Twin Rotor micro VTOL, new project, let me know what you think!
Hey everyone, I'm looking for thoughts and advice for my project.
I have spent the last month laying down the groundwork for a micro VTOL aircraft, which can be flown indoors autonomously. I've chosen this type of platform because quite frankly,
1) My only experience flying rc helicopters is my blade msr, and considering my current lack of piloting talent, I want to avoid large dangerous rotors and expensive crashes,
2) I believe that current twin rotor designs can be successfully scaled down into the micro size, as long as every component is optimized for this exact application,
and
3) I am interested in designing my flight controller completely from scratch, so my options are further expanded.
I will be using two brushed motors for initial prototyping. If I need greater RPM control I will move to brushless. I will be using an ARM7 microcontroller (or simmilar) which will have serial out (am I wrong in thinking that rs232 is the lightest/most supported interface?) and accept the inputs from my sensor package. I'm not gonna kid you guys, my only experience programming microcontrollers is from a few day experiment with a STAMP Basic 2. However, I'm not too concerned, I figure I can borrow code from Arduino, right?
Either way, ignoring my lack of programming experience which is limited only to what I learned in college, I have a considerable amount of experience using LabVIEW. I hope that this will jump start data acquisition + interface development, and I should be able to port my VIs into the ARM7 with a little luck...
Looking at what's out there commercially, I have not found an ARM7 board that is minimalistic enough for me to buy outright. So I'm planning on etching my own PCB at home. *crosses fingers*
I'll skip over the boring circuitry stuff and get to the cool part, the actual UAV design!
Both motors will be boom mounted and will rotate independently in 2 axis. Motor speed will be variable and independent of one another, of course, providing the third axis of control. Plan B: if the former proves to not work for a multitude of reasons, the two motors will be linked together on a single boom so they rotate forward and back dependently, however then I will lose the ability to spin on its Z axis.
I plan to hang the circuitry and batteries between the two rotors, to maintain a central and very low center of gravity. This will hopefully provide some stability on it's own.
Autonomous flight control will use parallel processing to sort and categorize data, from which my main flight control program will read this streaming data.
I'll stop explaining here, and open myself up to your opinions.
What do you think?
Just in case I did a poor job explaining my airframe design, look here for a commercial example of a twin rotor VTOL.
I have spent the last month laying down the groundwork for a micro VTOL aircraft, which can be flown indoors autonomously. I've chosen this type of platform because quite frankly,
1) My only experience flying rc helicopters is my blade msr, and considering my current lack of piloting talent, I want to avoid large dangerous rotors and expensive crashes,
2) I believe that current twin rotor designs can be successfully scaled down into the micro size, as long as every component is optimized for this exact application,
and
3) I am interested in designing my flight controller completely from scratch, so my options are further expanded.
I will be using two brushed motors for initial prototyping. If I need greater RPM control I will move to brushless. I will be using an ARM7 microcontroller (or simmilar) which will have serial out (am I wrong in thinking that rs232 is the lightest/most supported interface?) and accept the inputs from my sensor package. I'm not gonna kid you guys, my only experience programming microcontrollers is from a few day experiment with a STAMP Basic 2. However, I'm not too concerned, I figure I can borrow code from Arduino, right?
Either way, ignoring my lack of programming experience which is limited only to what I learned in college, I have a considerable amount of experience using LabVIEW. I hope that this will jump start data acquisition + interface development, and I should be able to port my VIs into the ARM7 with a little luck...
Looking at what's out there commercially, I have not found an ARM7 board that is minimalistic enough for me to buy outright. So I'm planning on etching my own PCB at home. *crosses fingers*
I'll skip over the boring circuitry stuff and get to the cool part, the actual UAV design!
Both motors will be boom mounted and will rotate independently in 2 axis. Motor speed will be variable and independent of one another, of course, providing the third axis of control. Plan B: if the former proves to not work for a multitude of reasons, the two motors will be linked together on a single boom so they rotate forward and back dependently, however then I will lose the ability to spin on its Z axis.
