T-rex 700N hex starter coupling

Another "engine starting issue" I ran into a while back was the starter coupling, or what I call the hex starter cup. It was cracked about a year ago, but had been working ok after some reinforcement with some metallic epoxy.

I only used one screw to secure the hex adapter to the starter shaft when I built the heli. It never gave any issue, till I got the new starter. With the new starter, even on just 12v, the starter coupling gave way and started spinning on the shaft, rather than with the shaft. This worn out the grub screw and the shaft, which eventually meant that I again, could not start the engine.


Unfortunately, I haven't got my macro lens when the shaft failed, so I was unable to get a decent shot of the wear on the shaft.

New one is cheap, but it was a bitch to get it off. It basically involves taking apart most of the screw below the swash plate, equally, if not, more tedious than on the plastic frame raptor 50. This is because of the design of the starter bearing block and also, the placing of the governor sensor. Because there was no way I could remove the coupling from the shaft to get the clutch bell/pinion assembly out, the coupling had to be drilled out.

I believe the cracking of the starter coupling is not common and the recent failure is a user-error, that is again, relatively uncommon. Still, it was quite frustrating.

Fromeco Arizona

1.5years after I got the Fromeco Arizona, I finally put it to use on the 700N, reason being I simply couldn't sell the new in package Arizona for a decent price.

The installation was a nightmare. The footprint of the arizona is some much larger than the dualsky vr-8l that I was running. I had to rearrange all the electronics on the rx tray. Wires are still as messy as before. The heatsink is smaller than the dualsky unit and it is much lighter, but the cat spline thingy that comes along with it takes a lot of mounting space.

I made a switch for it by taking a normal switch lead and shorting out plug to the rx lead. It is vital to short out the rx lead and not the charge lead of a non-failsafe switch.





The Futaba 6014FS receiver that was previously on top of the tray couldn't fit into the radio tray. So it was replaced with a 608FS.



I also replaced the Flightpower evo-rx 2100mah lipo with a Turnigy 25c nano-tech 1800mah. The wires on the turnigy are oversized.



I have also start using the XT60 connector made popular by the hobby city stuff. It is very tight and secure, but yet easy to remove, unlike deans. The connectors are like bullets with half end cup and thus, are very easy to solder. It should be possible to fit 10awg wires on these, but if you need 10awg, you probably need larger connectors. I believe they should be able to withstand up to 6s/8s spark. The deans on the Arizona was replaced with XT60 connector.


Flight Performance
Lipo performance can never be determine by tiny RX pack duty, so I will skip that. The Arizona performed ok, but it got pretty warm on a 32C day. I had the voltage output to the cyclic servo set at 6v, so it will probably get even warmer should the output voltage be dropped to 5v. The heatsink is definitely much less efficient than the dualsky. IMO, this regulator is not worth the price it cost, and the same pretty much stands for most regulators in the market. I am only using it because I can't sell it for a decent price. Otherwise, I would have stuck with the dualsky vr-8l, which actually runs cooler.

Seriously speaking, looking at the heatsink size and area of the arizona and most other regulator with even smaller heatsink, I don't see how they can do their rated 8A-15A in our hot tropical climate. I mean this is simple physics. No matter how good a linear regulator is, the amount of heat it has to dissipate is V*I, where V is the voltage difference between input and output. At 7.4v input and 6v output, doing 10A will mean trying to get rid of 14w of heat, which is impossible without running the regulator at higher than boiling water temperate. Spikes of 10A is ok, but continuous 10A is simply just B.S. by the marketing department, since nobody will ever pull 10A throughout the whole flight.

Overall the Arizona is a ok regulator, but there is no doubt it does get warmer than the VR-8L. The key features are the ability for a fail-safe switch, dual voltage output and decently sized heatsink. The current version of the Arizona, which mine is, are capable of doing 7.4v output to the cyclic servo.

Struggling with nitro...update on 700N

Update is long long overdue.

After almost a decade of nitro heli, I have almost decided that enough is enough. Perhaps it is time to move on to an electric-only fleet. The raptor 50 was sold a while back, the T-rex 700N is probably going to become a 700E in the future, but I don't really like the frame layout of the 700E.

Since the Beijing 2008 Olympics, nitro fuel has gotten really expensive. Not sure if it is LHS getting greedy or cost really increasing, but I honestly doubt it is the latter, considering that the strong SGD currency should be more than able to cushion most of the impact of cost increase.

It doesn't help that lipo from hobby city is getting cheaper and performing insanely well. The lipo on my 10s E-raptor are doing perfectly fine after 30cycles. If you live in the States, probably nitro heli is still cheaper to fly, considering that shipping from HK to US is expensive and 30% nitro can be gotten for under 20USD for club order which by-pass the greedy LHS.

Matters were made worse with the series of issues I had with my nitro heli, mainly because most of my nitro stuff are ageing. It was so bad that in one of the weeks, I only got 1 flight after making 3 trips to the field. Glow starter not working, starter not strong enough, starter battery not giving enough burst amp, fuel pump stuck...not to mention the stupidly heavy flightbox I have.

NEW STARTER
Starting a 90 size was never suppose to be easy, but I never thought it will be so difficult. I burned out my old starter and so got a graupner ECO-90 starter as a replacement. This is a really big and heavy starter compared to my previous starter. It supposedly have 238N-cm of torque on just 12V, which is close to the Sullivan Dynatron starter on 12V. Not bad for a $81 starter. Really powerful and strong. Unforunately, because it is so powerful, my thunder tiger hex starter shaft is just unable to start the engine without flying out from the starter cone cup. After a lot of effort and changing out the stock rubber cone for the K&S one, it is now ok, but still a bitch to get in.

Also, it seems that my old lead acid battery, both the 12v 7ah and 12v 12ah, are unable to sustain the current it can draw when starting the YS 91sr. That means new battery required. I ordered a 4S 5000mah 20C from hobbycity. Why 5000mah? Because 4s 5000mah is cheaper than all the other 4s 3000+mah 20C lipo. Cell IR of these 4s 5000mah 20C is around 1.3mohm/cell, measured using my Cellpro 10S. I used the stock 4mm bullets for connectors. This current setup works ok for the YS. I tried a 5s lipo which works great too.



NEW FUEL- Nitro Magic
I was first introduced to this fuel by my LHS. It was low smoke and made good power when engine temperature is close to normal running temp. However, there was one slight issue- It was made clear as water to showcase its purity. What that meant was that it is very hard to visually guage if your heli still have fuel when you are throwing it around the sky, unless you use a timer.
The "retail edition" now comes in green for 30% nitro and orange for 20% nitro. I got a case of the 30% to try and indeed, it does wake up the YS 91SR. Apparently I was told clear and pure version is still available. Not sure if it is just psychological or what, but the "green edition" seems to have lighter viscosity oil and slightly more smoke compared to the clear version that I tried. Anyway, I thought both perform well.


Only have one issue with this fuel. The container sucks. Firstly, the rectangular bottle, that nitro magic comes in, does not fit my flight box. Secondly, the cap they are using is not a standard coolpower/wildcat type, so I can't use my my old caps with nipple outlet for the fuel pump.