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Old 01-17-2018, 03:58 AM   #1
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Default McDonnell xp-67 e build

Figured I’d post this here. I’m shooting for all up weight around 3lbs. I have an idea on motors, but I thought you all might be the experts and have a few suggestions. Take a look at the build.

http://www.rcuniverse.com/forum/scra...l-xp-67-a.html
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Old 01-17-2018, 03:20 PM   #2
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Originally Posted by Mattg6o View Post
http://http://www.rcuniverse.com/for...l-xp-67-a.html
Figured I’d post this here. I’m shooting for all up weight around 3lbs. I have an idea on motors, but I thought you all might be the experts and have a few suggestions. Take a look at the build.
Link didn't work for me?

Jimmy
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Old 01-17-2018, 03:50 PM   #3
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BOttom link should work now.
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Old 01-17-2018, 04:55 PM   #4
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Very impressive, and ambitious, project. Please post the updates here as well.

What goes up, must come down. The trick is to keep it in one piece.
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Old 02-01-2018, 12:46 AM   #5
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Update
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Old 02-01-2018, 04:33 AM   #6
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What a complete waste of time! Just kidding. Quite an exciting project. Congrats !
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Old 02-02-2018, 02:26 AM   #7
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I know right. I’ll crash it immediately. Probably burn it up on the bench. It’s not like I work on it for 4 or 5 hours every morning yes it’s very exciting. I think you want one you can, it only requires demands your soul.
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Old 02-04-2018, 05:03 PM   #8
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Update.
I did some motor testing. I’m using turnigy sk3 2836 1500kv 31a 370w. I don’t have but 2 props. I’ll order more. Im really new to electric. I tested a 6x5.5 and a 7x6. The 6x5.5 pulled 20amps max. Made 220ish Watts. The 7x6 was spiking over 45amps. Way too much draw for the motor. What possible props could I use to really use the motor? I know it’s guesswork but I need to know which to buy to test. Also should I be trying to find a prop that can generate closer to the wattage the motor is capable of? Or does it never work that way? Do you just prop for amps?
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Old 02-04-2018, 05:52 PM   #9
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Originally Posted by Mattg6o View Post
... I know it’s guesswork but I need to know which to buy to test. ...
E.g. e-Calc, Scorpion-Calc, Drive Calc will get you in the ball park:
e-flight calculators (compilation) - RCG (sticky)

Originally Posted by Mattg6o View Post
... Also should I be trying to find a prop that can generate closer to the wattage the motor is capable of? Or does it never work that way? Do you just prop for amps?
It's current you should be looking at, power (in watt) is to broad.

It is a good practice to have some headroom built in. About derating motors, controllers, batteries, electronics in general:

Vriendelijke groeten Ron
diy motor tipsDrive Calculator
diy motor groupCumulus MFC
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Old 02-04-2018, 05:52 PM   #10
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Originally Posted by Mattg6o View Post
McDonnell xp-67 e build
Gorgeous plane!

Originally Posted by Mattg6o View Post
... Im really new to electric. ...
Some well-structured reading and handy e-tools for rainy/windy days.
Will save you, and us a lot of questions. Notably the 'what went wrong?' kind of questions
Will also prevent you from burning up several controllers and/or motors and/or battery:
E-flight primer and tools

And please, do your RC equipment, wallet, ego, battery, controller, motor, house/garage/car a big favour ... get a watt-meter. It will more than pay for itself, will save you at least one fried motor and one fried controller. Will also help you finding the best setup.
Keep watt-/multi-meter wires short
too long wires batteryside will kill ESC over time: precautions, solutions & workarounds

Vriendelijke groeten Ron
diy motor tipsDrive Calculator
diy motor groupCumulus MFC
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Old 02-04-2018, 05:58 PM   #11
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Originally Posted by Mattg6o View Post
... I have an idea on motors ...
Twin motors, motors in the wing:
Extend motor wires, and keep the battery wires short. Keep controller close to battery.

Too long battery wires can kill ESC: precautions, solutions & workarounds - RCG

Contents
  • Solution I & II, rules of thumb
  • Problem
  • Capacitor type & polarity (orientation!)
  • How & where (not) to add extra capacitors
  • DIY capacitor pack pictures
  • Capacitor & pack suppliers
  • Expert/manufacturer opinions, they all say the same ... & their rules of thumb.
  • Explanation, water hammer/knock analogy, theory, references, measurements

Vriendelijke groeten Ron
diy motor tipsDrive Calculator
diy motor groupCumulus MFC
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Old 02-04-2018, 07:43 PM   #12
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Ok. You gave me some excellent advice. I was going to run longer batt leads and put the esc in the nacelles. That would have added about 5 inches. So now I ask, can I run dual motors off a single esc provided it’s large enough? And I was going to cool my esc from all the ‘cool’ cooling openings in the nacelles. How critical is esc cooling especially if the equipment is oversized? Ie. 80a esc on a 40a total draw. I suppose I can always carve cooling paths to the center of the fuse and back to the nacelle.
This is the readings with 6x5.5. The 7x6 is too much prop. I even shaved it down to 6.325 and did a quicky balance and it still pulled too many amps. The whole shape of the prop is different tho. They are both apc e series, but the 7 has a wider chord pretty much the whole way. These are reading with the prop cone on as it would be in flight.
I’m a little concerned about going down too much in pitch because I think the wing loading is going to be a little high. Calculated stall speed is about 25mph. Of course this is all theoretical. If I go down too much in pitch I’m afraid the aircraft will have a tiny flight envelope.
Thanks a lot for taking the time to help me.


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Old 02-04-2018, 08:06 PM   #13
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Originally Posted by Mattg6o View Post
... can I run dual motors off a single esc provided it’s large enough? ...
You can run two brushed motors off a single brushed ESC.
You cannot run two brushless motors of a single brushless ESC, you need to separate brushless controllers.
(It has been done though, low power levels, selected components, motors will run 100% in sync).

BTW if this were my very first electric project I would start with a simpler/easier/cheaper single motor plane, e-learning curve and all. To get some e-routine and e-knowledge.
E-motors can start all of a sudden, without warning, with full torque available right from zero rpm up to full rpm, merrily hacking away at fingers, leg, private parts, with full and unstoppable force.
Motor and/or controller can go up in smoke in an instant, without the warning you get when an IC motor starts to run lean. And once the smoke is out, you can't put it back in.

Vriendelijke groeten Ron
diy motor tipsDrive Calculator
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Old 02-04-2018, 08:39 PM   #14
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LET me clarify. I’ve had e planes before. But they’ve all been arfs or bnf. I have never done “From scratch”
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Old 02-08-2018, 02:41 AM   #15
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Another update
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Old 02-09-2018, 11:22 PM   #16
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SMALL update. Waiting on some more supplies so I go over some of the electrics I have selected, all subject to change of course.
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