below : |
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| I'm not overly keen on the way this has been achieved. The bearings are
a reasonably tight fit in the CNC cups but I would have preferred a tight
press fit. This is down to the way it assembles in that the top large CNC
part can pivot up and down (as shown in the instructions) by removing a
couple of screws. For it to pivot and not be a problem for the bearings
to insert into their holders the bearing cups cannot be a tight push fit,
otherwise the frames just wouldn't close as the tail pulley bearings wouldn't
go down into the cup easily. You can't get any fingers or tools inside
the frames to help. The bearings do fit snugly enough to not rattle or
cause any radio frequency noise but I would have preferred a good tight
press fit. The other problem I have experienced with fitting the rear pulley
in this way is that if you have to remove it you can't get the pinion puller
onto the pulley. In my case I had to remove the upper frames and use a
hammer and centre punch to remove the pulley. The frame has some vertical
adjustment built into it to allow the bearing cup for the lower bearing
to move up and down and provide a good fit and remove any unwanted vertical
movement in the tail pulley overall. This is a nice option and was not
available on early frames. The next job was fitting of the main shaft and main gear, this also proved problematical due to the design. The instructions show that the top CNC plate needs to be pivoted up in order to fit the main gear. This is purely because the side frames have been built in such a way that the main gear cannot be inserted from the side as with a stock T-Rex kit. Whilst this frame pivoting idea may be fine when first building, once the radio gear is installed and all the wires cable tied in place it can be difficult to pivot the frames. The main gear only needs a couple of mm of extra clearance and it would fit fine through the side of the frames. Careful consideration should be given to routing of wires and use of cable ties to make sure that the frame can pivot after the radio gear has been installed. That is one of my main criticisms of this frame as I would much prefer to be able to change the main gear by just undoing the bottom main gear screw and nut. Of course this has no bearing on the flight characteristics but I like ease of maintenance. Next task is servo installation and until I read the instructions this proved somewhat of a difficult task as the servos just didn't appear to fit at all. However the frame has some adjustments built into it that allow the servo mount to slide backwards/forwards which gives just (and I mean just) enough room to mount the servos. There is little clearance between the servos and the main mast holder, and the control horn on one of the rear servos only just clears the casing of the front servo. I fitted HS56 servos as these are designed to fit this frame. The servos go in OK but the servo horns should be mounted first as you can barely get to the screws or the horns once they are mounted. Also note the tiny clearance behind the servos to the rear drive pulley. Everything misses but it is all very close indeed, which is fine for flight but in the slightest of crashes these components are likely to hit one another. Below are some pictures of the servo installation. In the pictures my servos are mounted upside down compared to the instructions. I took this decision as it made it easier for me to match push rods from the servos to the swash plate. Either way up will work but if you choose to do it the way I have you need to be careful of the servo horns hitting the top of the mainframe. |
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| From a geometry perspective the servo horns line up well enough with the
swashplate and I don't envisage any control issues from this setup. Rods
are all parallel with the main shaft and there are no significant arcs
that would cause a problem in swashplate movement. However if you want
extreme movements of the swashplate and mount further out on the servo
horn then you do start to run into problems of misalignment of the servos,
rods and swashplate. Having said that few people would need to go further
out on the servo horn than pictured. As shown you can easily achieve +/-
10° of pitch. Next was the motor mount, this item has proved problematical. MicroHeli have addressed this problem so please bear in mind that the comments here only apply to early frames. The original mount was made of 6061 aluminium and therefore quite soft. I stripped one thread whilst mounting the motor mount plus the arms on the mount look very thin given that they are holding all the torque from the motor. This did prove to be an issue, further down I document my flight experiences, one of which included a boom strike, the motor mount broke from the hard landing that caused this boom strike. Following this I fitted a new mount, flew two packs of hovering/circuits, landed, checked the motor mount and it is cracked in two places, exactly as the previous mount had broken. This part clearly isn't up to the job and either needs to be thicker at the point of fracture or made from 7075 aluminium. MicroHeli based on these experiences have now addressed this issue and the new frames are supplied with a much tougher motor mount made from 7075 aluminium. See the pictures at the top of this review for a picture of the new motor mount. Apart from these issues the motor mount is very accessible, changing motors is a simple task and gear alignment is nicely achieved by sliding the entire mount backwards and forwards in the frames. Some pictures follow of the broken motor mount and the replacement cracked motor mount following a couple of packs hovering, as mentioned earlier this is now resolved in later frames.... |
