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Old Dec 02, 2011, 03:34 AM
Chesterfield, MI USA
United States, MI, Chesterfield
Joined Apr 2011
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Build Log
Kaos MK II ARF...Glow To Electric Conversion

Well here we go.....My first Glow to Electric conversion I have always had a liking for the Kaos and this is my fist one. If all goes well with this build I would like to purchase a Birdi Super Kaos 60 kit and do an electric version of that as well.

I will not have time to start until the end of December but I wanted to discuss it, get feedback, and see what other peoples thoughts & ideas are.

Here is what I know so far:
Intended Use: This will by my first pattern trainer (Not first low wing or sport plane though)
Power: Electric

My current thoughts on a power setup (This is subject to evolve):
Motor: Rimfire .46
ESC: Castle Phoenix ICE 75
Flight Battery: 4S~5S, 3300mah~4000mah
Receiver Pack: 2S Lipo, 1500mah~2000mah
Prop Size: Currently Unknown
Receiver: AR6210
Radio: Spektrum DX6i
This is all going to be a pretty tight fit

Mods to be made:
Will need to add access for cooling air to enter and exit
Possible longer landing gear depending on prop size
Top hatch to be added to access the flight battery
Replacing the canopy with a Super Kaos canopy. (ordered it last night)
Will remove the existing covering and replace. May possibly keep the white base and just do my own trim.
Different nose gear set up since the stock once relies on the Glow Motor mount for installation and I won't be using it for electric power. Need to put some more thought into this and see what my options are
Seriously considering mounting a servo in each wing half for independent aileron control
I have put a lot of thought into a tail dragger an retracts but I am currently thinking I will pass on that for this project.

Once I get started I intend to include lots of pictures as I progress.

I am open to any other ideas and suggestions as well.

Well I guess that about covers it for now. I am really excited to get this project going!!! Wish I could start it now.

Chris "Mac"
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Old Dec 02, 2011, 07:08 AM
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Can I suggest that before you commit to a motor and cell count, you decide how big a prop you are able to fit with clearance that you're happy with, whether or not you decide to extend the landing gear.

Props come in diameter steps of typically 1", and stepping from 4 to 5S cell counts represent 25% increase in voltage so they are pretty coarse changes - but the choice of motor with Kv and weight that suits can be much finer. I'd suggest you can get a better result by selecting from a broad choice of motors after you've decided on the prop, rather than picking the motor then finding its Kv is just not quite right or that it would really be better on say 4.5S. Basically there are more motors to choose from than prop sizes.

That's not to say the Rimfire .46 might not end up being a reasonable choice. Indeed, if you are limited to 11" props and decide on 4S, you'll need the highish Kv it has compared to other motors with similar weight. On the other hand, if you want to use a 12" prop and 5S, its Kv is probably a bit too high.

Just my 2C, but in a ~6lb model, I'd be considering 6S from the start and looking for Kv around 600 for 11" and 500 for 12". The Hacker A40 range offers you nice small steps in Kv at similar price and weight to the Rimfire, and if you need a bit more weight up front and can use 12"+, the A50S is worth a look.

Looks like a beautiful model - good luck!
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Old Dec 02, 2011, 09:30 AM
jrb
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Joined Oct 1999
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Trike, or would you consider doing it as a tail dragger -- lets you use a larger diameter prop.

Also, would be quite helpful if you post the specs IIRC the ARF is .40 sized.


I've flown a lot of .40/.50 sized ARF on LiPo-5S & A123-6S (my favoratie!).



Always wanted to do a Kaos; tried to talk my Dad out of his .60 kit; but he finished it as glow:
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Old Dec 02, 2011, 08:52 PM
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From a nut case(me) who has been converting 25 planes I have from glow and gasoline(.40size) to 50cc. Know your prop clearance for SURE before deciding on motor or battery selection. THANKS,HUNKUS
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Old Dec 03, 2011, 11:46 AM
Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
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Hi Chris
Thought about the Kaos 40 for a long while, but from an electrocution of a CAD plan someone put in a lot of work on and then gave away for free on the web. The BARF bubbles up to the top every time I get a Tower catalogue - the model is just great looking, a fine example of its era.

Your mods to the BARF - all good stuff. After a lot of conversions and own designs, your battery access hatch is the line between easy battery swaps between flights and misery! Two aileron servos are a great idea - if you want to put them inside the wing where they belong, let me know, I have A Plan

As good advice above, sort out your motor etc and prop to define your maximum prop diameter. My 'large scale' version will, after much doodling, be a taildragger. What do you expect from a guy who's had four trike gear models in 32years of RC?

