Century Bell 47

[Globs]

Hi Donnie,

Looks a nice build, very familiar shapes appearing!!
Century do (as an add-on kit IIRC) to extend the lattice tail up to the cockpit that I have not seen on your build, but is on my heli.

It is funny to see a picture of the build assembled with the big motor sitting there, I need to strip mine down to start a motor clamp or bracket, and then I'll be taking the front servo tray out completely so I can clear the cockpit. So I'm be dismantling mine . Like the lights BTW - thanks for the photos - very useful. BTW is there a white light in the horizontal stabilizer too - or is that a reflection?

I may however add a strong new cockpit floor, as I'm wondering if a couple of 3S batteries (or 3x 2S) may tuck under the floor nicely and therefore leave the rest of the heli free.

Incidentally my motor is an in-runner so I could clamp it like Bell Bloke, but after looking at the photos in your thread I wold prefer to put in a mount plate in which case it will be mounted at the top regardless. I prefer the plate idea because I can guarantee the gear mesh is constant and its simpler (once the plate is made). A chunk of alu plate with a few lightening holes drilled should do I think.

[Donnie D]

Hi Globs,
Yeah, I'll probably add the extra truss pieces a bit later, after I get the motor mounted up and get this thing into the air for a test or two.

That is a reflection on the horizantal stabilizer, not a light.

I'm still working on my motor mount, think I'm about there. I'm trying to keep the clutch fan assembly as well. If I can make it work, I think it will be better than a direct drive. We'll see how it goes. I can allways go to direct drive if I have to.

Can you post links to the motor, pinion, electronics you are going to use? I allready have mine, but I would be interested.

Thanks
Donnie D

[Globs]

Thanks for the info!

My electric drive system consists of:

KD36-74-15XL 1100kv Brushless Inrunner $30
TR_P80A TURNIGY Plush 80A w/ UBEC Speed Controller $50
HPI 19T pinion gear (Part 100918) £10 ($15ish)

To run on 6s lipo.

I'm not sure how it will work yet of course, but it should in theory
I haven't tries the pinion yet, as an alternate I can use one from a Century Swift or even the intermediate shaft pinion from the Hawk (the mechanics of the Cenury Bell 47II).

[Donnie D]

Keep me posted. As slow as I am, I'm sure you'll get yours in the air before I do.

Donnie D

[Globs]

I started taking my '47 to bits tonight, in preparation for the electric conversion:



Not as easy getting the 50 out as in a simple helicopter, but it has a neat and simple gearing system! Just need to make a secure motor mount now, without a milling machine I'm going to have to get creative with a few alu sheets and some nuts and bolts!!

I also want to move the servos back like 'Bell Bloke' did, so the fan area may need some surgery too..

[Donnie D]

What is the tooth pitch if the pinion you are using?

Donnie D

[Globs]

Originally Posted by Donnie D

What is the tooth pitch if the pinion you are using?

Donnie D

The HPI Pinion has a mod 1 pitch I think. It's a perfect mesh and height for the century gear it has to drive. Another thingL HPI do loads of different teeth counts too, I just chose the 19T one to get the same gearing as Bell Bloke at a 1500 rpm flying headspeed.

I also decided to make my motor mount, a U-channel shaped bit of Alu with the motor bolted 20mm from the end in a fixed place. Where the mount fits the frame I'll drill holes in the frame and slots in the alu mount, so I'll slide the whole mount to mesh, then use 3mm bolts and locknuts to fix. This will work for in and outrunner motors,

[Donnie D]

Your mount sounds like the same thing I'm trying to use. I'm trying to keep the clutch and the only thing I'm waiting on is the adapter from the local machine shop to mount the clutch to the motor shaft. I found that I'll be able to tap the mounting holes on the mount for the 4mm bolts I'm gonna use by drilling it with a 1/8" bit then I can use the bolt to carefully tap the hole. Takes awhile, but it works. That way I won't need to bother with nuts. Where the mount meets the frame, I'll drill those holes a bit oversized and that will give me some adjustment room for mesh etc. Hope this all works. I can't fit any of it up till I get my adapter shaft.

Donnie D

[Globs]

This is my motor mount - just finished tonight!



Made from an old Vero case 2mm Alu end.
Cut to 70mm x 82mm, bent to 61mm wide with bends, 70mm long. I was aiming for 60.5mm - but it's close enough

I forgot to drill any lightening holes, but it's fairly light anyway.

