Tricopter motors

[OldFogey1946]

I am building a tricopter as per Davids Version 3. My last multi was a 250 class quad, which flew exceptionally well, but was not really the direction I wanted to go. Both David and Josh seem to favor tricopters for photography, so that is where I am going.
However, money, as always, is an issue, so I would like to use what I already have leftover, namely two 1400kv motors, and one 980kv. Any thoughts on using the two 1400's on the front arms (with 8" props) and the 980 on the rear with a 10" prop (all have 30amp ESC's)? My FC is a Naze 32 10DOF.
Just for general interest, I made the frame parts and legs out of aluminum, and the arms out of cedar (wood). Looks good!

 

[Jordan3367]

Hi,
In short, yes, I think that would work, but it would probably be better to use the same motors.
The Naze will try to operate as if it is running three of the same motors, so when one of the motors is different it might throw the motor mixing off. On the other hand, it's entirely possible that it will make no difference at all and your tricopter will work just fine. My advice would be to try it, but If you see weird flight patterns or terrible flying/tuning/turning, it is probably worth investing in a third 1400kv motor.

P.S. Tricopters rock.

 

[Snarls]

It may be better to just buy one more 1400kv motor to complete the set, but it is worth trying the 980kv. I suggest you mount the 980 closer to the frame than the 1400s because it will help mitigate the thrust difference. If you have the prop and thrust data for each motor then you could actually compute what difference in arm length is best to offset the motor differences.

 

[OldFogey1946]

Thanks for the thoughts. So it seems nobody has actually tried this. The trouble is, I do not know how the Naze 32 monitors the motors. If it adjusts the voltage they get, then my idea may very well work, as the revolutions per volt (kv) would be different on the 1400kv and the 980 kv, which would mean that a bigger prop on the slower motor could well provide some balance. If it uses current, however, then it will not fly, as the slower motor with a bigger prop needs less current (more efficient). So I will try it and see! I will let you know what happens, but that is some time away yet, as I am still building. Right now I am designing and making a servo/tail rotor tilt mechanism. I would love to buy the one from Flite Test, it is great, but I will not pay the crazy shipping costs. Flite Test, along with most US suppliers, charge far too much for shipping.

 

[Foam Addict]

I did do something similar, it flew fine, I don't necessarily recommend it though. The tricopter had assymetric control tending to drop toward the motor with the smaller prop disc, especially when rapidly descending. You have the right idea about positioning them though, and if you want by all means give it a tri!

 

[makattack]

There is no feedback from the escs to the flight controller, so the flight controller simply adjusts power to the motors as needed to satisfy the commanded input and using the accelerometers and gyros feedback. This will theoretically limit the performance limits of your tricopter if the motors have different performance characteristics. It'll fly, but not as well as it could.

 

[OldFogey1946]

Thanks to all, I will keep you posted once I'm done.

 

[OldFogey1946]

And just so I do not get into trouble, I just bought a tail rotor tilt mech from Flite test, their shipping cost has improved slightly, and it is way easier than making one. Thanks, guys.