Need expert opinion..

yuzri1984 · Oct 23, 2009, 12:19 PM

Hey all.. i new to this forum and to this VTOL interest. Im polytechnic Aeronautical Engineering student in Singapore and currently building a dual rotor VTOL for my final year project.. Please advise what can i do to make this model to be as stable as possible. Currently, im having problem with stability. The masking tape are just a temporary fix to hold those components.

NighthawkF-117 · Oct 23, 2009, 04:31 PM

First Fix masking tape on the shaft that hold the motor, that could be causeing vibrations. Second make sure that is level with the ground. Then add a gyro, here is a cheep on...
http://www.xheli.com/esky-gyro-ek2-0704b.html#
I have had luck with it on my helis. Next do you have a v-tail mixer between the two throttles/ESC? If not put one to the two output cables of your ESC and plug into the rudder and Throttle channel on your resiver. This will give you yaw. Then add the gyro between the cord that comes out of the v-tail and into the rudder port on your resiver. Now you have control for throttle and yaw. (if not plug another gyro into the V-tail and throttle port on the resiver like as the rudder).
Then you will need some form of pitch if you want to hover in a certin area. To do this i would add a servo to the boom that holds the motors so it will pivit forward when you push the elevator stick forward and will vice versa.
Hope this helped! Good luck!

Brandano · Oct 23, 2009, 05:34 PM

What are you using to control pitch? If the CG is close to the pivot axis you might not have enough pitch authority to control it with tilt alone. Full size tiltrotors either have a full cyclic or use a tail rotor- Also, gyroscopic effects will tend to keep the rotors horizontal while the fuselage tilts up and down.

RCvertt · Oct 24, 2009, 03:30 AM

Quote:

Originally Posted by yuzri1984

well i was suggested by my project supervisor for pitching we got to use a weight...

Not sure but I'm guessing you'll still need a gyro to control the weighted servo.

I would try using your battery as the weight if you choose that method. Sounds a little scarry and inefficient though compared to tilting the motors since you'll need enough empty room for the weight to move around in.

yuzri1984 · Oct 24, 2009, 05:31 AM

well i was suggested by my project supervisor for pitching we got to use a weight(think of a barbell attached to a servo) to do the pitching. so to move forward we jaz tilt the weight to a forward position and vice versa. its more like moving the cg. is it feasible guys ? i intend to have the rotor fixed rather than tilting it.

yuzri1984 · Oct 24, 2009, 09:17 AM

i see.. okey, will update u guys soon. thanks for the help.. if u got further suggestions, please do tell me yah..

Brandano · Oct 24, 2009, 05:22 PM

the moving weight will work within a range of tilt from the horizontal, but will add overall weight and won't work in extreme attitudes. Weight is at a premium in VTOL crafts. You could be better off swinging the rotors forward and back, effectively using the whole fuselage as a weight for pitch control

v22chap · Oct 25, 2009, 09:49 AM

A quick and simple pitch control could be done with using a smaller prop / motor on the tail behind the elevator much like the Canadair VTOL

Good luck on your project

Here is the url to this site to download the pic so you can make it bigger CL 84 pix

pakrat961 · Oct 25, 2009, 03:15 PM

I don't know if you've ever heard of Gary Gress, http://www.gressaero.com/

He's got a very similar design, and it performs quite well. But instead of using weights-shifting for pitch, he uses the gyroscopic effects of the counter-rotating props to induce pitch-forces.

Basically, because of the counter-rotation, if you tilt the motor&rotors towards/away from one another, the resultant gyroscopic forces will cause the craft to rotate about the pitch axis. It's not trivial, but it definitely saves you the weight of a big swinging pendulum. All you need is one or two servos to tilt the motors inward/outward.

He's got a patent on the concept, but if you're just using it for a project (not selling it, competing with him) you should be fine. :P

v22chap · Oct 25, 2009, 03:28 PM

I had forgot about him ,,, I have talked with Gary since about the first day of his first bird .... and some where I have a set of plans that he gave me ,,,but I sure can't find them now after about 10 yrs ... :O
But he does have plans that he will sell you for that bird at 19.95 ,,, he even has the motors and mixers and all the build materials listed to build it ,, or even buy the complete kit ....

Gary 's plans for the micro vader

I still think your best bet now is the 3rd motor on the back ,,, maybe not all the way at the back ,,,maybe right in front of the elevator / rudder ... like Gregg Covey's cessna VTOL project found here . Gregg's is more like yours and he shows you how he builds it too .

Good luck and keep us all posted how it goes .

