Which Flight Pack?

[Decky]

I'm making the transition from heli back to aircraft flying and I'm a bit out of touch with recent developments. I wish to replace the old radio gear with ancient Skyleader servos in my high wing trainer so that it will work with my DX6i. Eventually I'll want to transfer the installation to a larger model, probably a 66" bipe so will need to be man enough. So if I went for the AR6200 receiver, what servos, batteries and other kit would I need? I see the Hitec HS82MG comes highly recommended, would four of these be ok or a bit overkill? What about things like switch harness, etc? Any advice will be appreciated.

[Richard Wood]

Decky,

HS82MG servos are superb but unless your model is on the small

or very light side you might as well go for standard servos like Hitec

311s, 322s or 325s.

For an aerobatic bipe like the Pitts you might want to consider the

more powerful Hitecs with BBs & metal gears, or digitals.

Have a look on the Servoshop website at prices & specs.

Futaba servos will need the plugs trimming to fit in a AR6200 if I remember

right.

A standard switch harness with charging lead & a 1200mA/Hr  or so Nimh

preferably 5 cell 6V will be fine.

 

Richard

 

[Steve Hargreaves - Moderator]

A 66" bipe would be quite some model.....if it was a Pitts Special you'd be into something like quarter scale. You'd definitely need some pretty serious servos for this sort of model & IMHO I doubt a 1200Mah battery would be adequate.....especially if you went for digital units as these are much more current hungry than standard analogue units. Also bear in mind that running a 5 cell 6 volt pack will use more current than a 4 cell pack which will flatten your battery that much quicker.

 

Personally I would decide on the performance you are looking for, the type of model you're going to fly, (vintage, aerobatic etc) how many & what sort of  servos you want to use & then we can decide on a suitable pack.

 

The days of 3 or 4 standard servos in a model powered by a 500Mah 4 cell Nicad battery are long gone!!!

 

If I was setting up a quarter scale Pitts (& I do intend to one day...the Great Planes version with a 50cc petrol motor looks very nice !!) I would probably be looking at 4 digitals on the ailerons & a digital on rudder & elevator plus a standard servo on throttle.....so thats 6 digital servos & one standard unit. I wouldn't send that up with less than a 3000Mah battery on board......either C cell Nimhs (to cope with the current without the voltage collapsing!!) or a 2S Lipo & regulator

[Decky]

Thanks guys, lot to think about. Richard I had a look at Servoshop and the standard Hitec servos like 311s etc are even smaller than the HS82MG. Does that mean the HS82MGs would be more than is necessary?.

 

I'm not sure that digital servos are really necessary, I can see their advantages for precision 3D heli flying but for this application I only need to change direction occasionally . So if the servos have enough torque wouldn't analogue be ok? BTW I don't think the Great Planes Pitts Special is available in the UK.

[Richard Wood]

Hi Decky,

You've got me a bit confused there!

The 82MG weighs 22g & is a mini servo with one mounting hole per lug,

whereas the 311,322 etc. are standard size with 2 holes per lug & weigh 43g,

but are cheaper.The torque figures are similar I think ,however standard size

servos might be more robust in the long term,especially with stronger gears.

 

I don't have much experience with large aerobatic models so Steve's advice

is worth noting.

Your trainer will only require standard equipment unless it's a very big 'un,

so it might be worth having a seperate battery pack for your bipe.

 

Cheers

Richard

 

 

 

[Decky]

Ok thanks Richard, I see. I thought you were saying that I would need something bigger than the 82MG but I see that doesn't necessarily mean more powerful. I don't think I'll be using the trainer much after the Pitts so was looking for an installation that would be suitable for both planes (maybe a bit overkill for the trainer but that maybe that wouldn't matter).

[Tim Mackey]

Decky...is this any help?

[Decky]

Thanks, I looked at that but needed it translated into real examples. So for easy comparison I'm in the process producing a matrix spreadsheet using the Servoshop specs. Maybe I could post it somehow.

[Chris Channon]

Hi Decky,

Use standard sized servos, forget the digi stuff, really not needed.

 

Galaxy models do a four cell flight battery rated at 3,300mah for £5.99 this will do you well.

They also do standard sized servo's for ( i think ) £5.99) each, i have bought 16 of them and not yet had any problems.

 

There is a large Stearman from Great Planes available, in the build manual they reccomend the use of 3003 Futaba servo's, these are standard servo's if it is good enough for Great Planes  then it is good enough for me . ( and before anyone asks, yes i have the Stearman with 3003 servo's and it is fine ( actually, great !!!)

 

 

Regards as always

Chris.

[Decky]

Thanks Chris, I couldn't find the batteries on their website, maybe they've put the price up.

 

If the servos are recommended for the Stearman they must be fine fo the Pitts. Is that one servo per aileron or one per pair of ailerons? Richard says that the Futaba servos don't fit the Spektrum receivers without either changing the plugs or modifying them so I guess the equivalent Hitec would be the ones Richard recommended: the similarly priced HS-311,  HS-322 or the ballraced HS-325, all giving the same 3kg.cm of torque as the 3003s and equivalent size, weight and speed.

[Chris Channon]

Hi Decky,

 

Just looked ( and ordered again !!! ) at the Rx packs from Galaxy.

