avgrech

hello everyone i`m havingtrouble making up a way for connecting 4brush-lessmotors together for trust obviously thebrush-lessmotors are of 29 A each should i buy 4 speedcontrollers(one for each ) or can i buy 1 80 A speedcontrollerand connect them to the 80 A can any one help pls?

bobferguson

You need four speed controls for brush-less motors..

BMatthews

Yes, you need four separate controllers.

Brushless motors are actually 3phase AC motors. The controllers chop the DC from the battery into 3 phase AC power and vary the frequency and phasing using feedback from the motor. Because of this you can only run one motor from one controller. If you tried to run two motors on one controller it would see conflicting feedback on the three power lines and really bad things would happen.


With the brushed motors it is different. THose are plain DC motors and do not require the same critical timing from the controller. So if you use brushed motors you can run more than one from a single controller.

avgrech

would it work if i put a diode (one way valve ) on the 3 wires going to the motors to stop them feeding back to thecontrolleror will i still do damage???
any way 10x alotfor the help!!!!

BMatthews

NO! ! ! ! It will not help at all. The motors will either not run at all or you will burn out the motors and ESC. With brushless it is one motor per ESC. There is no way around that.

You need to have an idea of how a brushless controller works to understand this. Only two coils are actually powered at any one time. The ESC monitors the third coil to sense the rising voltage that it generates as it passes by the magnets. It uses that to determine the RPM the motor is turning and when to switch each of the three phases on and off to power the motor. But it can only do this for one motor at a time. If you try to put more than one motor onto the controller you will just confuse it and the ESC will try to switch phases at the wrong times. At the very least the motors would run poorly or at all and at the worst you'll burn up the motors and the ESC.

Maybe now you also realize why adding diodes to the wires would be a bad thing. For starters because the ESC converts the DC to AC you would not get power through the diodes in some directions when the switches are set for the reverse polarity. On top of that the diodes would distort or block the weak generated voltage that the ESC requires to sense the RPM and rotor position to know when to switch polarities and activate each phase.

avgrech

OK so .... 4 20 A speed controllers it is! no next problem how do i connect them together to make it go to only one port not to 4 different ones ?? sry for the trouble !

BMatthews

This is where it'll get sticky. If this is for a 4 engine model then you still need to get the power out to the motor nacelles. But the ESC wire is not long enough. Also with the high current levels you want to use thicker wire to ensure you do not get a voltage drop from the longer than normal power runs to the outer motors. A nice and inexpensive way to do this is build your wing with built in power buss bars. A good option that is cheap is to get some #12 or #10 solid or stranded house wire to use as the main buss bars that run in the wing from the center to the outer nacelles. In addition you'll need to get some servo lead extensions to reach the ESC's mounted in the motor nacelles.

There's another issue as well. Each ESC has a battery eliminator regulator in it that feeds power to the receiver and servos. But they will fight each other if you leave them all connected. The way around that is on THREE ONLY of the ESC's you clip the red wire of the servo lead that comes from the ESC's. Or if you're good I would suggest using a small pin to gently lift the lock for the pin in the connector and extract it out so it can be used again. Slip a small bit of heatshrink tubing over this pin to protect against short circuits. By lifting out the small red lead of three of the ESC's and only leaving one connected you will be running the radio system from the power from the one ESC so there won't be any conflicts. And since you need to use servo extension leads to get from the receiver to the ESC's in the motor nacells lifting the pin or cutting the leads in the extensions would allow you to leave the ESC wires alone.

doxilia

My Feedback: (3)

All excellent advice but if I may make a comment about multi-motor setups, I'd all together get rid of powering the radio system via the ESC BEC. If you're using 4 motors then there's a chance you are building something scale and will likely also need several servos. If on top of that you have a largish model (could be up to 60-70" span from what you describe), then these servos may be standard size or even digital (i.e., more power hungry).

