I'm trying to replicate this project at home, wherein strings attached to fingers and pulled by servos are used (instead of difficult pneumatics) to simulate an object in a glove as a version of haptic feedback. For example, if I wanted to simulate a cube in virtual space, I would not allow the user to bend the glove past the dimensions of the cube. To accomplish this, I have two ideas.
The first is to use a linear motor to resist on it's own. I've chosen to use a linear motor based off the info found in this question, but if you have other recommendations, let me know.
Alternatively, I'm worried that having a user pull against it will weaken the servo and shorten it's lifetime, so instead I should use a clamping mechanism on the string. However, is this a legitimate concern in the first place?
Best Answer
you could recreate that, but from a quick look at the design, it has several flaws. The fishing line used will be slightly elastic, limiting how hard a contact it can simulate. It only drives in one direction, so whilst it can simulate a grasp of a small object it cannot simulate interactions that force the hand closed. Also it is not grounded, so cannot simulate the mass of the object you are holding. Also you will have to have some constant torque on the cables to make them retract, even in free space.
You cannot use the type of motor you suggest for one simple reason. The device is by its very nature backdrivable. What this means is that when you are not contacting something the cable is pulled, and the motor spins. This means that you need the motor to have very low friction/inertia for your fingers to feel like they are in free space.
The best option is a coreless dc motor, as this has the lowest inertia. Using such a system when the user pulls producing more torque then the motor, the motor just spins backwards, with no damage to anything. You will probably need to only drive motors at continuous current, as in haptics you tend to drive actuators at stall for prolonged periods.