Colour scheme? Have a scrat around the likes of the SPA site for inspiration, this is a popular type.

5 or 6S sounds well worth considering. Being tight, I stick to 4S and they came nowhere near giving the GP BARF any kind of performance. GP do good aerodynamics but don't seem to understand 'weight'. Hence my own plan version...

If you stick to the trike, I looked at extending the motor mounts to make it matchthe cowl, then used a commercial trike nose leg. It would have fitted, but there was a fudge factor involved...

Good luck with your project, will be following.

Dereck
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Old Dec 03, 2011, 09:55 PM
DX5e fatal flaw- PM me!!!!
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It's like building a hot rod- you have to pick the tires first!

Dave
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Old Dec 04, 2011, 09:41 PM
Chesterfield, MI USA
United States, MI, Chesterfield
Joined Apr 2011
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Thank you very much all for the feedback and recommendations. That is what I was hoping to get from this thread.

Scirocco, I am on board with figuring out the prop size first. I recognize that I probably took the incorrect approach to begin with.

The approach I took was as follows. I have an electric Escapade 40 that is equipped to the manual recommendations. My version came out to just under 6 lbs. It has a RimFire .46, 4S 3300mah and a 70 amp ESC with a Spektrum 6210 and a 12 x 6 prop. I have found that this has ample power and thought it would be OK for my Kaos. I realize I am probably making a lot of assumptions here that I should not be. For starters the Kaos manual states 5-6 lbs and my craft, even stock, seem to come out on the high end of these manual numbers. I am sure adding an additional servo for ailerons, the battery hatch, larger wheels, and a few other things will also add weight as well. Maybe not a lot, each, but I do understand it all adds up. It would not surprise me if I end up between 6-7 lbs when all is said and done. I currently have 3 3S 3300mah and 3 4S 3300 packs but I am not at all opposed to buying larger packs. I don't want to limit myself that way at all. Another project I have this winter is a scratch build Four Star 60 and it surely will need the 6S packs at minimum.

Since we are gong to start with "Prop" size and work backwards from there what are the factors I should be considering in determining that "Prop" size? I know of course one factor will be what size will physically fit clearance wise on the plane. Unfortunately the manual does not give a recommended prop size so I can not even use that as reference for a starting point. The one thing I do know for sure is I am going to stick with a Trike gear and not turn this into a tail dragger. I don't mind re bending and/or purchasing new gear if I find that I need to extend them. Within reason of course. So I guess the second factor would be performance, correct? I really do not know much about how changing prop size is going to effect the performance. Any assistance here will be greatly appreciated.

Mac
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Old Dec 04, 2011, 09:46 PM
Chesterfield, MI USA
United States, MI, Chesterfield
Joined Apr 2011
48 Posts
Quote:
Originally Posted by Dereck View Post

Colour scheme? Have a scrat around the likes of the SPA site for inspiration, this is a popular type.
I am not sure about color scheme yet. I do have a few ideas in my head though. Probably a white base with red and blue trim or white base with rid and silver trim. What is SPA and what is the SPA site?


Quote:
Originally Posted by Dereck View Post
If you stick to the trike, I looked at extending the motor mounts to make it matchthe cowl, then used a commercial trike nose leg. It would have fitted, but there was a fudge factor involved...
What is a "matchthe cowl" cowl? I have been considering a cowl as I don't like the open look but have been leaning towards leaving the stock open look since it is a Kaos and that is the way Kaos's look. If I saw something appealing I might reconsider though.
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Old Dec 05, 2011, 12:43 AM
Chesterfield, MI USA
United States, MI, Chesterfield
Joined Apr 2011
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Originally Posted by Dereck View Post
Two aileron servos are a great idea - if you want to put them inside the wing where they belong, let me know, I have A Plan
I would love to see what you have if you don't mind sharing. I for sure will be putting the complete servo inside the wing. The only thing I would like to see sticking out is just the end of the control arm with the push rod attached.

Thank you! Mac
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Old Dec 05, 2011, 06:05 AM
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Australia, ACT, Kambah
Joined Feb 2001
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Quote:
Originally Posted by Mac333 View Post
Thank you very much all for the feedback and recommendations. That is what I was hoping to get from this thread.

Scirocco, I am on board with figuring out the prop size first. I recognize that I probably took the incorrect approach to begin with.

