Shepard Hangout Notes/Minutes 07-25-12

Action Items

• ACTION - J/Jeremy - Set up a hangout early next week to see what Greg’s calculations tell us.
• ACTION - J - Will also need to setup schedule to meet requirements from OHS for demo (ie poster)
• ACTION - J - We need to add Wilton’s idea about building a project prototyping kit to the Mach 30 drawing board.
• ACTION - Greg - Is going to work through calculations to test these assumptions.

General

1. We are currently 1 month and 6 days behind schedule.

1. We were supposed to have the preliminary design done by 06-19-12.

1. Question: Realistically, how much of this project can we expect to have done for the demo at OHS?

• J - Thinks we have enough wiggle room to get back on schedule.
• Jeremy - Still feel like we have a few unknowns, so could still likely miss the deadline
• Greg - note, the design is coming along, but still feel like we have big open questions about implementation (who builds it and where)
• J - This brings up a related question, and that is how we pay for the build (there has been talk of building 2 copies).  J recommends we just build one copy for now (simplifies schedule and cost management).

1. Consensus seems to be that building one for now is the way to go.

1. Greg - Of course anyone can build as many copies as they want, whenever they want.

• Greg - Agree with J about going down to only one build
• Jeremy - Is Quelab signed up to do demo at ABQ Mini-Maker Fair

1. Wilton - no
2. J - and they can swap in the HAB for demo

• J - will also need to setup schedule to meet requirements from OHS for demo (ie poster)

2. Question: If we don’t have the stand done, what’s our backup? We don’t want the OHS organizers to feel like we misled them.

• J - Last year, people were bringing partially built projects and it wasn’t a problem.

1. J - Need to get mechanical parts and tangible (shiny) things ready at least to show summit attendees.
2. J - DAQ team at Quelab can go ahead and start buying parts to build a DAQ prototype as long as each item is below $5 to $10.

• Wilton - Should look at making a project prototyping kit to help new teams get started. Kind of like a $200 first aid kit. Gives a group a known base to start from.

1. ACTION - We need to add this idea to the drawing board.

2. The DAQ portion of the preliminary design seems to have a consensus. We just have to come to a consensus on the mechanical design.

Greg’s Questions

1. Greg has made some comments on the Shepard hangout minutes that covered the preliminary mechanical design.

1. https://docs.google.com/document/d/1M5qMFE-SNDYR_yHCI5XGnKLK1Xq17f7NVWNOhb3XkyU/edit

2. J - Initial design used guide rails and shot for low mass shrapnel rather than high mass shrapnel.
3. There are two main questions that Greg has raised. Jeremy thinks the first question goes back to the discussions we had when we first decided to be inclusive of the NAR guidelines in our design.

1. Are balsa wood and cardboard really the best materials to be using for the motor mount? Won’t they increase the risk of shrapnel?

1. Greg - Need to actually figure out what the danger of shrapnel is rather than going by gut feeling or back of the napkin calculations.

1. J - Feels comfortable using NAR allowed materials.

1. Greg - Still would rather make sure to have a quantitative measure of danger.

2. Greg - Had a hard time visualizing the mechanical design from the original minutes.

1. J - Described preliminary mechanical design from last hangout as Greg sketched it during this hangout.
2. Greg - Feels that there are a couple of false assumptions in the original design.

1. First - The RepRap design is not rigid enough and has too much adjustment for an engine test stand.

1. Greg - Also adds 50% more chance of errors. Makes the stand harder to align to make it work.
2. Ethan - A recommendation for Shrapnel; For safety, I recommend the addition of polycarbonate sheet on the outside of the motor frame. Common setup for test stand out here. Allows you to see in and have a safety cage. If observation is not important and the test stand it small enough, plywood sheet is sufficient. Usually what you would use for home flooring. It's just a 1/2" polycarbonate shield.

2. J & Greg - The D12 motor has the highest max thrust, which is 30 Newtons.
3. Greg - Added a ratchet mechanism to his sketch.

1. J - Not sure you want to fix the position. Allowing the mount to slide dissipates energy.
2. Greg - Thinks dissipating the energy through the frame will work if there are exhaust ports in the motor mount.

