Hello folks,
I’m not to the stage of coding yet and will probably have lots of questions when that time rolls around but for now I’d appreciate some help with components and configuration.
My project is to make a sleigh for Santa Clause. I have salvaged a child’s battery powered car and stripped off everything except the metal chassis and motor/gear train assemblies. I plan to operate the motor drive and steering using an Arduino Uno in conjunction with a 2 axis joystick and suitable motor controllers. When it’s time to code for the motor drive system I’m sure to be back at the forums for help.
My main problem at this time is the front wheel steering system. The sleigh will weigh in at well over 120 lbs so I have a linear actuator (4” stroke, not feedback pot) set up to drive the steering linkage. My thinking is that with the front wheels in straight (neutral) position the actuator is at ½ extended. The ‘X’ axis of the joystick will be used to move the actuator rod in or out to turn left or right. The kicker is that when the joystick is released I want the steering to return to ‘neutral’. One way I think I can do this is to set up a simple voltage divider at 2.5V to emulate the neutral position of joystick and use this as an analog input to the Arduino. If the joystick is moved beyond the ‘dead zone’ the code will enable a second analog input that is fed by the joystick pot and override the fixed voltage. This would push/pull the actuator until the turn is completed and the joystick is released (back to the ‘dead zone’) and the fixed voltage brings the wheels back to neutral.
Can anyone help me by poking holes in this plan or offer suggestions on a better way to accomplish this? Thanks in advance for your time and help.
No need for any external voltage - the fixed value for straight-ahead can be in the code.
But you need to clarify how you are driving the linear actuator - if its a DC motor one without
a feedback pot you have no control loop and it won't be able to return to centre.
You either need open-loop control (stepper) or closed-loop control (encoder/pot).
Hi Mark,
Many thanks for the reply. It's a 12 VDC actuator without feedback. I didn't consider a stepper because of the force I believe is needed. I could mechanically attach a linear pot to the linkage for feedback but don't see where that would help. By using an 'If' statement to apply the joystick voltage once deflection exceeds the dead zone can't the reverse also happen? That is, the fixed level would be reapplied (Else) once the joystick is released and returned to the dead zone?
Without feedback you have no idea where the actuator is at, so releasing the joystick
could be used to stick at the current rate of turn, but not straight line. Perhaps that's
what you meant?
Hi Mark,
Yep, I can finally see the obvious. There must be an error signal to compare with the fixed value in order to get things to return to neutral. The actuator is slow enough that I can probably get by with just moving the joystick the other way to get the wheels back to 'straight ahead' position. Thanks for your input.