Geroler Motor Displacement Calc | Hobby Project

[Stormer]

Hi. I want to design a custom Geroler motor for a hobby project of mine, but I want to calculate the torque it can produce at a given pressure and for that i need to calculate the motors displacement, but how do i do that?

 

[Baluncore]

Hi. I want to design a custom Geroler motor for a hobby project of mine, but I want to calculate the torque it can produce at a given pressure and for that i need to calculate the motors displacement, but how do i do that?

To find the torque, you must look at the areas that oppose the input and output pressures. You must also look at the radius to those areas. For a geroler, those areas are the sides of the gear teeth multiplied by the axial length of the gear. The radius of the geroler crank is important in computing torque.

Also does it matter in any way that i will feed it a compressible fluid (gas) like air i stead of a liquid like oil or water that it usually uses other than the clearances for leakage?

If the inlet pressure and the outlet pressure are fixed, then the torque will be due to the differential areas. But pressures are determined by external connections.

 

[Stormer]

To find the torque, you must look at the areas that oppose the input and output pressures. You must also look at the radius to those areas. For a geroler, those areas are the sides of the gear teeth multiplied by the axial length of the gear. The radius of the geroler crank is important in computing torque.

Well the CAD program does not output the area. So how can i calculate it?

 

[Baluncore]

Well the CAD program does not output the area. So how can i calculate it?

When the tip of the tooth touches the fixed roller, the exposed faces of the tooth oppose the differential pressure.
The pressure on the centre of the tooth face is on the other side of the rotor from fixed rollers. The centre of the rotor is on the crank pin and applies twice the tooth force to the crank.
The depth of a tooth multiplied by it's length, is the face area = A;
The differential fluid pressure is = dP;
The tooth force is; F = A * dP;
The crank force is 2 * F;
The crank radius is R;
The torque is T = R * 2 * dP * A;

 

[Baluncore]

I can't think of a more difficult motor to make. You will need a set of valves machined into the shaft to direct the fluid. You will need a diagonal shaft with modified splines at both ends, or a crank.

If one gear rotates against another rotating gear it is a gear motor, or a gerotor.
If one gear rotates inside a fixed gear it is some type of vane motor, or a geroler.

It would be easier to make a traditional two-gear motor, or a gerotor with a rotating spool to carry the rollers, with an inner rotor profiled like the rotor in a geroler. Those ways your inlet and exhaust ports can remain fixed.

 

[Stormer]

or a gerotor with a rotating spool to carry the rollers, with an inner rotor profiled like the rotor in a geroler.

So are you saying that a geroler with a rotating outer housing (and inner rotor) is not a geroler?

The reason for wanting a geroler over a gerotor is because the "pins" can be rollers that can reduce friction and wear. And they can be hardened steel. And because it will be easier to machine the housing with the pins than making a gerotor housing. Because presision pins is off the shelf parts, and drilling and reaming a hole to a precision fit is pretty easy.

 

[Baluncore]

So are you saying that a geroler with a rotating outer housing (and inner rotor) is not a geroler?

Geroler is not a technical term, it is a Trade mark. You will need to ask the holder how they define a geroler.

Will the centre of the rotor in your motor be fixed, or will it orbit the shaft?
That has implications to the valves you will use to direct the fluid.

 

[Stormer]

I was thinking the housing with the rollers would rotate together with the "star" yes. So i can have a simple fixed valveplate.

 

[Baluncore]

If you look at the roller-gerotor diagram in my post #7, you will see that there is a maximum fluid volume between two rollers when two rotor lobes touch those two rollers. That area is at the top of the rotor.
You will also see that there is a minimum fluid volume at the bottom of the rotor where a rotor lobe is between two rollers.
For a 6 lobe rotor, the displacement per shaft revolution is 6 times the difference between those volumes.
For an air motor, the compression ratio will be the ratio of those volumes.