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Galaxy models mystic - help on electric conversion

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david ellis 707/06/2019 11:27:12
7 forum posts

I have a 20 year old mystic kit never started, and would now like to build it with an electric motor due to noise restrictions at the club I've recently joined

Has anyone on here done this?

If so, what motor/prop combination did you use?

I see it was originally sold as a 60 size plane, but I was recommended to get a 75 two stroke, from someone at my previous club who had a mystic

(still have the 75, never used)

I have seen some '60' replacement motors (e.g. turning G60) but not seen anything advertised as a '75' replacement

Any advice appreciated

Bob Cotsford07/06/2019 16:51:53
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7984 forum posts
444 photos

I had an OS 120 Surpass in my Mystic (it was a bit of a porker!) so off the top of my head I'd say you want around a 1300-1800 watt motor depending on how you like to fly. So, first question - what cell count are you looking at running? For 6s you are looking at a 75- 85A rating, for 8s 50-60A. Something like an Aerodrive 5055 430kv on 6S for 1300W or 5065 320kv on 8S for more poke might be suitable, though everyone has their favourites often dependant on budget. I have several .60-.90 two stroke sized models running 5055 430kv motors on 6S with 15*8-15*10 props, it seems a fairly safe setup so far pulling up to 1300W. 6S esc's are relatively cheap, 8S ones tend to cost a fair bit more so watch out for that unless you have a fat wallet.

Bob Cotsford07/06/2019 16:58:20
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7984 forum posts
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ps - my Mystic came well used, and judging by the bulkhead drillings it had been flown at some point with a good sized petrol motor. It was nylon covered with a good coat of colour on top so no doubt it could have been built a lot lighter. I still doubt whether a .60 two stroke would have made for a very exciting model, with a 1.20 four stroke it was a nice club aerobat.

Paul C.07/06/2019 17:54:03
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592 forum posts
143 photos

Hi David, I am currently building a Mystic that I got from Pegasus Models I remember these from years ago back in the late 70's early 80 ' s and always fancied one. Have seen them fly with ST2000 and 90 two strokes but I am going for ASP 120 FS (purchased from Bob Cosford at Weston Park, hi Bob)

The kit was laser cut and good quality wood, but this is a 70's design and is a 'builders kit' you don't just glue pieces together you have to fettle them to fit first, instructions are limited but ok if you have built before. It's big so you will have no problem fitting lipo's etc .

Can't help to much with electric set up but Bob knows his stuff, my knowledge of electric set up would fit on a pin head 😨. I did buy a Turnigy G 110 and dlux HV speed controller for Seagull Yak 90 , loads of power but never finished the project sill lying in the shed.

Cheers Paul.

Paul C.07/06/2019 18:55:55
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592 forum posts
143 photos

😳 Bob Cotsford 😩😩😩 sorry Bob , I hate this predictive text 😈 even when I spell things correctly the blasted machine changes it 😈😈😈😈😈

Glad I checked before I posted this, can't tell you what it changed blasted too 😱😱😱😱😱

Bob Cotsford07/06/2019 20:45:59
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7984 forum posts
444 photos

Hi Paul, you should see some of the messages that I end up sending via sms! I'm no electric expert, but what I've suggested has worked for me on half a dozen models.

Paul C.07/06/2019 21:02:16
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592 forum posts
143 photos

Hi Bob , I am still on the 4 strokes as long as I can will resort to electric at some point I suppose 😂 . From what I have seen the Mystic is a really nice flying model and from the construction it looks to be able to take some serious abuse not like some of the modern ARTF we get today.

Can't make Weston this year but should be ok for Cosford.

Paul.

david ellis 708/06/2019 11:32:16
7 forum posts

Thanks for the reply Bob, much appreciated

I was looking to use 6S for the cost reasons you mentioned

I'm thinking that I'd be best with a motor designed to use a max of 6S, as I assume I'd be able to get max power from it with 6S

The one I've seen so far from Hobbyking is a

PROPDRIVE v2 5050 580KV, thats max 2000W at 90A max on 6S

Someones uploaded a prop test that shows

15x8 - 22.2V / 1961W / 88.8A / 6.15kg thrust

Which appears to be ideal from what little I know

It does sound a little too good to be true - 'PROPDRIVE' isn't a make I've heard of before

david ellis 708/06/2019 11:44:00
7 forum posts

Thanks for the reply Paul,

Mine IS an original kit - bought in early 1990's if memory serves me correctly, so no laser cutting here

I used to build precedent kits (fly boy, bi fly etc..), and currently finishing a TRI-40 as an electric trainer to get myself back into practise as not flown for more than 20 years - I'm not sold on the ARTF "foamies" yet

The club 'expert' had one that he used a 75 two stroke in it and it flew beautifully, hence the purchase

But the new club I've joined has noise restrictions, hence the plan to build it as electric - and having seen the performance of the electrics at Weston Park, looking forward to trying it

Not going to Weston Park this year because of overlapping holidays, but booked North Weald instead - not expecting it to be as good, but never been, so want to try it

Denis Watkins08/06/2019 12:37:38
3884 forum posts
60 photos

Just an headsup David, an observation of this model already flying well on 75 - 90fs

Their respective power outputs on glow fuel are in the order of 1100W to 1300W

Bob Cotsford08/06/2019 15:59:16
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7984 forum posts
444 photos

Propdrives seem ok, at least the 42mm ones that I have do. 580kv turning a 15*8? That 2000W is the 15 second rating, e-calc thinks a 15*8 will draw 107A for 2165W and that it will cook itself. I have a couple of 595kv motors running on 6S but I'm really limited to 12 or 13" props on those giving me around 1200-1300W. Ok in a WotsWot and Bolero but I would really look for something around 430-500kv for the Mystic.

