Design Philosophy for Rigatoni’s Automated Steering Subsystem - Revision history

Mbayyari3 at 05:31, 20 May 2020

2020-05-20T05:31:06Z

Kcarter47 at 03:54, 26 November 2019

2019-11-26T03:54:57Z

Kcarter47 at 03:51, 26 November 2019

2019-11-26T03:51:27Z

Kcarter47 at 03:50, 26 November 2019

2019-11-26T03:50:29Z

Kcarter47 at 03:48, 26 November 2019

2019-11-26T03:48:25Z

Kcarter47 at 03:47, 26 November 2019

2019-11-26T03:47:54Z

Kcarter47 at 03:44, 26 November 2019

2019-11-26T03:44:16Z

Kcarter47: added text to stepper image

2019-11-26T03:43:55Z

added text to stepper image

Kcarter47 at 03:42, 26 November 2019

2019-11-26T03:42:31Z

Kcarter47: adding image(?)

2019-11-26T03:40:58Z

adding image(?)

← Older revision		Revision as of 05:31, 20 May 2020
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	Kyle Carter is a 4th year computer engineering major at Georgia Tech set to graduate in the summer of 2020. He is a member of the RoboJackets RoboRacing electrical team, currently working on the autonomous evGrandPrix go kart, a.k.a. Rigatoni. When he first joined RoboRacing, there was little documentation on the designs for the previous robots and to fix that has decided to document his team’s work on the steering subsystem for Rigatoni in a Wiki article, providing other and new RoboRacing members with useful information while fulfilling a documentation requirement for ECE 3005 (Professional and Technical Communication).		Kyle Carter is a 4th year computer engineering major at Georgia Tech set to graduate in the summer of 2020. He is a member of the RoboJackets RoboRacing electrical team, currently working on the autonomous evGrandPrix go kart, a.k.a. Rigatoni. When he first joined RoboRacing, there was little documentation on the designs for the previous robots and to fix that has decided to document his team’s work on the steering subsystem for Rigatoni in a Wiki article, providing other and new RoboRacing members with useful information while fulfilling a documentation requirement for ECE 3005 (Professional and Technical Communication).
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		+	[[Category: RoboRacing]]

← Older revision		Revision as of 03:54, 26 November 2019
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	The encoder firmware is quite long, so it better viewed on the RoboJackets RoboRacing GitHub [https://github.com/RoboJackets/roboracing-firmware/blob/evgp_steering/new_cari/encoder/encoder.ino here].		The encoder firmware is quite long, so it better viewed on the RoboJackets RoboRacing GitHub [https://github.com/RoboJackets/roboracing-firmware/blob/evgp_steering/new_cari/encoder/encoder.ino here].
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		+	= Additional notes =
		+
		+	The RoboJackets RoboRacing electrical sub team has divided the tasks to building the electrical system for Rigatoni into four more sub teams: drive control, e-stop, radio control, and steering control. What is written in this Wiki only focused on the electrical steering control but other sub-sub team members are welcome to add articles similar to this one to fully document the design of the electrical system in Rigatoni. This Wiki is also welcome to be changed in the future with changes to Rigatoni’s electrical steering system.
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		+	= About the Author =
		+
		+	Kyle Carter is a 4th year computer engineering major at Georgia Tech set to graduate in the summer of 2020. He is a member of the RoboJackets RoboRacing electrical team, currently working on the autonomous evGrandPrix go kart, a.k.a. Rigatoni. When he first joined RoboRacing, there was little documentation on the designs for the previous robots and to fix that has decided to document his team’s work on the steering subsystem for Rigatoni in a Wiki article, providing other and new RoboRacing members with useful information while fulfilling a documentation requirement for ECE 3005 (Professional and Technical Communication).

← Older revision		Revision as of 03:51, 26 November 2019
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	=== Encoder Firmware ===		=== Encoder Firmware ===

−	The encoder firmware ~~can be found~~ on the RoboJackets RoboRacing GitHub [https://github.com/RoboJackets/roboracing-firmware/blob/evgp_steering/new_cari/encoder/encoder.ino here].	+	The encoder firmware is quite long, so it better viewed on the RoboJackets RoboRacing GitHub [https://github.com/RoboJackets/roboracing-firmware/blob/evgp_steering/new_cari/encoder/encoder.ino here].

