Spacewalker half scale 168" electric

[Andy Boylett]

I forgot to take a picture of the big block of blue foam after I had carved it into a cowl shape, but here it is all glassed up. Its white because I always use white polyester resin.

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Now I have got to sand it nice and smooth before removing the blue foam.

[Andy Boylett]

The springs I ordered for my scale undercarriage have now arrived and I have been trying to find a way of fitting them without loosing a finger or two . Does anyone know of a mini spring compressor?

Anyway, I have managed with the use of some levers and thick gloves to get the springs in, but with a smaller retaining bolt (can't get the propper one in whilst trying to hold a 35kg rate spring in place!

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[Phil Clark]

Polyester resin over blue foam?......I assume you've covered the foam plug in something (brown tape) to prevent the poly resin eating the foam?

Phil

[Andy Boylett]

Hi Phil,
I did a small trial 'cowl' first, for my LMA Genesis. I used a really thin brown tape over the foam, then kept the glass-work thin and sanded it in situ (as you suggested). Then, because the cowl was thin, I found I could actually remove it from the foam without breaking anything. Having removed it I applied a layer of chopped strand inside and hey-presto one stiff cowl.

I am not sure whether this big cowl will come off the foam plug whole in the same way as the Genesis, but a little test 'pull at one side suggests it might.

Fingers crossed

Cheers, Andy

[Phil Clark]

Good ohh.......

[stuart cotgrove]

The springs I ordered for my scale undercarriage have now arrived and I have been trying to find a way of fitting them without loosing a finger or two . Does anyone know of a mini spring compressor?

Anyway, I have managed with the use of some levers and thick gloves to get the springs in, but with a smaller retaining bolt (can't get the propper one in whilst trying to hold a 35kg rate spring in place!

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Love that U/C. Work of art in itself... Are the metal parts brazed, or silver soldered or is it aluminum/other?

[Andy Boylett]

Stuart,
The u/c is all ss and I was going to Tig weld it but after discussion with Phil I went for silver soldering. It has worked well, I just had to make sure all the joints were a really good fit - with Tig I can away with bigger gaps and just fill them in.
Cheers, Andy

[Andy Boylett]

I have made myself a tool to preserve the ends of my fingers while assembling the u/c springs...

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Now I can replace that temporary bolt with a 4mm one.

[Andy Boylett]

I have now started to finish off the wing centre section. It needs completely sheeting plus needs the wiring tubes put in. Here it is with wiring tubes in and top side sheeted....

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[Andy Boylett]

Wing Centre Section

I have now finished mounting the sheeted wing centre section to the fus and have completed the bolting mounts at the trailing edge...

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And now I have inverted it ready for first fitting of the undercarriage.....and I have made purpose fitting support for whenever the model needs to be upside down...

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[Andy Boylett]

My son Sam (and test pilot!) helped me assemble the whole plane for the first time today. Its quite exciting seeing it in one piece...

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Does everyone have a caravan in the middle of their back garden?

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And a mini-digger by the garage! Bit of a mess but building work going on.

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And here is Sam....

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[DAVE JOHNSON]

Andy--thats looking brilliant---looking forward to seeing it in the flesh at next months exhibition---DAVE

[Andy Boylett]

I cant complete the airframe ready for covering without getting all the control gear ready, so here goes.

I am using AR9000 receivers and Turnigy 31kg high voltage servos. The receivers can take 8.4v (2 cell LiPo) and so can the servos. The reason the servos use HV is that it reduces the current requuired (power = voltage x current, so higher voltage means less curtrent needed for the same power). The result of all this is that I do not need any voltage regulators. Whilst this is good it also means that I cannot use any of the Powerbox type of units because they all incorporate voltage regulation to a lower voltage.

So, here are all the parts I need to connect some how...

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In that pile there are:
4 x 2 cell LiPo's
8 x switches
8 x 15amp diodes ( to allow connection of 2 batteries to each receiver)
2 receivers
4 voltage sensors and displays
telemetry sensor for voltage
telemetry sensor for temperature
telemetry transmitter

In an earlier discussion it was suggested that it is not a good idea to put over 10amps through the end of a standard receiver and that it is better to send current to the servos outside the reciever (like in a powerbox). I have therefore decided to build my own 'Powerbox' running at 8.4volts.

Here is my circuit diagram and the start of making it..

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The circuit board in the middle is the standard pre-drilled board with copper strips on it. I was going to use this but I searched online and found a program that calculates how wide the copper strip needs to be for the current you are using. This type of board was no good.
In the pic above you can see another type of board on the left. this is just completely covered in copper. I marked this out with tracks wide enough to carry 10amps and then carefully removed the copper where needed - you can see how much wider the tracks are on my home-made board...