Fitted up to check position and mark frame holes:


I then drilled the frame (3mm) and then fitted it back, marked where the holes needed to be and drilled 3.5mm holes in the mount. 3mm bolts are fine as there are 4 of them - the same as the number of bolts holding the frame to the helicopter in fact...

Fitted finally here:


I used 3mm hex bolt + washer on the inside, and 3mm locknut + washer on the outside, works very nicely.

All done and ready for electrics:


You are brave keeping the clutch, although it is a nice touch. I just wanted minimum weight and maximum simplicity. I took the starter shaft out too - Bell Bloke left his in for some reason. Servo jiggling time next, new trays etc for those to be set back into the chassis.

[Donnie D]

I may not be able to keep the clutch. Will know when I get my adapter shaft from the machine shop. May have to drop back and punt.
Your build is coming along nicely.

Donnie D

[Globs]

Well I fired mine up without the head fitted, sounded a bit like a lorry starting up but seems good, although a bit vibey at low revs - not sure why that is, it smooths out at faster revs so I guess it's an odd frame resonance or something from the tail.
I'll have to check it's smooth at 1500 rpm - the target headspeed.

I also noticed the Plush 80A ESC snatches a bit at really low throttle settings, with super-soft start it's much better to jump up to low power and then shut down the same way - with a jump, it may be because my 1100rpm/v motor only has two poles and the ESC is not quite sure what's going on then. A clutch would be ideal for that!

I'll just have to avoid that spot - perhaps mixing in a switch so I get an engine stop/start action, mixing in 5% up throttle or something.

Next item is to attach the pitch servo by a complicated metal bracket to the side, and then work out how to mount the front servos on/in the fan cover. I'll need ail-left, elev, ail-right in that case as the rods are too short for a single aileron servo. In theory I could use two smaller servos - an Inolab D261 either side would be nice - no trimming needed to the fan cover, but I haven't got any - and I need to use these regular servos (3152 futaba, 5kg/0.16sec) if I can.

[Globs]

OK - here is my re-located pitch servo, after a fantastic amount of fiddly sheet metalwork in 1mm alu:



May have solved the low-speed snatch problem, my Hughes 450 does it too, so I added TH->TH mixing at -15% to my RD6000 mix1 and now I just flick the switch to 'start' the heli and it starts up to an idling blade, then I'm good to go

It actually looks rather scale too - to start and return to a nice low speed.

[Donnie D]

Lookin really great. I'm really enjoying watching the process. Man I hope the machine shop gets my adapter shaft done this week. I'm gettin real itchy. Think I'm gonna try to use the clutch without the fan as I think the simplicity and weight savings will outweigh any benefit I might get from it.
Donnie D

[Globs]

Cut out and folded my new servo bracket today. This has tabs so it can be bolted to the frame and also hold the end of the latticework, as well as obviously holding the ail and elev servos.



I'll need to dig out some of the fan molding but not very much, then I can bolt it in.
I'm going to bolt the tank arms in from the inside before the bracket goes on, as there is no starter block installed for it to screw into now.

I also lowered the wheels so they touch the ground (5mm below the skids now), and changed the self tapper between the lower tail ladder and the undercarriage/frame to a decent 3mm hex bolt - much easier to manage.

As you can see in the picture the front now just needs a floor and a way of supporting the canopy/battery in a soft manner, so a hard landing does not wreck it. Not sure where to put the battery(s) - under the seat may be a good idea - I need to balance the heli first I think and try out some dummy weights. I may hinge it off the front landing support and rubber-band it to the fan housing. The usual canopy support sticks may not be used.. haven't decided yet..

[Globs]

Hi Donnie, hope you have got your motor adapter by now!

I've been hacking away at the fan housing and installing servos. To get the rods straight I had to mount them below the 1.5mm alu. plate I made. The plate bolted in fine, if I was doing it again I'd move the side (elev) servo back a touch so I could get bolts in - I have to use tyraps instead on that side!!



I moved the aileron balls inside the cranks (You do not have to take them off to do that) to give a straighter line, and bent and cut the rods. The elevator rod is the old throttle rod used without modification, just like the old pitch rod is still used as-is.