The approach I took was as follows. I have an electric Escapade 40 that is equipped to the manual recommendations. My version came out to just under 6 lbs. It has a RimFire .46, 4S 3300mah and a 70 amp ESC with a Spektrum 6210 and a 12 x 6 prop. I have found that this has ample power and thought it would be OK for my Kaos. I realize I am probably making a lot of assumptions here that I should not be. For starters the Kaos manual states 5-6 lbs and my craft, even stock, seem to come out on the high end of these manual numbers. I am sure adding an additional servo for ailerons, the battery hatch, larger wheels, and a few other things will also add weight as well. Maybe not a lot, each, but I do understand it all adds up. It would not surprise me if I end up between 6-7 lbs when all is said and done. I currently have 3 3S 3300mah and 3 4S 3300 packs but I am not at all opposed to buying larger packs. I don't want to limit myself that way at all. Another project I have this winter is a scratch build Four Star 60 and it surely will need the 6S packs at minimum.

Since we are gong to start with "Prop" size and work backwards from there what are the factors I should be considering in determining that "Prop" size? I know of course one factor will be what size will physically fit clearance wise on the plane. Unfortunately the manual does not give a recommended prop size so I can not even use that as reference for a starting point. The one thing I do know for sure is I am going to stick with a Trike gear and not turn this into a tail dragger. I don't mind re bending and/or purchasing new gear if I find that I need to extend them. Within reason of course. So I guess the second factor would be performance, correct? I really do not know much about how changing prop size is going to effect the performance. Any assistance here will be greatly appreciated.

Mac
Most would recommend that you fit the largest diameter prop you can, up to as much as 25-30% of span, while of course ensuring you are happy with the ground clearance for the prop, considering the surface you are going to fly off.

The reason you won't find a airframe prop recommendation is that the manufacturer built it as a .40, and as far a I can see .40s nearly always use 10 and 11" props. The prop size is sort of assumed. If you can't measure or calculate, you can bet being a .40 ARF 11" will definitely have enough clearance, and this review confirms it.

The reason most will recommend a larger prop over a smaller is larger props (essentially a bigger disk accelerating a significantly larger volume of air a lesser amount) produce thrust more efficiently, ie more thrust per unit of input power to the prop. But larger diameter props absorbing the same power require more torque at lower rpm. Fortunately electric motors can more readily develop that lower rpm torque so why not take advantage of the motor characteristics and use the relatively limited battery energy as efficiently as possible while delivering the go we want. Some would argue it is not that electrics use big props, it's that glow motors, particularly 2 strokes have to compromise on overly small props because they can't deliver much power at low rpm.

Re your question on effect of prop size on performance: An electric motor 'wants' to spin up around its no-load speed, loosely defined by input volts x Kv. Add a load (prop), and it still wants to turn at as close as it can to the same speed, but needs more current to develop the required torque. Change to bigger and bigger props, and it will still want to try to maintain rpm, and draw more and more current doing so. It will do that until either it overheats, or the battery becomes unable to deliver the demanded current.

A bit of very rough prop theory: Increasing prop diameter at constant rpm will result in power required increasing proportional to the 4th power of the diameter, ie going from 11" to 12" is a 9% diameter increase, but a ~40% power increase. So an increase in prop diameter can overload motor, ESC and battery surprisingly quickly. Increasing prop size doesn't happen without some reduction in rpm, so the power required increase is not quite that big, but still very significant.

Along with the power required increase, increasing prop diameter at constant rpm increases thrust proportionally to the 3rd power of diameter.

The third change is cell count, ie voltage. Motor RPM is proportional roughly to voltage, although losses will mean it it not quite linear. Trouble is cell count steps are big: 2S to 3S > 50% voltage increase. 4S>5S 25% voltage increase, ie big rpm increases. As the power required to turn a given prop is proportional to rpm to the 3rd power, an extra cell makes a BIG difference.

Last is pitch: both power and thrust are directly proportional to pitch.

How does that practically relate to changing prop size? IF (and it's a big if sometimes) your motor, ESC, battery system can cope with the power increase AND you remain within the efficient operating current for the motor, simply increasing prop diameter at constant pitch can yield a substantial increase in thrust. The tradeoff is higher current and thus reduced runtime, and also a relatively small penalty in pitchspeed because rpm won't be maintained as load increases. Efficient range: you're in the ballpark if loaded rpm > 70-75% of no load rpm as estimated by Volts x Kv . Similarly, adding a cell makes a big difference to both thrust and power required.

