Propulsion: VSP
Overview
The Voith-Schneider Propeller (VSP) is an ideal variable-pitch propeller because its thrust can be adjusted in terms of magnitude and direction. Control of thrust direction and magnitude is achieved solely through blade pitch, enabling rapid, sensitive, and precise adaptation to the set conditions.
VSP drives in more complex setups usually need 3-4 extra steps, including fine-tuning and calibration, to work correctly. The propeller must be securely mounted to the vehicle's body with all necessary precautions, and the servos must be set up properly. This is essential for the propeller to function effectively.
Propeller mount
Please follow exactly this guide.
Ring limiter
The ring limiter is an essential element for driving a VSP. It ensures that the control rod movements remain within its boundaries, preventing damage to the actuators/servos. Additionally, it maps common control signals to the short travel distance of the control rod.
The VEKTOR Core integrates a total of six software ring limiters, each fully customizable.
The following key concepts should be clear before continuing with the configuration of VSPs:
A wrongly configured ring limiter can damage the VSP and its actuators/servos in a matter of seconds!
The last logic/control component before the physical PWM outputs to VSP servos should always be a ring limiter.
Slight changes to the following parameters can significantly alter the behavior of the VSP.
Without meticulous calibration, the propeller does not achieve expected performance and efficiency.
Center
Registers: VSPx_ACTUATOR_X_AXIS_CENTER & VSPx_ACTUATOR_Y_AXIS_CENTER
To ensure flawless function of the VSP, the control rod should be exactly centered while idling. The virtual center is considered the default position of centered servos, which is 1500μs. If the previous guide is followed, the VSP rod should already be centered quite well, though some minor adjustments may be necessary.
By setting custom values to the two registers, it is possible to fine-tune the centering of the X and Y axes of the control rod. By default, these registers contain the value 1500. You may try narrow values to see how they affect the rod position, starting with 1490 or 1510 to observe changes in the control rod's idle position.
Once the calibration is done, save the values to the flash memory.
Radius
Register: VSPx_RING_LIMITER_RADIUS
To maximize the power of the VSP, the control rod should be allowed maximum movement. The radius of the rod should be set so that it barely touches the VSP ring. A well-set center is a prerequisite for this configuration. If multiple VSPs are used, their radii should be the same or similar. The ideal radius is when the control rod barely touches the center ring while moving in every direction.
Recommended values are around 100 µs to 200 µs.
The input of the ring limiter is mapped to the maximum extension of the radius. This means the entire input length of 1000 μs to 2000 μs of the ring limiter will be mapped to a length of (-radius) <-> (+radius).
E.g. with a radius of 100 µs, the input mapping is from 1000μs (1000 µs to 2000 µs) to 200μs (-100 µs to +100 µs).
Thrust angle
Register: VSPx_THRUST_ANGLE_OFFSET
The exact direction of the thrust mainly affects configurations with a single VSP. When the control rod is moved to create thrust in a certain direction, the VSP does not generate thrust at the mathematically correct angle but is usually shifted by 10 to 15 degrees towards the direction of rotation.
The register takes a correction value from 0 to 359 of the thrust angle.
According to the direction of rotation we suggest a correction of about 10-15 degrees. The register value should be either around 10 or 350.
If 2 or more VSP are used, leave the VSPx_THRUST_ANGLE_OFFSET register at 0.