Mach 30 #EngineerSpeak Hangout Sept 19, 2013

Discussion Topic:  Shepard Structure Requirements v2.0

Attending: Chris, J, Juli, Jeremy, Matt, Mary, Aaron

Start: 

End: 

Minutes:

• Agenda review
• Review where we are at in the Shepard development process

• Jeremy/J - About a year ago we built the first version of Shepard, primarily for OHS.
• The board approved upgrades for Shepard in 2013 leading to a kit version for students, scouting troupes, etc.
• We had some resource shortages which has slowed the progress down.
• Aaron has done some R&D with the structure using Misumi extruded aluminum, but we need to make sure we’re hitting the requirements properly.
• That puts us a quarter behind, the structure should have been done by the end of Q3.
• We want to move from wood to aluminum, and want to make sure we don’t miss anything important during that transition so that we can move straight to the kit version.

• Some prelim questions about the structure

• What is working?

• Matt - Current wooden structure works fine. Thrust sensor works great.
• J - The ability to slide the structure over a block is an advantage for classroom and demo use.
• Matt - ditto
• J - The calibration pulley arrangement works well so that the configuration of the test stand doesn’t have to be changed.

• What is not working?

• Matt - Temperature sensor doesn’t work that well.
• Matt - There was some confusion on what a “rail shield” was in the BOM.
• Matt - Cut list had a few cuts that were incorrect. Small span piece was too long and had to be trimmed down.
• The drawer guide bearings get clogged when we fire the test stand if the shield is not in place.
• J - The pulley arrangement is nice, but things don’t stay lined up. String slipping off the side of the pulley, the weights hang too close to the structure.
• J - Alignment is an issue with the dimensional lumber and the speed with which Mach 30’s copy of Shepard was put together.
• J - Metal is better than wood from a fire safety perspective.
• Jeremy - The current structure is fairly labor intensive.
• J - The test stand is heavier and larger than we would like.
• Matt - The temperature sensor is great, but measuring against the wall it takes a few seconds for the heat to propagate through. It would be better if the software continued to collect temperature data after the thrust measurement has stopped.

• What are the activities that need to be supported?

• J - Fire motors and record data from the firings.
• J - We need to be able to calibrate (the load cell) the stand easily.
• J - We need to be able to ship it more easily (and cheaply).
• Jeremy/J - Needs to be easily set up and torn down for demonstration and educational purposes.
• Mary - Will be presenting at conferences and transporting to schools. Will be multiple test stands at one site, so they’ll need to be able to transport more than one (maybe even 10).

• This is to support teacher training. 10 to 12 teachers would each get their own test stands.

• Aaron - We need to specify that it needs to be mounted to a stationary object.

• Matt - Maybe instead of a block use a ground stake.
• Mary - With most of our schools we’ll have access to a field, instead of on a sidewalk.

• Review key initial questions

• Q2. Who is this for?

• Original answer - The Shepard Test Stand is for anyone wanting to learn about measuring the performance of rocket motors. This includes open source spaceflight designers who will design and build future test stands (at Mach 30 or elsewhere), Mach 30 operators who will use future test stands in other Mach 30 projects, students and educators who want to bring rocket engineering into the classroom, and anyone else interested in how rockets are tested.
• Recent answer - Our demographic is a middle school (6th through 8th grade in the U.S.) teacher who does not have the support of an IT department, and who does not have computer expertise beyond how to connect a USB cable and install software, but has the desire to introduce their students to rocket science in a safe and hands-on way.
• Any comments?

• J - What grade levels will CCSSC be working with?

• Mary - Middle (basic algebra and calculations) to high (heat propagation, required thrust calculations, etc).
• Matt - We also have college level engineering students who have to take a thermodynamics class, and could use it Shepard for hands-on use.

• Aaron - Middle school seems to be the highest level of interest from students and teachers. This seems to be the low hanging fruit.
• Jeremy - We’ve been using the term “grandma test” to help guide our development. We want to just plug it in and have it work.

• Q4. What features does it need to have (now)?

• Be easily set up and torn down for demonstration purposes.
• Be easy to package for shipment to any event at which it will be used.
• Provide a stable base on which to test model rocket motors.
• Accommodate Estes rocket motor sizes A through E.
• Provide the ability to measure thrust and motor casing temperature while keeping an accurate timestamp for each data point.
• Conform to the safety requirements as outlined in section 8.3 of the NAR Standards & Testing Committee Motor Testing Manual Version 1.5.
• What else?

• J - Needs to be easily calibrated.
• J - Need to be much more conscious of the transportation and shipping issues due to CCSSC’s need to transport many at a time.
• Jeremy - After assembly the set up and tear down needs to be as close to tool-less as possible.

