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08-03-2011 06:12 AM  6 years agoPost 1
rtdillon

rrApprentice

Huntsville, AL

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Folks,

I started conversation in another thread about building a LARGE quad copter for AP work. I will paste my other posts into this thread, and I invite input.

Right now this is an intelectual design conversation. all positive ideas and constructive criticism are invited.

No,No..The other left!

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08-03-2011 06:13 AM  6 years agoPost 2
rtdillon

rrApprentice

Huntsville, AL

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1ST post in other thread
Gentlemen,

I am considering building one of these with 4 of the rimfire motors designed to replace a 65cc gasser. Each one swings a 26x12 prop. It will require 160amp ESCs.

Other than the obvious dollar risk, am I crazy?

Ok, ok, unusually crazy. My goal is to lift about a 25 lb payload for a 4-5 minute flight.

No,No..The other left!

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08-03-2011 06:15 AM  6 years agoPost 3
rtdillon

rrApprentice

Huntsville, AL

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2nd Post on other thread in response to comments
Joel

I am probably going about this backwards. Basically I looked at the largest electric motor that was not scary expensive, and it requires a 160 amp ESC. It runs on 12s 5000 mah packs. Each motor puts out up to 6500 watts constant and can burst to 8400 watts. That is 26 Kw of power.

243 oz total battery weight.
209 oz total motor weight.
80 oz total chassis weight (estimated).
16 oz total electronics weight (estimated).
34.25 lbs estimated weight without payload.
25.00 lbs payload goal.

Which works out to about 270 watts per pound.

I have not found recommended power per lb information yet. Any input?

No,No..The other left!

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08-03-2011 06:16 AM  6 years agoPost 4
rtdillon

rrApprentice

Huntsville, AL

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Replies
I have a few replies in the other thread and will copy them here once I receive permission from the originator.

No,No..The other left!

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08-03-2011 06:22 AM  6 years agoPost 5
rtdillon

rrApprentice

Huntsville, AL

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Parts under considerations so far
VOLTZ 5100 mah 65C 6s packs 2 per motor, 4 motors so 8 per flight.
Rimfire 65CC motors
CC 160 amp ESCs, 4 each
custom build chassis, 80 oz or less design goal.
control electronics still under evaluation, recommendations?

No,No..The other left!

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08-03-2011 04:37 PM  6 years agoPost 6
GyroFreak

rrProfessor

Orlando Florida ...28N 81W

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You have my permission to copy any of my comments/posts in any thread. This will be very interesting. I will be following this thread.
Thanks
Paul - Gyrofreak

I think about the hereafter. I go somewhere to get something, then wonder what I'm here after ?

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08-04-2011 07:13 PM  6 years agoPost 7
rtdillon

rrApprentice

Huntsville, AL

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Joels reply from the other thread.
RTDillon,

There are a number of ways to design such a beast. It's an iterative process, and it depends on your constraints.

For example, you could choose to constrain your motor selection to a given motor, which will then dictate the optimal cell count for the optimal RPM with the optimal propellor for the optimal thrust. Once you determine the thrust with that setup, you can determine the all up weight of the system (assuming an airframe weight and electronics weight as you have done), and see how much thrust remains for lifting your payload. I think you'd want to design the system so that it had a 30-50% margin available for lift beyond the weight of the airframe and the payload.

Let's say the aircraft really does weigh 60lbs. If we say it has a lift target of 200 watts/lb, that means it's going to consume 60x200 = 12,000 watts. At 12S, that's 270A total. The load is spread to 4 motors, and 4 ESCs, which is only 67.5A per motor/ESC. 12,000 watts spread over 4 motors is 3000 watts per motor.

If we agree that 200 watts/lb is as much as you need, then you can actually use smaller motors, and smaller batteries, and smaller ESC's to keep the weight of the system down. This will reduce the power consumption of the system. So you can repeat the exercise by figuring out the weight of the system with smaller motors.

By your calculations, you have 15lbs of battery. If we assume ~700g for the 6S 5000 battery, you seem to looking at carrying about 10 batteries, so a 12S 5P setup.

The 12S 5P 25,000 mAH setup can provide 20,000 useful mAH capacity. If you consume 12,000 watts, this battery system can provide power for
20,000mAH / (270A * 1000mAH/AH) * 60min/H for 4.44 minutes.

If you assume that it's really 270 watts/lb, then you're talking about consuming 16,200 watts, 365A, and 3.28 minutes flight time.

It is true that you'd need to find pusher propellors to match. So make sure you can get them (or make them if you must) before you get too deep into it.

I had thought about doing this sort of large multirotorcraft a different way though. I think that using 2 bladed flybarless rotor heads would be excellent for this purpose.

