SteeringSensor - Revision history

Elcanoadmin: /* Steering state Summer 2024 */

2024-08-16T01:33:09Z

‎Steering state Summer 2024

Elcanoadmin: Added current steering state to provide information on what sensors are being used and how we are currently receiving the angle values to the DBW board.

2024-07-24T22:31:38Z

Added current steering state to provide information on what sensors are being used and how we are currently receiving the angle values to the DBW board.

JosephBreithaupt: /* Ackermann Steering Geometry: wheel angle and turning radius */

2019-07-09T05:33:45Z

‎Ackermann Steering Geometry: wheel angle and turning radius

JosephBreithaupt: /* Ackermann Steering Geometry: wheel angle and turning radius */ added images

2019-07-09T05:28:21Z

‎Ackermann Steering Geometry: wheel angle and turning radius: added images

JosephBreithaupt: /* Ackermann Steering Geometry: wheel angle and turning radius */

2019-07-09T04:44:09Z

‎Ackermann Steering Geometry: wheel angle and turning radius

JosephBreithaupt: /* Absolute wheel position: Analog */

2019-07-02T03:43:02Z

‎Absolute wheel position: Analog

JosephBreithaupt: /* Absolute wheel position: Analog */

2019-07-02T03:40:56Z

‎Absolute wheel position: Analog

JosephBreithaupt: /* Absolute wheel position: Analog */

2019-07-02T03:22:42Z

‎Absolute wheel position: Analog

JosephBreithaupt: Created page with " = Steering Angle Sensor = To change or maintain travel direction, the system must know which way the front wheels are pointing. Elcano tricycles accomplish this task with a..."

2019-05-20T02:54:13Z

Created page with " = Steering Angle Sensor = To change or maintain travel direction, the system must know which way the front wheels are pointing. Elcano tricycles accomplish this task with a..."

New page

= Steering Angle Sensor =

To change or maintain travel direction, the system must know which way the front wheels are pointing. Elcano tricycles accomplish this task with a rotational position sensor placed on the front steer wheels. Each trike has two steering columns, and both are instrumented for redundancy. The sensor is mechanically mounted to the shaft. Since the system uses Ackerman steering, the turn angle of the two wheels will be slightly different. More information is below.
Rotational position sensors may be incremental or absolute. An incremental position sensor only reports discrete changes in rotational position and possibly direction of rotation. Absolute position sensors report the current angle of the sensor shaft. Absolute position sensors have advantages for sensing wheel angle, such as always knowing the current wheel angle at the power-on state. Elcano test vehicles use absolute rotation sensors.

== Absolute wheel position: Analog ==

Analog position sensors typically communicate angle using current or voltage levels. In these devices, current or voltage is a function of the angle. Example:

%ATTACHURL%/volt-angle.png

== Absolute wheel position: Digital ==

Digital position sensors communicate angle digitally. Two ways a sensor can accomplish this task is by encoding the measured position into a binary stream (serial communication) or by encoding the position in binary by driving several output pins high or low (parallel communication).

== Reducing Sensor Noise ==

The problem with sending an analog signal over a long wire to the Arduino is that the wire acts as an antenna and picks up noise. Thus we connect a twisted wire pair from sensor to Arduino that has Signal In as well as the return. The return wire is connected to the ground wire at the sensor. The return wire may have picked up noise when it gets to the Arduino. The Arduino subtracts the analog value of return from the Signal In. Since both wires have picked up approximately the same noise, subtracting them gives a more robust reading. The Signal In return signal goes to an analog input on the Arduino, and is not connected to Arduino ground. The test vehicle analog sensor uses four wires: power, ground, signal, and signal return.

Another alternative is to use an analog-to-digital converter to digitize the voltage reading from the sensor before it reaches [[C2]]. All analog signals are sensitive to noise from the environment, especially nearby electronics. This noise appears as voltage changes on the power and signal wires of the turn sensors and is visible with an oscilloscope. Because noise creates changes in voltage on the signal and power wires, it creates erroneous angle readings.

--Main.JosephBreithaupt - 2017-02-11

== Sensors used ==

We have gotten the best results from RTY060LVNAX 60 degree analog rotary encoder with a 5V range.
Other possibilities:

- TT Electronics 6127 sensor giving 5V analog output over 360 degrees https://www.digikey.com/products/en?keywords=987-1393-ND . Has six times less resolution than a 60 degree sensor, and the minimum resolution can get lost in the noise.

- EMS22A50-M25-LD6 Digital rotary encoder. This produces 1024 steps over 360 degrees, in SPI. It will give a resolution of 0.35 degrees. Requires a change to Arduino.

- TLC1549CP 10-bit analog-to-digital converter with serial control. This could be used to digitize the voltage from the RTY060LVNAX, reducing noise from analog transmission. Requires a change to Arduino.

