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Review: Trex 250 Super Combo

August 20th, 2009 1 comment

trex250_boxAs soon as Align released the Trex 250 I wanted one, such a fun practical size, however like most other new releases there are always teething problems so I thought I’d hold off. Eventually I got around to getting one the other week as the super combo deals were just getting too good to ignore. The Trex 250 Super Combo comes with everything you need except the transmitter, receiver and batteries which is quite impressive.

The first thing you notice is the box is just so dam small, it is quite literally a work of art how they manage to fit an entire model plus electronics into a box less than 30cm wide.

In the box

  • pre-assembled head
  • pre-assembled tail unit
  • pre-assembled main frame with the motor loosely attached for packing
  • 1x Align GP750 Gyro
  • 3x DS410 cyclic servos
  • 1x DS420 tail servo
  • 1x RCE-BL15X 15A Brushless ESC (Build-in 5~6V adjustable BEC)
  • 1x RCM-BL250 Brushless motor(3400KV)
  • 1x Motor pinion gear 15T
  • 1x 205mm Main blades (plastic)
  • 1x 200mm Main blades (plastic)
  • 1x40mm Tail blades (plastic)
  • 1x42mm Tail blades (plastic)
  • 1x #00 Phillips screw driver
  • 1x #0.9 Hexagon screw driver
  • 1x Tweasers

Pre-Assembly

The pre-assembled head and swash was completely lock-tightened everywhere as was the tail unit, of course the only way I could know that was by taking it all apart first (which I recommend you do). The main frame was mostly lock-tightened, in my case the worst that would have happen was I would have probably just lost a couple of bolts, of course this is down to how much care is taken with pre-assembly in the factory, you may not be so lucky.

The Build

trex250_buildThe upper head links are one piece which makes final assembly of the head a lot easier as there are less links to measure and get wrong. The link coming up from the swash needs to be made, which is a simple process of making too links the same length according to the manual (something we all should be used too).

The frame is pre-assembled and only really needs a quick check over, it is a good idea to think about how you will route the servo wiring and sand the appropriate carbon edges to avoid wires being cut in flight by the frame (remember there really is limited space on this heli). The power cables coming from the motor will either sit left or right hand side of the frame and depending on your setup may come close or touch the frame. The motor comes with a small amount of heat shrink pre-installed where the 3 wires exit the motor, I decided in the interest of preserving my motor wires to add more heat shrink to avoid any direct wear.

Main gear vertical alignment was another consideration I had during the install. Because this is one of the later kits with various different upgrades etc to address and improve performance I have one of the new main gears which actually has a one-way bearing hub. Unlike the older version which has the one-way bearing seated directly into the maingear itself. The advantage of seating the one-way bearing directly into the maingear is that you are able to get the vertical alignment of the maingear to tail gear perfect. In my case I had to re-shim the main gear to get the vertical alignment to the tail gear perfect. Luckly the motor pinon wasn’t a problem as it’s quite tall and allowed for up and down adjustment of the maingear which was helpful. All that said I probably could have left the vertical maingear alignment as it was but hey I’m picky and it’s worth doing right in my opinion.

trex250_tail_hornThe tail setup as per manual was straight forward enough, the first main issue is servo horn length which is very important. Too long and you have too much mechanical gain, too short and the tail is not fast enough or has low mechanical gain. What works well and is stated in my version of the manual is the inner most hole on the round servo horn (servo horn that comes with DS420). After adjusting the push rod length so that the tail slider was centered the GP750 with no setting changes had almost perfect limits, which I increased slightly to get maximum throw.

The DS410 servos dropped straight in the frame no problems, the 2 front aileron servos are stacked hence the push-rod lengths are different, so care must be taken with push-rod length, subtrims and ATV’s. The DS410 servo horns holes are small and are incredibly difficult to get the “long ball ends” to self-tap without stripping the plastic holes (ask me how I know). I managed to get them to self tap by putting the horn on the bench and applying massive pressure to the hex driver with one hand (almost with my chest on top of my hand) while turning with the other. The good thing is because you have 4 Align servos, you have 4 servo horns which means you can practice on one to get your technique right, and still have 3 good ones for the cyclic. I also recommend using a drop of CA on the threads to fix them snug in place.

The canopy is a tight fit or at least mine was so a little trimming was needed but otherwise no problems there.

trex250_side1

trex250_bottom

trex250_with_canopy

Accesories

  • Battery: Outrage 3s 860mAh 30c which fit and work great.
  • Receiver: Spektrum 6100
  • Transmitter: DX7

Flight Test
I have only had a couple of flights on it and it seems pretty sweet, the tail feels locked in with basic stuff like circuits and piros. Flying sideways fast the tail starts to jitter a bit, also with large gusts of wind but it certainly hasn’t let go (inverted fast backwards would be interesting). I have the gain at about 50% on my DX7 which feels good any more than that an it starts to oscillate in hover.

