CDR Notes

Intro / Mission

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Structures

• Brahm - do you have an OpenRocket with simulation values?

  • Jake - we do have the model, but not in the presentation

  • Brahm - is the motor already picked out

  • Jake - currently going with ???, current apogee is ~11000 ft

  • Brahm - what is TWR

  • Jake - by the way the DTEG does (worst case, highest mass over average thrust) it's 5.1

  • Brahm - are you getting off the rail fast enough

  • Jake - we're at 76 ft/s, ESRA says 100 ft/s is recommended but okay if we can prove it will get off rail and we're doing a test flight and further simulation

  • Brahm - you were a lot overweight last year

  • Alex - we think b/c we didnt account for recovery hardware

• Brahm - is there FEA on the boat tail?

  • Will B - currently no

  • Wellin - is that the carbon fibre version of onyx

  • Jake - yes, it's 36% infill

  • Brahm - is there a plan to do a test? we've never done a boat tail that took all the load and wasnt metal, are we sure it can transfer the load

  • Jake - we can conduct further analysis like an FEA and do some kind of test

  • Wellin - is that easy to do an FEA

  • Matt - it's possible

  • Matt - I dont want to be a corporate shill, but MarkForged just launched some tool that lets you do measuring and modeling ??? (audio was choppy)

  • Jake - we'll make sure that this is flight that can take the load

  • Wellin - talk to Dr. Cormier, he was interested in the design and (simulation?)

• Wellin - whats the thrust plate

  • Jake - takes the load from the motor, usually aluminum, this year combined into the boat tail. Enables the motor retainer to get screwed on

  • Wellin - saw the thrust plate is a risk, is it different this year?

  • Jake - not really, never seen a failure in a thrust plate before

• Brahm - why are centering rings modeled in shear?

  • Will - as load from the thrust form the actual motor are moving, centering rings are perp. to motor and airframe, as the airframe moved the centering ring will move as well, so they need to be durable enough

  • Brahm - generally centering ring only connected to airframe, not to motor tube, should just be centering the motor and not taking any forces

  • Will - I agree with that, mistake in conceptualizing

  • Wellin - what are these arrows showing (flight conditions - boost slide)

  • Will - all forces shown are derived from the actual thrust of the motor

  • Wellin - what's going on with the arrows going to the right (arrows on left side of drawing)

  • Will - body tubes will be in compression as we move forward

  • Wellin - arent all forces forward, in the direction of flight?

  • Jake - shows loads from perspective of the booster tube, trying to show the compression of the tube

  • Wellin - we talked about this last year, free body diagram is a bit confusing but I got what you're saying, everything is under compression from this inertial resistance to the force accelerating it upwards

• Humphrey - what are the bulkheads made of

  • Jake - machined aluminum

  • Humphrey - mentioned tensile strength of epoxy holding bulkheads to body tube, aren't those tubes going to be mostly in shear in deployment

  • Will - values from the datasheet of the epoxy, also doing lap shear testing to ensure strong enough

  • Humphrey - ??? I missed it

  • Will - we need to do more testing on the strength, for our testing we had two samples per configuration so we had a small sample size

  • Wellin - suggest listing these as stresses (in Tensile testing slide) rather than forces

  • Will - we list as forces b/c each doesnt have perfectly flat geometry, so only output we got was loads at failure

  • Wellin & Carter - dont we know geometry / thickness from the cutouts? seems straight forward

  • Will - our cutouts were not uniform in shape, want to do again

  • Wellin - seems like what you want to do is standardize this

  • Brahm - are you following ASTM standards for tensile testing standards

  • Will - yes

• Brahm - are we planning on doing any other analysis, specifically on nose cone?

  • Will - we'll be doing further analysis on nose cone, currently modeled as a "perfect" model with a smooth surface

• Brahm - something about motor retainer load being too large, should be only 30 lbs, it's only holding the casing.