In short, forget about onboard ESC BEC's on multi motor setups. Remove all the power leads from the ESC's (or extensions) radio connections. Your ESC will act as rheostats alone now. Then, in your power (lipo) circuit which can be fed by one or several batteries (in series or parallel or both), introduce a separate BEC such as Castle's 10A or 20A BEC Pro. This will provide more than enough punch to drive the radio system. If you wanted to go a step further, you could plan for a separate radio battery all together. LiFe cells are nice, reliable and light. Depending on their chemistry (say for A123's) you can use a voltage regulator to bring them to a constant 6V if you like. If you do, you'll be happy you introduced a diode to your on board electronics! If you use LiFe's just make sure you never let them get close to the edge of discharge, they will head off the cliff like you won't believe and 4 motor aircraft make nice holes in the ground... [8D]

Have fun and show us a picture of the model!

David.

avgrech

well i was going to do a version of the Jupiter k3 aerofoil but with straight wings instead of bent back as a friend of mine sad that it`s harder to fly when there angled back so i taught use a lot of power and make it a cargo plain even do a couple of jokes by putting stuff inside and dumping it in mid air on someone or something hehe that is what i want to do. here is the Jupiter k3 :http://www.youtube.com/watch?v=2FQ4F...x=5&playnext=3     

BMatthews

Angling them back slightly isn't any big deal. But make it straight if you wish.

If you're looking to make a slower flying cargo style model use an airfoil with a higher value for the camber. Something in the 4 to 6% camber range would be good. The model won't be fast with such choices but it'll fly better when carrying a payload. And it'll lift off and fly at slower speeds than that Jupiter K3.

avgrech

so i can use the Jupiter plans and just make a better aerofoil and it would be good for flying ??

BMatthews

I would say yes to that with some reservtions. The Jupiter doesn't have a lot of wing area. It's setup to be pretty close to a transport jet airliner in appearance. But airliners cruise at higher speeds so they don't need as much wing area as a slower flying load carrier. And generally our models can deal with slow flying since we need to keep them in sight for visual reference to fly well. In that way you'd be far better off with something more resembling a C130 Hercules. Or possibly the old C119 Flying Boxcar ( http://www.the-blueprints.com/bluepr...flying_boxcar/ ).

For an airfoil intended for load carrying and slow STOL style flying I'd suggest going with something like a Goettingen 501. This deeply undercambered airfoil looks like it has flaps that are perpetually deployed. But an 84 inch old timer I have with this airfoil flys very nicely. I think it would be an excellent airfoil for a model intended to fly around at a slower speed for camera work or other precision load carry flying. Or perhaps split the difference and use something like the Selig S4310 or SD7034. Any of this last series would produce a nice high lift coefficient without acting like it has a parachute attached to the model.

The Jupiter as built and flown in that video just didn't seem to want to slow down well at all. Not what I'd want for an aerial photography platform or for a model intended to drop lightweight payloads for fun. And likely not a great choice for any sort of heavier instrument packages either. The rise in the landing speed from a heavier load combined with a rise in the stall speed using the airfoil of that wing they used would likely result in some tendency to stall easily and drop a wing during the landing approach. Not something you want if there's a lot of dollars of payload on board.

avgrech

i just want aslow flyinghuge cargo plane . i liked theJupiterbecauseof it`s size and relative simplicity to build. (i like to drop things on peoples heads hehe)
so i was thinking to do the same length along the preplanned wing (angled) and them make it a straight wing. they might be a bit huge but i dint think that its a problemhavinga wingspan too big or is it ?
(on the picture the same colored lines the same lengths)

BMatthews

The wing would not just be made straight. If you do that the nose will be too short and it'll require too much nose weight.

avgrech

so i imovethem back tat a bitfurtherin front than the middle ??
wouldit work then?

BMatthews

It would be easier to balance if you did that. But truly from what I saw of that video it's just not a good slow flying design. It's a bit of a racer in fact. I think you'd do much better with something else and just modify it from being a single to a twin or four motor design.

