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Pitbull 3


oipigface

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I’ve moulded an additional piece of lead to fit around my Futaba receiver. It weighs 105g. The CG with configuration as in the picture is at about 104mm. Replacing the 1600mAh 18500 with the 1100mAh 18350 would release a further 30mm of fuselage nose. Given that I haven’t yet started to consider where the switch is to go, I think I will stick with the 18350 until I find that tungsten swarf.

3337D6F8-521D-4E1A-9987-BE37180AB5E0.thumb.jpeg.b783a7805c350434a8fffc95fd62a267.jpeg

 

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Using the the tungsten swarf you have talked about would put a higher weight further forward.

Possibly negating some if the benefits of moving the mass further backwards.

 

🤔. Just a thought 🤣

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Pierre reports a pitcher model after shortening the nose on his test model.

It is much harder to balance a model that has shorter moment arms. Getting them to settle on a balance point.

 

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I think you are really pushing your luck with the 18350's. 1.1Ah batteries will only have around 800mah of usable capacity plus you're running them at times above their constant discharge rating so at that load their capacity will be even lower. May get away will 1-2 climbs, races and landings then best to charge..

If it was me it'd be tempted to modify the servo mount to incorporate an 18650 mount where the batteries sit below/above the tail pushrods if there's room

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1 hour ago, Lloyd_d said:

I think you are really pushing your luck with the 18350's. 1.1Ah batteries will only have around 800mah of usable capacity plus you're running them at times above their constant discharge rating so at that load their capacity will be even lower. May get away will 1-2 climbs, races and landings then best to charge..

If it was me it'd be tempted to modify the servo mount to incorporate an 18650 mount where the batteries sit below/above the tail pushrods if there's room

Well, yes. I  suggested as much in my Jan 30 post. I think there is no room in the tail boom. Using something heavier than lead may be possible, and something I haven’t investigated closely yet is that one cell may fit under the joiners. The two cells would then have to be connected with a plug and socket, and I had sort of earmarked that space for the switch. 
Keeps me off the streets!

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Hi Lloyd,

     I looked at the space you suggested last night. The bottoms of the servos are close to touching the top of the boom, the tops are 1mm or so clear of the access hatch. So, no, there’s no room for anything there. I did think that moving the servos to the rear might be a way of accommodating one cell. But given that it’s a factory installation, and that moving batteries behind the CG could easily destroy the point of the short nose. I’m unwilling to disturb it.

     On the plus side, I have established that the switch can be fitted under one of the MPX connectors, so the only things to go in the nose are weight, receiver, batteries and wires. The batteries you’ve suggested may well allow a weight configuration better than the moulding I’ve made. I’ll get the ruler out and scratch my head a bit more.

      Thanks.

 

     

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In the old days of "crunchy" 60" racing , we did have one guy, Eric, who had an ultra slim fuselage with a very small battery, which he connected up to a portable charging system in between races !

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You'd only be moving a small amount of weight behind the CG and close to the CG. Would need some structure to hold it or you could hot glue it in. The corner inertia reduction gains by shortening the nose come from keeping the weights be it front or rear as close to the CG as possible.

Plus your receiver looks enormous. I fly FrSky and the RX6R receiver that I'd use in this type of model is miniscule in comparison.

 

Battery mount PB3.jpg

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2 hours ago, f3fman said:

In the old days of "crunchy" 60" racing , we did have one guy, Eric, who had an ultra slim fuselage with a very small battery, which he connected up to a portable charging system in between races !

Good old ‘Fluffy’ - a unique and innovative model!

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Stefan Bertschi
On 08/02/2022 at 17:17, oipigface said:

..... think I will stick with the 18350 until I find that tungsten swarf.

 

Ask Daniel (ze German) he told me that he has some tungsten swarf. 

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13 hours ago, Stefan Bertschi said:

Ask Daniel (ze German) he told me that he has some tungsten swarf. 

Could that be the same Daniel that I got mine from?

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  • 1 month later...

…. and 6 weeks later, I have finally squeezed it all in, including the switch. It’s taken so long because I ran into trouble in a ‘quick’ project that I started in the middle of January. That project - a Prandtl since you ask - is now in its box awaiting a maiden, so I returned to the PB3. Getting the gear in involved casting a 160g piece of lead to fit behind the noseweight provided by Baudis. (I used the noseweight as a plug to make a mould in damp sand.) When this and the noseweight are in place, the CG is at about 98mm, which is where I wanted to start. With the noseweight alone it is at 106mm. I sliced  the new piece into four 40g pieces, so that I can easily vary the CG in four 2mm increments. 
     With the small battery in place under the LE, the Rx and switch fit in front of it with a little bit of room to spare. To achieve this I had to shorten the switch leads. I could make a little bit more room by shortening the servo leads as well. I think a 1600mAh battery will fit in if three of the 40g bits of lead are taken out. Then the CG will be at the recommended 104mm. With the servo leads shortened it is possible that the longer battery would fit in with the CG  at 102mm. 
    I’m looking forward to the maiden now.

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Here you are Graham!

The inside nose cone is really only half of one. A reinforced strip of carbon fibre runs along the bottom. Time will tell if it is up to the job. Note the servo wires which enter the nose cone at the bottom of the fuselage (which is upside down in this photo), and the switch which is hot glued in the right place. The servos are fitted behind the wing, so the only things to add are battery (1100mAh), receiver and noseweight.

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First the battery, which slides in under the wing and on top of the servo wires, with the power and balance leads just showing at the rear of the fuselage cutout.

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Here it is, halfway in. The wires need to be carefully positioned so they don’t interfere with each other.

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Battery connected and pushed home. Next up is the receiver. The wires are a couple of centimetres over length but can be fitted in with a twist or two to keep them in order. I wrapped the aerials around the receiver and taped them down at right angles. I know this isn’t generally seen as good practice. The alternative would be to cut a groove along the top of the noseweight, and fit a vertical tube just opposite the switch. I might do this if this installation fails its range check.
 

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Out of space. Continued in my next.

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Receiver in place:


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Now you see why the location of the switch is crucial. 

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The noseweight provided by Baudis gives a CG at 106mm. It is beautifully moulded to fit perfectly into the inside nose cone. I used it as a plug to mould an extra 160 gram weight. My moulding was good enough to reproduce the notch which enables the weight to hang over the edge of the fuselage cutout. I sawed the 160g weight into 4 equal pieces. If they are all installed, the CG is at 98mm. Each one taken out moves the CG back 2mm. The photo shows the CG at the position recommended by Baudis. There is probably enough space to fit a 1600mAh battery if the switch is relocated further forward.


40A9C09D-81D0-4821-8B7D-9789F71CAAD2.thumb.jpeg.ab8e0ad0ce60ab0b3a478d566397a75e.jpeg 

CG at 98, my preferred starting point.

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Checking that the system switches off correctly:

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