The 3,300 4.8 flat pack is still available, they also do a 1300 mah pack that is a lot cheaper but still very good, ( i charged one of these up last friday and it took 1650 mah )

on it's first charge ! very good value.

 

Re the Stearman, it has one servo per pair of ailerons ie one servo does one side top and bottom.

 

If i can help anymore then just give me a shout,

 

Regards

 

Chris

[Decky]

Sorry Chris I searched on 3300 and 4.8 but the only 4.8v 3,300mah battery I can see is £11.99 (item 4405530 on http://www.galaxymodels.co.uk/). The 1300mah is £4.99. Do you have the item number please?

 

Decky

 

 

[Richard Wood]

Hi Decky,

If you wanted to use Futaba servos with Spektrum rx's the mod to the servo

plug is really quite simple.

All that's required is to trim off the polarising plastic moulding on the plug.

The plug might be a fairly tight fit in the rx but this is actually quite desirable.

Having said this Hitec servos are generally excellent & need no surgery

on the plug!

 

Richard

 

[Decky]

Thanks Richard, I have no particular yearning for Futaba servos so may be worth going for Hitec with their Karbonite gear train (for what it's worth).

 

Decky

[Richard Wood]

Good choice.

 

[Decky]

Thanks.

 

One other issue I noticed: 4.8v or 6v? There seems to be pros and cons for each. Some say for weight saving that it's best to go or 4.8v and that 6v isn't necessary, others say that 6v will give better servo torque and a wider safety margin above the 3.5v Rx cut-off should the voltage drop.

 

Decky

[Richard Wood]

Decky,

6V will give you more torque according to the maker's figures.

When I bought my Spektrum 6i, the chap in the shop recommended a 5 cell

6V NiMH as apparently there were some instances of 'brown-outs' with

Spektrum gear on 4 cell batteries.So to be safe that's what I use with it!

 

The story is that If the battery is loaded up with high current the voltage

can drop to below the safe the cut-off level & cause the brown-out.

A 6V battery certainly gives you a bigger safety margin & is probably

worth using over a 4.8V.

 

Richard

 

 

 

[Decky]

I'll probably go for 6v then, do you think a 1200 / 1500mAh would be enough? This has similar weight to the old 4x AA battery box I was using before.

[Richard Wood]

Decky,

For 5 standard analogue servos a 1200-1500 6V battery will be ok.

Galaxy list a whopping 6V 3300 Rx battery item no. 4405535 which might

be worth considering, bearing in mind the extra weight.

 

[Decky]

Yes it was the weight I was thinking about, I'm not sure how much lee way they'll be for heavier batteries. Maybe better with 2 or 3 sets of 1500s to save weight and extend flying time by swapping them over.

 

Decky

[Richard Wood]

A fully charged 1500 Rx battery should give you a good couple of hours

flying with the setup you have.

Probably enough for a day & you won't need to change batteries.

It's worth investing in a battery checker & to check the state of your receiver

battery after every flight. I'm a bit paranoid about this admittedly!

Better safe than sorry etc....

NimH's can be fast charged after the initial slow charge so you can re-charge

at the field if you need to.

Just make sure of course that all control runs are bind free & that no servos

are stalled at full travel so there isn't excessive drain on the battery.

 

Richard

 

Edited By Richard Wood on 10/03/2010 09:13:02

[Richard Wood]

Just to confuse you a bit more Decky consider using a 2s Lipo (7.4V)

with a 6V regulator.

Lipos are much smaller for the same capacity.

This is the bang up-to-date way of doing things but you will need a Lipo

capable charger.

Have a look on the BRC website for these.

 

 

[Decky]

Many thanks for the advice Richard, I have some 2s Lipos and chargers so using a 6v regulator sounds like the way to go.

 

Just to confuse matters further, I've now received the build plans for the bipe and it's designed for one servo controlling all four ailerons. So for that I may need something a bit beefier than a standard Hitec, something like a HS485 HB perhaps.

[Richard Wood]

Decky,

Consider replacing the single servo & all the associated controls & bellcranks

etc, with one servo for each aileron - such as an HS85MG.

It's often much better & easier this way.Obviously a little modification to the

plans is need with provision for routing the wires thought out - not usually

too difficult to sort out.

Your Rx will need to drive 4 servos from the aileron o/p.

One servo controlling 4 ailerons on a big bipe is a bit beyond my experience

but if you do it this way go for the best you can such as the £40 odd 955MG!

 

Cheers

Richard

 

Edited By Richard Wood on 10/03/2010 12:49:04

[Decky]

Richard,

Thanks, I know what you mean but I'm not sure at this stage how much head room there is in the upper wing to intall the servos and bellcranks. Replacing one servo with four sounds like a challenge, the wires would have to run down the cabane struts somehow. I don't know why it was designed to use just one servo, apart from the fact that the full size is designed the same: the upper ailerons are controlled by the lower ailerons by means of connecting push rods. I figured that if the 3kg.cm of torque of the standard servos is recommended to control two ailerons on the much larger Stearman, I wouldn't need much more than 6kg.cm to control the four ailerons plus the weight of the push rods. So maybe something like the Hitec HS-645MG which is supposed to deliver 7.7kg.cm of torque, at about £26 would be cheaper than four individual servos and wouldn't require any mods to the design (looks like the 955MG has been superceded).

Decky

Edited By Decky on 11/03/2010 00:39:25