The shorter aileron rods were bent and cut down, and I tapped an M2 thread onto the ends. This I found was way too small for the century ends so I put a bit of small heat-shrink on the thread, screws in nice and tight now. I should have extended the heatshrink down the rod as the metal rods can touch, but I'm on 2.4GHz so I may get away with that



So now I have a good solid installation of the head without intruding into the cabin, I just have to site the RX and gyro and then concentrate on the tail linkage.

The old text-book linkage is dreadful so I have a flexi-link and a 2mm CF rod that I may use in place of the plastic inner, then I can route it nicely through and put back the horizontal stabiliser that got in the way of the old linkage.

[Donnie D]

Looks like you're almost there. Looking good. I did get my adapter, but I think I'm gonna skip the clutch and just direct drive it. I have a nice super soft start with the ESC I'm using so it will probably be ok. I'll still need the adapter shaft as the motor I'm using has a 6mm shaft and I cant find a 26T pinion to fit. I have 3 pinions ordered and should have them by the first of the week. If all of that goes well I may have it airborne next weekend. I ain't counting on it though.

Donnie D

[GyroAl]

Glob, that looks great. I always wanted to do a complete cockpit for mine but that would require the moving of the servos from the stock position. I see you have done so. Maybe this winter I will get some time to make similar changes on mine.

Here is a video of mine with the OS46, shooting landings and autos:

http://www.youtube.com/watch?v=I-Pn4KNf-RU

Your electric conversion would eliminate all that smoke!!

I also have a 4-stroke version of their 30 sized S-300. Not only does it sound very scale-like. Another nice feature of it is that it also does not smoke very much, almost not at all. so it also looks better in the air. Consequently, for many years, I have been thinking of converting the Bell 47 to OS 70 four-stroke engine power, but always seemed to find other projects to get in the way. Century just kept launching to many newer kits I guess.

[Globs]

Nice flying there GyroAl, good to see the front of a heli as well as the back
Proper autos too - what pitch do you have set for the long auto part of that?

You can get much less smoky fuels and lean out (with a temperature gauge) to make smoke almost a thing of the past with nitro, but as I have a noise issue I thought I'd go for electric. The prompt was seeing Bell Bloke's build and listening to a friends Century Swift - you can really hear the rotor blades whizzing around!!

I'm quite pleased with the install, just using 1mm alu. for the pitch servo, 1.5 for the servo tray (with bent tabs to attach to the frame) and 2mm for the motor mount.

My CF tail snake seems to work out well too, with roughed up CF ends and sockets it's very strong and seems to work well from my 'Van-Dango' BMS-661DMG tail servo, a gift at $22. I'm uploading a Youtube video of the install (just to get all the angles) so I'll post that up soon, although since I took it I'm re-routed the snake to go under the horizontal stab. to make it miss the bottom tail nut completely.

Youtube:

Century Bell 47II helicopter electric conversion walkaround (1 min 47 sec)

Note the radio is an RD6000 upgraded to the JP 2.4GHz system, giving a £10 6ch RX. I may use Spektrum later to add a channel but this works well plus the RX location is excellent!!

[Globs]

I need to buy some batteries soon, but I am unsure of the power budget.

My 450 flies for 8 minutes on 2.2Ah (3s). This gets the batteries warm.
So the current draw = 2.2 * 60/8 = 16.5A

Now Bell Bloke claimed on the Bell 47 a 30min run on 8Ah packs (6s)
This means current draw = 8 * 60/30 = 16A

This means the Bell47 only needs twice the power of a 450 sized Heli (P = VI) which does not sound correct at all..

On a Century swift a 5Ah battery will last 12 minutes: current = 5 * 60/12 = 25A.
Say we have 500watts at 1500rpm, that's 500/24 = 21A

So being conservative at 25A draw, a 5Ah pack needs to be a 5C rating to supply the power and will last for 60/5 = 12 minutes. However 5C sounds low, and a 25C pack on the 450 gets warm enough, at 16.5A in a 25C 2.2Ah pack. 16.5/2.2 = 7.5C, a 25C pack is ok - a C margin of 25/7.5 = 3.33.

So our 5C pack becomes 5 * 3.33 = 16.7C, or 20C.
So I compute a 6s 5Ah 20C pack should be fine, opinions please?!

[Donnie D]

I bought 2 Hyperon 3S, 4200mAh, 35C batts I'm gonna connect together in series for 6S. I don't know how well they will work for this because I figured it out the way I figured everything else about this build, I guessed. Got my fingers crossed though. You think they will be OK?
Have you been able to test your pinion yet?

Donnie D