17 Days To Zero-G: Gripper Parts Released, Rotational Sensors, and Other Electonics Stuff

Ok, with only 17 more days to go until our flight, how are we doing?

  • The parts for the first-iteration gripper mechanism have been released for production as of today. Here’s a screen print from Solidworks of what the assembly looks like:
    Gripper Rev 2a Assembly

    This is basically half of the planned gripper mechanism. With the joints oriented horizontally like this, we should be able to test this in 1g without having to worry about what happens to the pads when you turn the joint lockers off. The weird pad shape is to allow for better conformability to the target surface. At least kinematically this should work for spherical surfaces of 6″ diameter and greater.

    We’re about a half-day behind our original plan, but should have hardware in to test a functional prototype this weekend. The idea being that if something doesn’t work as expected, we still have two weeks to work on a backup plan or a modified approach.

  • While it isn’t on our critical path, I really would like to have angular position feedback on each of the “bogies” (the crescent shaped parts). The current plan is to have the joint locking and pads activated manually by the person running the experiment, but the long-term goal is to make this fully automated. Due to the characteristics of the system (as discussed in previous posts), we needed a small, lightweight sensor that also does not provide significant stiction or torsional resistance at the joints. As part of the consulting work Altius did last year, I researched angular position feedback options, and found a really sweet non-contact sensor option that we now want to try out. The sensors are ~11g each, very compact, and the “target” and sensor body are not physically connected. There still is some technical risk, but they’re cheap enough that we’ll order a few to test out this weekend. Here was my first stab at a model for mounting the position sensor onto the current design.
    Angular Position Sensor Concept

    It’s still in the conceptual stage, but we’ll be doing some testing early next to make sure that it can work for our application.

  • We also did a design review on the electronics system, and ordered the gearmotor for driving the boom. Since the joint lockers need 24V, I’m going to have to go to a 7cell LiPo battery (which also means getting a new charger). This also means that with a gearmotor rated for 12V, we might be able to get peak speeds in the 2-3ft/s range. That’s complete and total overkill for this project, but having the ability to “turn the thing up to 11” if we ever want to is nice.

Hopefully tomorrow we should start getting back into the boom deployer detailed design, with the hopes of having the hardware for that finalized and out for production by Friday.