• Matt - Hammer and screw driver should be the minimum amount of tools.
• J - We also need to avoid highly complex tools for assembly, like masonry bits.

• Matt - Temperature sensor is great, but only reads the temperature of the casing with a delay. There would need to be a configurable delay after the end of the firing to continue to record.

• J - Our temperature requirement is based on NAR specifications.
• J - This can make for less exciting data?
• Matt - Can we measure the flame temperature directly?

• J - Jeremy and I did our homework, and the current IR sensor can measure the full range of the exhaust temperature. Would this be useful for CCSSC?
• Matt/Mary - We want both.
• J - What if we had the IR sensor movable so that you could choose whether to measure the case temperature or the exhaust temperature?
• Matt/Mary - This would work great.
• Aaron/J - We’re already going to be working on the structure and sensor positioning fits right into that.

• Q6. What are the legacy requirements?

• Original answer - This is the first project of its kind at Mach 30, there are no existing projects it must interface with. However, since the system includes desktop control software, that software should run on all three major PC platforms (MS Windows, Mac OS X, and Linux). Additionally, it should use standard connections back to the control software (for example, USB, Ethernet, or similar connections).
• What else?

• J - Are we still wedded to the concrete block?

• Chris - Maybe, the stakes seem like they would be more error prone.
• Aaron - Especially when you’re going into problematic soil.
• J - Needs to be mountable to a concrete block without specialized tools.
• J - There’s probably at least a strong preference for the concrete block.
• J - Should we switch to the standard height open core block?

• Chris - Has a plan that may make this a moot point. ACTION - Make sure this gets captured for a later design discussion.

• Q7. Who is going to build this?

• Original answer - It is assumed that initially volunteers within the Mach 30 community will build this test stand. The designs will be open so that ANYONE, without necessarily a technical education in rocketry, propulsion, or engineering, would be able to build and operate a Shepard Test Stand.
• What else?

• J - We did not list teachers and students originally, but we need to now. This is important for CCSSC’s use especially.

• Q8. How many do we want to make?

• Original answer - One (for now). The current goal is to create a design variation of the test stand to be built as a kit for others to assemble and operate. In that case there will be as many of the kit design built as there is demand.
• What else?

• J - Mach 30 intends to sell these kits, so we need to set it up as a product.
• Mary - CCSSC purchases a lot of robotics kits and sees this working the same way. The teachers are getting $200 kits from CCSSC for robotics.

• The $150 to $200 range for a kit is pretty reasonable.
• It helps if it’s reusable and has a data component. Teachers want to do real, relevant, hands-on experiments with their students rather than just learning from a book.
• J - That means all our costs need to be down around $78 (parts and labor).
• Mary - I need a youth large of a Shepard BYOB (Bring Your Own Block) t-shirt.

• ACTION - Get Mary one of these t-shirts.

• Q9. What is the budget?

• Original answer - $200, firm. If there is a conflict between function and budget, for this iteration, budget should trump. Our goal is not to make the perfect test stand, it is to make the first prototype of a test stand and see what we can learn from that experience (both about test stands, and about our processes). We can always go back and do another iteration to meet the design requirements if needed. Holding to a firm budget minimizes the amount of time spent trying to make it perfect (once you are out of money, you have to wrap up the project, successful or not). Even a "unsuccessful" prototype will teach us important lessons to apply moving forward. This budget does not include "consumables" such as motors, nor tools, but the $200 cost for the stand itself keeps the basic project affordable if standard tools found in Hackerspaces/Makerspaces can be used. Any manufacturing that has to be hired out to a third party will be taken out of the $200 budget, and should be avoided to keep this project more practical for groups interested in building the test stand.
• What else?

• Aaron - The new R&D structure comes in right at $40 minimum.
• J - Let’s use a $100 structure development budget (firm), and shoot for a goal of around $40. That gives us 2 prototypes and some head room for mistakes.

• Jeremy - I would go with $125 to $150 for 2 prototypes and mistakes.
• Aaron - Would go with $150.
• J - Let’s use Greg’s trick of a threshold of max $150 (to meet the minimum requirements), and the objective is $100.

• Q10. What is the timeline (for v2.0 structure)?

• J - 12/31/13 is the stake in the ground to have the prototype structure done. This means that it is built, has the DAQ attached, and is being fired.
• Jeremy - Will this work for CCSSC?

• Mary - Yes, that timeline will work. We need access to a prototype to finalize the curriculum.
• The NASA grant doesn’t specify anything to be spun up until summer 2014.