1. Ethan - Could you use a propulsive tee method?
2. Yes. That seems to be where the design is heading.
3. Ethan - We have an AN fitting Tee on the end of the vent line to make it non-propulsive. Army-Navy tube fittings for gas and fluid.
4. J - Would be okay with this design.

1. Greg - Agree.
2. J & Greg - Need to add port holes and (maybe) tubing to the sketch.
3. Ethan - Two ports diametrically opposed is sufficient. At least twice the area of the input port. The exit port area is twice the input port area. http://www.russellperformance.com/mc/adapt_fit/fit_tee.shtml That is the Tee used for non-prop venting. Then the input port is therefore the inner diam of the motor case.

1. J - The input port should be sized to either the inside of a D or E motor then.
2. Greg - Just wants to drill holes and not mess with fittings.
3. Wilton - Posted polycarbonate pricing. http://www.use-enco.com/CGI/INSRIT?PMAKA=619-3601

3. Greg - Feels that using the Big Daddy frame would add too much complexity and failure points.

1. J - If motor is touching metal, you need at least a factor of safety of 2. We also need to destructively test this setup.
2. ACTION - Greg is going to work through calculations to test these assumptions. http://en.wikipedia.org/wiki/Cylinder_stresses

1. Ethan - stress = Pressure * tube radius/wall thickness hoop stress.

3. Wilton - Could we plug a nozzle on an Estes motor to test this?

1. J - Feels it would be hard to force the motor into failure. It would just be better to use a firecracker of equivalent explosive force.

4. Add “use at your own risk” tag for tubes after a motor failure.

1. J - Recommendation would be to replace the tube after failure.

5. J - Do we still need it to slide.

1. Greg - We want ease of use and ease of replacement of parts. This makes it so that a sliding design will work better.

6. Jeremy - Do you create different tubes for different motor sizes?

1. Greg & J - No, we’d just use the motor adapters that Estes has, or make our own.

7. Wilton - Worried about the need for extra tools.

1. Greg - Assumes that Hacker/Maker spaces will have the equipment to do what’s needed.

8. Wilton - What about attaching the ratchet mechanism.

1. Greg - You can use some other mechanism like clamps on the rails.

Four concerns about metal motor mount idea.

1. How are the sensors (thermocouple) going to be installed.

1. Cut a slot.

1. How do you cut this slot?

1. Milling operation (grinder, dremmel tool). Drill two holes and then use a file worst case. (solution is material dependant)

1. Assumption is Hackerspaces will have these tools.

2. How are the rail guides going to get attached to the motor mount?
3. How is the stop system for the motor mount going to be attached (ratchet mechanism).
4. Two vs three rails? Which to use?

J - Trying to answer these questions about an aluminum motor mount vs steel  is a very different discussion.

• We need to address the questions above until you know what the motor mount material is. Again, we need to do calculations.

Ethan - On material choice. Given you guys are running a fairly lightweight test stand on 10 lbs. You ought to be able to build this with stock alumimum parts from either McMaster Carr or the hardware store. Typically 1" Aluminum C-channel suffices for struts. And 1/16" aluminum plate suffices for plate material. And it is fairly simple to tap drill attachement holes and tap screw threads for attachment. Your current idea with the RepRap config is good. The steel threaded rods can take it fine. The issue would be if the joiners can take the stress.

Ethan - If I may also comment on the overall design. I had been part of a UAV building project and we made a fairly simple engine thrust test stand for a 15 lb thrust electric propeller motor. It might be something to note on the design. It was a 1/2" MDF wood base plate mounted with machine screws to a heavy steel desk. Under a university license. So I assume open. University of Illinois, Urbana-Champaign, Design-Build-Fly team. They are unfortunately defunct, but I recall the design. We were part of AIAA. I do not believe we reported on the test stand, but a starting point to find it would be here: http://www.aiaadbf.org/

ACTION - Set up a hangout early next week to see what Greg’s calculations tell us.

2. Would it be better to use a simplified mount design with two attachment points instead of one? Greg seems to be thinking of using guide tubes on either side of the body tube of the rocket. Those guide tubes will then run on rails.

1. Greg created sketches here: https://plus.google.com/100798207019355823942/posts/RLr2tj3FQZy?utm_source=chrome_ntp_icon&utm_medium=chrome_app&utm_campaign=chrome