Spacewalker half scale 168" electric

[Andy Boylett]

I have now finished putting my dual supply battery system into a nice mounting and installed it on the control board for my plane....

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There it is in the middle, with the diodes and heat sink poking out through the top. This unit now has 4 batteries connected to it through 8 high current switches. Each pair of batteries then feed through the diodes, so preventing damage to the remaining battery if one were to fail. Then power is fed out directly to each half of the planes servos. Each half is completely independant with no links between them. The 'power box' is also connected to each of the 2 AR9000 receivers (on the left above) by fly leads that transfer the servo signals out.

Some of the receiver outputs go directly (not through the power box) as they are low current. These are the throttle signal to the esc's, the signal to switch the planes lights on, and the telemetry system connection.

I am always paranoid about vibration so I mount everything on shock absorbers. My favourite system is the one I have used here, seen in the photo above. I mount a piece of high resilience foam to the mounting board. This has velcro on it. The underside of the receivers (and the power box) have velcro under them, and then there are straps around them to make sure they stay put. This gives a lovely soft and very flexible mounting, whilst maintainng very good fixing.

[Andy Boylett]

I found another photo of the mounted power box...

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[Andy Boylett]

I have now added the 4 receiver batteries to the 'control' board. The batteries are inside a fire-proof bag so that they can be charged in situ (I heard of someone burning all his planes last year when he was charging a LiPo in situ).

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That extra 1000mah LiPo in th ecentre is for the lighting system.

[Mike altham]

Andy,

What lighting did you get in the end?

Im still un sure of which to go for?

Mike.

[Andy Boylett]

Andy,

What lighting did you get in the end?

Im still un sure of which to go for?

Mike.

Mike,
I went for Avago LED's bought from Farnell. These are very high power and very high Lumens. Here are the links....
White......http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1686144
Red.......http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1678960
Green....http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1678958

You also need to buy 5 watt rated resisters to suit your battery voltage.

Regards
Andy

[Andy Boylett]

Have any of you ever heard of or used this company? EMCOTEC
http://shop.rc-electronic.com/e-vendo.php?shop=k_emcotec_e&SessionId=&a=catalog

These guys started off making components for aircraft and then branched into RC planes. I have been talking with them for some time regarding their components for large electric models.

The product range they offer seems to cover everything needed electronics wise for large models. They have 'power boxes, servo matching etc, etc.

In the discussiions I have been having with them I have found them to be very technical and very knowledgeable, including discussing many aspects of my large electric plane design with me. The product that I have been discussing with them is a brilliant one that I have simply not been able to find anywhere else at all.

When using high power electric planes they are extemely dangerous when 'armed' but at stand-still with the prop not turning. Electric motors give their maximum torque at this point so if someone mistakenly gets in the way, not realising the motor is armed, then they will likely lose a body part . The other issue with large electric is how they are 'armed' to make them live. The common practice is simply to connect up the final part of the battery circuit by plugging one of the battery connectors in. With 12 cell LiPo systems this connection often also makes a loud 'crack' and emmits a large spark!

EMCOTEC have developed a solid state switch for high power electrics. This means there are no moving parts and all the switching is done electronically (using FET's).
The switches can either be controlled from a spare channel on the transmitter (like having throttle hold for a heli) or by using a fail-safe magnetic switch. You can see this magnetic switch in the photo below. When the switch is in place, with the safety flag dangling then the power is off...

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The one shown in the photo above can handle 120amps continuously - and they really do mean continuously. This will take 240amps peak! I am fitting one of this size in my LMA Genesis.

EMCOTEC have just brought out an even bigger power switch. This one can handle 180amps continuously or 360amp peak. I am fitting 2 of these units in this half scale Spacewalker....

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This means that we will be able to fully arm the plane ready for take-off with all batteries fully connected to both motors, yet keep it in a safe condition. Then when we need to fly, just pull out the 2 magnetic plugs.

Has anyone seen this type of device before?

[Robert Mahoney]

Hi Andy, I have been using two of the units for over a year, one one 6cells the other on 10cells. They are great in the safety of electric flight. I am now using there new electronic switch that does away with the manual switch! The electronic switch works two controllers!
If you want more info please email me and I will give you my P/No
Keep the watts up

Robert Mahoney

PS the BMFA electric safety have been looking at this type of switch!

[Andy Boylett]

Thanks Robert,
Myslef and my son fly all electric and we find that the issue with big electric is the ic users who do not understand them ie a large electric model is sat there not making a noise, is fully armed ready to go and then some one just strolls over and starts poking a finger at it while talking about it. I am glad to hear that the BMFA are discussing this. I think that we need to have some pretty clear guidlines (rules in my view) as to how elec should be approached. As regards large elecs (say over 7kg) I think there should be some sort of arming/disarming device.

We have been using our own manual device for the past 2 years and it has worked really well. It is just a simple plug made by epoxying a deans plug socket into the side of the plane (or in the cockpit) and then pluging a Deans plug inot it with a piece of wire soldered to both terminals. The plug is just fitted into the positive wire. The ic fliers at our club have been acustomed to looking for the 'plug' and knowing that if it is in then it is armed. Also, when someone helpfully goes and collects a plane they also know that they should pull the plug out to dissarm it.

Interesting that you have now gone for the receiver controlled switch now. I was actually thinking of using the magnetic switches because of the visual effect that they have.

I have emailed you my phone no.
Cheers, Andy

[Andy Boylett]

Here are few more details of the control board that contains all the electronics...

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This above photo shows the 'balance wires' from the LiPo batteries. I have extended these so that they are outside the firesafe bag that the batteries are in. This way I will be able to charge the batteries through these balance wires without discturbing any of the power connections.

