Tutorial written by Yosser D'Avanzo, 2016.
Congratulations on completing the basic tutorial! Now that you know how to use your Multipurpose Mobile Manipulator robot, we encourage you to explore new gripper designs. One way to create new grippers and attachments are with laser cutting and 3D printing, allowing you to create custom modifications to your robot for custom tasks. Each arm of the Multipurpose Mobile Manipulator comes equipped with up to five slots for servomotors, where each servo can be mapped to a different variable in setLeftGrippers() and setRightGrippers().
The three main types of servos are positional rotation, linear, and continuous rotation. Positional rotation servos are the most common and can have varying rotational ranges they can turn to (usually 0 to 180 degrees). Linear servos extend outwards and are used on the extension arm. The final type of servos are servos modified for continuous rotation. All three are supported for the gripper connectors.
Designing grippers is very case specific: no one gripper can do every task!
That being said, here are a few tips and tricks to help make functional gripper designs:
- Grabbing objects from the sides is usually a lot harder than finding some way to hook them. It isn’t always possible to do this, like picking up a ball, but when possible should be done.
- More joints gives you more flexibility, but also more room to fail. A very dexterous hand with all six servos acting in a new axis of motion would allow for extremely detailed and fine work. The big problem with this is that this also provides six axes where the hand could fail in. A solid piece of aluminum acting as a hook is nowhere near as versatile, but is much less likely to suffer a critical failure.
- Use leverage! Servos come equipped with gear boxes, but that doesn’t mean that mechanical advantages like gears and pulleys can’t be used to multiply that power.
- Make easily printable designs. For example, if a part requires a lot of supports to be printed with it, it might be better to print it in flatter pieces and assemble it separately. Simply rearranging parts can have also huge impact on the success of 3D printing.
- Springs come in many types, sizes, shapes, and designs. Springs are relatively inexpensive and come in extension, compression, and torsion varieties. These specifications can allows weak servos perform heavier and more complex tasks by providing extra force, such as a clutch in a claw to providing oscillating force control.
- Simple 2D kinematics provides information on any joint in a mechanism moving on a plane. Using these equations can allow a robot to raise a glass of water without spilling a drop by keeping the final theta constant. This also plays a huge role in fine spatial manipulation by calculating the motion between tips of joints to exact positions desired.