Coax rotors & torque

#1
So I've been struggling with this for a while: how the hell do I keep the speed of the top rotor the same as the bottom rotor on a coaxial helicopter?

Any difference in speed between the two rotors causes torque on the chassis, resulting in unwanted yaw.

I tried using gears, but they just can't handle that amount of power and slip regularly (haven't tried large gears yet, but that would make the chassis huge...)

The problem seems to be worse when ascending/descending, so it's not like I can just shove a tail rotor on it to counter the torque (because it's not a fixed amount of torque), and also that's fixing the the symptom, not the problem.

I did manage to create a coax rotor system that is decoupled enough from the chassis that no torque is transmitted to the chassis, but then I get the speed problem.

If I allow torque to be transmitted to the chassis, the speed problem seems to improve, but then I get yaw from the torque...it seems that it's REALLY sensitive to any slight difference in the amount of friction of the rotational parts (e.g. if you use an unpowered wheel as a bearing on the bottom rotor, and a swivel as a bearing on the bottom rotor, you get a speed difference...presumably they have different rotational friction?)

Has anyone managed to solve both problems at the same time?

One more thing: is there a complete list of blocks which shows how much rotational friction they have?

Also I need a solution that's like a piston but doesn't act like suspension when extended :p My swash plate is very wobbly...
 

Shade

Active Member
#2
Do you have pics?
Different speed on coaxial heli are usually caused by different of mass on each rotor. If they are perfectly identical they will spin at the same speed
 
#3
I'll post some when I get home. Both rotors are identical (built with symmetry tool with X, Y, and Z selected), so there is no mass difference. I checked everything multiple times to make sure that lift is the same (i.e. all props are in the correct orientation etc), so there must be something else causing it.

The other I think I was thinking about is that a while ago (like a year or so ago) I observed that a wing panel underneath a rotor *seemed* to react to downwash (which I thought Besiege didn't model), so I wonder if the downwash from the top rotor si affecting the bottom rotor...or am I imagining it?
 
#4
So I've been struggling with this for a while: how the hell do I keep the speed of the top rotor the same as the bottom rotor on a coaxial helicopter?

Any difference in speed between the two rotors causes torque on the chassis, resulting in unwanted yaw.

I tried using gears, but they just can't handle that amount of power and slip regularly (haven't tried large gears yet, but that would make the chassis huge...)

The problem seems to be worse when ascending/descending, so it's not like I can just shove a tail rotor on it to counter the torque (because it's not a fixed amount of torque), and also that's fixing the the symptom, not the problem.

I did manage to create a coax rotor system that is decoupled enough from the chassis that no torque is transmitted to the chassis, but then I get the speed problem.

If I allow torque to be transmitted to the chassis, the speed problem seems to improve, but then I get yaw from the torque...it seems that it's REALLY sensitive to any slight difference in the amount of friction of the rotational parts (e.g. if you use an unpowered wheel as a bearing on the bottom rotor, and a swivel as a bearing on the bottom rotor, you get a speed difference...presumably they have different rotational friction?)

Has anyone managed to solve both problems at the same time?

One more thing: is there a complete list of blocks which shows how much rotational friction they have?

Also I need a solution that's like a piston but doesn't act like suspension when extended :p My swash plate is very wobbly...
I am strucling with same problem but here is best what i can do you put 2 rotors on single block on top and at the bottom and then connect the block *in this case start block* to the frame
i dont know why but you need to adjust the upper rotor speed because besiege likes to be that way
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#5
OK so I did a load of experiments tonight, and concluded that something in the game is buggy. I built a number of variations of ultra-simple coax setups and ALL of them a) had a net torque greater than 0, and b) eventually developed Toilet Bowl Effect (look it up). At first I thought it could be a block type with a COG that is off a little, but having tried it with completely different blocks and got the same result, I've ruled that out. I wondered if it was some sort of randmisation of the physics engine, but no - it always yaws in the same direction, and the TBE always occurs at the same point, in the same direction, with the same severity.

Something else that I have discovered: the large and small props have the same amount of lift (if you space the small prop 1 block further from the shaft, so the rotor diameter is the same), BUT the large prop is MUCH more prone to inducing torque on the body. Lift panels are WAY WAY WAY more stable (no TBE that I can discern), although they still have a net torque >0. Don't think it's as much as the props generate, though.

Putting sliders between the shaft and the prop seems to help a little (presumably because you get a better disc loading + some dishing of the disc), but it still generates torque on the chassis and still develops TBE at some point.

So for the moment, we have to either a) deal with it and learn to control it when piloting, b) use methods that cure the symptoms rather than the problem (e.g. a counter rotating wheel in the fuselage linked to the same controls as throttle & collective, with it's speed tweaked to counter the rotation...or a tail rotor with the same control binding), or c) wait for a fix (sod that). I think heavier choppers are less prone to the effect as well, so there may be another option - make a heavy chopper with a low disc loading (i.e. giant rotor diameter, low RPM).

Meanwhile, I'll investigate how a swashplate affects this.
 
#6
OK so I did a load of experiments tonight, and concluded that something in the game is buggy. I built a number of variations of ultra-simple coax setups and ALL of them a) had a net torque greater than 0, and b) eventually developed Toilet Bowl Effect (look it up). At first I thought it could be a block type with a COG that is off a little, but having tried it with completely different blocks and got the same result, I've ruled that out. I wondered if it was some sort of randmisation of the physics engine, but no - it always yaws in the same direction, and the TBE always occurs at the same point, in the same direction, with the same severity.

Something else that I have discovered: the large and small props have the same amount of lift (if you space the small prop 1 block further from the shaft, so the rotor diameter is the same), BUT the large prop is MUCH more prone to inducing torque on the body. Lift panels are WAY WAY WAY more stable (no TBE that I can discern), although they still have a net torque >0. Don't think it's as much as the props generate, though.

Putting sliders between the shaft and the prop seems to help a little (presumably because you get a better disc loading + some dishing of the disc), but it still generates torque on the chassis and still develops TBE at some point.

So for the moment, we have to either a) deal with it and learn to control it when piloting, b) use methods that cure the symptoms rather than the problem (e.g. a counter rotating wheel in the fuselage linked to the same controls as throttle & collective, with it's speed tweaked to counter the rotation...or a tail rotor with the same control binding), or c) wait for a fix (sod that). I think heavier choppers are less prone to the effect as well, so there may be another option - make a heavy chopper with a low disc loading (i.e. giant rotor diameter, low RPM).
Meanwhile, I'll investigate how a swashplate affects this.
You should write bug report about that physics engine randomation thingy thing cuz we cant be the only ones who find that annoying
 

ITR

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Staff member
#7
You should write bug report about that physics engine randomation thingy thing cuz we cant be the only ones who find that annoying
Randomization in a physics-engine is an artifact of using Unity/PhysX and floating point numbers, and can't be done something with. And as he mentions, it's not random, so it's likely to be something else :p
 
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