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This shows the small receiver controlled switch that can turn the lights on/off. It can handle 3 amps continuous so is more than up to the task.

[Andy Boylett]

I have now completed building the other outer wing section and fitting the ailerons..

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Servos and linkages are all completed and fitted as well. I have used:
- Turnigy High Voltage 31kg/cm, Titanium gear servos
- a rose joint at outer end from McGill Motorsports.
- a machined aluminium heavy duty clevis at the servo end.
- 50mm aluminium servo arms with screw clamp system at servo head.
- 3mm stainless steel threaded bar.
- 6mm OD with 3mm ID carbon tube.

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[paul hughes]

Andy, I used the same clevises on a model as you have on your servo arms. I found that on the first flight i lost the "C" clip from the end of the pin. luckerly i spotted this before the pin removed itself, since then I replace the pin with a bolt and lock nut, not as pretty, but much safer. It would be a shame if you put in all these electronic safety features then lost the model for the sake of afew m3 screws.

[Andy Boylett]

Andy, I used the same clevises on a model as you have on your servo arms. I found that on the first flight i lost the "C" clip from the end of the pin. luckerly i spotted this before the pin removed itself, since then I replace the pin with a bolt and lock nut, not as pretty, but much safer. It would be a shame if you put in all these electronic safety features then lost the model for the sake of afew m3 screws.

Paul, thanks for the advice. I was already concerned with the flimsy clips provided as I had already bent one by accident and it no longer fitted snuggly. However, I don't like using bolts as the pivot because all the load is taken on the pointy part of the thread and they very quickly can get worn. Whilst this is not a failure issue it does provide a little slop in the linkage. With the massive ailerons and 31kg/cm torque I am using in this build I want to avoid any slop. I have already drilled and reamed the holes in the servo arms so that they are a perfect sliding fit on the pins provided with the clevis, so I really want to use these still. I am now thinking that maybe a proper circlip would be better. Failing this I can probably drill/tap the end of the clevis pin to take a small 2mm cap head bolt.
Regards, Andy

[Andy Boylett]

Following that advice from Paul I started looking for external circlips to fit a 3mm OD shaft. I found a guy selling them for £1.05 each, then a guy selling them 12.60 for 50, but then good old RS components
http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=289-180&x=21&y=14
£2.28 for a pack of 100 pucker engineering circlips.

[Chris Lane]

www.modelfixings.co.uk have them.

[Phil Clark]

Hi Andy

I'd still prefer not to see the C clips unless you can find some that are a VERY good & tight fit & you are willing to replace the C clip every time the linkage is disasembled. From experience, these small C clips are very delicate and never return to the original shape after removal.

Other alternatives....

1) Use an M3 cap with a short section of plain shank as the bearing surface. IIRC, M3 x 25's have about 1/4" of plain shank...all you'll need to do is remove 15-20mm of thread leaving enough for a washer & nyloc

2) Drill the ends of the existing pins and use split pins......but again, replaced the pns every time the linkage is disassembled.

Phil

[Andy Boylett]

Phil,
see my last post above above....
I am not going to use the C clips as they are flimsy. Nice ideas of yours, but split pins or P clips I find fiddly and not great. Also, the non-threaded shank on 3mm bolts I checked is still slightly loose in the hole (they are a clearance fit in a 3mm hole). I think engineering circlips are better and failing that a drilled/tapped hole to take a 2mm retaining bolt. I have checked the groove size in the pin and it is perfect size to match the circlip so I have ordered proper external circlips. These are fitted using circlip pliers so not going to come off. These are extremely reliable, strong and would not need replacing when removed/re-fitted.......in fact the thrust from both of my motors on this plane is taken on 2 external circlips fitted onto the motor shaft.
Andy

[Phil Clark]

I'd like to see these fitted at some point Andy.....I'm not going to be convinced of their suitability until I have seen them for myself. I've used much larger circlips & the correct pliers on various applications myself.....never an issue in the larger sizes (1/2" +), but I have concernes over very small ones.

Phil

[Andy Boylett]

Phil,
I have lots of experience of very small circlips as all electric brushless outrunner motors under about 35mm in diameter are held together on the motor shaft by tiny external circlips. These are mostly 2.5mm, 2.7mm and 3mm and require the special small circlip pliers we have. If any of these circlips were to fail the whole of the outrunner casing, complete with prop would go flying off into the distance and potentially kill someone.

The key to these working well is that they are fitted properly, which requires the correct tool. I see lots of people using pliers, screwdrivers etc to remove them and this can end up in the circlip being strained beyond its allowable tolerance thus making it permanently slightly larger than it should be - then of course slightly loose when re-fitted.
Cheers, Andy

[Phil Clark]

I fully appreciate that Andy........& I have also witness a small brushless motor let go ....hence my concerns over small circlips.

If you have these fitted on Monday, I'll have a good look during the next inspection.

Phil

[Andy Boylett]

Hi Phil,
Well someone had obviously either fiddled with their motor or crashed it previously. The reason circlips are so good is that they can take imense loadings on them. The circlip is designed to take a thrust load on a shaft and the whole of the cricrumfernce of the circlip is being loaded in shear. There is so much metal taking the shear load it is likely the shaft will break first. All the small motors I have seen break, including some of my own, have either been previously dismantled or they have had a knock. Brushless motors are particularly susceptible to a knock because if the plane tips up on the ground the outer 'can' of the motor can smack the floor.

The motors my plane is using will produce 40 to 50kg of thrust, all taken on a circlip.

The application of holding a pin in a clevis will have a thrust load of about zero.

My circlips will not be on clevises by Monday as I only ordered them today (a bag of a 100) but I can maybe rob another one off the end of a small motor.

Andy