Servo Controlled Hat-Bot
With my Robo-Drums, Wristy-Bot, the simpler parts of the system have come together quicker and easier than I'd have expected in my wildest dreams. Not so much the Hat-Bot frame.
The picture above is the 3D render of the frame I'm building from aluminium parts of some discarded gym equipment, left on hard rubbish a few years back. The bottom cymbal will rest on pad in the middle of the bottom rail. The top cymbal will hang from an M6 bright steel rod that will run through the centre holes at the bottom and top and be lifted and dropped via motor on top of the frame. I'd been thinking of using a car door lock motor, like with Stick-Bot and Kick-Bot, but it may not have enough thrust to quickly operate a heavy object like a cymbal, its shaft clamp and shaft. There's also the problem of needing 3 positions, closed, half open and open, to get the necessary full range of hi-hat control. I'd thought of adding a potentiometer and coding servo control, but the door lock motors have 2kg maximum thrust and won't provide the necessary thrust in a servo environment for the necessary acceleration ncessary for high tempo hat height position changes.
Then today, I came across the Australian outlet for Maker Store, the commercial affilate of OpenBuilds, going by the branding logo, at least. As well as the usual run of parts and toys for CNC machine nerds, they also do servo motors (useful on CNC machines for automated tool changes) and the ones they sell have thrust that peaks at 12kg/cm, rather than my door lock motors' 2kg at the end of a 20mm "bang-bang" motion. The servo motor has 3 times the thrust, metal gears and could be constructed with a rack and pinion lift mechanism. (Rack and pinion, for the non-technical musicians interested in this stuff, is a toothed bar (rack) that matches a round gear. (pinion)
Your car probably has "rack and pinion steering" with a pinion gear gear at the bottom of the steering shaft and a pinion between the front wheels, allowing the turn of the steering wheel to create horizontal motion that pushes and pulls the steering rods to turn the front wheels. Being a Servo motor means there's an elctrical feedback that can measure where the motor is turned to. It senses where it is, so stick-bot can know where "open", "half" and "closed" are. The microcontroller does the rest, reading the appropriate MIDI signals to set the top cymbal position.
A high thrust servo motor, with metal gears and interchangeable mechanical fittings, makes for a potentially better fit for this heavier lifting job than the door lock motors will be doing on the simpler parts of Wristi-Bot. There's a reason drummers use their foot on a pedal to open and close the high-hats, it's harder work that whacking a skin. In fact, that's also why Kick-Bot will probably get 2 door lock motors in parallel, because it needs more energy to make a kick drum boom. (But it doesn't need precise positioning, like a hi-hat pair.)
Even better, these heavy duty servo motors only cost $5 more than the door lock motors and it cost me $6 for a linear, short action pot and it turned out to be too stiff an action, that would suck thrust from the main job, lifting the top hat. No brainer, really.
Here's an animation of my preliminary servo hat lifter...
...and here's a picture of the Maker Store servo-motor...