Would you build it yourself from scratch or get an ARF and modify it? If you'd build it yourself what materials are you the most comfortable to work with? How much of a payload do you want to be able to carry aside from the model, radio gear, motors and battery pack(s)?

What brands and designs are available in your part of the world since you're living in Malta? Some links to the companies would help.

avgrech

well if anyone knows a good freight plane design please tell me , i want to carry about 1 kg at max, i Malta it is much better to buy fromeBayand so as from the local shops the parts because a lot more,imaginewhen i wanted to but my first airplane the guy wanted to sell me a gas trainer pane of almost 2meterswingspan for the price of 590eurosthat is about 800 usdollars you can justimaginethe rest and he absolutelydid not want me to go electric but when i went to the club they told me to ignore him and they told me to never buy from him or anyone else in this country as most of themboughtand ended updisappointedwith thepriceto quality ratios .

avgrech

i did some moreresearchand i found these :http://www.youtube.com/watch?v=2yxJG9YuiYE
what do you think of them and if i double the size as i want thembigger, what do you think better ???

BMatthews

The way that one flies is far more what you want an unloaded cargo plane to fly like. It'll get doggy and faster enough with the payload added. No need to start with something that is fast and has high flying speeds before any payload is added.

That one you provided the link for is a simple box style model made from the 7mm thick blue styrofoam that is sold in the USA for insulting laminated wood flooring set down over concrete. While it's a nice design you'll need something more structurally solid for carrying a 1 kg load. Also you'd want to have a wing that is more than a single 7mm curved sheet. So I think you may need to start from the beginning and design what you want. Or perhaps find a plan for an aerial photography model and modify it.

avgrech

ok so you have struck myimagination i would like to make my own , what do i need to watch out for to make my own design and are there anyratiosto wing sizes or anything of the sort???
i like the idea you gave me !!!!!!!

BMatthews

THAT'S THE SPIRIT! ! ! !

First off to carry a 1kg payload and to also fly reasonably slowly the model will need to be fairly large. Something in the range of 1.5m (60 inches) to 2m (78inches) wingspan. To nail this requirement down further start by assembling the sort of payloads you expect to carry and actually weigh them instead of just guessing. A kilo is actually a LOT of stuff when you stop and think about it. If it turns out that your airborne camera and a couple of balsa parachutists are actually closer to .6 to .7kg then that means a lot and suddenly the idea of a 1.3 to 1.5 meter span becomes very doable. As for dropping things simple considerations about safety says that they should be light. Again this means that your payload may well be lighter than 1kg.

Along with weighing your intended payloads also measure their size. The fuselage cargo area will need to be sized to match this aspect.

These are all the basics that you/we need to nail down first before you even bother to think about what the size will be, what it will be made with, powered with or even what it will look like.

At this smaller size range you can expect an airframe and related equipment weight of around 1 to 1.2kg if built with care and clever design choices. Lighter structures will need to be used and this often means a change in how you build things but it isn't hard to accomplish. Even lighter would be entirely possible for someone with more building experience but since I gather you're very new to all this we won't try to make you run before you walk.

As a start check out the links to design tools in the sticky thread in the Aerodynamics forum. Also there are a few similar links in the sticky at the top of this page.

You don't need to know EVERYTHING either. There's this very valuable design trick called "plagarism" that has worked very well since the dawn of time. Find a model or full size aircraft that has a fuselage shape large enough for your needs. Then use the wing and tail areas scaled to your own size. There may be some minor changes needed but often they are all more about what structure you wish to use than the wing and tail areas. The only big deal in most cases will be the need to slightly reduce the vertical tail area in some cases. Our model designs tend to operate with a more reward CG location and if left alone the combination of the rearward CG and large vertical tail area can make the model slightly spirally unstable. This means that in a steeper turn the model may want to try to tighten the bank angle and wind harder into the turn.