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| Once built the frame is not as rigid as one would hope, in order to combat
this MicroHeli provide a lower CNC frame brace. This item can be seen pictured
at the top of the review. The lower frame brace does help greatly with
the overall frame rigidity and in my opinion it is a worthwhile addition
to the frame. Another critiscism is that the whole frame is exposed in
a crash as the mast will act as a lever on the rest of the frame and significant
damage will be caused from impact. MicroHeli have acknowledged this in
previous communications on the forums and this frame is not built for ultimate
resilience but instead ultimate performance. I will explore this performance
in the flight testing. The frame contains two possibilities for mounting the gyro, this can be on the provided top plate above where the boom mounts to the main frame or alternatively an optional platform is provided that can allow an upside down mount of the gyro under the tail boom. I chose the second option based on bitter experience mounting gyros on top of the boom and having them smashed in a crash. |
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| The next item for consideration is the boom clamp mechanism. The boom is clamped into place using four screws into two separate boom clamping brackets. The clamps go right around the boom but the CNC top plate just has a round indentation in it for the boom to locate against. Whilst this does work well enough, this is not as well designed as I would like and the clamps don't come down nicely around the boom, leaving a gap, which depending on boom size (which does differ) could leave a small gap or a larger gap. I would much prefer it if the boom clamps tightened down solidly with no gap at all, leaving no question of any metal parts vibrating and causing RF noise. In my case the gaps are large enough to not to be of concern but this doesn't look tidy. I didn't want to tighten the screws any further for fear of stripping the thread in the aluminium clamps, which had happened already on the first 6061 motor mount. Below can be seen some closer views of the tail clamping. These screws also need some serious loctite, I used red 222 initially and you can see from the pictures above that one screw is working it's way loose. Blue 243 locked it in place solidly. I had to change my tail belt not long after this build as it was worn out, when I removed the boom I noticed that it had been squashed a little by the clamping mechanism. Clearly the screws and clamps do provide plenty of grip and clampdown very hard on the boom despite my worries of stripping threads. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| The next item to discuss is the battery tray, which is something that I do like on the frame. It has the ability to tilt through an arc and this gives some very nice options with regard to battery placement as well as a nice mounting point for ESCs or BECs. The tilt mechanism is adjusted by screws on the side of the frames. This works extremely well and allows for any number of different cells to make best use of the space available. Plus it is precut to allow solid mounting of velcro ties to hold the pack in place. Some pictures below .... | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| The frame without any radio gear came to a weight of 86 grams. Setup was a straight forward procedure, easily getting the +/- 10 degrees of pitch I wanted and adequate throws on the servos for cyclic movement. Overall conclusions from the build Positives: original design 1.5 millimetre carbon excellent looks upper or lower motor mount options very easy adjustment of gear mesh for motor to main gear adjustable battery tray choice of two gyro mount positions adjustable rear bearing cups Negatives: durability maintenance of main gear (pivoting frame) tightness of bearings in rear cups tail boom clamps Flight Testing Before going into the flight testing it is worth mentioning the exact configuration used for the flight tests. The tested machine not only had the MicroHeli frame but also their flybar system, mixer arms, 120° swash plate, CNC tail gearbox, extended tail shaft, tail pitch slider SE and CNC tail rotor system. The model was equipped with the standard plastic rotor hub with double dampers and plastic blade grips. I had installed HS56 servos and for the tail an HS50. The gyro is a CSM 560 SL with the revision four software. For the tests I am using the Medusa 28--032--2800 motor in a 4S configuration. This motor is one of the most powerful I have tested when utilised in a 4S configuration. It is fair to say that this is a heavily upgraded trex. Lifting off into the hover the machine was very stable and felt very much like flying the new XL trex although this is a machine based upon the original V2 specification. Due to the ccpm configuration collective