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Monthly Archives: January 2012

So I’m back at school again, so I returned to where I left of with the dog. The chassis has been sitting around in CAD form for a while, two days ago I printed this thing. It’s my first time using one of the commercial 3D printers. It’s the same 3D printer I keep seeing at universities, of the Dimension brand, that prints extruded plastic with a weaker support material.

For a job the size of the quadruped, the print time was 44 hours. The chassis had to be put on its side and diagonal across the printing bed to even fit.

When it was done printing after 44 hours, it was a piece of plastic encased in a support material block. For the fancy Objet printer in the other lab, the support material seems like a powdery material you have to pressure wash off. This material you had to peel off with your fingernails and some metal picks resembling dentist’s picks.

And after some frustration and an hour or so of picking away, it looks like this:

The little gaps will need some creative sanding, and I’ll have to re-bore the holes. Otherwise, I’m getting closer to mounting the motors, legs, and valves. The next step is to 3D print the precision valve parts with the UV resin Objet printer.

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I was pretty happy with my previous quadrotor build, because it was good for its purpose (to provide aerial shots with the GoPro camera). It was large but stable with its long arms, but those arms also added much additional weight to the frame. Moreover, the entire thing was made out of wood and steel machine screws.

My main goal was to make it light and small enough to work as an aerial surveillance drone that would last for practical lengths of time. Since Spirit MK2 is in fact modular and can thus house a helipad, my thought at the time was to create a larger landing platform (Spirit) with its tank tread drive modules and have it carry the quadrotor to its destination. The quadrotor would then fly vertically, take a 360 panorama of the landscape and maybe fly around any areas of interest, then return to the mother-ship (turning Spirit into an aircraft carrier!).

It would be a wonderful splicing of two of my projects (a drone within a drone). As mentioned in earlier posts, I bought a very cheap video camera transmitter/receiver combination that I have housed on this quadrotor. At 40 or so grams, it certainly weighs less than the 400g weight added by the GoPro and mount. With only 150ft of transmission range, the system would greatly extend the usable distance of the quadrotor if the video receiver was mounted directly onto Spirit and later relayed back. And with that, here’s my progress on the MiniQuad so far:

The arms are now aluminum C beams, but the mounting plates are still particleboard. It seems I’ll never fully upgrade to metal until I’m able to buy a mini-lathe and a mini-mill. Fiberglass and carbon fiber were out of the question of course, since I’m limited to the selection at the Home Depot, and I was not able to find any source of significantly large pieces of styrofoam to cut. As a result you have a (proportionally) lighter and compact quadrotor. Motors are now directly mounted to the beams, and I’ve added some plastic landing gear made of Polymorph/Shapelock/Instamorph material. Those standoffs you see there are in fact wooden dowels.

The landing gear was heavy and failed often since it was a last minute add-on with zip ties on the previous quadrotor, so this new addition is a nice feature. The whole assembly is lighter, I promise! It was worth the hours spent rebuilding a smaller chassis. Here’s the MiniQuad’s frame next to the BigQuad’s frame:

The scale may not be apparent in the picture but the diameter of the Mini is less than half that of the Big. I have no idea on how this will effect its wind stability but this smaller size allows the quadrotor to sit on the central module of Spirit without any problems.

As of now, the MiniQuad is almost complete mechanically. The two standoff totem poles in the first picture will be replaced with a lighter material, and will support the canopy of the quadrotor. I’m hoping for something fitted and nicer than last time (a plate of plexiglass) to protect the electronics from dirt and flips. The rat’s nest wiring is shown in the next picture. I’ll clean it up after everything is sorted out.

Here’s the camera mount. It’s the same Polymorph material molded around the camera. This stuff is getting really useful when I don’t want to machine anything. Great for low strength, custom mounts!

My next step in this process is reconfiguring the software on the Arduino. I’ll probably do that tomorrow, but due to sudden and odd rain (Southern California) I won’t be able to do many outdoor tests. Since my brother’s room is vacant after he moved most of his stuff out to school I’ll fly it around in there. Video transmission does work, but it can only display on screens for now. I’m waiting for a to-USB adapter so I can record/view the video from my laptop.

 

The x-axis is slipping in the reverse direction. Forward is fine, maybe a little oil will fix it. Y and Z axes work just fine, but the motor doesn’t like low speeds with the motor controlling program I wrote. I’ll have to change some of the pulse timing for smoother operation. I found out the set screws don’t really work with threaded rod, so I’ll have to make some solid shaft adapters. The control will come soon! It seems easier to write a G-Code parser for the Arduino right now and just have the printer blindly print files, but a nice interface like on Replicatorg might be nicer. I might just end up doing both, since writing it myself will ultimately be more customizable than modifying the source code. It’ll be important once I start using some funky tools.

3D Printing has risen to an undeniable level of popularity in the last years. From something that was hardly known to be possible to the public, 3D printing has made it to public access. Projects like the RepRap and the Makerbot have gained some momentum. My own project team, Fab@Home has done its part to contribute to this community.

