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AlignRC Thunder Power RC
AFjetmech

Heliman

Rocky Mount, N.C. USA

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I am just starting one of these and of course I'm sure everyone has heard how vague the instructions are. Recommended motors are from 450kv and up. I'm shopping for a motor and checked the Castle software using a 450kv motor for a target headspeed of 1400. Now this is my first 5 bladed project and largest heli to date. First, is that a good head speed for this heli? If so, then I will be needing a motor in the 500-520kv range as the software says the ESC will be maxed out for 1400. This is using the gear ratio of 13.8 to 1. I found this ratio on the Roban site, not in the instructions anywhere. Any insight is appreciated. Thanks, Chuck.

10-04-2016 01:24 PM
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mcfast

Key Veteran

Quebec Quebec Canada

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I think that 1400 is a bit fast, it should be more around 1000 for a 800 size, but I am not a export, what size blades are you using ?

P.S. sorry for the spelling or the grammar I am dyslexic!

10-04-2016 02:44 PM
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don s

Key Veteran

Chesapeake, VA

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80% range is around 1150, 85% is 1230. You should have enough wiggle room with the 450kV setup. My 820 does decent aerobatics at 1200, and even though you'll be a bit heavier, you'll also have 3 more blades than I.

E820, Raptor G4N, X50F/E, E620, Forza 450, and some planks.

10-04-2016 03:14 PM
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AFjetmech

Heliman

Rocky Mount, N.C. USA

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I guess that is my ultimate question. Head speed. I figured my 1400 would be the max as I run that on my 700 4 bladed Agusta. Just not sure of the MD500 with it being so large. The blades are 700mm scale flat bottom. I am assuming that with a 1200ish head speed, the tail is going to hold well. Can't find a build log for one of these anywhere.

10-04-2016 03:42 PM
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don s

Key Veteran

Chesapeake, VA

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If you're able to swap pinions, you'll have even more wiggle room. I think the tail will be fine for scale flight.

E820, Raptor G4N, X50F/E, E620, Forza 450, and some planks.

10-04-2016 04:31 PM
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AFjetmech

Heliman

Rocky Mount, N.C. USA

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Thanks Don. I was really hoping it would fly fine at a lower speed than I was figuring. As far as changing pinions, yes that is possible, but I don't want to have to remove these mechanics unless absolutely necessary. They are well hidden in the dog house and won't be easy to install and remove. That's why I wanted to be sure on my motor/headspeed decision.

10-04-2016 05:03 PM
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Andy01

Senior Heliman

Brisbane, Australia

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It depends a bit on flying style. If you want to do agressive sport or mild 3D, then 1400rpm may be OK (if everything else holds up to the loads). If you want to fly gentle scale-like, and want to use 800mm blades, then around 1000rpm is probably more appropriate.

I don't know anything about the Roban mechanics gearing, but I would think that 1400rpm is much too fast for an 800 sized 5 blade.

I fly my 4x 820mm EC-145 (4x 820mm x 64mm asymmetrical HeliTec blades) at 1050rpm, and it is fairly responsive.

In my experience the slowest you really want to aim for as a governor speed on a Castle ESC is around 90%, preferably closer to 95%.

Assuming that your Castle figure was the maximum governor speed of 1400rpm at 95%, then 100% would be 1474rpm with a 450kV. Dropping to a XNova 4035-400kV would give you a 100% speed of 1310rpm, and 90% would be 1180rpm, which would probably be about the maximum headspeed if using 5x 700mm blades and flying fairly aggressively.

Other options may include;

XNova 4030-350kV - between 1032rpm (at 90%) and 1090rpm (at 95%), so 1100rpm would be quite doable. Motor power would be fine for gentle flying at 2500W (unless it is going to be a very heavy model)

Xnova 4035-300kV with a smaller pinion to suit. This is the motor I have in my EC-145 and it is great.

Colin

Vario Long Ranger 700e
Seahawk 600
UH-1N 500
Baumann EC-145 800+ (coming soon )

10-05-2016 09:18 AM
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AFjetmech

Heliman

Rocky Mount, N.C. USA

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Thanks Colin. I just checked the Castle software again. With the 450kv I'm getting this: 1100 @ 85%, 1150 @ 88%, and 1200 @ 92% with the Edge HV ESC selected. I've ordered a 450kv motor and will try these head speeds. The few videos I've seen show it flying very well with what appears to be the stock 700mm blades but there is no posted info about head speeds. I guess if the speed has to be in the 1100 range, I'll just have to check the temps and make sure the ESC has adequate cooling or rip everything out and change the motor pulley.

10-05-2016 01:39 PM
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AFjetmech

Heliman

Rocky Mount, N.C. USA

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Battery question. This is a pretty heavy heli, so does anyone think that 25c batteries will fly it OK? My plan was to go 35c minimum, but see a pretty good deal on some 25c batteries.

10-22-2016 03:07 PM
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sean911sc

Veteran

SoCal

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What's the weight of the heli? Higher "C" rating are less stressful on the batteries. What type of flying will you? That also is a factor to consider.

In regards to the mechanics being in a tight location - take then out and give the fuselage a once over. If its pre-assembled verify everything is correct, lube, Loctite, etc. You what to know the in's and out's of the heli. You'll have to do maintenance at some point so its a good idea to know what's involved.

Sean

10-22-2016 09:20 PM
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AFjetmech

Heliman

Rocky Mount, N.C. USA

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Mechanics have been in and out several time during the build and I'm plenty familiar with them by now. That's not the issue. I was just wondering if anyone had flown a heli this big with 25c batteries. It will probably weigh between 18-20 pounds. I'm just going to stick with 35-45c batteries and not worry about it. The deal on the 25c batts is long gone now anyway. Maybe for the better.