I plan to hang the circuitry and batteries between the two rotors, to maintain a central and very low center of gravity. This will hopefully provide some stability on it's own.
Autonomous flight control will use parallel processing to sort and categorize data, from which my main flight control program will read this streaming data.
I'll stop explaining here, and open myself up to your opinions.
What do you think?
Just in case I did a poor job explaining my airframe design, look here for a commercial example of a twin rotor VTOL.
Replies to This Discussion
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Permalink Reply by Jonathan Lussier on -
Hi Jeff,
I recently ordered the ARM7 dev board (http://www.futurlec.com/ET-STM32_Stamp.shtml) so I'll see what its like. The main benefit is that you can use xduino code (arduino-like functions).
I'm interested in a micro quadcopter (horizontal flight biplane/vertical flight landing/takeoff) using the same ARM7 CPU but on a custom board with integrated gyro and accel and compass (yaw). I should work on an Eagle layout with the cpu and accelerometers this weekend, I'll let you know how it goes.
Mechanically, the only issue I'd say (I saw this on an RCGROUPS post regarding an avatar-like r/c heli) is that the torque of your tilt servos will act negatively on your chassis, IE: the body will tilt instead of the rotors. At higher speeds it's more negligible since the rear H-stab will have an aero influnce (mainly drag).
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Permalink Reply by Jeff on -
Let me know if you like the board, it looks like a nice set up.
I agree that the gyroscopic forces from twin rotors will be difficult to overcome. I appreciate the advice on that. The reason I chose 2 rotors over 4 was to increase maneuverability in a smaller package. I may have a solution to this, but I need to run the math. What if I switch to heavier brushless motors and mount them between the two rotors, in the center of the airframe? The gyroscopic forces of the axial mounted motors might overcome the rotors. Or maybe not. I'll be looking into this today.
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Permalink Reply by Jeff on
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wait. by linking the rotors to roll in and out, I can control the pitch of the entire craft. I was planning to control roll by varying rotor speed, however that will cause additional gyroscopic forces, so I may need to incorporate variable blade pitch. I can control yaw by tilting one rotor forward and another backwards.
am i missing anything?
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Permalink Reply by Peter Seddon on -
I am surprised you will need the computing power of an ARM when the Tricopter and Quadrocopter both 'fly' using an Arduino 328p platform. My Tricopter (http://shrediquette.blogspot.com/) uses only 50% of the 328p programme space.
The smaller the physical size the greater the control and stability problems and the higher the performance of the control loops. I would be looking to use brushless motors and possibly digital servos.
I would have thought yaw and roll are controlled by tilting both the rotors (same and opposite directions) and pitch by the differential speed of the rotors.
Good luck and let us know how you get on.
Peter
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Permalink Reply by Jeff on
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That is a fantastic tricopter! Very nice work. I will be checking your blog often to see how it is going, and also to read through your development.
I had chosen the ARM7 because I'm going to be using some fairly complicated flight control loops. However as I said above, I do not have much experience in the microcontroller world, so I am open to suggestions. I will check out the atmel 328p tonight.
I don't think I'm reinventing the wheel with flight control, but this is my understanding of the flight control. please direct me if I'm mistaken:
(Right rotor CC, Left rotor CW:)
gyroscopic Pitch (nose up/down): Tilt both rotors inwards, gyroscopic forces pull nose up
thrust Roll (roll left, right): Increase rotor speed on left rotor, airframe will roll left (and possibly yaw nose left)
gyroscopic roll (second choice): Tilt right rotor forward, gyroscopic forces will roll aircraft left
thrust Yaw (rotate left/right): Tilt right rotor forward, left rotor backwards: yaw CC nose left, gyroscopic forces cancel out)
I have two identical brushed motors that were main motors from two ultra micro RC toy helis. I might start with theses just to save some cash$$, but I appreciate the advice on the brushless motors.
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Permalink Reply by hypergolic on -
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