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 The other important part of an automated steering system is knowing the angular position of the steering column. The decision to keep the seat and steering wheel so that it can still be driven manually required the design to include an absolute rotary encoder rather than incremental encoder or limit switches. An absolute rotary encoder differs from an incremental encoder in that it can keep track of absolute angular position, even when powered off, whereas incremental encoders only report a change in position. Limit switches positioned at the limits of the steering angle were considered, however the steering would have to go through a zeroing sequence upon start-up, and the current angle would be held as a variable in software which does not account for physical shifts in the steering position that could be induced in a crash or other disturbance during a race.
-[[File:MFG AMT22-V.jpg|325px|thumb|right|'''Figure 3.''' An image of the CUI Devices AMT222B-V absolute rotary encoder with its various bore sockets.]]
+[[File:MFG AMT22-V.jpg|325px|thumb|right|'''Figure 2.''' An image of the CUI Devices AMT222B-V absolute rotary encoder with its various bore sockets.]]
 An absolute rotary encoder allows for precise feedback to the software of the steering column’s real-time angle, rather than just assuming the angle within the software. It also allows the autonomous system to know precisely the angle of the steering column upon applying power. This way it does not matter the angle the steering column was left in when switching from manual to autonomous control.
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 = Circuitry =
 Since this is a custom build, many of the parts need custom circuitry in order to communicate with each other. All of the designing of the circuitry was completed in Autodesk Eagle and included custom part schematics designed by members of the electrical steering sub team. The schematic shows the different electrical components used and connections made on the steering PCB, including the various switches, connectors and the microprocessor.

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 The other important part of an automated steering system is knowing the angular position of the steering column. The decision to keep the seat and steering wheel so that it can still be driven manually required the design to include an absolute rotary encoder rather than incremental encoder or limit switches. An absolute rotary encoder differs from an incremental encoder in that it can keep track of absolute angular position, even when powered off, whereas incremental encoders only report a change in position. Limit switches positioned at the limits of the steering angle were considered, however the steering would have to go through a zeroing sequence upon start-up, and the current angle would be held as a variable in software which does not account for physical shifts in the steering position that could be induced in a crash or other disturbance during a race.
 An absolute rotary encoder allows for precise feedback to the software of the steering column’s real-time angle, rather than just assuming the angle within the software. It also allows the autonomous system to know precisely the angle of the steering column upon applying power. This way it does not matter the angle the steering column was left in when switching from manual to autonomous control.
 The two most common types of encoders operate optically or magnetically. Optical encoders require photo-sensors and a led to read in differences in light to understand where the absolute angular position of the shaft that they are attached to. Although they are precise, they are susceptible to interference from inconsistent light and dirt, so they are not ideal for use on a racing go kart. Magnetic encoders use Hall effect sensors with magnets to read in angular position, and although they are rugged, they are not as precise as optical encoders and are susceptible to interference from other magnetic fields, which can be an issue if they are positioned near a stepper motor, which would be an issue as a stepper motor is being used in Rigatoni.

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 === Decision Process ===
-[[File:Nema 23.jpg|350px|thumb|right|'''Figure 1.''' An image of the Nema 23 closed-loop geared stepper motor and its gearbox.]]
+[[File:Nema 23.jpg|325px|thumb|right|'''Figure 1.''' An image of the Nema 23 closed-loop geared stepper motor and its gearbox.]]
 In order to have an automated go kart, the go kart must be able to steer on its own, and to do that it must be able to move the steering column on its own. To achieve this, a secondary motor dedicated to driving the steering system must be installed. This motor must be able to rotate to precise angular positions and have enough torque to be able to turn the steering column, so a stepper motor was chosen instead of a servo. Although servos have built in potentiometers and are accurate, many do not have the torque required to maintain a steady position. A stepper motor does have the necessary torque but requires a driver to take the angular input and turn the motor to the correct position. Stepper motors are made up of a DC motor with multiple coils to drive it. These coils are powered in a specific sequence allowing the motor to turn in steps. They have much more torque than a regular DC motor at low speed and are good for precision at low RPM. Because they move in predictable steps, rotational speed control is easily achieved. Unfortunately, stepper motors do not have internal feedback for their position like servos do, so an external solution is required, such as an absolute rotary encoder.