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TriMaxGripper & Linear Servo Actuator (GM)

3D Printing a Positional Servo Actuator

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TriMaxGripper & Linear Servo Actuator

It is a custom 3D printed Conforming Gripper driven by a Linear Servo actuator for Grappling things about to float off in Space. (well maybe the metal one could).

Between the Gripper and Actuator is a custom Strain sensor made from Graphite Foam.

In this version I have designed the guide rails into the body of the actuator (for protection and a sturdier steadier motion).

The feedback gear also incorporates a lug which slots into the feedback potentiometer spindle.

I am not sure which MCU to use at the moment :- Parallax Propeller or Deo-Nano (FPGA)
I am leaning on the Propeller as I have written an emulator that allows it to talk with MyRobotLab, which is a neat Gui which allows for a lot of remote experimentation.

This 3D printed version is lightweight, fast and strong.
Specs :-
Stroke 45mm
Speed :- Circa 1cm/sec using a 2 cell Lipo battery
Force :- Easily 3Kg (my kitchen scale max_ed out so could not measure over 3Kg)

It works exactly the same way as a rotational servo, except the feedback potentiometer is driven off the "Lead Screw".

The signal off the feedback potentiometer is tapped into an analogue port of my Parallax Propeller system - the driver board accepts 2 analogue inputs and can drive 2 motors using "H" bridge.

This means that i have not only full control over the acceleration & speed but also a possibility to include a touch sensor on the tip of the actuator ( I have the sensors ...just have to design a fitting 3D mount ).

  • 1 × Micro-Controller Any Microcontoler can be used as long as it has at least 1 analog input
  • 1 × Multiturn Potentiometer 10K 10 turn preset potentiometer
  • 1 × Deo Nano - FPGA
  • 1 × GM general purpose motor
  • 1 × Ultimaker 3D Printer and PLA filament

View all 6 components

  • The System In a Nut_Shell

    chiprobot08/20/2014 at 14:22 0 comments

    It is a 3D printed Conforming Gripper actuated by a 3D printed linear actuator, controlled locally or remotely

    The basic idea is to promote 3D printers as standard equipment aboard a Space station.

    This way anything that gets broken can be easily replaced..... even designed by someone back at Houston... then beaming the STL file to be printed at the space station.

    Also each Astronaut will have in his/her pocket a number of FPGA chips .... as they are like Programmable circuits capable of running systems in parallel.

    All the 3D print STL files are already available as Open source ....links in the description.

  • Conductive Graphite & 3M Ear_Plugs = Sensor

    chiprobot06/25/2014 at 20:55 0 comments

    Just had my delivery of Conductive Ink & 3M Ear_Plugs !!!!!

    I have started to make some custom Resistance Force sensors to fit to the push rod end of the actuator.

    They will be used a a Force Feedback system so i will be able to calculate pushing forces..

    The video of how I made them can be found Here :-

    Its a messy job "2 by 2 Hands of Blue" however the results are promising - just have to design 3D printed housing for them.

    This is the first "Stab" at creating some sensors.....

    Here is a test of the foam sandwiched between two halves of a finger tip and lined both sides with copper foil for connectivity.

    The resting resistance is circa 700 Ohms lowering down to 300 Ohms on compression.

    Starting to take shape :-

    Compression Chamber test print No.1 

    I need a Pull sensor and not a Push sensor so my first idea is to create a sliding piston type (the 3M Plug only alters slightly in diameter on compression meaning that it needs little clearance with the side wall)

    Have to process 3M earplug and the Galvanised screw should be a Nylon one (or maybe not - have to test after ink is dry)

  • Which GM Motor ?

    chiprobot06/23/2014 at 16:01 0 comments

    A number of Hackaday members have PMed me asking which version motor is used.

    Its a  pretty generic one - and below is a Schematic of the dimensions that will fit my 3D chassis.

    There are a number of variants of this motor type and there are even different Gear / voltage versions.

    Search keywords ( DC Gear Motor yellow ) will get you in the right direction.

    So anything that resembles these dimensions can be used.

