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View Full Version : [Project] Handmade 5DOF Manipulator with tactile feedback



Antonb
05-17-2010, 04:12 AM
http://www.youtube.com/watch?v=1qpc4G3NQhk


Materials List:

Polystyrene sheets: 0.5mm, 1.5mm and 2mm thick (Evergreen Models).

Polystyrene tubing: Various

Brass sheet: 0.5mm thick

Brass tubing: Various

Servos & Motors :

2 x HS-805BB (Shoulder yaw & pitch joints)

1 x HS-485HB (Elbow joint)

1 x HS-322HD (Wrist joint)

DC motor with 300:1 gearbox (Gripper)

Tactile Feedback: Quantum Tunnelling Composite (QTC)

1 x custom-made Electrical Rotary Union (Elbow-to-Wrist joint)

1 x SKF Thrust Bearing (AXK 2542) + 2 x SKF Thrust Washers (AS 2542)

Various springs

Polystyrene glue

Epoxy glue

Heat glue

Multi-strand wire

Heat-shrink


Tools List

Scalpel

Studding knife

Small saw

Small files – various cross-sections

Sanding paper

Dremmel

Hand-drill

Vice

M3 & M4 taps

Heat-gun

….generally speaking the more the better!


This is a project I’ve been working on, for a solid month. It is a 5 DOF manipulator arm which has been designed and built entirely in my livingroom without any CAD / CAM. In other words all parts are designed and cut by hand. The material I used was styrene.

A few words about Styrene

The main construction material used is Polystyrene (or simply Styrene), which is widely available on most hobby stores. For bulk quantities or for those coming from the States, you can contact Evergreen Models – they will stock every styrene sheet / tubing you will ever need.

Styrene is a soft, normally white plastic, which is very easy to handle and will bond very nicely when glued with polystyrene glue. I normally design the part I want to make directly onto the styrene sheet and cut it off using scissors. For internal cut-outs I use my Dremmel with a 2.5mm diameter Carbide cutter. If I need my part to be thicker than the sheet’s thickness, I make multiple identical parts and glue them together. When you make parts like that, make sure you leave the drilling for the end - this will ensure holes are aligned across all glued sheets.


http://www.01mech.com/sites/default/files/images/Manipulator_1.JPG


http://www.01mech.com/sites/default/files/images/Manipulator_2.jpg


http://www.01mech.com/sites/default/files/images/Manipulator_4.JPG


This manipulator arm has been built without CAD drawings; entirely with the method described above. It comprises 5 DOFs: a yaw and pitch root (shoulder joints), an elbow joint, a wrist joint and a gripper. The wrist joint is fitted with a custom-made electrical rotary union that will allow for continuous rotation of the end-effector (gripper) without electrical connectivity problems. Basically the electrical rotary union eliminates the need for cables between rotating mechanical assemblies.


http://www.01mech.com/sites/default/files/images/Manipulator_3.jpg


The gripper comprises two fingers each fitted with a Quantum Tunnelling Composite (QTC) pressure sensor. These sensors are basically pressure sensitive resistors that under pressure change from insulators (R >10 M?) to conductors (R < few Ohms). The two sensors are wired in series and the signal is fed directly to the controller of the wrist joint.


http://www.01mech.com/sites/default/files/images/Manipulator_5.JPG


http://www.01mech.com/sites/default/files/images/Gripper1.jpg


http://www.01mech.com/sites/default/files/images/gripper2.jpg


A few words on the control

Each axis of motion is controlled via a 'Supermodified' combo. The arm was built using the first generation of Supermodified controllers which work in conjunction with a magnetic encoder (1024ppr) ( http://forums.trossenrobotics.com/showthread.php?t=3924). The second generation comes with 4 times the resolution (4096ppr) (http://forums.trossenrobotics.com/showthread.php?t=4021) so i am really looking forward to try out those babes on the second generation 6DOF manipulator. Supermodified controllers are direct replacement boards for the original servo electronics, that allow full PID speed and position control of the servo. Based on the ATMega 368P (fully Arduino compatible with half the footprint of Arduino nano and 4MHz faster) also allow for controlling 4 digital IOs, as well as 4 analog inputs.

So for example the gripper’s pressure sensors need not be fed back to the main controller, since the Supermodified controller board of the gripper can handle the analog signal from the sensors and report back to the main controller (in the video that would be the PC). The Arduino merely plays the role of a USB to I2C bridge. Btw the gripper’s DC motor has been a recent addition since its predecessor - a tower pro 90 micro - proved inadequate. The tiny DC motor powers the dual parallel-link finger assembly by using a tiny pulley system having an extra-strong thread acting as its timing belt :))).

The remaining servos have all been “Supermodified”. The joint hierarchy is as follows:

Shoulder (yaw) -> Shoulder (pitch) -> Elbow -> Wrist -> Gripper

The wiring is fairly simple and straightforward since each Supermodified controller can be ‘daisy-chained’ with other Supermodified controllers, minimising complexity and offering a neat end-result. The whole manipulator arm wiring effectively comprises a single 4 core cable (Power and I2C comms), running from one servo to the next according to the hierarchy above. I2C comms are then fed to the Arduino, which for the time being acts as a USB (com) to I2C communication-bridge between the host computer and the Supermodified servo controller network.

Adam
05-17-2010, 08:25 AM
Very impressive work. Bonus points for style and being handmade.

MikeG
05-17-2010, 08:35 AM
That a very nice arm and control system. I really like the rotary gripper.

I per-ordered supermodified v2 a while back with the plan is to build a 6 axis robotic arm.

Antonb
05-17-2010, 10:17 AM
Thanks for the positive feedback. Just to let you know im currently working on a 6DOF manipulator based on the Supermodified and I am soon going to release the designs online

MikeG
05-17-2010, 11:17 AM
Cool... My son and I visited the local hardware store this weekend to pick up materials to build the links.

Do you have the Supermodified v2 boards? I pre-order them a month or two ago and I'm still waiting.

Anyway, the idea is to wire up an embedded web server.

jes1510
05-17-2010, 11:30 AM
Beautiful work! I love the aesthetics. It comes off pretty biological without looking too freaky or industrial. I like!

Antonb
05-17-2010, 11:54 AM
Cool... My son and I visited the local hardware store this weekend to pick up materials to build the links.

Do you have the Supermodified v2 boards? I pre-order them a month or two ago and I'm still waiting.

Anyway, the idea is to wire up an embedded web server.

The Supermodified arrived today straight from the assembly line :veryhappy::veryhappy::veryhappy:

We will be sending-out invoices by Friday. I am pretty pleased so far

Stobs
05-20-2010, 07:58 AM
Very nicely done, quite impressive to me! Makes me contemplate as to whether I'm going to hack my very first servo or not! Ah, decisions, decisions! ;)

gonzo
03-09-2011, 04:52 AM
Hi, Anton.

That's a quite amazing project you built.
I'm curious about the tactile sensor do you use.
Could you tell what brand, spec and where I can buy it?
I'm planning to make a manipulator with compliance control ability.
Looking forward for your reply.
Thanks

djsures
03-11-2011, 05:50 PM
hats off to your hardwork, dude. i can see a lot of passion and time went into the design and cutting each part.