I fly some relatively large helis, like my 40lb Air Crane, which has a 6 bladed head, 2000mm disc. It uses a NEU2230 2Y motor, which is capable of 10,000 watts. But, I actually only consume 1950 watts flying around. In general, nearly all of my scale helis consume ~50 watts per pound. My sense is that you could use rotor heads, and budget 100 watts per pound, and have a craft that works beautifully.

There is more mechanical complexity if you choose the rotor head route. You need servos to change the collective pitch of the blades. If you make the servos all move the same direction, then you don't need any special electronics to handle the collective pitch, because no mixing would be required. You'd simply have all servos for a given head connected via a Y harness, and "throttle" would control blade pitch. And real throttle (RPM) would be governed by the ESC and set constant.

At any rate .. I think it's quite doable. And perhaps, you can make the airframe / motors smaller than you think, which will use less power and require fewer and lighter batteries. It all helps.

Joel

No,No..The other left!

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08-05-2011 06:36 PM  6 years agoPost 8
Joel Rosenzweig

rrVeteran

Marlborough, MA - USA

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RTDillon,

Any more thoughts on what you plan to do?

Joel

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08-06-2011 04:18 AM  6 years agoPost 9
rtdillon

rrApprentice

Huntsville, AL

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Work got in the way! :-(
I have to obtain funding first. It will be almost $2000 for the motors and speed controllers. I have a friend interested in purchasing my 700E and that will fund the power system. I am going to stay with fixed pitch at first to keeps things simple.

Any recommendations for the control board? I don't need exceeding agility, more rock stable. A GPS Position hold would be a nice feature too!

I am thinking the first attempt at a chassis will be from plywood or 4" square PVC pipe. Not lightweight but it should help get the physical design worked out and prove the concept. Any suggestions?

Once operational I can design another chassis that is lighter and stiffer.

I have a camera platform available from a friend that will allow Pan and Tilt, now i have to figure out zoom. That depends upon the camera.

Folks were talking about needing pusher and puller props. I don't understand, why would I need pusher configuration?

No,No..The other left!

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08-06-2011 04:33 AM  6 years agoPost 10
Joel Rosenzweig

rrVeteran

Marlborough, MA - USA

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On a quad, two motors turn clockwise, and the other two turn counterclockwise. This is done in order to balance the torques between the 4 motors so that it is stable and controllable.

Because two of the motors are turning in the opposite direction, they need propellors that were design to turn that way. Hence the need for both types of props.

Now if you went with rotor heads, you'd still run them in opposite directions like the props, but you'd use symmetrical blades, so you wouldn't need special rotors.

I think that PVC is not going to provide enough rigidity for this application. Plywood might work, but it will be very heavy. Your best bet would be to use carbon fiber sheet.

As far as controllers go, there's the MultiWii series (like the Quadrino), the KK board, and others. They are inexpensive, but don't feature GPS loiter capability.

There's the ArduCopter controller which does feature GPS loiter capability. It's more expensive, but might be a good option.

There's the MikroKopter electronics flight controller and navigation system. It features excellent stability and GPS loiter. It's about 3x the price of the ArduCopter.

There's the HoverflyPRO + GPS that promises to do the same, but the GPS option has yet to be released (to my knowledge). I think it's planned for release in September.

I use the Quadrino, which I have found to be very good. But it has no GPS capability. But it does have auto-leveling, which is really quite good.

You might consider building a smaller quad first to get a handle on the flight control system before you try the big one. It might help you avoid some costly mistakes.

Joel

Joel

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08-06-2011 03:16 PM  6 years agoPost 11
rtdillon

rrApprentice

Huntsville, AL

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Good Point
You have a good point. I am considering starting smaller. I also have to go look fo 26" Pusher props...if available.

No,No..The other left!

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08-06-2011 03:29 PM  6 years agoPost 12
rtdillon

rrApprentice

Huntsville, AL

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Zinger to the Rescue
Zinger has all of the prop sizes in both configurations I could possible need.

No,No..The other left!

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08-07-2011 02:33 PM  6 years agoPost 13
rtdillon

rrApprentice

Huntsville, AL

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Costs
Analysis of the costs has taken this idea beyond my budget limits.

269.99 x 4 Rimfire 65cc
271.98 x 4 160 amp CC ESC
191.00 x 8 Voltz 6s 65c 5000mah batteries
51.80 x 2 Zinger 24x12 pusher props
37.65 x 2 Zinger 24x12 puller props

or

1079.96 motors
1087.92 esc
1582.00 batteries
178.90 props
3928.82 Subtotal

This does not include the chassis or electronics.
Then one still has to add in the cost of the video system, meaning the video mount and controls.

This is technically feasable but not economically justifiable. I'm crazy but not stupid.

No,No..The other left!

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