We are using three Pololu SMC 24v23 controllers to drive two linear and one rotary actuator, all via UART with the Pololu protocol.
For security reasons we are looking for a way to override the UART commands in case of emergency, for example if the main microcontroller that sends the UART commands fails.
We have seen in the manual (Sections 4.3 and 4.4) that unused RC channels can be used as Limit Switches. This functionality is useful with the rotary motor, which only needs to be stopped, however, in the case of linear actuators, in an emergency one needs to fully retract and the other one to fully extend.
Is there a way to configure this behavior with unused RC inputs or modify the firmware to achieve this behavior?
That is, one of the drivers to stops the connected motor, another to drives it fully forward, and the third one to drive it fully backward.
Unfortunately, there is no way to configure the Simple Motor Controller (SMC) to behave that way with limit/kill switches.
You might be able to implement that kind of fail-safe override into your microcontroller’s software, but that doesn’t address your concern for your main microcontroller failing. For example, you could use a kill switch on the SMC you want to simply stop, and have your main microcontroller poll that SMC with the “Get Errors” command. Then, while the limit/kill switch error is triggered, you can have your program move the actuators on the other SMCs how you want.
In fact we already have the functionality implemented in the microcontroller; we are looking to add another layer of security to the system.
We are considering implementing limit switches on the RC inputs so that the SMCs stop moving the motors and directly apply the necessary voltage to the controllers output, do you know if this would be safe for the controllers or should we find a way to disconnect them with a relay?
If possible we would like to avoid the use of relays, as they are prone to failure and we could be adding more problems than we avoid.
I do not recommend applying a voltage to the motor outputs on the Simple Motor Controller.
By the way, please note that the RC inputs on the SMC expect an RC signal (even for use as a limit switch), so if you are planning on using normal momentary switches, you would need to use one of the analog input pins.
By the way, please note that the RC inputs on the SMC expect an RC signal (even for use as a limit switch), so if you are planning on using normal momentary switches, you would need to use one of the analog input pins.
Ooh, that’s right!
Can we log a ticket requesting that behavior be added for the Alternate Use of the analog pins in the firmware?
Given the current options (None, Forward limit switch, Reverse limit switch, Kill switch) it seems that it would be easy and very useful to add two more (Forward move switch and Reverse Move Switch).
