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HomeScale✈️AircraftScale HeliScale Helicopter Main Discussion Docs  S-76 Build
11-23-2016 08:11 PM  3 years ago
Thumper217

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Slidell, LA - USA

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11-23-2016 08:12 PM  3 years ago
Thumper217

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11-23-2016 09:09 PM  3 years ago
Copter Doctor

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

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very clever, very clever indeed! drive a rotary, fly a rotorcraft
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12-07-2016 12:19 PM  3 years ago
Thumper217

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Well I've finally bit the bullet, broke out the Hysol and went to town...She's finally standing solidly on her own legs!

Still have plenty of room in the cockpit and cabin for the interior details.

Here the mechanics are just clamped in place, I'm still working on the alignment.

Thumper
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12-07-2016 12:27 PM  3 years ago
Copter Doctor

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Looking great!!drive a rotary, fly a rotorcraft
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12-08-2016 11:44 PM  3 years ago
Mojave

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Palos Verdes, Ca. USA

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That is one sexy heli... It looks to be coming along nicely.
Barry
All helis and planes have an expiration date stamped on them...you only find it after you crash!!
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12-09-2016 03:10 AM  3 years ago
Thumper217

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Thanks guys. I'm hoping to start on lining up and mounting the mechanics this weekend.

I'm still looking for a source for the blades. I need four 950mm or there abouts preferably with swept tips.

Andrew
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12-09-2016 06:00 AM  3 years ago
Keygrigger

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Mississauga, Ont. Canada

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It's coming along really nicely, Andrew. Hope to see it at Dalton next year. Take care.

Don
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12-09-2016 03:29 PM  3 years ago
Thumper217

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Thanks Don, I will definitely be at Dalton this year!

I'm looking for some advice on batteries. The mechanics are set up to run on 12cell, 10,000mah. I was planning on using four 6cell, 5,000mah batteries as that's what I use on all my other helicopters, two in parallel and then those in series.

Pulse has some 6cell 10,000mah batteries that are designed for large drones that would be great because they are just slightly larger/heavier than a 6cell 5,000mah and I would only have to use two which would save space and weight. My concern is that they are only rated at a 25c discharge rate. I normally use 35C or greater so I'm wondering if the 25C discharge rate will be OK for scale flying? Let me hear what y'all think.

Andrew
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12-09-2016 04:25 PM  3 years ago
Keygrigger

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Mississauga, Ont. Canada

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Hi Andrew:

What you should look at is the amount of current that the larger battery at a lower "C" rating still supplies. The 10,000mAH pack will supply 10,000 x 25 = 250,000mAH peak capacity or about 250A in normal terms. Your system will most likely have (haven't looked back to check) between a 120 and 200A ESC but even on a heavy lift-out or high angled bank, might only put a 75 to 80A spike load on the battery. Your 4 pack will supply 10,000mAH at 35c or 350,000mAH current which should translate to 350A capacity draw and remember, both have a spike draw much higher than that. Your current batteries will be more than enough even though they might be a bit heavier than the twin 10,000's. No matter which way you go, you should have more than enough.

I am now starting to fly an MD7 700 size helicopter that I plan to change to an 800 in the future. It is not a light helicopter by any means but it will be nowhere near the weight of yours. I am currently flying it at a low speed of 1000rpm with a high speed of 1200rpm. It's draw is minimal for its size as it had drawn a maximum current in a spike of 50.2A and in power output, it was only 2167 watts from a motor that can develop up to 7125 watts. In normal flight, it lumbers along at an average of 660 watts. As I increase the weight with shot bags, I am sure that the power consumed will rise and so will the draw on the batteries but even when I flew this in Florida in 90+ degree weather, the batteries were barely above ambient temperatures and you could still grab the motor. The ESC didn't exceed 88F degrees in any of the fifty or so flights I have had, some of them up to 12 minutes in length. I know that Butch can be a much better source of information for that model than I could but I am sure you will not outdraw your batteries

Hope this helps.

Don
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12-09-2016 08:06 PM  3 years ago
ssmith512

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Indianapolis, IN USA

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I concur with Don. If they are a true quality battery pack, 25C should be OK for the type of flying we do. I use 6000mAh 30C packs (2ea 6S in series) in my Roban Cobra. I dont exactly baby that heli around. Never had a battery issue yet.

My suggestion, and I am assuming the batteries are going up front, get the largest capacity, heaviest batteries you can fit. I can almost guarantee you will need the nose weight. Might as well make it "usable" nose weight in the form of battery capacity.
Steve
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12-11-2016 11:41 PM  3 years ago
Thumper217

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Thanks guys for the information. Once again continuing my education with more math formulas, where would we be without math!

I will be running a 160amp esc, which I know is overkill but it gives me confidence, which I have found to be critical for my ability to fly.

This weekend I've been working on the mechanics installation and will update my progress later.
Thumper
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12-12-2016 01:33 PM  3 years ago
bwellmaker

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Long Island

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Looking great Andrew,

My 76 uses 4 6S 5000 packs. For my application it works. The packs are install 2 on each side, just inside the cabin doors. All packs are forward of the main rotor shaft that helps with keeping the CG forward. The big a$$ motor is also forward on the mechanics that also help with CG. My 2 each 2S RX packs are forward of the mechanics as well.

