outrunner motor = gimbal motor?

Hello there!

I'm designing a system used to control the rudder position of a small (2m) boat. I came up with the following:

I wanted to test controlling an Electical Speed Controller(ESC) with my microcontroller before ordering the $300 parts, so I ripped a motor and ESC out of my RC car and started testing. This is when I discovered that the motors can't spin slowly. Upon further research I discovered everyone is using gimbal motors, that have more poles and windings, producing more torque on lower speeds. I figured this is what I need.

I found some outrunner motors now, the Pichler website says it does have 14 poles, just like this gimbal motor I found on Hobbyking. I've seen a lot of gimbal motors and they all seem to be outrunner motors, does that mean all outrunner motors are also gimbal motors?

For a bonus question: Is the type of motor the reason it spins fast or is that just the ESC and should I try a brushless control IC instead?

I've never seen motors for a rudder, but I would imagine if it needs to be slow running then they would simply use a gearbox on a normal fast running motor.

Running a motor at slow speeds drastically reduces your power, and cripples the cooling for the motor as well.

Do you really need two motors coupled in that way?, why not just a thrust bearing at the other end?.

Don't know what actually makes them different, but the tell is in the numbers the "#Kv".

The first one is -
kV (RPM per volt): 1700

The second is -
140Kv
So the second one is designed to turn slower.

Nigel Goodwin said:

I've never seen motors for a rudder, but I would imagine if it needs to be slow running then they would simply use a gearbox on a normal fast running motor.

Running a motor at slow speeds drastically reduces your power, and cripples the cooling for the motor as well.

Do you really need two motors coupled in that way?, why not just a thrust bearing at the other end?.

Click to expand...

Yes it's weird. We would like to participate in the microtransat race, so we need this system to be robust. We opted for a servo at first, but my teacher asked about redundancy, which we didn't think about before. If the servo fails our race is over. By coupling two motors we have a backup in case the first one fails.

I made the reduction in the worm drive 1:100, which is the best i could find. Putting a gearbox on the motors themselves would mean they become very hard to turn when off, so then I can't couple the motors like this anymore(right?).

shortbus= said:

Don't know what actually makes them different, but the tell is in the numbers the "#Kv".

The first one is -
kV (RPM per volt): 1700

The second is -
140Kv
So the second one is designed to turn slower.

Click to expand...

Thanks, I didn't notice that! They all seem to have lower KV ratings indeed.

Timmehh said:

Yes it's weird. We would like to participate in the microtransat race, so we need this system to be robust. We opted for a servo at first, but my teacher asked about redundancy, which we didn't think about before. If the servo fails our race is over. By coupling two motors we have a backup in case the first one fails.

I made the reduction in the worm drive 1:100, which is the best i could find. Putting a gearbox on the motors themselves would mean they become very hard to turn when off, so then I can't couple the motors like this anymore(right?).

Click to expand...

I presume such details are taken care of in proper systems?, such as a clutch mechanism to disconnect the motor when not in use?. As it is, the worm drive means you can't turn the rudder anyway, and would have to spin the motors (a LOT with 100:1).

Nigel Goodwin said:

I presume such details are taken care of in proper systems?, such as a clutch mechanism to disconnect the motor when not in use?. As it is, the worm drive means you can't turn the rudder anyway, and would have to spin the motors (a LOT with 100:1).

Click to expand...

Yes in proper systems, but this is gonna be my system :S. I have no experience in the mechanical part of this stuff so this will be the proof of concept and the clutching will be done next year by another group of students that kind of knows more about this than me.
What do you mean by not moving the rudder? The sea is not supposed to move it, but both motors should be able to turn this to both directions right? The gearing ratio is here because we might have to make very small adjustments, say i need to correct by just 2 degrees, that would not even be a full rotation of the drive motor.

Timmehh said:

Yes in proper systems, but this is gonna be my system :S. I have no experience in the mechanical part of this stuff so this will be the proof of concept and the clutching will be done next year by another group of students that kind of knows more about this than me.
What do you mean by not moving the rudder? The sea is not supposed to move it, but both motors should be able to turn this to both directions right? The gearing ratio is here because we might have to make very small adjustments, say i need to correct by just 2 degrees, that would not even be a full rotation of the drive motor.

Click to expand...

I presume it's VERY important that you can turn the rudder manually?, the worm gear will prevent that - so no different adding gearing to the motor.

Nigel Goodwin said:

I presume it's VERY important that you can turn the rudder manually?, the worm gear will prevent that - so no different adding gearing to the motor.

Click to expand...

ahh i see where you're coming from. I should have maybe told you the boat will be crossing the atlantic on it's own, oopsie. There's no need for manual control because there's no one on it.

In which case I'd go for one geared motor.

You can do that, however torque is massively reduced, esp if you dont have any feedback.