As Denis points out, you only need 1200w or so, with the 120 Surpass (1500W-ish?) mine had power enough to fly big, open classic-style ballistic aerobatics.  The 1800W topping my suggested range would be hooligan territory.

Edited By Bob Cotsford on 08/06/2019 16:01:29

david ellis 712/06/2019 23:10:20
7 forum posts
Posted by Bob Cotsford on 08/06/2019 15:59:16:

but I would really look for something around 430-500kv for the Mystic.

Hi Bob,

I'm still trying to get a general understanding of matching electric motors - so I hope you don't mind replying to my thoughts below

I was under the impression that the KV rating dictated the speed (and hence the diameter) of the propeller

So, you have a bigger prop for a 430 motor, and a smaller prop for a 580 motor

And generally, a bigger prop is more efficient on a slower model, and a smaller prop for a faster flying speed

In my ignorance, I thought that as long as you had a motor of the right wattage (in my case, I thought at least 1500W be right), then you just pick the KV to suit the size of prop (and flying speed) you want

I'm not sure exactly what size of propeller would suit the Mystic (I pulled out the plan but it's not to scale) - but as I want it to fly fairly slowly (I'm used to flying a super sixty), then I'm assuming something like a 15 or 16 inch prop would be good

Does this sound about right?

I guess the problem I'm seeing is that lower KV motors seem to require 8S or higher battery packs to get their rated power - I guess that more power would draw too many amps from 6S, so upping the voltage allows more power without going too high in current

So maybe it's better just to have a high voltage ESC and a 8S battery pack?

Trevor Crook13/06/2019 08:57:20
855 forum posts
65 photos

David, your summary is basically correct. I've never electrified a model of that size but estimates of just over 1kW seem about right. I electrified the smaller Magician and that flew nicely on a 3s setup producing about 450W.

The only 6s model I have is an Avios 1450mm Spitfire. This weighs 6lb and uses a 380kV motor to turn a scale 15x10 3-blade prop. Unfortunately I haven't measured the power, but there's lots of it, it takes off on half throttle and I only use full throttle for big loops. I'm estimating it's at least 1kW. Plenty left in the 3000 pack after an 8-minute scale flight.

I think you will be in the right ball park for the prop size you are aiming for with a motor around 500kV. The great thing with leccy power is that, armed with a wattmeter you can try a very wide range of props to get the results that you want. Just make sure the model is securely anchored/held by a helper when measuring!

Trevor Crook13/06/2019 09:01:05
855 forum posts
65 photos

Oh and I think the leccy version looks much neater without lumps of metal sticking out of the nose! I moved the Magician's cockpit forward too as I preferred the look

Modified Magician

Nigel R13/06/2019 10:07:11
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3067 forum posts
475 photos

"120 Surpass (1500W-ish?)"

Mine showed 9100 rpm on 15x7 APC. The calculator I have used many times shows that to be around 1250W.

Accounting for electric system inefficiency, I'd guess 1500W would be equivalent.

 

"I have several .60-.90 two stroke sized models running 5055 430kv motors on 6S with 15*8-15*10 props,"

Bob's setup sounds ideal to me.

 

Trevor, that looks nice

Edited By Nigel R on 13/06/2019 10:07:31

david ellis 713/06/2019 10:26:54
7 forum posts

Trevor, that’s looks really good - was it hard to move the cockpit forward?

Nigel, thanks for the feedback, a 15 inch prop sounds good - you don’t happen to know what current it’s pulling do you?

david ellis 713/06/2019 10:28:16
7 forum posts

Trevor, that’s looks really good - was it hard to move the cockpit forward?

Nigel, thanks for the feedback, a 15 inch prop sounds good - you don’t happen to know what current your electric models are pulling do you?

Bob Cotsford13/06/2019 11:13:52
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7984 forum posts
444 photos

second attempt topost - grr!

A logfile from my Provost (5055 430kv, 6S, either 15*8 or 15*10, can't remember which offhand) peaks at 56A with a fresh battery, then later peaks are around 46-48A but the average current is probably around 30A, it's surprising how little time is spent on a steady throttle!

provost log.jpg

Trevor Crook13/06/2019 13:50:46
855 forum posts
65 photos

David

The cockpit move was quite straightforward, but I can't remember all the details and no longer have the model, so I can't give a definitive guide. Obviously the angled top side pieces have to be remade. I used the supplied canopy, so I think I made sure that this would fit the new former at the rear of the cockpit first. If you make that former to fit the back of the canopy moulding, allowing for the thickness of the top side sheet, then make the new side sheets, you should be fine.

The Magician is a really nice-mannered aircraft, and given that bigger normally flies better, your Mystic should be superb. I've attached another picture showing the battery compartment.

Trevor

Modified Magician

Nigel R13/06/2019 14:02:15
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3067 forum posts
475 photos

"Nigel, thanks for the feedback, a 15 inch prop sounds good - you don’t happen to know what current it’s pulling do you"

No worries. I could make a guess on fuel consumption for the 120, but no idea on the electric - but Bob's posted details on his setup smiley

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