All Acrylic P&T

Well I am using the Pololu A4983 stepper driver. I chose it because of the higher current rating figuring that even at 1 amp that it would be less prone to overheating. In testing it works well at 1/8 step and gets hot but not too hot and never gets worm when the kill line(sleep) is activated. Even at 1fps it's cool to the touch. I am going to put a heatsink on the board as a just in case since the board will be in a tiny box with no ventilation. For my pan & tilt head there will be 2 in a small box. If I ever go to higher current motors I will use Gecko drivers but to do this will require a little more work. As for motor voltage years ago I had a friend who does a lot of Moco work in the movies told me that for micro stepping the supply voltage should be around 4-5 times the rated voltage of the motor. This seems to work in the past with no problems. I also would love to try church's driver board.

cheers
RCFisher

Brian (bdodds),

You have not accounted for the fact that he is using worm gearing, in a worm gear chain the friction from the worm gear to the worm wheel is infinite. This means the load cannot move the rotating shaft of the motor without damaging the drive train (and this would require much more force than the gear chain is designed to support, think applying an additional lever to the camera mount and using that leverage). Worm gearing is typically used for two reasons: compactness of a high reduction gear train (a small worm and gear can produce a reduction ratio of several hundred to one, which would require numerous transition stages in a spur or pulley chain), and to take advantage of the "braking" effect from the infinite friction relationship from the gear to the wheel, that lets one cut power to the motor between moves, even on axes that are working against gravity.

Additionally, stepper motors have greater torque per unit of current consumed than traditional brushed DC motors. Steppers are also capable of moving quite fast when the right conditions are provided, and smoothness is a function of your driver's capability, and the practice of proper acceleration patterns. Very high acceleration can be achieved by using a chopping-style driver that lets you exceed the voltage rating of the motor in combination with parallel wiring of the motor. Using parallel wiring and a chopping driver, one can exceed the rated voltage of the motor by several times and achieve very high acceleration, and therefore very high speeds. Unfortunately, this requires expensive drivers and very well-designed control logic, meaning most trying to solve a high-speed problem will instead settle for a high horsepower brushed DC or AC motor.

However, your position that centering the load on the key positions of each axis reduces the torque required is true, of course, taken to its extreme, the best position for the camera would directly next to the output gear on tilt and slew axes, as then the load is presented with the shortest lever relative to the motor =)

!c

Brian,

Generally speaking, unless you gear down a lot (> 100:1), you should stick with full steps if you intend to use the sleep/disable lines. This is because when the power is removed from the motor, the motor rests back into a full step position. Using a very high reduction ratio (I use 120:1, for instance) the sight change is unnoticable with most lenses, but it does go into the nearest pole when the power is removed.

The motor will not go back into the previous microstep position when powered back on, it remains at the last full-step position. The OMTLE simply hits the disable line between each move, and re-enables only right before the next move is executed. To do otherwise should not have any effect, but to use a little more power =)

!c