The tail in general probably needs a little work, even with a considered build there is a bit too much slop for my liking. There are a couple of options, Align have released a second version of their “Chinese Weight” tail hub and grips part number: H25095A. Also Micro Heli has a full CNC tail unit upgrade which looks “the nuts”. There are also custom Chinese weight mods and tail bearing/spacer improvements that can be made see here:

http://www.helifreak.com/showthread.php?t=107276

Collective punches seem overly soft but I believe that maybe due to the plastic blades… I’ll be upgrading to carbon blades. Flipping and rolling the the heli seems slow and hence takes up more space. The manual states 40-45% swash mixing for both elevator and aileron, I might increase that a fraction and with harder dampers and carbon blades I should be in business.

Summary
All things considered it is an amazing heli for it’s size no question. The head quality is great (yes I know it’s Align), all carbon and the kit contains a decent gyro. The only thing that lets it down is a lack of attention with respect to the tail, probably due to rushing it to market, one thing that is certain is Align will fix the tail, however we the public are the beta testers.

Rating: 7/10 (would be more with an improved tail)

REVIEW: G-Force 700N Clutch Block Kit with Engine Mounts

July 17th, 2009 No comments

Here is a great review on the new G-Force clutch block which improves the gear stripping problem: http://www.rcheliresource.com/review-g-force…

G-Force Clutch Block and Engine Mount

Review: JR DSX9 and Spektrum DX7 Voltage Regulator

July 6th, 2009 6 comments

How safe is it to use lipo transmitter batteries in either the DSX9 or DX7 and if it’s not safe why is it not safe?

LM2937ES Voltage Regulator (DSX9)The JR DSX9 and Spektrum DX7 use the LM2937ES 3.3v Linear Voltage Regulator, basically the more voltage you supply it the hotter it gets. As it turns out the maximum supply voltage for the LM2397ES is 26v. This is quite interesting given we know we are drawing about 300mA either with a supply voltage of 11.6v via NiMh or 12.6v via Lipo, both of  which are well with in the stated acceptable limits of the regulator according to this document: LM2937ES 3.3v Voltage Regulator Datasheet

This only leaves heat as the number one suspect for failure. Interestingly enough there is no heat sink anywhere to be seen on the regulator in either the DX7 or DSX9. Both installations of the voltage regulator  are also clearly inside a sealed plastic TX case which doesn’t help matters. Throw into the mix an above average ambient air temperature and you have conditions for the voltage regulator which are not so favorable. But… if you use the NiMh battery you’ll be fine according to the powers that be?

Inside back DSX9

Just for the record a fully charged 8s NiMh battery is 11.6v (maybe slightly higher if it’s old) and a 3s Lipo is 12.6v, so there is a difference of 1.6v. So by implication, offically if you change your supply voltage by 1.6v in less than ideal circumstances (described before) you will toast your transmitter. I’m not desputing that some people have been unlucky and toasted their TX voltage regulators by using lipo batteries. The issue I have is that the margin for error in terms of supply voltage is incredibly fine for a hobby which has such an emphasis on safety.

Summary

Is it safe to use lipo TX batteries in either the DSX9 or DX7? Clearly it’s not safe, however some people are getting away with it, the regulator will easily take the voltage but the heat generated is the weak link. Whether you get away with it is likely to be on a case by case bases largely dependent on your use of the transmitter and the environment it’s operated in.

Also see: http://heli.brixtonjunkies.com/2009/07/02/transmitter-lipo-3s-11-1v-stepdown/

Review: MicroHeli Trex 700 MOD 1.0 Gear Conversion

June 28th, 2009 No comments

The ultimate main gear upgrade to strength the Trex 700 drive train.

http://www.rcheliresource.com/review-helidirect-trex-700-mod-10-gear-conversion/

rcheliresource.com

Review: CY Radix 690 vs Radix 710 (Stickbangers)

June 19th, 2009 No comments

Radix 710 sb

First impressions of the Radix 690’s are the blade is very light, has a wide cord, stiff, with a beautiful finish. On the Trex700 they seem very aggressive and much harder bog compared with other blades I’ve tried. They also seem to track pretty well too for a light 3D blade.

Moving onto the Radix 710, obviously the finish and quality is on par with the 690’s. There is a noticeable difference however, they are super poppy compared with the 690’s. Pop too much though and it will cost you headspeed, but that is to be expected, nothing a bit of collective management wont fix. They track slightly better in forward flight, mainly I think due to the extra size. Cyclic response is slightly slower, but maybe a little cleaner, particularly noticeable during flips/piro flips.

Over all both the 690’s and 710’s have their place.

Radix 690

Is a really aggressive blade with fast cyclic response with no sign of bogging during powerful moves.

Radix 710

Is an incredibly poppy blade which is slightly more graceful overall when compared with the 690.  The blade does however require sligntly more collective management for hardcore 3D, but well within limits.

Summary

They are both great blades, it really depends what flight characteristics you are looking for.

My choice is the Radix 710, just because I love the extra pop that you get.  And with a well tuned engine the extra load on the head can easily be managed with careful application of the collective. I’m not writing off the 690’s as they could be very useful in liven up a slower heli or a tired engine. Or maybe you just want a super aggressive heli 😛