scale up quadracopter idea

whatever

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There are very cheap rc quadracopters on the market using small brushed motors, I'm wondering if you could use the output that runs the four motors,
( assuming its some sort of pwm ) to run larger brushless motors, using the voltage going to the small rc brushed motors as the input for throttle control
on a large quadracopter set up.
 
yup......the idea is:
use the output to motors of tiny quadracopter : use that voltage as input to throttle wires on brushless controller ( somehow if its possible ), it might be an easy way to make a scaled up version that still has gyro/stability via the tiny boards on the tiny quadracopters.
 
It might work OK. It depends on a couple of factors, though.

First off is the fairly simple seeming one of decoding the signal to the brushed motor drive into a form that can be used by the brushless motor controllers. This seems easy, but it needs to be fast, as any delays add to one of the time constants inside the control loop. I believe some of the quadrotor builders have found that all ESCs are not equal in this respect and that quadrotors need ESCs with a fast response. In this case you also need to make sure that your decoding circuit will have an equally fast response.

The second potential issue depends on the loop constants being sufficiently tolerant that they will work OK with a bigger machine with a higher mass. I suspect you might be OK, as the problem is probably worse when going from a slower response machine to a faster response one, but there may be a degree of control overshoot because the system will be tuned to expect a faster responding quadrotor. The speed of response for these things is largely a function of size and mass, as it's primarily driven by the moments of inertia around each axis.

Sounds like and interesting experiment, though, as as some of the smaller brushed motor quads are fairly cheap, you won't lose too much if it doesn't work.
 
thanks jeremy I just read your response.
I've bought a cheap quadracopter of ebay, its an amazing bit of engineering and very tiny. The diameter is about the span of your hand.
Flying it is quite a skillful process. I"ve maybe spent 4 or 5 hours and nowhere near mastering it as yet. The brand I got is made by udi r/c .
The battery used is approx 3.7v. They say there is a 6axis gyro in it, how that works I have no idea, but it must be extremely small.
I will do some basic measurements as time permits on voltage output to motors ( I dont have oscilliscope so a bit limited in what data I can get)
I suspect using motor voltages to run a controller to a bigger system, there will be some unexpected results. The gyro certainly stabilises the tiny craft,
it would be interesting to see what happens on a larger vehicle.
I think you would be right about response times. For example, with the motors spinning at low rpm and holding the craft in my hand, simply tilting the craft
you can hear the motors rpms changing immediatly in response to hand movements ( the gyro trying to keep it stable). These tiny quadracopters are really very impressive. After seeing how many crashes I've had playing with it ( they are extremely resilient to crashes), the idea of building one that could potentially lift a human would be a crazily dangerous thing to do.
 
yup thats the idea, when I get time I'll test the motor wire voltages.
 
yes!!
measured motor signal on quadcopter its 1-4v but its pwm ( hertz unknown)
so the problem is how to connect quad motor signal to ebike controller throttle input or maybe to an esc
diagram below any suggestions??
wiring.jpg
 
Look up op-amp integrator on the web with google image search, there's a lot of schematics on how to build one; some of the electronics sites also show how to calculate the resistor(s) and capacitor(s). The idea is to change the PWM into a continous average voltage. R-C filters may also do what you want but the integrator along with an op-amp buffer can isolate the pwm output from the throttle input, which might be a good idea in case of controller failure.

Is even possible (though I don't know exactly how ATM, maybe with 555 timers in retriggerable one-shot mode) to failsafe it so if any of the PWM signals fails for more than a certain amount of time all of the throttle signals are shut off, and the copter falls straight down. (presuming that without one of the motors it cant' fly at all? if it can, then perhaps simply have it cut back the throttle on it's opposing motor so it doesn't flip).


Some multimeters have a Hz function on them, does yours? If so you can get the pwm freq. which might help with the design of the integrator.
 
Why fiddle about with this and not just get a flight control board for brushless controllers, they are amazingly cheap for what you get:

http://www.hobbyking.com/hobbyking/store/__24723__Hobbyking_KK2_0_Multi_rotor_LCD_Flight_Control_Board.html
 
Yes I've also come to the conclusion just use a quadcopter designed for esc controllers, I'm guessing all the esc controllers use the same input signals, if so it should be possible to use any size outrunner. I did a search for cheap brushless type quads but they are a bit pricey, cheapest I could find was about $150usd ( walkera brand from memory)
thanks amberwolf for suggestions, but it will be simpler to use quad with brushless esc outputs.
There seems to be so many people building these things there's bound to be somebody make one you can lift a human with.
 
amberwolf said:
You'd have to replace the brushed controllers with brushless ones, to use brushless motors.

It would be farily simple to take a toy quad and upscale it and keep the control system . The response time for a larger copter would be slower so this should still be stable. Taking the pwm signal and making it drive a 3 phase PMBM motor would be easy . I would want to use a cobalt steel lamination / neo magnets design to keep weight down as the motor weight is a good part of the total. This could be a tethered copter useful where you are not going far ...high voltage wires to feed the power might not be a good combination with whirling props.. Even if this were a drone it would be helpful for rescue work where people are trapped on a ledge or fallen down a cliff and sending down rescuers is a high risk.
 
Why would you not just order one of these? http://www.hobbyking.com/hobbyking/store/__19534__HobbyKing_Multi_Rotor_Control_Board_V2_1_Atmega168PA_.html
 
I've just recieved quadcopter with kk2 board, need to get it flying and learn the ins and outs, but the esc's/motors any size should work assuming all the escs use basically same signals ( pretty sure there are different types though), is a long term project to upscale to a large quad
 
that would be a mad thing to see :)

i just finished building my tri copter. using HK parts and a KK2.0 board.

here's a video of my maiden flight with the tri. first time it flew and my first flight with a multi rotor...
apart from the tree "incident" i don't think i did too badly.....

[youtube]Ztv6AQ1v5No[/youtube]

i am currently waiting for parts to build a second cheaper one for FPV use.
i want to learn on the cheaper airframe so i don't (hopefully) damage the glass one.....

Jason.
 
nice crash!! i've got a kk2 brushless quad flying, but I learned on small quad and the throttle was on left stick,
now I have to relearn using right stick as throttle, slow process in my case.
that tri looks almost like a cross between a plane and a copter, if the motors could rotate to horizontal once in the air, it would be fast
 
there are a few VTOL RC aircraft out there.

[youtube]IK_-yTrwNtU[/youtube]

since that flight, i have bought a cheaper (and more sturdy) alloy frame and im building a second tri to learn on,
so when i crash again, i wont destroy the glass frame in the above video...

this one in particular looks like it is fun.

Jason.
 
You should check out what these guys did... not quite the same idea, but close. They used 16 motors to lift their pilot and it worked pretty well.
http://www.theverge.com/2011/11/2/2532113/first-manned-multicopter-flight-germany
 
mmmm might accidentally create a rocket thruster for fast take offs,
I still think scaling up is very possible, the big turnigy motors will have plenty of thrust,
all the electronics is already done via the kk board, just the size will influence stability and
whether or not the kk boards can be adjusted to create a stable platform at large scale is the question.
A combination of large quadcopter and something that can glide would be safe way to go.
My thinking is use quad for lift off and landing, in flight use them for horiz thrust.
 
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