- AMS5043 Magnetic Angle Encoder. This requires that a cylindrical magnet be mounted precisely on the shaft. The sensor has an indent for the magnet, but the indent in not in the right place. Difficult to get robust readings from the part.

- It is possible to tap into the feedback wire on the linear actuator. This reading suffers from hysteresis.

- Putting a current sensor on the actuator lets us measure the power draw, but this is not adequate for control.

== Mounting the Steering Angle Sensor ==

The steering sensor is mounted directly the top of the steering knuckle. In the top if the steering knuckle is threaded rod that is kept in place using a jam nut. On the end of that threaded rod is a coupling nut that has been locked in place using a jam nut. From the coupling nut an adapter has been 3d printed that connects the coupling nut to the Steering angle sensor. The steering angle sensor is help in place using a piece of flat metal bar with a 90 degree bend.

Mounting in this position is beneficial by reducing the amount of mechanical play that the system is exposed to and therefore reducing false readings.

== Ackermann Steering Geometry: wheel angle and turning radius ==

Many road vehicles use a variation of Ackermann Steering to allow a vehicle with more than two wheels to turn smoothly. The challenge of steering a multi-wheel vehicle in a circle is that all wheels are at different distances to the center of that circle, so they must turn to different angles and spin at different speeds. The trike used in the current Elcano system solves the speed differential problem by having only one drive wheel and un-driven steering wheels. The steering differential problem is solved using Ackermann steering geometry. With a basic understanding of Ackermann steering and right triangle geometry, we can predict variables like the turning radius of different wheels and the steering angle of different wheels. The inner turning wheel and outer turning wheel turn at different angles and have different turning radii. These calculations find both dimensions.

'''Principle Formulas:'''
Ackermann steering geometry is based on two right triangles. Every calculation comes from right triangle trigonometry and the Pythagorean Theorem.

%ATTACHURL%/Angles.png

'''Key Variables:'''
* Length = vehicle wheel base length, measured from front hub center to back hub center
* Width = distance between center of the front wheels
* A_inner = turning angle of inner front wheel
* A_outer = turning angle of outer front wheel; A_outer < A_inner
* R_inner = turning radius of the inner front turning wheel
* R_outer = turning radius of the outer front wheel

%ATTACHURL%/TrikeTurning.png

Initial known variables: Length, Width, A_inner

Unknowns: A_outer, R_outer, R_inner

'''Calculations:'''
First, create the inner wheel right triangle:
* R_inner = hypotenuse
* Length and "x_inner" = remaining sides
* Tan(A_inner) = Length / x_inner
* x_inner = = Length / Tan(A_inner)
* R_inner = sqrt[(x_inner)^2 + (Length)^2]

Now create the outer wheel right triangle:
* R_outer = hypotenuse
* Length and "x_outer" = remaining sides
* x_outer = x_inner + Width
* R_outer = sqrt[(x_outer)^2 + (Length)^2]
* A_outer = Tanh(Length / x_outer)

Now check that the dimensions make sense:
* R_outer should be larger than R_inner
* A_outer should be smaller than A_inner

'''Important:''' These idealized calculations do not replace experimentation. Turn radius accuracy will suffer if there are traction losses, changes in road surface height, geometry changes during steering, and other variables not considered in these calculations. Furthermore, if the vehicle is moving during a steering angle change, the turning radius changes while moving and the vehicle will not turn in a circle with a fixed radius.

-- Main.JosephDonan - 2017-05-17

← Older revision		Revision as of 01:33, 16 August 2024
Line 92:		Line 92:

	Both prototype trikes are using the 60-degree angle sensors on the left wheel hub with the 360-degree angle sensor on the right wheel hub acting as a backup sensor. The current noise experienced from the left angle sensor is 10-15 analog read values or 48-73 mV recorded on the DBW v3 board and the resolution currently provided meets the current needs when steering with the RC controller. The steering angles are currently being returned through the steering board via an RJ-45 cable to the DBW board with each sensor having its own return line and power being provided locally from the steering board.		Both prototype trikes are using the 60-degree angle sensors on the left wheel hub with the 360-degree angle sensor on the right wheel hub acting as a backup sensor. The current noise experienced from the left angle sensor is 10-15 analog read values or 48-73 mV recorded on the DBW v3 board and the resolution currently provided meets the current needs when steering with the RC controller. The steering angles are currently being returned through the steering board via an RJ-45 cable to the DBW board with each sensor having its own return line and power being provided locally from the steering board.
		+
		+	[[File:SteeringPerformance.png\|600px\|Solenoid Brakes]]

← Older revision		Revision as of 22:31, 24 July 2024
Line 88:		Line 88:

	TODO: determine if these equations accurately predict the inputs from the turn angle sensors while the trike is stationary or moving.		TODO: determine if these equations accurately predict the inputs from the turn angle sensors while the trike is stationary or moving.
		+
		+	== Steering state Summer 2024 ==
		+
		+	Both prototype trikes are using the 60-degree angle sensors on the left wheel hub with the 360-degree angle sensor on the right wheel hub acting as a backup sensor. The current noise experienced from the left angle sensor is 10-15 analog read values or 48-73 mV recorded on the DBW v3 board and the resolution currently provided meets the current needs when steering with the RC controller. The steering angles are currently being returned through the steering board via an RJ-45 cable to the DBW board with each sensor having its own return line and power being provided locally from the steering board.