Assume a baseline 4S, 11x8 approx 100 oz thrust, 74 mph pitchspeed, 580W in @41A
Next step, 4S 12x8, ~ 116oz, 70mph, 715W in @ 52A
next 5S 11x6, ~117oz, 70mph, 837W in @ 48A - less efficient than 4S 12x8, but if 12" won't fit does deliver an increase in thrust.
To illustrate the benefit of increased diameter and pitch 4S, 13x10, Eflite Power 46 Kv=670 (IMO 13" is too much for Kv=800 on 4S): ~ 128oz, 73mph, 723W in @53A.

While it's not that hard to get lots of thrust with bigger props, I'm not sure extending the gear would be justified, at least not before flying with an 11" prop. My calculator suggests that an 800 Kv motor on 4S with an 11 x8 should deliver about the same thrust but with higher pitch speed as the 12 x 6 you had on the Escapade, and use about the same power, around 600W assuming a reasonably (> 80%) efficient motor. Also, the 11x8 at around 9800 rpm should be delivering about the same static thrust (about 100 oz) as the Tower .46 spinning an 11x6 at 11200 rpm in the review, and give you slightly better pitch speed. That's roughly 1:1 static thrust to weight, not to be sneezed at. So there's probably not a lot wrong with your initial idea, even if you had assumed 12" like your Escapade but end up limited to 11".

And if you want to 'borrow' the Escapade system you've got a nil cost test system, except for maybe a couple props to try out.
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Old Dec 05, 2011, 12:23 PM
DX5e fatal flaw- PM me!!!!
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Just to drop in my data-

4.5/5.5 lbs trainer (repairs, don't ask...), about a 60 inch span, 4s battery with a 770kv aprox. 600 watt motor, 12x6 prop works just right, plenty of pull for a 5lbs trainer, and it pulls it to an unreasonably high (for a trainer) top speed.

Dave
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Old Dec 05, 2011, 12:46 PM
jrb
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Tower Hobbies Kaos 40 ARF: http://www.towerhobbies.com/products/towa2052.html .

Wingspan: 55 in. (1398mm) Wing Area: 566 sq in (36.5sq dm) Weight: 5.5lb-6 lb (2.5-2.7 kg) Wing Loading: 22-24oz/sq ft (67-73g/sq dm) Requires: 2-stroke .40-.46 or 4-stroke .52 engine and 4-channel radio w/4 standard servos


Once again this catches my fancy!

Like my winter Toledo Special w/skis probably would do: A123-6S, ICE-50, E-flite Power 60 BL; but as a Trike w/Vario 4 blader versus the APCE 14x12.
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Old Dec 07, 2011, 05:15 PM
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If I recall correctly my 5s 4000 just fits on the nose. When I converted mine back in the day the cost is what kept me to 5s. It might be worth looking into 6s and a smaller prop. If me mind serves me I bent custom gear to fly the 11 inch screw.

Tommy D
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Old Dec 07, 2011, 07:11 PM
Visitor from Reality
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Quote:
Originally Posted by Mac333 View Post
I am not sure about color scheme yet. I do have a few ideas in my head though. Probably a white base with red and blue trim or white base with rid and silver trim. What is SPA and what is the SPA site?




What is a "matchthe cowl" cowl? I have been considering a cowl as I don't like the open look but have been leaning towards leaving the stock open look since it is a Kaos and that is the way Kaos's look. If I saw something appealing I might reconsider though.
My apologies - a mix of typing on my iSpend pad - spousal unit bought me it but it has never impressed me that much - and too many pills for what I won't bother you. I tend to miss hitting the space bar between words and obviously failed to proofread that posting

An outrunner is much shorter than a matching glow engine on its mounting. As you'll be wanting to keep the shape of the model, you'll need to add some spacing to put the prop in the correct position. A side benefit is that if you use some form of tubular spacers, that should leave plenty of firewall area to secure a steerable nosewheel to.

Still keep telling myself I should alter mine back to a trike gear - it looks far more 'typical'.

Will shortly post my aileron servo mounting drawing. It's pretty easy to incorporate into a complete airframe once you have the covering off. If you use the like of Hitec's HS 225 servo, you'll have plenty of servo power with little extra weight. I use 225s for rudder and elevator on models not much smaller than this too.

D
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Old Dec 08, 2011, 12:13 AM
Chesterfield, MI USA
United States, MI, Chesterfield
Joined Apr 2011
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Quote:
Originally Posted by scirocco View Post
Most would recommend that you fit the largest diameter prop you can, up to as much as 25-30% of span, while of course ensuring you are happy with the ground clearance for the prop, considering the surface you are going to fly off.

