So I started working on a design for some animatronic gauntlet blades. After looking at several options for motorizing the mechanism I decided on a servo system- primarily for its versatility, light weight and low power requirements.
I obtained a super low profile linear slide to base this on. It has very little friction and is really light weight. The drive servo (an old servo I had sitting around) has been modified to continuous rotation and the internal potentiometer has been retired in favor of a multi turn external pot that will be geared to give position feedback. I modified a servo wheel and turned it into a drive gear to speed up the final drive, otherwise it would be way too slow since most servos are designed for high torque instead of high rpm. The average servo turns around 50 -60 rpm while the fastest digital servos turn around 160 rpm. This particular servo is rated at 94 oz-in. torque and .13 seconds to turn 60 degrees @ 6V. This translates to roughly 77rpm.
In order to speed things up I'm gearing the servo 2.91:1, which gives a rotational speed of 224.07rpm. The final drive will be rack and pinion using a drive gear that is 1.75" diameter (5.495 in. circumference.) If we take 5.495 in. x 224.07 rpm we get a drive speed of 1231.26 in/min, or 20.52 in/sec. This gives an 8 in. blade extension a time of .39 sec. without dropping the torque rating too low to move the blades with some authority. It can always be faster and stronger but this will be a good first test.
The only other option was to make my own servo. I found a small geared motor that turns 350 rpm at 35 oz-in torque @6V. I'd just need to add some control circuitry so time will tell if that proves to be a better solution- at least for light weight blades. I could probably shave .1 second off the extension time using this setup.
Here's what I've got so far-
I obtained a super low profile linear slide to base this on. It has very little friction and is really light weight. The drive servo (an old servo I had sitting around) has been modified to continuous rotation and the internal potentiometer has been retired in favor of a multi turn external pot that will be geared to give position feedback. I modified a servo wheel and turned it into a drive gear to speed up the final drive, otherwise it would be way too slow since most servos are designed for high torque instead of high rpm. The average servo turns around 50 -60 rpm while the fastest digital servos turn around 160 rpm. This particular servo is rated at 94 oz-in. torque and .13 seconds to turn 60 degrees @ 6V. This translates to roughly 77rpm.
In order to speed things up I'm gearing the servo 2.91:1, which gives a rotational speed of 224.07rpm. The final drive will be rack and pinion using a drive gear that is 1.75" diameter (5.495 in. circumference.) If we take 5.495 in. x 224.07 rpm we get a drive speed of 1231.26 in/min, or 20.52 in/sec. This gives an 8 in. blade extension a time of .39 sec. without dropping the torque rating too low to move the blades with some authority. It can always be faster and stronger but this will be a good first test.
The only other option was to make my own servo. I found a small geared motor that turns 350 rpm at 35 oz-in torque @6V. I'd just need to add some control circuitry so time will tell if that proves to be a better solution- at least for light weight blades. I could probably shave .1 second off the extension time using this setup.
Here's what I've got so far-