Tuesday, March 8, 2011

Getting Up to Date

So the last few of these blog posts have been recap of what has happened, as far as the project is concerned, in the past couple of weeks.  This post will be my attempt at getting all caught up so I can start to enforce a development schedule.

The current status of the project is as follows.  My roommate and I wired up the robot using electrical tape so that it can be directly connected to the four batteries wired in parallel.  The motors are also tied directly together and share current from the 6V super battery.  We then wired it through an old analog multimeter so that we could gauge the current drawn by the motors.  This way, we don't have to listen to questionable data sheets and motor curves.  Here are the results of our weight testing for both motors.

The peak current is the current required to get the motor started, and the steady current is how much it takes to move steadily along.

The current direction with the robot is as follows:

  1. We will be using all four batteries in parallel to provide 6V to both motors.  This puts less strain on the motors, extending their life, although it will mean less speed.
  2. The motors will be wired together in parallel as well, which means both motors will always turn in the same direction.  While differential steering would be easier to maneuver, using the already provided steering will will make the robot's movements more realistic and applicable to actual cars if the project ever expands that far.  The elegance in this lies in the fact that if appropriate hardware and mechanics are provided, the same software could work identically on many different machines.

Things required to do to finish compiling data are:

  1. Get a force measurement of some sort of how much force is required to turn the steering wheel.  This will probably be similar to the graph above with a weight vs. force graph.  With this data, it is then possible to buy a adequately rated servo to turn the wheel and drive the robot.
  2. The stall current of the two motors.  I tried testing this when my roommate and I were doing load testing, but the current spiked past 20A which was the maximum current of the multimeter.  This data would be good to know when taking into consideration protecting the motor controller from overcurrent.  Stall current will cause damage to the motors so when it is detected, the motor controller can be shut off.
Things that will require doing to make the robot functional:
  1. Research and decide on an effective method of getting the robot to steer.  The only two options so far appear to be using a motor to slowly steer the robot, or buy servo to do the steering.  The motor would be cheaper, but it would require switches and types of control to monitor how far the wheel is turned.  A servo would have this functionality built in, but would be much more expensive.
  2. Finally design and build the motor controller.  Because I still have 8 MOSFETs of proper rating left over, all that is required is for me to design a schematic and finally solder together the controller on a PCB board.
So that's what's left that needs doing and where the rUD2 project is currently.  Hopefully I can get something done this week and finally get the ball rolling.

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