The reason you won't find a airframe prop recommendation is that the manufacturer built it as a .40, and as far a I can see .40s nearly always use 10 and 11" props. The prop size is sort of assumed. If you can't measure or calculate, you can bet being a .40 ARF 11" will definitely have enough clearance, and this review confirms it.

The reason most will recommend a larger prop over a smaller is larger props (essentially a bigger disk accelerating a significantly larger volume of air a lesser amount) produce thrust more efficiently, ie more thrust per unit of input power to the prop. But larger diameter props absorbing the same power require more torque at lower rpm. Fortunately electric motors can more readily develop that lower rpm torque so why not take advantage of the motor characteristics and use the relatively limited battery energy as efficiently as possible while delivering the go we want. Some would argue it is not that electrics use big props, it's that glow motors, particularly 2 strokes have to compromise on overly small props because they can't deliver much power at low rpm.

Re your question on effect of prop size on performance: An electric motor 'wants' to spin up around its no-load speed, loosely defined by input volts x Kv. Add a load (prop), and it still wants to turn at as close as it can to the same speed, but needs more current to develop the required torque. Change to bigger and bigger props, and it will still want to try to maintain rpm, and draw more and more current doing so. It will do that until either it overheats, or the battery becomes unable to deliver the demanded current.

A bit of very rough prop theory: Increasing prop diameter at constant rpm will result in power required increasing proportional to the 4th power of the diameter, ie going from 11" to 12" is a 9% diameter increase, but a ~40% power increase. So an increase in prop diameter can overload motor, ESC and battery surprisingly quickly. Increasing prop size doesn't happen without some reduction in rpm, so the power required increase is not quite that big, but still very significant.

Along with the power required increase, increasing prop diameter at constant rpm increases thrust proportionally to the 3rd power of diameter.

The third change is cell count, ie voltage. Motor RPM is proportional roughly to voltage, although losses will mean it it not quite linear. Trouble is cell count steps are big: 2S to 3S > 50% voltage increase. 4S>5S 25% voltage increase, ie big rpm increases. As the power required to turn a given prop is proportional to rpm to the 3rd power, an extra cell makes a BIG difference.

Last is pitch: both power and thrust are directly proportional to pitch.

How does that practically relate to changing prop size? IF (and it's a big if sometimes) your motor, ESC, battery system can cope with the power increase AND you remain within the efficient operating current for the motor, simply increasing prop diameter at constant pitch can yield a substantial increase in thrust. The tradeoff is higher current and thus reduced runtime, and also a relatively small penalty in pitchspeed because rpm won't be maintained as load increases. Efficient range: you're in the ballpark if loaded rpm > 70-75% of no load rpm as estimated by Volts x Kv . Similarly, adding a cell makes a big difference to both thrust and power required.

Assume a baseline 4S, 11x8 approx 100 oz thrust, 74 mph pitchspeed, 580W in @41A
Next step, 4S 12x8, ~ 116oz, 70mph, 715W in @ 52A
next 5S 11x6, ~117oz, 70mph, 837W in @ 48A - less efficient than 4S 12x8, but if 12" won't fit does deliver an increase in thrust.
To illustrate the benefit of increased diameter and pitch 4S, 13x10, Eflite Power 46 Kv=670 (IMO 13" is too much for Kv=800 on 4S): ~ 128oz, 73mph, 723W in @53A.

While it's not that hard to get lots of thrust with bigger props, I'm not sure extending the gear would be justified, at least not before flying with an 11" prop. My calculator suggests that an 800 Kv motor on 4S with an 11 x8 should deliver about the same thrust but with higher pitch speed as the 12 x 6 you had on the Escapade, and use about the same power, around 600W assuming a reasonably (> 80%) efficient motor. Also, the 11x8 at around 9800 rpm should be delivering about the same static thrust (about 100 oz) as the Tower .46 spinning an 11x6 at 11200 rpm in the review, and give you slightly better pitch speed. That's roughly 1:1 static thrust to weight, not to be sneezed at. So there's probably not a lot wrong with your initial idea, even if you had assumed 12" like your Escapade but end up limited to 11".

And if you want to 'borrow' the Escapade system you've got a nil cost test system, except for maybe a couple props to try out.
scirocco,

Thank you very much for all the time you have taken to explain all these things to me. It has been a huge help. It is looking like my original idea for power setup might work well even though I came to that set up for many of the wrong reasons. I guess even a blind squirrel finds a nut sometimes.

I am thinking that for right now I will go with the same set up as my Escapade but with an 11" inch prop. It seems safe for now and will be my baseline. I can always make adjustments from there.
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