My bird tips the scale at 42 LBS flight ready. Steve made a good point about keeping the weight forward as much as possible as you "WILL" need it. I had to add about 12 oz forward of the instrument panel to get the CG correct after the cockpit was installed. I believe top aft mount turbine power train installation is taking "pounds" of ballast forward to get the CG correct.

The 160 ESC should be more that enough. Running the 950 mm M-Bades with a head speed of 1040, it runs in the 40 amp range at around 1500 to 2000 watts with the Peka mechanics. They are completely different than the custom mechanics you are using. I can fly around 6 minutes with some reserve. I may be way off on my numbers as it has been sometime since a download. I will get you some numbers you could use as a reference.

B
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02-08-2017 01:57 AM  3 years ago
Thumper217

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Hey Butch,

42 Lbs is a lot and I'm trying to come in under that if I can but I will use that number as a max. All of my batteries will be mounted as far forward as possible. In addition to the flight packs I will probably use three 2s batteries for electronics and accessories. I've already noticed that cycling the electric landing gear, deployable steps gear doors takes a good amount of power so I will try to use batteries for any extra weight required. The mechanics I'm using are definitely lighter than the set of Peka ones but unfortunately the motor is mounted aft of the main shaft.

Build has been going a little slow while I took care of some personal matters but now I am starting to get back at it. I've installed the tail drive shaft, intermediate gear box and tail rotor gear box. I used three bearings to support the 8mm tail drive tube in a 25mm boom tube. The tube fits nicely up in the top of the tail boom. The intermediate tail box is a 50 degree unit from Vario, its a pretty tight fit but that actually made it easier to support. I used another short section of tail boom to run up to the pylon and supported that short shaft with two bearings. The tail rotor gear box I got with the Peka mechanics that I originally bought for this project. It is from Heli-Factory in Germany and is a really sweet piece of engineering and machining. However, when I spun it up for the first time I discovered that the rotation is the wrong direction. Instead of turning clockwise when looking from the left it is turning counter-clockwise. Unfortunately this gear box is not reversible either.

The last 4 photos are of the TRG. The end on shot of the helical bevel gear is the input shaft. I'm interested to see everyone's opinion on which direction it should be turning. There is an arrow on the housing indicating a direction and it to me it seems the reverse of what it should be but I'm probably wrong
Thumper
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02-08-2017 02:02 AM  3 years ago
Thumper217

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I've located a suitable replacement gear box that is perfect. The direction of rotation can be reversed, it can be mounted on either the left or right side and it is available with a 120mm long output shaft and 8mm diameter input shaft which is exactly what I need.

The problem is its made by Baumann in Switzerland and they don't ship to the USA!

Has anyone ever run into this before and is there any solution?

Andrew
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02-08-2017 02:23 AM  3 years ago
Thumper217

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I must say that the tail drive system from the mechanics back is super smooth. When I spin the drive shaft at the mechanics end its really easy and spins the tail rotor freely (in the wrong direction but still smooth). I also wanted to thank Barry (Mojave) for supplying me with a bushing for the coupler at the mechanics end. Mine did not come with one and luckily Barry was able to help me out.

Andrew
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02-08-2017 04:44 PM  3 years ago
bwellmaker

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Long Island

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Hey Andrew,

Your bird is looking great. I really like the tail drive system and will be following your example on my 67.

If you can trim 10% off the weight that would be huge. I built mine pretty lite in general but when you start adding fuse detail, full cockpit, a cabin, lighting, paint, etc it adds up pretty fast.

I feel I could maybe save a few pounds at best if I were to build the same heli, with the same equipment used with the original build, simply with changes in the build process I have see or learned over the years.

Helis such as the 76 are per-destine to be pork butts. If you can save a little here, a little there, you may be able to get under 40. Even at 42lbs, its will fly great.

B
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02-09-2017 03:28 AM  3 years ago
Mojave

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Palos Verdes, Ca. USA

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Hi Andrew, this is really coming along nicely. I'm glad the tail drive bushing worked out for you. I'm machining a bunch more for future builds and spares. BTW, that TR is a work of art, very nice...
Barry
All helis and planes have an expiration date stamped on them...you only find it after you crash!!
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02-09-2017 04:52 PM  3 years ago
coptercptn

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Mesa AZ. USA

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Andrew, you can't flip the "driven gear" to the other side of the shaft? I don't see a pic of the whole gearbox, so I don't see the issue with reversing tail rotor direction....?Home of the "Sea Cobra".....
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02-10-2017 11:46 AM  3 years ago
Thumper217

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Slidell, LA - USA

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Jim,

Unfortunately, there is no room on the other side of the gear box to accommodate the gear. I'll get a better picture of it later today and post it up here so you can see.

I did learn while taking this one apart that they use two sets of two set screws one stacked on top of the other to secure the hub onto the shaft. I had never seen this before and it took me a while to figure out why I couldn't get the hub off of the shaft. The person that assembled it last time used green Loctite everywhere so it took some heat and patience to get it apart and I thought the hub was just really stuck on there. Luckily I noticed the other set screw deep in the threaded hole before I did any damage trying to get them apart

Andrew
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