Greg Covey

NighthawkF-117 · Oct 25, 2009, 04:48 PM

[quote=v22chap]I still think your best bet now is the 3rd motor on the back ,,, maybe not all the way at the back ,,,maybe right in front of the elevator / rudder ... like Gregg Covey's cessna VTOL project found here . QUOTE]
I second this. Sounds easy. You might not even need a ECS.

yuzri1984 · Oct 26, 2009, 10:05 AM

so we tilt it towards/away from each other instead of the norm forward/aft direction? ok, dats something enriching..hmm.. u got any ideas on the mechanisms to tilit rotor? my imagination is poor..

v22chap · Oct 26, 2009, 10:42 AM

Yuzri
Gary Greese's idea is using the helicopter precession idea .... Take a toy gyro and spin it up and then push it lightly from the back and see what direction it goes ...then push it from the side and see what happens ( it will tilt the opposite direction you pushed it from ).... this is his control mechanics . The motors set in a 4 gimble axis so they can move any direction .

I would really suggest stay with the simple setup you have and add the 3rd motor/ esc / and gyro's to keep it simple as Gary's setup is hard to do let alone understand and you already have most of the things you need and built for the other way,,, which should get you in the air and get a good grade with minimal work .

yuzri1984 · Oct 26, 2009, 11:35 AM

thanks v22chap..im kinda unsure which setup to use actually.. appreciate all the suggestions and stuff. ill update my progress wif ya guys.. oh yah, was told by my project supervisor dat my project will also be entering a flying competition, with obstacles and such.. i got a pdf file of it.. do feel free to browse them guys..as always, ideas n suggestions are welcomed.

Brandano · Oct 26, 2009, 06:46 PM

I agree with V22. Tricopters are a tried and tested setup, and this field is fraught with the unknown and unexpected as it is. It's already a challenge to get something like this to hover reliably, let alone fly through a course, so go for the configuration that gives you the greatest chance of success

Oct 23, 2009, 12:19 PM	#1
yuzri1984 Registered User Join Date: Oct 2009 Posts: 7	Need expert opinion.. Hey all.. i new to this forum and to this VTOL interest. Im polytechnic Aeronautical Engineering student in Singapore and currently building a dual rotor VTOL for my final year project.. Please advise what can i do to make this model to be as stable as possible. Currently, im having problem with stability. The masking tape are just a temporary fix to hold those components. Attached Thumbnails 54.6 KB · Views: 110 54.8 KB · Views: 69 52.8 KB · Views: 73 8 X 6E 8 X 6EP 115.5 KB · Views: 42 121.9 KB · Views: 49 117.1 KB · Views: 57

Oct 25, 2009, 09:49 AM	#8
v22chap Registered User Join Date: Jan 2003 Location: Goshen, Indiana, United States Posts: 1,989	A quick and simple pitch control could be done with using a smaller prop / motor on the tail behind the elevator much like the Canadair VTOL Good luck on your project Here is the url to this site to download the pic so you can make it bigger CL 84 pix Attached Thumbnails 11.1 KB · Views: 71

Oct 26, 2009, 11:35 AM	#14
yuzri1984 Registered User Join Date: Oct 2009 Posts: 7	thanks v22chap..im kinda unsure which setup to use actually.. appreciate all the suggestions and stuff. ill update my progress wif ya guys.. oh yah, was told by my project supervisor dat my project will also be entering a flying competition, with obstacles and such.. i got a pdf file of it.. do feel free to browse them guys..as always, ideas n suggestions are welcomed. Attached Files SAFMC Challenge.pdf (1.03 MB, 44 views) This is the competition we will be entering..

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Oct 23, 2009, 04:31 PM	#2
NighthawkF-117 Registered User Join Date: Jan 2009 Posts: 339	First Fix masking tape on the shaft that hold the motor, that could be causeing vibrations. Second make sure that is level with the ground. Then add a gyro, here is a cheep on... http://www.xheli.com/esky-gyro-ek2-0704b.html# I have had luck with it on my helis. Next do you have a v-tail mixer between the two throttles/ESC? If not put one to the two output cables of your ESC and plug into the rudder and Throttle channel on your resiver. This will give you yaw. Then add the gyro between the cord that comes out of the v-tail and into the rudder port on your resiver. Now you have control for throttle and yaw. (if not plug another gyro into the V-tail and throttle port on the resiver like as the rudder). Then you will need some form of pitch if you want to hover in a certin area. To do this i would add a servo to the boom that holds the motors so it will pivit forward when you push the elevator stick forward and will vice versa. Hope this helped! Good luck!