  • Printing advice

    chiprobot06/05/2014 at 09:39 0 comments

    A number of people have contacted me with regards to the 3D building process to make one themselves :-

    My best advice is only to be careful whilst printing the gear part.

     .... its printed with a wall thickness of 0.4mm

    as it makes a 0.4mm spline that fits into the slot of the feedback potentiomenter.

    If your printer fails to make the spline then you can easily slot/melt in a thin metal vane. (no worries)

    Its also a good idea to print the Leadscrew first to see how your printer deals with the overhangs involved (If they dont form neatly then reduce your Z steps to finer detail .....

  • Linear - Glue Stick .....noooooo

    chiprobot06/05/2014 at 09:22 0 comments

    Why I designed this Linear Servo Actuator....... (the long story behind)

    My old project Glue Stick + Servo = Linear Actuator  had been troubling me for a number of years :-

    It was bulky and Glue_y...... although it used off the shelf parts, it was not one of my neatest constructions... however it worked - and is still working..

    My latest 3D printed actuator will be replacing the one I used to control my TriMaxGripper

  • My Robot Lab

    chiprobot06/05/2014 at 08:58 0 comments

    Currently the actuator is being controlled by MyRobotLab Open Source software

    It is an Arduino/Mega based system environment with great connectivity for  Robotic control .

    Though I am currently writing a Parallax Propeller Service for the above to rev up the Baud rates.

View all 6 project logs

  • 1
    Step 1

    Its prints without support in the orientation of the supplied STL files.
    I print mine with 0.1mm Zaxis 

  • 2
    Step 2

    I choose a Wall thickness of 0.8mm for most parts ....

    ... the Feedback gear was printed using 0.4mm wall thickness

  • 3
    Step 3

    Sand down the guide rails "Slightly" to enable a glide fit, you can even lubricate them with grease from a "Lip Gloss"

View all 4 instructions

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Discussions

OneShot Willie wrote 07/09/2014 at 21:48 point
I was thinking of the spring of a common ink pen in a hole that exposes the side of it, thus creating a range of resistance along the travel of the post. As such, even a slot cut into the side of the piston wall with a flat piece of copper would work, and probably be less resistance now that I think about it. And, if the earplug was impregnated with conductive material, or perhaps had it incorporated into the material, you could use a connection from the push/pull rod to complete your rheostat.

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OneShot Willie wrote 07/08/2014 at 23:24 point
I wonder if you could create a place for a spring to be embedded halfway through the wall of the pull sensor, and make a "halo" of wire around the foam itself to create a rheostat.

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chiprobot wrote 07/09/2014 at 15:21 point
Thanks for the feedback.... sounds a good experiment to try out...
Indeed I think its possible if you use Graphene..(which is processed from Graphite) which can be heated by applying a voltage across it.
I have seen it done Here :- http://www.youtube.com/watch?v=ADrb6jFdfLU&list=PLbQqm4rNo625vtlCny-OP02R3cKyawZZj&feature=share&index=9
Hmmm heating elements (even mini ones) would be profitable in many applications.

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laurens.weyn wrote 06/22/2014 at 13:31 point
I had this idea too! I even did the whole glue stick with sliding potentiometer prototype you did! I used a DC motor instead of a servo, but other than that exactly the same thing: http://imgur.com/2338tiu
I didn't have a 3D printer (and still don't) so I was never able to get any further, and I'm not good with 3D modelling anyways. I really wanted to do it though.

But yes, LOVE this project! I want to get a 3D printer just so I can print a bunch of these. It would be great if you made one with a longer range as well (just a suggestion)

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Jasmine Brackett wrote 06/12/2014 at 00:27 point
Hello Chiprobot, love your stuff on Let's Make Robots. Can't wait to see what you come up with next on Hackaday Projects.

We are really pleased you want to take part in The Hackaday Prize. We've updated the submission process, so if you want to officially enter this project - login and use the 'submit to' under your project images on the left hand side.

Also, we're starting community judging soon, so now is the time to make sure you've added all the details to the project to give it the best chance of winning. You may want to tailor your description to make it clearer to people why it should win and how it's 'connected'.

Got any questions? Give me a shout. Good luck

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