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You can also in th epic above that as well as cutting the tracks I have also drilled all the holes needed for the layout I am using. This board layout is actually 2 completely seperate circuits (each half of the board), one for each receiver. Each half has 2 battery inputs that feed through diodes (2 each for security) and then the 2 feeds are connected ready to be fed to all the servos. I have put 'jumpper' leads out to each connection on the receivers and connections out for each servo.

After laying out the board I had another idea and so you can now see a second small circuit board to the right...

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The reason I added the second board was so that I could seperate all the signal wires from the power side.....each of the white receiver signal wires is connected on this small board to the outgoing servo wires.

More pictures on the next post.

[Andy Boylett]

The next few pictures show more detail.

This is how the boards are mounted, screwed on one side and sat on foam to help damp any vibration..

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The other main thing I have done is to add 2 brass heat sink srtips to the diodes. In the photo below there are 2 sets of jumper wires comming out at the top to go to each of the receivers and 2 sets of wires to the servos (one from each receiver) going out at either end....these are heavier gauge for the higher current to the servos.

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In the above photo the 4 battery connections come in at the bottom. Then above them you can see the diodes, 2 for each supply. After the diodes there is a cross connection to connect the supplies into a single one for each receiver - if you look carefully there are 2 small red wires running horizontally. If you were ever to open one of the 'proprietry' battery backer devices that allow you to connect 2 batteries to your receiver, then the above is exactly what you will see (except that they usually use 5 amp diodes which are much smaller and have no heat sinks). Here's another photo..

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[Dave Parry]

You lost me with the circuit boards, then again you can’t put brains where there is none, looks very technical and very scary to me, I’ll stick to being a petrol head, keep up the good work Andy.

[Nick Reeves 3055]

can you give anymore details on the voltage monitors and displays??

[Andy Boylett]

can you give anymore details on the voltage monitors and displays??

Hi Nick,
In the picture above you can just about see that where the 4 wires from the battery come into the box, there are also 4 smaller gauge wires next to each. these 4 wires are fed to the voltage monitors that are to be mounted on the dashboard in the cockpit. The monitors are these...
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=330534618144&ssPageName=STRK:MEWNX:IT

So, on the ground voltages can be clearly seen.

Now in the air I have a telemetry system that transmits back to a base station which I have attached to my transmitter. This is configured to continuously monitor voltage of 2 packs (one on each receiver) and the temperature of each of the 200 amp speed controllers.

I will post some photos soon as I have completed the full control setup,
Cheers, Andy

[Andy Boylett]

A couple of people have asked me about the "battery backer" system using diodes.

It really is very simple. I know the circuit diagram I showed looks complicated, but that is just because I had laid out all the connections for servo and receiver wires. Here is what it is without all the other stuff...

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Both the battery negative wires are just attached together and with the positive wire as shown above you have your dual power supply for your receiver and servos. The diodes are just an electronic component that prevents any current flowing backwards through it. This means that if one battery shorted out, the other battery could not discharge through it.

Here are a couple of photos looking inside a proprietry dual battery supply device I have in one of my other planes..

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Don't be fooled by thinking it is complicated. The 2 big components on the right are the diodes (£1 from Maplin). These are the ONLY things in this device that are to do with dual power supply. All the other electronics are for turning the led warning lights on and off at the right voltage levels.

In my planes I do not like the simple led light system becuase I use LiPo's. For LiPo's I like to see the actual voltage the battery is at, hence why I use those little displays shown in the last post.

[Andy Boylett]

I thought it might be helpful to also show another smaller dual battery supply I have built for my genesis. This one is very simple in that all it does is takes 2 battery supplies, feeds then through a small box and then into a receiver. The small box contains the electronics that stop one battery from damaging the other.

This is the circuit diagram and the home-made circuit board..

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The little section to the right with no copper is so that I have somewhere to put screws when I attach it later. The layout of the little circuit board is exactly in line with the circuit drawn above it. I have again used 2 diodes for each battery supply as this gives ultimate reliabillity.

Here it is made up into a completed unit..

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I use 2 connections to the receiver just to spread the current out a little.

Here are some close-up pictures of each side..

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You will notice that the 4 diodes are not all the same way round. This is because they all feed into the middle of the board so that the supply from each battery goes through 2 diodes and then ends up together on the middle 'track'.

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There are more pictures in the next post...

[Andy Boylett]

The completed 'dual battery supply' unit..

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