So here’s where I enter. My main interest with 3D printing technology was to apply it to bioengineering. Take some cells from various tissues you want to reproduce, and culture them in a bio reactor. When the cells are sufficient in quantity, load them up in some form of semisolid gel and extrude them with extreme accuracy. Under the right biotic culturing conditions, and with the right blueprints and precision, you can reproduce tissues. Combine those tissues, and voila! ORGANS.

But it doesn’t just stop there. Of course you can satisfy the organ donor waiting list and help hundreds of thousands of people live normal lives again. But there is more. Say you have vestigial features you have in an organ that you could be better off without. Why not harvest some cells and rebuild a new, better organ to accomplish what you need more efficiently? With organs made with your own cells, there would be no chance of rejection. Organ printing can do things impossible to achieve with regular evolution.

There’s more. My brother suggested this one to me. In agriculture, highly developed breeds of corn are developed through genetic modification. Each corn plant must be propagated by hand by trained technicians. But with 3D bioprinting, there is so much more you can do. Engineer a convenient capsule to house the plant and artificially create your own seed packets for an otherwise fragile sterile plant! Print these out in mass quantities to grow crops that are otherwise unreasonable to use. Of course it’s a stretch in development, but I’m sure engineers will not fail to impress with their innovations.

Now imagine layering cells from different organisms together so closely that they develop in unison and equal to one another. Imagine a chimeral tree that produced different fruits at different times throughout the year, or an animal that contained the genetic material of different species that were otherwise incompatible. Imagine silicon printed with living cells. Transistors and neurons printed together to form viable human/machine neural networks! You can tell I’m excited about the possibilities with this technology.

So here’s my first 3D printer:

Only the chassis is shown + motors. If may not be the most efficient mechanically, but I’m proud to say that this printer was entirely of my design. Only if you count the current extrusion tool too, which I modified and developed as my assignment on the Fab@Home team. The whole thing is made of acrylic, which I got cut since I don’t own a laser cutter (though it would be nice considering the reasonable cost of these lasers).

Here are some of my CAD drawings in designing this thing. On and off, acquiring the parts (it’s surprising how difficult it is to find accurate 3/8″ aluminum rods) and designing the printer took part of my fall semester. I didn’t have time to get the acrylic and assemble the whole thing until winter break when I got home.

First iteration concept. I tried to make the extrusion surface independent of the 3-axis gantry to make sure vibrations from the motors wouldn’t perturb the printed object.

Second iteration (I discovered the scene/render option in SolidWorks)

With the stepper motors and the 1/4″-20 standard (not the expensive Acme stuff) threaded rod, the setup can theoretically reach tens of microns of resolution with microstepping. However, due to the inaccuracy of my extruder, that resolution probably won’t make much of a difference. The extruder I have is a syringe with a plunger that is driven by a drive screw that is driven by a continuous rotation servo motor.

Comically, the syringe tubes were taken from the sharps disposal section of my lab (it probably wasn’t that wise of an idea). Good thing the lab wasn’t dealing with anything medical. I will have to replace them with sterile tubes once I begin wet testing, since contamination is a huge issue.

Here’s the extruder:

Clear acrylic looks nice, but it’s terrible to photograph effectively.

I’m using EasyStepperDrivers from Sparkfun to drive the stepper motors in this project. Coupled to an Arduino coupled to ReplicatorG (for now until i develop my own), I’ll have to make a custom .xml file for the servo extrusion configuration.

The next challenge for this project is to get viable structures to print. It’s a difficult problem right now for bioprinting, as finding a 3D blueprint of an organ or biological structure requires identifying hundreds of different materials. My two material setup probably won’t be able to accomplish that, so for now I’m stuck printing with two materials.

I’m ordering sodium alginate + calcium chloride to experiment with. When mixed, the calcium causes the alginate to form closer bonds and become more solid-like. With some living cells in between, I can hopefully build up some reasonably sized structures. I intended to use the cells from a rosebush on my lawn, but my winter break is proving to be too short for me to culture the cells now. Added with an internship at an electrical/civil firm I’m working for right now, it’ll have to wait till the semester. I hope I have time.

I was debating between two styles of approaching bioprinting. Some scholars researching bioprinting use inkjet technology to deposit bio-ink laden with living cells to deposit many small layers of living cells to build up tissues. Since the volume of the drop of liquid ejected from an ink-jet is reasonably close to the volume of a cell, the inkjet can reliably deposit cells to their target. However, inkjets use bubbles generated by heat from a resistor or by mechanical shock to create such precise droplets of ink. Therefore, cell survivability is an issue. The other approach is to bundle many cells into workable unit voxels. The larger units could be placed accurately while maintaining cell survival. I’ve decided to make both systems.

Coming up next semester, (if I can get access to a biolab) actual printed cells! And a belt drive inkjet system.

