Microheli CNC T-Rex 450 washout arms
Written by Ashley Davis Friday, 25 February 2005 00:00
Washout ArmsThe following is a review of the MicroHeli CNC Washout Arms set.
The first part of this review will center around the build quality of the Washout Arms.
Initially some good close up photos of the hub and arms to give you a feel for the attention to detail.
Initially I had a good feel of the washout set, looking for slop or unwanted movement in any lateral or vertical direction. The whole unit is extremely solid and slop free in any direction you wish to stress it. My next thought was to take it apart and have a look at it in pieces. You can see the pictures of this below. It is also necessary to fit the linkages for the swashplate connection onto the washout arms. I have detailed the pictures for this below as well.
Having disassembled the unit my first observation was that the metal screws did not have any locktite in evidence. Given that this is a metal to metal screw it is possible that vibration will work the screw loose so I would recommend checking this and applying some 222 locktite to keep it all secure on reassembly. Aside from this there was nothing of concern found in taking the unit apart.
Fitting the swashplate linkages was a simple matter of pushing out the locator pin on the plastic arms and then re-inserting it onto the MicroHeli arm. Having done this the movement of the plastic arm at the pin pivot point was a tiny bit stiff but nothing to be of concern. One way to remedy this would be to just carve away a little of the plastic to make a looser fit. I decided not to do this as the resistance to movement was so minimal.
The next task was to insert the washout arms onto the main shaft with the anti-rotation pins from the bottom of the rotor hub inserting into the two holes in the washout arms hub. Here I ran into some problems.
My locator pins were angled outwards slightly which meant that they didn't match the holes drilled in the washout hub. A couple of hours with a pair of pliers managed to get a fit, all be it a rather stiff and notchy movement. I wasn't at all happy with this as the washout arms should move freely with no resistance at all. The problem is the Align rotor head being molded plastic and not having a high enough accuracy in the molding to allow the pins to be totally parallel to the main shaft. I had a spare rotor head, so I thought I would try that one for fit. Fortunately this one was almost spot on and 5 mins with the pliers and it was moving freely. One tip I would offer is hat because the anti-rotation pins can bind slightly in the holes it is a very good idea to CA the anti-rotation pins into the rotor head, it would be no fun if these were to work loose in flight.
The above minor problem could cause some frustration for T-Rex owners with badly out of alignment anti rotation pins. I have discussed with MicroHeli the possibility of doing two versions of the center hub, one with slots for use with the plastic main rotor hub and one with holes for use with a CNC main rotor hub where pin alignment should be guaranteed. MicroHeli are looking into this.
Having got free movement on the washout all that was left was to connect it all up and reset my pitch curves accordingly. Pictures of the final assembly can be seen below.
A quick check of mid stick revealed that I had about two degrees of pitch and the washout arms were not horizontal. This was easily adjusted out on the links from the washout arms to the flybar control arms.
Having got this sorted another check revealed -9 negative to +11 positive total pitch range. Perfectly OK as attempting to get to +/- 10 would probably result in having to do half turns on the ball links which I would prefer not to do.
Servo movement on the collective was free and not an effort for the collective servo with no evidence of strain or notchy movement. My efforts with the pliers had obviously paid off.
My overall opinion on the build quality is that this is a very nice piece of engineering, movement of the arms is silky smooth and there is no evidence of slop or any type of unwanted movement in the arms. On the negative side there was no locktite on the metal screws holding the arms to the hub and the anti-rotation pin alignment could be problematical depending on the accuracy of the molding on different main rotor hubs. MicroHeli are looking at this following my feedback on the review. Lastly as a safety precaution the anti-rotation pins should be CA'd into the main rotor hub to make sure they can't be dislodged by the up/down movement of the pins in the washout hub guide holes.
Flight Report
Having flown this a little more I can appreciate the part these washout arms play in refining the cyclic response on the T-Rex.
The original standard washout arms had some horizontal play in them which contributed to a lazy response on the cyclic. This play is now gone and allows for a finer resolution and more immediate response to cyclic inputs. Marry this to the MicroHeli flybar set and this precision of movement increases again.
The washout arms also offer the option of getting a larger/smaller overall cyclic movement as the balls on the washout arms can be moved either out or in to adjust the overall cyclic response. For me the standard setup is just fine with the balls on the second to outer hole.
I like the smoother feel these washout arms can introduce, cyclic inputs are a little more predictable. If the washout arms are added as a single upgrade then I'm not sure that massive benefit is gained as the precision in the washout arms is lost in the slop on the standard flybar.
However, combine this washout set with the flybar upgrade (or similar modification) and things change significantly as the control inputs now have no slop and any stick movement is translated directly to the paddles. This gives a more positive feel and finer resolution of control for hovering maneuvers.
My overall opinion from flight testing is that as a single upgrade the benefit is lost due to the other areas of the head that have slop in them. If the other areas of slop can be tightened up then the overall benefit can be realised. One way to do this is through the MicroHeli flybar set but other modifications are available that can also tighten up the overall head slop in the linkages. Once the whole head is tightened up and slop free the washout arms produce a very nice level of precision and control.
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