I Interned at the exploration division of Honeybee Robotics in Pasadena, California during the summer and fall of 2012. The exploration division of Honeybee Robotics specializes in the development of drilling and sampling systems to be used on the Moon, Mars, or asteroids. The highly experienced team at Honeybee has had three dust removal or sampling tools sent to the surface of Mars and one sample processing system. It was a distinctly different experience from my NASA internships beginning on day one. There was no lengthy IT or safety training I was shown my computer, given a list of requirements for my first drill, and got to work. It was a refreshing change from my previous experiences.
The goal was to develop a drill which could be deployed from one of the small payload containers embedded in the wheels of the Jet Propulsion Laboratory (NASA/JPL) Axel prototype Mars rover and drill into the side of a cliff. These are the basic requirements given when I began my internship:
The drill bit I needed to use had already been selected, a Relton Groo-V 1/8 in bit, which is very effective drilling into hard rocks, especially when combined with percussion. Most of us are familiar with rotary drilling, it is what is commonly used for drilling wood, metal, and other materials. Rocks are extremely hard and brittle. Hammering the drill bit into the hole introduces cracks in the rock, making the material much easier to cut. This results in significantly faster penetration rates, lower energy consumption, and a reduction in bit wear. The drill bit is much tougher than the rock, even though it may not be much harder. This is important because some rocks (such as saddleback basalt) have a compressive strength of 280 MPa, significantly stronger than even the best concrete. Percussion is even more important for drills going to other planets, because water cooling isn't an option.
In the design of the drill, it was decided to use off the shelf parts wherever we could, so a much larger Hilti hand-held rock drill was disassembled to see what parts might be useful. We chose to reuse the percussion clutch components because of the difficulty that it would take to manufacture new ones. The percussion clutch components in the Hilti drill were made out of hardened steel and also had a coating on them, making them very strong and abrasion resistant so the pieces could be slammed against each other many times. Recycling these components saved money and time.
Integrating these COTS components added some difficulty to the drill structure. The stationary part of the percussion mechanism (not shown) has a lot of sharp edges where it was fixed into the drill. The Hilti drill used an injection molded plastic piece to retain that part. Modifications to the percussion clutch would have been very difficult due to the small size and hardness, and it also be difficult to make a negative of that shape in aluminum to secure the part. This led me to 3D print the clutch fixture out of plastic on an SLA machine. While in the process of designing the drill components I concluded that since I needed one small part of small drill 3-D printed, I may as well print the whole thing.
For the drill rotation and percussion I chose a 100 Watt Maxon motor with a diameter of 22 mm, and a 10 mm Maxon motor for advancing the stroke. The drill motor was integrated to the 3D printed chassis and the stroke motor (Z-axis) was mounted to the back of the linear slide. The drill motor had an integrated 2 stage gearbox but still needed an additional reduction of 3:1 for the output. It was a packaging challenge to fit the gears in such a small space but I was able to make it fit, and the flexibility of 3D printing to fabricate any geometry helped.
The sample was collected inside another plastic container, shown above, and was extracted from the drill by rotating in the other direction to deposit it. The percussion worked in both directions and was also a great help in removing the sample.
The final product was delivered to the Jet Propulsion Laboratory in 3 months. During field trials, it was proven capable of drilling through multiple rock types and collecting samples from horizontal and vertical surfaces. Honeybee Robotics had never made a smaller drill, nor one that was as inexpensive as this one, the project was far under budget.
While the project was a success, it did not come without some lessons that were learned the hard way. Recycling components from other products can be great, but you don't always know what you are getting. Our machinist found that the rotary percussive mechanism was hardened not just on the percussive surface, but almost everywhere. As a result one of the tapped holes had to be made with an EDM. Luckily, this operation was only $75.
In the first picture you can see a bright nickel coating on the housing of the drill. Although this certainly added some style, I regret doing it and wish I had skipped it. The plating mask was complicated and the vendor was not able to do it. The vendor should have refused, but attempted anyway and added a month long delay to getting my parts. The plating build-up was much thicker than it should have been and the part required light machining so the motor could fit. As a result the vendor learned a lesson as and stopped offering that service with masks. I learned not to make intricate masks and get a sanity check before trusting if a vendor can perform as advertised, especially when it is through a subcontract. Finally, I learned to do more planning when taking on a project, and resist the urge to begin modeling and engineering right away.
Adventures in 3-D Printing
After falling in love with the idea of having my own factory on my desk, I finally got a 3-D printer.
The significance of having a 3-D printer is not that I simply have another toy. It isn't even that I have a new tool that will allow me to make things that I can dream up or that I will be able to gain experience in design tolerance and go from ideation to prototype. I think the real significance of my 3-D printer is that I know I am joining a movement that will have a hug impact on our economy and culture, and will probably be as big as the computer revolution. The ability for individuals to manufacture their own objects and products in their own home will drastically change consumerism and will probably have a big change on intellectual property rights when consumers have the ability to make physical objects.
I chose to get a Makerbot Thing-o-Matic because the company has heritage in building low-cost 3-D printers and because they are a for-profit company so I knew the product would be supported. I could have gotten a RepRap for significantly cheaper but decided against it just because of the challenges that I have faced in the past when working with open-source projects.
Another cool feature about the Thing-o-Matic is that it comes with an automated build platform, which allows me to print many objects in a row without my interference. I could leave it home printing all day while I am at school.
It will really let me get creative in making things, like last-minute parts for my capstone project, camera mounts for rockets, actual rockets, small design projects, and of course the rapidly growing collection of things that already reside on Thingiverse.com
Slide-show below showing the build process (in reverse order for some reason).
As an early adopter may expect, the instructions for assembling the makerbot were not always good as one might like. The instructions were entirely online, which is good because a paper copy would probably weigh a significant amount, and I was content to just read them off of my screen. As the Thing-o-matic has been revised and changed piece-by-piece, one could tell which instructions had been written for earlier models by their clarity. The newer instructions were quite helpful with lots of pictures, but the old ones occasionally left us scratching our heads - though usually not for long. Luckily there were user posted comments for every page of the instruction manual, and those pages were well organized.
The instructions claimed that it would take about 16-20 hours to complete. Although I did not time myself, I believe that it took longer than that for myself. Ellen Farber assisted for the entire first half of the project, and then I continued on my own. I found during the final stages that it became easy to make mistakes during assembly, and there were a few times that I had to take apart major sections. I had the body panels accidentally reversed a few times, before finally coming to a configuration that works. It was magical when I first turned it on and a thin string of semi-molten plastic emerged from the extruder.
The most challenging and the most frustrating part of the entire process was the calibration of the machine after it was completely built. This took the most amount of time. The bug that kept getting me was a 'slipping' of the Y-axis during some builds. Eventually, I discovered was because I did not have stepper motor types I thought I had, and the stepped motor controllers had not been adjusted to the right settings.
The next challenge was spool management. This is a serious issue until you can print the parts that are needed to keep the spool rolling and in the right place.
My biggest challenge at the moment is dealing with warping on the build surface. As it turns out the Automated Build Platform results in a significantly reduced quality of the print in exchange for automation. The belts also wear out over time, making things worse. But the absolute worst thing about the ABP has to be that you cannot level it. It is front heavy because of the DC gear-motor, so the little bit of slop in the rods throws the whole thing front heavy. I am trying to weigh my options, which are 1) Buy the heated build platform in addition to the ABP, 2) Get a titanium belt for my prints (about the same price) or figure out something else.
BS Mechanical Eng