To avoid the trouble of pouring another motor mount, we bought a new mount from the Robot Marketplace. It’s pretty nice, but pretty simple. It makes me wonder how hard it would be to avoid all this casting mess with a mill. A mill would be nice.

It’s interesting to see how far we’ve progressed on this project by investigating the mounts. We started off with some jigsaw’ed 2×4’s that clamped down with rubber sheets for friction. Many facepalms were had. Working on this robot was another educational experience.

It was like communicating with myself last summer and wondering why in the world I chose to do things the way I did. Axle too large? Hammer it in. Discount possibility things will have to be taken apart later.

Here’s a nice garage-spanning table I made with my dad as a bonus. It’s nice that we don’t have to work on the floor anymore.

Here are the failed attempts at shaft collar wheel hubs that sheared off during our previous run. We started with JB weld, moved to epoxy/gorilla glue? mixture, and settled with some extra strength epxoy. Still didn’t work.

However we have opted to mount the reduction sprocket directly onto the wheel. By the sheer weight of the things we were afraid the hardened steel would be impossible to machine with our inadequate tools. However, we found out that the inside is extremely soft most likely cast iron. Machining worked well, and this solution seems like a confident final solution to our wheel hub problem. It’s a wonder we didn’t think of this painfully obvious solution earlier. More facepalms all around.

I worked at the urological department of UCI Medical Center as an intern for robotic surgery, and it gave me some ideas on how to improve robotic surgery and how to improve its cost effectiveness. For the multi-million dollar price tag, robotic surgery doesn’t currently do what it was cut out to do.

We have yet to see surgeons operating with near telepathic efficiency on patients thousands of miles away. At best it has only been a slight telepresence of a surgeon supervising operators in a faraway room. The Da Vinci robotic system is operated by a surgeon only ten or twenty feet away connected by wire.

Of course this is limited by the heavy and secured datapath that must be maintained over the course of the surgery to effectively carry out the surgery. But given the high speeds of information propagation these days, why isn’t telesurgery more popular? Surgeons should be able to operate in places too inaccessible or distant from their current location with near full effectiveness (with a nursing staff to match of course). And with some improvements in machine vision, maybe even fully robotic automated surgical procedures in the future.

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So here’s my first robot arm. I’ve had the CAD files done for a while, but I had no time to actually fabricate this thing until now during winter break. The 4-axis frame sans gripper looked like this rendered in SolidWorks:

The base didn’t  turn out as expected since acrylic is expensive and I didn’t want to waste any scrap. I substituted it with a smaller piece of acrylic mounted on some cut up 1×2’s. Yes wood, we meet again. The frame itself was laser cut out of one (surprisingly small) scrap of 6mm acrylic. The arm frame I designed isn’t exactly the strongest or most stable of all possible configurations, but adding steel servo supports was too expensive for my college budget. As a result the base rotation joint is unnervingly unsupported. I will probably need to add a shaft support later if this arm is going to make any fast movements.

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The four servos for each arm DOF are all Hitec brand servos. The gripper and the end effector servo are both from Sparkfun electronics. I was very unimpressed with the gripper. Nothing fit like the site advertised and the medium servo they said would fit needs to be mounted at a strange angle to even fit mounted on the gripper, which seems to be shamelessly taken from Thingiverse (or maybe it is the other way around, which in case I offer my apologies). Either way, the gripper is made of aluminum with decently strong construction, though it is pretty imprecise in its bearings. I won’t be doing any precision gripping with this particular effector.

I’m currently working on some air muscles too, to try to make a Festo style fin ray effect gripper out of molded Polymorph. We’ll see how that turns out later on.

The arm itself is under strain when the position is not exactly neutral, which may be a problem if the arm needs to hold its position for any amount of time. By the way the servos are humming, it seems like I will have to add some counterweight/spring neutralization of the arm’s dead frame weight. Mounting springs between joints would reduce the required torque output of the servos for holding off-centered positions.

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So how does this relate to robotic surgery/telesurgery? I suppose part of me at the end of last summer thought it would be cool to create a cheap/simple system that would require little data transfer and still be able to effectively operate on patients over long distances. This robot arm “might” have that capability, but I am highly doubtful the precision is even close to acceptable.

Future work: I plan to increase the functionality of the servos by modding all of them with the Openservo magnetic encoders. That way I can use velocity profiles etc. to make it all run more smoothly. I’m currently making a simple control system that uses potentiometers on a miniature scale version of the arm to puppet the arm. In the future I will use servos for force feedback. The potentiometers connected to an Arduino and an SSC-32 board I obtained for free from my lab’s clean out giveaway + some XBee’s + a cheap video TX/RX system might allow me to manipulate objects from a distance. That would be one step closer to telesurgery right? Maybe even mount it onto Spirit MK2 and have a nice military IED diffusing robot clone.

At very least, I’ve downloaded some industrial arm controlling software if I ever want to make five more of these things and start my own production line.

OR maybe even make myself one of those robot arm helpers Tony Stark plays around with in Iron Man. Oh the possibilities.