10-23-2016 04:34 AM
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Andy01

Senior Heliman

Brisbane, Australia

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25C lipos are more than enough for scale flying.

At 20lbs, and flown in a scale like manner, you are likely to be pulling around 1200W for FF on a large multiblade (around 60W/lb, probably a little less). On 12s, this means around 27A, so assuming you are running 5000mAh, you will be drawing around 5-6C.

I have been running basic blue Turnigy 5000mAh 25C 6s for around 6 years now, and they are close to as good as new. I use these in my EC-145 (4x 820mm asymmetrical blades & 2x 150x41mm tails) at 1050rpm, and it normally draws around 25A.

If you were going 6s or plan on flying VERY aggressively, then more than 25C may be warranted, but I would suggest that 20C would probably be OK.

Colin

Vario Long Ranger 700e
Seahawk 600
UH-1N 500
Baumann EC-145 800+ (coming soon )

10-23-2016 09:35 AM
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AFjetmech

Heliman

Rocky Mount, N.C. USA

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Thanks again Colin. This is exactly the answer I was looking for. I actually have two blue Turnigy 5000 6s 40-50c lipos that I just took out of one of my 700 Agusta scales. I've been flying those batteries for over 7 years now and was unsure if I should continue to use them. They have never been discharged below 40% and always charged at 1c. They still balance perfect and are rock solid. I don't know the internal resistance as my charger does not have that feature, but I'm not sure how much that would matter anyway as I'm not looking for the high discharge rate required for 3D flying. Definitely have gotten my moneys worth out of them and now I'm thinking I should just use them in the MD. Your input is greatly appreciated. Thanks again, Chuck.

10-23-2016 05:26 PM
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Mojave

Elite Veteran

Palos Verdes, Ca. USA

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My Big R22 with a 7' diameter rotor sees 48 amps on average, with spikes in the 70 amp range on hard climb outs. I've been running the same Gens Ace 30C packs, for years now with no issues. I have buds that are running Turnigy packs for many years with no issues also. Scale machines don't have the same power demand issues that 3D machines have. The power consumption is even better when we run a clutch, as the load on the lipo is rather low at start up, when the rotor first starts getting up to speed.
Barry

All helis and planes have an expiration date stamped on them...you only find it after you crash!!

10-24-2016 03:31 AM
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AFjetmech

Heliman

Rocky Mount, N.C. USA

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Take a look at these tail rotor blades. They are 150mm from bolt hole to tip. These are what came with the kit but seem too large to me. Can't find any info on what size blades were supposed to come with it. They are nice blades and balance perfect so I was wondering if they could be cut down. A video I saw on the Roban website shows one flying with s two bladed tail and they appear at least 20mm shorter than these.

10-24-2016 04:41 AM
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Copter Doctor

rrProfessor

Enterprise/ft.rucker ,al- home of army aviation

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! say use em'. As long as they clear the main blades and horizontal fin it should be fine. They may even prove to be necessary if you are running a five bladed head.

drive a rotary, fly a rotorcraft

10-24-2016 06:21 AM
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Andy01

Senior Heliman

Brisbane, Australia

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Yeah, keep them unless you think that they really look out of place. You can never have too much tail authority in a big slow RPM scale heli.

The tail blades on my EC-145 are 150mm long by 41mm chord and they provide plenty of power even with 4x heavy 820mm x 64mm wide chord asymmetrical main blades at 1050rpm.

Colin

Vario Long Ranger 700e
Seahawk 600
UH-1N 500
Baumann EC-145 800+ (coming soon )

10-24-2016 09:04 AM
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AFjetmech

Heliman

Rocky Mount, N.C. USA

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Thanks again gents. I'll use them for the first few flights to check the tail authority and if they are much more than needed I may replace them or attempt to trim them down maybe 10mm for a slightly more scale look. Plan to paint them so they will really look big once they have some red and white striping.

10-24-2016 11:24 AM
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Thumper217

Senior Heliman

Slidell, LA - USA

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Andy and Emile are right, you will need all the power you can get for good tail authority with the five blade head. One word of caution on this model is that it tends to really like to squat back on the landing gear when taking off and landing so you have to watch the tail especially with those long blades. They are longer than the tail fin strike protection and will be the first thing to hit the ground or even tall grass, which can damage the tail drive gears, ask me how I know?

I'm running a 5 blade head with 700mm scale blades and actually went with a four blade tail with shorter blades but with a wider chord. the blades you have look to have a pretty narrow chord, which looks great scale wise but might not provide enough power.

Thanks for sharing your build and asking questions, I'm learning a lot from everyone's replies. She's really lookin' good!

Andrew

Thumper

10-24-2016 12:12 PM
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AFjetmech

Heliman

Rocky Mount, N.C. USA

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Thanks Andrew. The blades being longer than the strike protection is one thing than concerned me. RC Aerodyne sells all their 800 size MD500's with the 4 blade tail rotor. This one came from the German website. I found some information about the full scale MD-500 being available with a 4 blade tail option for noise reduction but you don't see any pictures of them anywhere. The full scale version of this one has a two bladed tail so I was kind of glad it came that way and want to paint the tail blades to match it. So I'm hoping I will have more tail authority than needed and can at least trim these so they will not strike the ground. Thanks again for your input. Chuck.

10-24-2016 01:35 PM
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