Oct 23, 2009, 05:34 PM	#3
Brandano Registered User Join Date: Oct 2004 Posts: 1,382	What are you using to control pitch? If the CG is close to the pivot axis you might not have enough pitch authority to control it with tilt alone. Full size tiltrotors either have a full cyclic or use a tail rotor- Also, gyroscopic effects will tend to keep the rotors horizontal while the fuselage tilts up and down.

Oct 24, 2009, 05:31 AM	#5
yuzri1984 Registered User Join Date: Oct 2009 Posts: 7	well i was suggested by my project supervisor for pitching we got to use a weight(think of a barbell attached to a servo) to do the pitching. so to move forward we jaz tilt the weight to a forward position and vice versa. its more like moving the cg. is it feasible guys ? i intend to have the rotor fixed rather than tilting it.

Oct 24, 2009, 09:17 AM	#6
yuzri1984 Registered User Join Date: Oct 2009 Posts: 7	i see.. okey, will update u guys soon. thanks for the help.. if u got further suggestions, please do tell me yah..

Oct 24, 2009, 05:22 PM	#7
Brandano Registered User Join Date: Oct 2004 Posts: 1,382	the moving weight will work within a range of tilt from the horizontal, but will add overall weight and won't work in extreme attitudes. Weight is at a premium in VTOL crafts. You could be better off swinging the rotors forward and back, effectively using the whole fuselage as a weight for pitch control

Oct 25, 2009, 03:15 PM	#9
pakrat961 Registered User Join Date: Mar 2004 Location: Southern Cal. Posts: 16	I don't know if you've ever heard of Gary Gress, http://www.gressaero.com/ He's got a very similar design, and it performs quite well. But instead of using weights-shifting for pitch, he uses the gyroscopic effects of the counter-rotating props to induce pitch-forces. Basically, because of the counter-rotation, if you tilt the motor&rotors towards/away from one another, the resultant gyroscopic forces will cause the craft to rotate about the pitch axis. It's not trivial, but it definitely saves you the weight of a big swinging pendulum. All you need is one or two servos to tilt the motors inward/outward. He's got a patent on the concept, but if you're just using it for a project (not selling it, competing with him) you should be fine. :P

Oct 25, 2009, 03:28 PM	#10
v22chap Registered User Join Date: Jan 2003 Location: Goshen, Indiana, United States Posts: 1,989	I had forgot about him ,,, I have talked with Gary since about the first day of his first bird .... and some where I have a set of plans that he gave me ,,,but I sure can't find them now after about 10 yrs ... :O But he does have plans that he will sell you for that bird at 19.95 ,,, he even has the motors and mixers and all the build materials listed to build it ,, or even buy the complete kit .... Gary 's plans for the micro vader I still think your best bet now is the 3rd motor on the back ,,, maybe not all the way at the back ,,,maybe right in front of the elevator / rudder ... like Gregg Covey's cessna VTOL project found here . Gregg's is more like yours and he shows you how he builds it too . Good luck and keep us all posted how it goes . Greg Covey

Oct 25, 2009, 04:48 PM	#11
NighthawkF-117 Registered User Join Date: Jan 2009 Posts: 339	[quote=v22chap]I still think your best bet now is the 3rd motor on the back ,,, maybe not all the way at the back ,,,maybe right in front of the elevator / rudder ... like Gregg Covey's cessna VTOL project found here . QUOTE] I second this. Sounds easy. You might not even need a ECS.

Oct 26, 2009, 10:05 AM	#12
yuzri1984 Registered User Join Date: Oct 2009 Posts: 7	so we tilt it towards/away from each other instead of the norm forward/aft direction? ok, dats something enriching..hmm.. u got any ideas on the mechanisms to tilit rotor? my imagination is poor..

Oct 26, 2009, 10:42 AM	#13
v22chap Registered User Join Date: Jan 2003 Location: Goshen, Indiana, United States Posts: 1,989	Yuzri Gary Greese's idea is using the helicopter precession idea .... Take a toy gyro and spin it up and then push it lightly from the back and see what direction it goes ...then push it from the side and see what happens ( it will tilt the opposite direction you pushed it from ).... this is his control mechanics . The motors set in a 4 gimble axis so they can move any direction . I would really suggest stay with the simple setup you have and add the 3rd motor/ esc / and gyro's to keep it simple as Gary's setup is hard to do let alone understand and you already have most of the things you need and built for the other way,,, which should get you in the air and get a good grade with minimal work .

Oct 26, 2009, 06:46 PM	#15
Brandano Registered User Join Date: Oct 2004 Posts: 1,382	I agree with V22. Tricopters are a tried and tested setup, and this field is fraught with the unknown and unexpected as it is. It's already a challenge to get something like this to hover reliably, let alone fly through a course, so go for the configuration that gives you the greatest chance of success