response was much more immediate than with a non-ccpm config and cyclic response was as one might expect of a well set up ccpm configuration using high quality servos. The machine feels well-balanced and very predictable. Tail response was almost digital in nature with a rocksolid hold and excellent stopping without bounce. The machine was not exhibiting any excess vibration and all in all was very smooth and progressive in response to command inputs. Based on this indications are good that the 3D capabilities of this machine will be very solid indeed. Moving into circuits the feel of the machine is extremely positive and again very predictable. The whole machine feels very nicely balanced and was generally a pleasure to fly in either fast or slow circuits. For just general flying around, circuits, fast approaches and various hovering manoeuvers the frame performed faultlessly. The flight characteristics reminded me very much of the way the Heliup carbon frame flies. The next question to be answered is whether this frame is as comfortable inverted? I had opportunity to try this today as the weather was nice and calm (5-10mph). In order to give me some perspective I flew a completely stock trex (V2) and did some basic 3-D, flips, stationary rolls and some half piro-flips. As well at some basic inverted flying. I also did some loops and rolls. Having got used to the performance of the stock machine I then switch to the MicroHeli upgraded machine. The immediate obvious difference was the stability of the MicroHeli machine in comparison to a stock trex. The controls also felt generally more accurate. First manoeuvre was a half sideways flip to inverted to check inverted hovering stability. The MicroHeli machine is noticeably more stable in an inverted hover and also flipped to the inverted in a more controlled fashion. This more accurate feeling to the flight characteristics was apparent in all the 3-D manoeuvres I tried and was quite confidence inspiring. However, the trex did catch me out later which resulted in a rather untidy landing in a tree while flying inverted. The only damage from this crash was a bent main shaft, the rest of the frame survived without any bent parts. Overall I was very impressed with the flight capabilities and accuracy from this machine and would much prefer performing 3-D with this in preference to a stock machine. Nearly all the moves were tighter and more controllable with very little wandering off-track or falling out of manoeuvres. With MicroHeli's claims that this frame is for performance rather than durability I would have to agree that I have been impressed by its capabilities. Overall conclusion It has taken some time for this review to make it onto trextuning. This has been down to updates and changes to the MicroHeli frame in response to testing by trextuning and other pilots around the world. The advanced professional frame is much improved over the original frame that I looked at a couple of months ago. Some parts have been made more durable and others have been given extra adjustments to allow for better fit and finish. I am pleased that MicroHeli have reacted to customer feedback in this way. In terms of performance I have been impressed by the capabilities and accuracy of flight afforded by a heavily upgraded machine such as the one used in this review. In fairness this review should concentrate on the frame and to that end the more accurate cyclic and collective response is a direct result of CCPM control with good servos. The servo geometry is good and provides interaction free movement through the servos range. The frame doesn't suffer any adverse vibration and the various bearing holders, clamps and adjustments on the frame allow for a great deal of tailoring of the frame to meet specific needs. In terms of build I have some reservations with regard to the durability of this frame and also that the servos are very exposed in their positions around the main mast. I would prefer a tighter fit on some of the bearings (specifically the tail pulley and bearing cups) and I'm not overly keen on the tail boom clamps. Lastly I don't like having to pivot the upper main frame in order to change the main gear. Quality of components is excellent and machining of the CNC parts is of good quality. I also like that the carbon parts of the frame are of 1.5 millimetres thickness, which provides a good deal of rigidity. Should somebody be unfortunate enough to crash or break some of the components of their MicroHeli frame then MicroHeli do provide a full set of parts for this frame. Which is a nice option and does cut down expense should the inevitable happen. Lastly this frame is fairly unique in terms of its bling looks and is distinctive in terms of its design. Which for some would swing a purchasing decision. In many ways I feel that this has been a mixed review. There are things that I like about this frame and things that I don't like. However, flight performance is in line with MicroHeli's claims and therefore for the experienced pilots this frame does offer improved flight characteristics. For novice pilots I would not recommend this frame as durability is not the focus and for beginners making crashing more expensive is a bad idea. If you have this frame rate it using the TRexTuning rating system ..... |
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