I started to search information about the new motor controller - Talon. I saw there is a function of Breaking and Coasting (which only now I noticed that the other motor controllers have). I tried to search for more information about the functions, but it just confused me more. Someone can tell me what are those functions (Breaking and Coasting) and what they do?
In addition to my searches on the Talon. My team used until now the Jaguars motor controllers. Is there more pros in Talon than the Jaguars? What are they?
The coast setting causes the motor to continue to coast to a stop after voltage drops to 0 volts, whereas the brake setting causes the motor to more abruptly stop when voltage drops to 0 volts. Im uncertain as to the inner workings of the motor controllers which allow this functionality, so someone else can help out there hopefully.
Pros for the talon are:
Smaller footprint
Lighter
Has a complete conformal coating (no worries with metal shavings around them!)
Pros for the jaguar are:
If you plan on using CAN, this is your only option
The difference between brake and coast comes into play when the command being sent to the motors changes from some nonzero command to a zero command. When the command is nonzero, obviously, the motor will be spinning; changing and keeping the command at zero will eventually let the motor stop.
Brake and coast are two different ways to allow the motor to stop. If the motor controller is set to coast, when the command changes to zero, the motor controller simply uncouples the motor from the power, and lets the friction of the system bring the motor to a stop. When a motor controller is set to brake, however, it not only uncouples the motor from the power when the command changes to zero, but also shorts across the motor’s terminals. This brings the motor to a stop more quickly because the motor, which is still spinning by itself, acts as a generator that, because its terminals are shorted together, now is powering itself to spin in a direction opposite the direction that it’s spinning in.
For more information, look up how an H-bridge controller works.
Hey thanks for the information!
As a result of this information and thinking about it, another question came to my mind. If I click on disable, do the motors still spin? If yes is it legal on FRC competition?
If the system is working as designed, with no broken or miswired components in the chain from cRIO to DIO module to Digital Sidecar to motor controller, then all motors and relays are turned off when the robot is disabled. That is the entire point of the Disabled mode.
If motors still run when the robot is disabled, your robot will not pass inspection.
I think you’re asking if it’s ok if a motor on the robot coasts to a stop even when disabled.
Yes, this is permissible* as long as it is occurring due to a mechanisms momentum and not a motor continuing to receive voltage from a speed controller/relay.* Whether you use the brake or coast setting is entirely up to you; you are neither required or prohibited from using it.
This does bring up a topic on safety to consider with any motor powered mechanism. Even when dynamic braking mode is active on a speed controller it will still take some non-zero amount of time for the mechanism to come to a full stop. So remember that not only will dynamic braking not hold a device stationary, it will not instantly stop a mechanism like, say, a shooter wheel. Always give all robot components time to come to a full stop after disabling before considering the robot safe to approach.
In terms of linearity and motor control, the Jaguar is sliiightly better than the talon, but both are superb compared to the old 884s. Jaguars allow you to use CAN and all the cool features along with it. However, Jags are often seen as less robust.
Talons are brand new this year, and I’m not too sure how they’ll hold up over the course of the season. However, they do have very nice linearity and also have the benefit of being completely debris proof. Because of the smaller robot body size this year, Talons are going to be much easier to find space for.
According to the experiment performed by Team 2928, Jaguar top speed and Jaguar reverse speed are identical. Talon top speed and Talon revese speed are not. In addition, the Talon motor profile shows much more noise towards relative minimum and maximum points than the Jag does.
I assumed that more percise speed control would make for better driving, especially while turning. Did I miss something in making this assumption?
Those tests are interesting, but they were run with essentially no load (except windage and vibration) so they really can’t be used as a motor control metric for loaded applications.
Also, most of the things you noted are likely just due to sensor noise and decoding. If you look at the Victor graph, you can clearly see the quantization in the sensor readings.
Look at the time and RPM scale on the graphs and you can get a ballpark idea of the amplitude and frequency of the noise. Compare that to the physical system under test.
Under load, Talons and Jaguars are both quite linear.
Thanks for pointing that out, I hadn’t knoticed that before. I’ll be sure to make sure I know what I’m talking about next time I go around dispencing advice.