For a prototype I would also suggest staying with something that has a high mounted wing. This will increase your stability to a high degree. It also makes it easier to produce a way of holding and dropping your payloads.

avgrech

well as building experience and knowing how to make stuff it`s not much of a problem as my father is an engineer my bro also something of the sort and i`m flowing in their footsteps, we have just finished doing a model boat in wood so that took us about 2 weeks but i had school and stuff, and dad is a teacher at my school so he could not do anything , and so.. , what i mean to say i think we know how to make stuff and we have most of the tools and so....

BMatthews

For your first own design don't complicate the task. Keep it simple. Later on you can mess around with anhedral, sweep and gyros if you want. But for now stick with the overall shape of a C130 Hercules or C-160 Transall. Straight wings will avoid a lot of complex structural issues and at the same time will better ensure that you end up with an easier to fly model.

What other models have you built from kits or from scratch and what materials did they use? I'm hoping that you'll say "a couple of wooden sailplanes" because the methods used in the wings and the emphasis on light weight are what you'll want for your load carrying twin. I know you say that your family has a lot of tools and engineering knowledge. But designing and building lightweight model airplane structures is very specialized and that only comes from some experience with building models.

In any event the key to a large but lightweight model is to build a lot of air into the structure. This means using lightweight built up wings and tail surfaces. The fuselage must also be built up with a skin that is mostly self supporting to be able to leave room for the payload. All of this requires careful design and a good amount of past experience.

As far as water balloons go please don't plan on dropping anything such as that onto anyone. Water balloons from up close are great fun. But when dropped from 50 to 100 meters they are falling fast enough to cause serious injury if they hit someone. I remember reading some years ago about pranksters throwing water balloons off a tall apartment building. Car windshields were smashed. And a person that got hit on the head received a concussion and permanent neck injury from the impact. Water isn't soft when it's moving at a high speed. Dropped out on the runway water balloons make a great looking "explosion" but stick to dropping them out there and not onto cars or people.

avgrech

Ihave a bit of bad news. i have neversuccessfullymade anintentionallyflying aircraft, what we havesuccessfully done is other typer of thing that have flown unintentionally like a boat and a car with no radio!.

i`d like to use lots of foam as i have just bought a couple of massive sheets of the stuff but i don`t have any balsa wood , but i got second best as i got pine wood that i can make as thin as .5 mm thick , but itwould n`t be very strong obviously , i also got the tools to make them in irregular and regular shapes very precisely.

we have used thismethodto make aclassiclooking boat by cutting 10mm by 300mm by 1.5 mm thick strips to cover the bottom of the boat. in thecaseof a plane i can cover it with a tin film of resin that looses 75% of it`s weight and be very strong.

from those two aircraft i`d prefer theC130 Hercules, so is there any done plans to just do so therewould n`t be a problem of me doing a bas plan ?

BMatthews

In that case I'd suggest you back off and look at some single motor trainers. You need to walk before you run and learn to fly before you tackle a big payload carrying model.

For getting into flying models you can use the pine and foam. Many foam core wings are built using a wood veneer that is about .7mm thick to cover the wings instead of balsa. When used in large sheets like this and with the support of the foam under them the final structure is actually very strong. Not strong for local stress loads such as landing gears but more than strong enough for wider spaced loads such as G loads from flying.

And there's no reason why you can't build "normal" wood frames using pine if it is knot free and you can get it in various thicknesses. You just need to make the wood thinner than balsa and provide more formers and stringers to properly support the pine. Done well the weight penalty for an all pine model is not all that bad. In prewar Germany and in wartime England and the US when balsa was needed for life vests and emergency life rafts modelers built many good flying designs using pine or similar woods.

You can also use that foam with some easy to add skins for strength. I had very good luck some years back using newspaper over foam to produce control line combat models. I was amazed at how strong and light the results were. But before you can do this you need to figure out and assemble a hot wire cutting rig and get ready to cut up that foam into wing and tail cores and form a fuselage to work with.

There's no need to forget about this idea of a payload carrying big twin or four motor model. You just need to put it to the back of your mind for a couple of seasons while you learn to fly and master some other simpler designs first.