For our grabber mechanism, we are designing a claw-like design that uses both a rigid frame and flexible TheraBand to gently and accurately pick up objects of various sizes and weights.
The rigid frame is comprised of two flat, four sided, frames, tensioned together at the start and pulled apart with two servos when going to grab an object. When completely closed, the rigid frame supports the object from the bottom and ensures the object is secure.
The TheraBand, which surrounds the sides of the frame, creates a wall in front of the frame. When the frame closes on the object, the TheraBand bends around the object, creating a tight and secure grab on whatever object is being picked up.
We chose to go with this design because it is lightweight and allows flexibility in what can be picked up. Because we don’t know the specific dimensions and weight of the object we will be required to pick up at competition, this design allows for flexibility to gently and accurately grab any object less than 20cm^3 and 2 kg.
Features and Capability
Theraband
The use of TheraBand allows for a wide range of objects of various shapes and sizes to be secured. By attaching theraband across two rigid frames opposite one another, the object can be centred between these two planes, which are then actuated shut. The elastic force of the TheraBand will increase as it encloses to fit the object. With this, the elastic force creates a strong enough normal force with the object in the horizontal direction, which will correspond to a higher friction force between the theraband and the object thereby opposing the gravitational force of the object.
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Actuation
The grabber actuates the two rigid frames allowing them to close around the object being picked up. This is accomplished using a central shaft in combination with two servos which are mounted to the frame. String is attached to either frame, which connects to a pulley attached to each servo on either side of the grabber. Once activated, the two servos winch the frames in opposite directions thereby opening the grabber. Actuation in the opposite direction in order to close the grabber is done mechanically using elastic bands, which will force the frame shut once the object is secured. This was done in order to reduce power consumption during flight, as power will only be drawn initially to open the grabber when picking the object up.