What gyros for a quadcopter? - RC Groups
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Nov 17, 2006, 08:32 PM
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What gyros for a quadcopter?

I am in the process of building what I am calling a quadcopter for lack of knowing the correct name. Its like a tricopter but uses four motors instead of three. The plan involves four motors with four ESCs, three gyros, three veetail mixers, rx and Lipo batteries.

The question is; will gy240 gyros work for the setup? I want it to be a nice reliable setup.

I am not sure of the difference between rate gyros and hh gyros, and what would be best.

Motors will be four HImax HC28120850 with 10x4.5 counter rotating props, Phoenix-25 ESCs, and Vee-tail mixers so I can use a straight 5 channel radio. However, I also have a T7CHP. I would like to stay away from transmitter mixing for now because it will be enough of a chalange to get the machine flying the way it is.

I know that some others have made this type of aircraft and would apreciate any help. The final goal is for a AP set up.

If I have success with this project I might make up some plans for others to follow.

Thanks, JK
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Nov 17, 2006, 09:16 PM
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v22chap's Avatar
JK . welcome to the VTOL board ,,there are a lot of good guys here with a lot of technology and brain power to pick from .

I don't think the 240 will do what you want as it recovers to the previous position to quick .

A simple test to do with any gyro for airplane prop VTOL's is to hook it up and rotate the gyro ,round and round and round as best you can ,,,as many times as you can with out unplugging all the wires.( usually 4 or 5 turns) .You watch the servo to see how far it moves and how long it stays moved. For your application it needs to move almost all the way to one side stop and stay there as long as you can turn the gyro around evenly and rather fast .(one turn per second or so ) ... If the gyro can do this it will probably be able to keep your quad level enough to be flyable.

The difference between rate and heading hold ,,is hard to discribe ,,but I guess the best would be to say rate is a manual tranmission and HH is an automatic one.
Rate just slows the axis control down and puts in enough control to allow you to follow it and it does this rather slowly for the most part .

Heading hold uses the advanced part of the piezo gyro to capture the intial location of the bird and does every thing it can to keep that location no matter what you throw at it and it makes many corrections very fast to do this and this is what is needed on the tail of a 3-D helicpter .

This is why HH doesn't work good for what we are doing as none of us need that fast of control or that many controls per second on the VTOL's ,,it makes our birds with slower controls and longer control moments bounce around from one position to another trying to find the spot it intialised at.

We have found that the ACT Europe dual input / output gyro works well as does Horizons Revolution PZ-200 sport rate gyro ( well at least ,,they work with the above test ,,no one has used them on thier VTOL yet, Well I have use the ACT on mine but it is collecitve type ) VTOLman came up with this test and he uses the old blue or white cased ARCAMAX gyro's ,,but you can't buy them any more.

Hope this mess explained it ,,I tried to make it as simple as I could but probably mess it all up. I sure someone will step up and correct me or help out any how.
Good luck
Nov 17, 2006, 09:38 PM
Registered User
Could a person turn the gain down on a 240 to slow things down a little?
Thanks for your nice reply by the way.
Do you think that the rest of the equipment is on track so far?
Nov 17, 2006, 10:28 PM
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v22chap's Avatar
As I remember ,, VTOLman said he couldn't turn the 240 or 401 down far enough to get them to work ... but if you have one or so ,,, I would try it first ,,,just to make sure as some times things work or don't work for other people. I have been proved wrong many times and have proved others wrong also ... There are to many variables and factors that enter into a VTOL to make a golden rule of thumb.

The rest of your setup sounds right on to me .
Nov 18, 2006, 02:17 AM
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shanghai_fool's Avatar
Larry, its been a few weeks since I hovered mine but I found that you can use different gyros for different purposes. I was having all kinds of trouble trying to duplicate vtolmans setup until I got the vtail mixers in front of the gyros. I was first having trouble with roll using motor rpm. I discovered that most any gyro does not like an off-center control when initializing. Of course this presents a problem when feeding the throttle into the gyro. All internal tx mixes produced an off center starting point. After installing the external vtail mixer and putting throttle into one input and aileron into gyro then into other mixer input, it worked as advertised. I could crank the gyro gain almost all the way up and it would keep the wing remarkably stable. As vtolman said, you could try and push one side of the wing down and it would push back against you. I tried several different gyros and even the cheap Align piezo worked ok for this position. I believe it was in hh mode but I am not 100% positive as I had the gain on a rotary control and if you turned it to one side , its hh and the other side is standard. It worked better on one side than the other but now I'm not sure which.

The other problem is the pitch which is where I think there are problems with most gyros. I am using the CSM SL560 which I think will work as it performs the test you mentioned. The Futaba GY401, Align, and GWS PG03 did not.