← Older revision		Revision as of 05:33, 9 July 2019
Line 49:		Line 49:
	== Ackermann Steering Geometry: wheel angle and turning radius ==		== Ackermann Steering Geometry: wheel angle and turning radius ==

−	Many road vehicles use a variation of Ackermann Steering to allow a vehicle with more than two wheels to turn smoothly. The challenge of steering a multi-wheel vehicle in a circle is that all wheels are at different distances to the center of that circle, so they must turn to different angles and spin at different speeds. The trike used in the current Elcano system solves the speed differential problem by having only one drive wheel and un-driven steering wheels. The steering differential problem is solved using Ackermann steering geometry. With a basic understanding of Ackermann steering and right triangle geometry, we can predict variables like the turning radius of ~~different wheels~~ and the steering angle of ~~different~~ wheels. The inner turning wheel and outer turning wheel turn at different angles and have different turning radii. These calculations find both dimensions.	+	Many road vehicles use a variation of Ackermann Steering to allow a vehicle with more than two wheels to turn smoothly. The challenge of steering a multi-wheel vehicle in a circle is that all wheels are at different distances to the center of that circle, so they must turn to different angles and spin at different speeds. The trike used in the current Elcano system solves the speed differential problem by having only one drive wheel and un-driven steering wheels. The steering differential problem is solved using Ackermann steering geometry. With a basic understanding of Ackermann steering and right triangle geometry, we can predict variables like the turning radius of each wheel and the steering angle of the two front wheels. The inner turning wheel and outer turning wheel turn at different angles and have different turning radii. These calculations find both dimensions when given the inner turning radius (R1 in the image), wheelbase, and front wheel distance.

@@ Line 51: / Line 51: @@
 Many road vehicles use a variation of Ackermann Steering to allow a vehicle with more than two wheels to turn smoothly. The challenge of steering a multi-wheel vehicle in a circle is that all wheels are at different distances to the center of that circle, so they must turn to different angles and spin at different speeds. The trike used in the current Elcano system solves the speed differential problem by having only one drive wheel and un-driven steering wheels. The steering differential problem is solved using Ackermann steering geometry. With a basic understanding of Ackermann steering and right triangle geometry, we can predict variables like the turning radius of different wheels and the steering angle of different wheels. The inner turning wheel and outer turning wheel turn at different angles and have different turning radii. These calculations find both dimensions.
-'''Principle Formulas:'''
 Ackermann steering geometry is based on two right triangles. Every calculation comes from right triangle trigonometry and the Pythagorean Theorem.
-PUT STEERING ANGLE IMAGES HERE
+[[File:wheel-angles-small.png|center]]
 TODO: determine if these equations accurately predict the inputs from the turn angle sensors while the trike is stationary or moving.

@@ Line 10: / Line 10: @@
 Analog position sensors typically communicate angle using current or voltage levels. In these devices, current or voltage is a function of the angle. Example:
-[[File:wheel-turn-angle_360-degree-sensor.png | border]]
+[[File:wheel-turn-angle_360-degree-sensor.png | border | 640px]]
 == Absolute wheel position: Digital ==

@@ Line 54: / Line 54: @@
 Ackermann steering geometry is based on two right triangles. Every calculation comes from right triangle trigonometry and the Pythagorean Theorem.
-%ATTACHURL%/Angles.png
+PUT STEERING ANGLE IMAGES HERE
-%ATTACHURL%/TrikeTurning.png
+TODO: determine if these equations accurately predict the inputs from the turn angle sensors while the trike is stationary or moving.
 -- Main.JosephDonan - 2017-05-17

← Older revision		Revision as of 03:40, 2 July 2019
Line 9:		Line 9:

	Analog position sensors typically communicate angle using current or voltage levels. In these devices, current or voltage is a function of the angle. Example:		Analog position sensors typically communicate angle using current or voltage levels. In these devices, current or voltage is a function of the angle. Example:
		+
		+	[[File:wheel-turn-angle_360-degree-sensor.png \| border]]

	== Absolute wheel position: Digital ==		== Absolute wheel position: Digital ==

← Older revision		Revision as of 03:22, 2 July 2019
Line 9:		Line 9:

	Analog position sensors typically communicate angle using current or voltage levels. In these devices, current or voltage is a function of the angle. Example:		Analog position sensors typically communicate angle using current or voltage levels. In these devices, current or voltage is a function of the angle. Example:
−
−	~~%ATTACHURL%/volt-angle.png~~

	== Absolute wheel position: Digital ==		== Absolute wheel position: Digital ==