BG Rotors make better reaction wheels than reaction wheels.

[Geonovast]

Some quick testing is showing that running the rotors is giving me much more precise control over the craft's orientation than using the actual reaction wheels.  I know a lot of people have complaint about how unrealistic the in-game ones are.  I'm wondering what the people who know more about the real-world application than I do would think about this setup.

Might be interesting to do an entire save with all in-game reaction wheels disabled.

[MechBFP]

What happens when you turn on the brake? Do you get counter rotation?

I assume turning them off they will eventually slow down but don’t provide counter rotation?

Edited June 4, 2019 by MechBFP

[cantab]

Wonder if you can make a control moment gyro too? A CMG would have a rotor spinning parts at a constant rate, and you'd then have that mounted on a hinge. Should provide powerful torque.

[FleshJeb]

2 minutes ago, cantab said:

Wonder if you can make a control moment gyro too? A CMG would have a rotor spinning parts at a constant rate, and you'd then have that mounted on a hinge. Should provide powerful torque.

(4500kNm * 200% braking) * X gyros = X gyros you can fling things off moons with.

EDIT, just realized a CMG is a different thing.

Edited June 4, 2019 by FleshJeb

[Geonovast]

14 minutes ago, MechBFP said:

What happens when you turn on the brake? Do you get counter rotation?

I assume turning them off they will eventually slow down but don’t provide counter rotation?

Hitting the brake stops the rotation immediately.

Trick is going to be setting it up so you can still aim with WASD. 

[KerikBalm]

I was also thinking along these lines, for making a more realistic reaction wheel set.

It would be nice if we had rotors where the ends don't spin (relative to each other), but the middle does. It would be pretty convenient for many things

[MechBFP]

12 minutes ago, KerikBalm said:

I was also thinking along these lines, for making a more realistic reaction wheel set.

It would be nice if we had rotors where the ends don't spin (relative to each other), but the middle does. It would be pretty convenient for many things

Stack two rotors on top of each other, but flip one of them upside down. Then connect the outer parts to each other using cubic struts and regular struts. 

13 minutes ago, Geonovast said:

Hitting the brake stops the rotation immediately.

Trick is going to be setting it up so you can still aim with WASD. 

So no need for torque dumping I take it?

Edited June 4, 2019 by MechBFP

[Geonovast]

6 minutes ago, MechBFP said:

So no need for torque dumping I take it?

I'm not 100% sure what that is, but I'll go with... no?

If you stop the motor by applying the brakes, the ship stops turning, right away.

[Guest]

I think it’s when you need to de-saturate the gyros or they eventually stop working effectively. It would be crazy if this was needed, Kerbal physics being what they are >_<

[KerikBalm]

1 hour ago, MechBFP said:

Stack two rotors on top of each other, but flip one of them upside down. Then connect the outer parts to each other using cubic struts and regular struts. 

Or use the nodes of a fairing, or surface attach and use offset

There are ways, but part most have partcount go up/drag penalties/ are hard to make symmetric.

A single part for this would be so much more elegant.

1 hour ago, Geonovast said:

If you stop the motor by applying the brakes, the ship stops turning, right away.

If the ship rotation was entirely caused by the motor spinning, then when the motor stops, so should the ship

[MechBFP]

1 hour ago, Geonovast said:

I'm not 100% sure what that is, but I'll go with... no?

If you stop the motor by applying the brakes, the ship stops turning, right away.

Reaction wheels stop working once they reach full speed. In real life you then need to use some other force, like RCS or the earths magnetic field to provide energy instead to keep your craft stable while you slowly stop the wheel from spinning.

That’s because stopping the wheel also creates torque (unlike in KSP apparently lol. )

[KerikBalm]

Well if the ship was rotating, and it stop because you braked the motor/wheel, then it would seem that stopping it does cause torque.

I think ksp handles it right, my single motor contra rotating co axial helo designs basically depend on it

[OHara]

I made a Mun-mission rocket that uses BG rotors instead of built-in reaction wheels (kerbalx).

I connected the pitch/yaw/roll inputs to the rotation rate of the wheels, and thus the rotation-rate of the craft as it reacts, in contrast to the built-in reaction that give a torque in response to input.   

This input scheme means the wheels stop when the input stops, so this system can never saturate, nor can it counter a persistent external torque.

The B.G. servos, as opposed to the rotors, are much easier to connect to the inputs, but their maximum rotation rate is about 45°/second so I need to mount relatively large flywheel, compared to the craft.   Flywheels on servos work well for small probes.

[Corona688]

On 6/4/2019 at 12:50 PM, Geonovast said:

I'm not 100% sure what that is, but I'll go with... no?

The answer is "yes".

There will be a point at which spinning the engines produces no further torque - when they are already at full speed.  At that point you will need to use a reaction engine instead, while you slow down your wheel.  That is called "torque dumping".

There are also gyroscopic forces to worry about this way.

Edited December 13, 2020 by Corona688

[vv3k70r]

On 6/4/2019 at 5:24 PM, Geonovast said:

Some quick testing is showing that running the rotors is giving me much more precise control over the craft's orientation than using the actual reaction wheels.

Controller is asigned to pitch/y/r?

 

[OHara]

20 hours ago, Corona688 said:

The answer is "yes".

To be fair, the question was "Does Genovast's use of rotors and their brakes to rotate a craft require torque-dumping?"  in the context  of questions whether the torque from spinning up the rotor was propetly cancelled by the opposite torque from applying the brakes.  KSP/Unity accounts  for those torques correctly, so in that context  "no need for torque-dumping" is a helpful answer.

The OP was not suggesting use to rotors counter a persistent torque, where you  would eventually run out of rotor speed and need to dump the momentum with thrusters.

3 hours ago, vv3k70r said:

Controller is assigned to pitch/y/r?

You quoted Genovast's post where he had not connected the rotors to any inputs, using only the right-click menus.   The craft on kerbalx, that I linked to later, does connect KAL1000 Controllers to pitch/yaw/roll.

[vv3k70r]

9 hours ago, OHara said:

You quoted Genovast's post where he had not connected the rotors to any inputs, using only the right-click menus.   The craft on kerbalx, that I linked to later, does connect KAL1000 Controllers to pitch/yaw/roll.

They can be asigned directly without controler. But in such a case they could need two motors for each axis.