I was having major problems trying to hover using flaperon mixing for the pitch servos as in hovering you are only using a very small servo movement on the end of the servo travel to do corrections. I believe you said that vtolman had to use some off-center control pushing to hover. That why I decided to go to the leadscrew motor tilt control and just use the tilt servos for minor control with the gyro. That way I can use the full servo travel to tilt the motors only a few degrees for control. That is much the same as you are using the cyclic for control and not the tilting.

I hope this helps some. If its not clear, then just tell me. I still do not fully understand the pitch gyro usage. I need more practice.

Nov 18, 2006, 09:51 AM
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v22chap's Avatar
vtolman had to use some off-center control pushing to hover.
Yes that is what he did ,,so he didn't have to put in another servo or lead screw for tilting ,, and he only tilted to the 60 degree position . (30 degrees past straight up )
He said it was hard to learn hovering with the elevator stick almost all the way back , which he did so that he had full forward throw of the elevator stick to make the small pitch tilting control servos could also do full forward (60 degrees ) tilting .It also left him with barely enough control sometimes while hovering especially outside in the wind .

I probably would have just tried mounting the two pitch/ yaw control servos in a sliding tray and used one servo on a rotary knob to do the tilt ,,but lead screw is just great , but probably more weight ,,although the lead screw system on my bird only weighs like 1lb , motor/gears and lead screw.
I just need to build a quick bird like VTOLmans so I can talk more reliably about it.
Nov 18, 2006, 08:00 PM
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shanghai_fool's Avatar
Speaking of leadscrews, my rotating tray with leadscrew seems to work well. I tried the sliding tray but it changed the servo travel too much. The tilting tray works pretty good as it balances the relays against the motor/props and takes very little effort to rotate them. The only torque required is at the forward end of travel as you are pulling the tray directly toward the screw. The leadscrew is small and doesn't weigh very much and I'm using a standard servo as it was easy to modify. I tried the links you gave for leadscrews but they don't have retail sales. I am going back to LA for 3 weeks so I will look for a small diameter Acme thread. I need about 5 revolutions for a 7 second tilt time. I had to modify the tilt servo position a little to fit in the available area.

This thread was about gyros and I just wanted to give my 2 on the motor control. Thats the only one I have good experience in. I will start a BA609 thread as soon as I have enough input. This is my first iteration in scratch building a VTOL and there is a lot to learn. I think most of the functions in the 609 are applicable to the V22 which I will probably build if I can get this to work. I would still like to build with cyclic when I can get 3 blade, small diameter control. I think that will be necessary to be able to scale this design larger. Theres just not a lot of choices in available cr props to do it properly. Its just taking a lot of electronics and servos to do it properly. I haven't even started on the flaperon problem yet. As you can see from the videos, the flaps are directed fully downward when hovering to keep the down thrust from pushing the plane forward and only come up when tilting the motors forward. I think this will need separate servos from the motor pitch servos.

Yes, this needs it own thread. too many problems.

Nov 21, 2006, 03:38 AM
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hardlock's Avatar
Originally Posted by shanghai_fool
After installing the external vtail mixer and putting throttle into one input and aileron into gyro then into other mixer input, it worked as advertised.
Donald, can you elaborate on this more? The logic evades me as how can the gyro connect to a single mixer with dual inputs and outputs and control two servos (motor controls in this case) Maybe a diagram would help those like me that are slow to these concepts.

BTW, I'm working on a tri-coper design that needs this same info:


I've since added a JR-G410T unit for elevator to the horizonal tail rotor but can't get the HH to work. It doesn't seem to really need it anyway as it does a good job of keeping it where it needs to be yet still allowing my control input to respond without overcontrolling. BTW, I'm mixing throttle into elevator for the motor so am not at center when the gyro starts up but maybe it "sees" the elevator channel first as that's what it's plugged into?

My roll is mixed in the TX with throttle into flaperons and works better than in the video now that I've reduced the DR to 5% for 30%. I removed the expo as well as it was causing PIO for the extra lag time it added.

A quick qyro would seem to be required here also and have a couple cheap ones ordered to test. I'd like to know how to use just one if possible.

The ESCs are connected to aileron and ch6 for the internal mix. I'm thinking I'll need an external mixer to be able to use just one gyro and put it in the aileron line to the mixer? Am I right on this or should I just add a separate gyro to each ESC and hope I can "sync" them close enough to keep them from fighting each other?
Nov 21, 2006, 04:38 AM
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shanghai_fool's Avatar
Since I can't draw, I've hijacked a diagram from another thread. You will run into the same problem if you are using internal tx mix for flaperons. The gyro needs a centered control (plain ailerons) to work properly I think. DO NOT use gyro output to esc. Most esc will not see mininum throttle that way and refuse to operate. At least mine does. I have given this much thought in my BA609 and have decided to add separate mixer for flaperons and not use the motors for this. I will "Y" connect a separate aileron and flap control to this mixer and take the mixer outputs to the real flaps.

You are correct in using just a small aileron control for roll as it doesn't need very much rpm change to cause a great effect. I think mine was about 10%.

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