Controlling a robot with wheelchair motors and two linear actuators

[wirvin]

I am working on a project with the following requirements. I will do my best to explain the best I can. The robot is basically a “work platform” similar to Jongig’s 4-motor Yardbot. My robot has only 2 motors (hence 2 drive wheels in a skid-steer arrangement), with casters for balance/support. Below is the list of specs that I can give you at this point. Let me just say that I am not a robotics expert by any means. My background is in Mechcanical Engineering.

Drive Motors: 24VDC Wheelchair motors, roughly 6-8A current usage at no load.
Linear Actuators: 12VDC, 150lb actuators with potentiometer feedback (RB-FRA-14) X 2
Any “standard” R/C system (Futaba, Spektrum, etc)

The required functions are as follows:

Drive motors:

• drive forward and back, and turn left and right in a skid-steer arrangement, just like a power wheelchair
• Set the drive speed, basically like cruise control on an automobile.
• When the remote/joystick is moved again, the unit must come out of cruise control (i.e. to make a turn), and resume cruise control, either when the lever is released, or when a button or switch is pushed.

Linear Actuators:

• Extend and retract the actuators.
• Set the position of the actuators such that one can be retracted (i.e. when the robot is turning), and the returned to the set position upon release of the lever of push of a button or switch.
• EACH actuator needs this capability independently of the other.

It’s really a two-phase process.

1. I need to get the appropriate controls in place to tell each major component what to do.
2. I need to make it radio-controlled.

I would greatly appreciate any/all input from members of this forum, and I’ll be glad to clarify or add information as much as I am allowed.

[wirvin]

We are already looking at using the Sabertooth 2X25 motor controller for the drive motors, and possibly the Sabertooth 2X12 for the linear actuators.

For the “cruise control” feature, it’s largely based on the configuration of the motor controller and which channels they are connected to.

Could you be a little more specific about what you mean here? This is really the key aspect that I don’t understand at this point.

Thanks,
Will

[cbenson]

Relays alone would do the job - so long as they can handle the current. Motor drivers / controllers are best for variable speed and/or automatic control.

[cbenson]

Some joysticks have a spring return (usually used on the throttle) while others remain in their last position. For a “cruise control” you could use joysticks which do not have a spring return. Just an idea.

[cbenson]

You really only need R/C DC motor controllers. These connect between the R/C receiver, battery and actuators. You can use one dual R/C for the drive motors and another for the linear actuators. For the “cruise control” feature, it’s largely based on the configuration of the motor controller and which channels they are connected to.

[wirvin]

The linear actuators act independently of one another. Is a dual motor drive the best choice, or would individual drivers for each actuator work better? I’d prefer to stick with the dual controller if possible due to the lower cost, but I really just need the best solution. One solution that has been proposed to me has relays and contactors in line with each “side” (+ or -) of the actuator (rather than using any type of controller at all for the actuators). This seems like an over-complicated, and possibly much more expensive, option than what I really need.

EDIT: The actuators will be acting as though they were on a 3-position switch (extend-stop-retract). Is a controller even necessary, or would a relay alone do the job?