  • Will - I did FEA with the screws in the motor retainer, each screw is the weakest point, it shouldnt have a large amount of force acting on it

• @Will Merges (RIT Student) - Did you or are you going to take into account holes in the bulkhead between the av bay and the parachute bay when doing your FEA and other analysis? Several strands of at least 22 gauge wire need to get passed through for deployment charges.

  • Will - not modeled but will rerun

• Brahm - are we buying FG tubes now?

  • Jake - we are not winding, just buying

  • Brahm - why not, just do a wrap

  • Alex - we decided not to pursue at the PDR due to risk with team bandwidth, we will pursue after current work is done

Avionics

• Jim - how is there only one screw switch hole if there's multiple screw switches

  • Aaron - have to look into that

• Wellin - buckling concerns in the delrin support bars?

  • Donovan - modeled as a tensile load w/ their ground weight not under acceleration

  • Wellin - but it accelerates up w/ the rocket, going to need to model with this acceleration

  • Humphrey - agree w/ Wellin, current FOS is okay if we hit 5-6 gs

  • Yev - some confusion, the 180 Newtons is it's weight in flight not on the ground

• Joe how did we decide on 8 hours for the BRB battery life being long enough

  • Aaron - long enough for last year 

• @Will Merges (RIT Student) - One of the comp rules (that we were actually in violation of last year) says we need a method to read out altitude that isn't listening to beeps audibly, how are we doing that this year?

  • RRC3 should have a SPI readout

• @Jim Heaney (RIT Student) Design not manufacturable via machining in current form, will changes be made?

  • Donovan - going to test laser cutting current design before altering design for backup manufacturing method

• Wellin - why Delrin?

  • Easily manufacturable, resistant to chipping, lightweight

  • Not acrylic because it is brittle

  • Not completely settled on Delrin

• Wellin - why rectangular holes for support bars to slot into

  • Easy to CAD and trivial to laser cut

• @Will Merges (RIT Student) wiring diagram? Dual redundancy?

  • No

  • Using DE-9 breakouts to connect to ematches

  • dual redundancy through using 2 computers

  • Will - may want to look into passing charge lines through both cables to give dual redundancy in the cables

• Matt - how can we assume 8 hours is enough for the BRB if GPS lock is lost in flight

  • Matt - should give ourselves more margin for how long we transmit once we land, right now 2 hours budgeted

  • Aaron - confusion

  • Aaron - confident we can find the rocket in 2 hours

  • Will - If we lose GPS lock, getting bad GPS data but can still read signal, 2 spare hours is not enough time (basically foxhunting)

  • Aaron - will look into increasing battery life, may optimize battery life by only turning on during certain times in flight

Backplane

• Alex - how is this integrating into the rocket

  • Ben - it don't control anything except the reaction wheel, it only rides along

• Grace - this is abbreviated version, when is the CDR for this?

  • Ben - later, before the end of the semester

• Grace - when will the budget? be decided

  • Ben - don't know

• Jim - were weights of boards considered in av bay

  • Yev - not really, but total weight is assumed to be 2kg which is a good estimate considering we're removing fiberglass coupler and two charge lines since it's single bay deployment (heavy 22 gauge wire)

Reaction Wheel

• Jim - How would the rocket respond if your control system breaks down and the reaction wheel is pinned at full speed?

  • Yev - already answered earlier

• Jim - VESC motor controllers are very large. Is there space for them in the avionics bay along with the other 8 PCBs that will be in there?

  • John - VESC and batteries are mounted in the coupler, not in av bay

• Jim - i2C is not a very resilient standard to be run over long distances through wires, are you implementing any sort of software error checking/correction? If not, what's the worst-case implications of communication issues between the driver and your main system?

  • John - We don't foresee the i2c lines being long enough to cause issues, will be looked into

  • Wellin - How is this connected with Backplane

    • John - Integrating with backplane, backplane sends i2c commands to VESC in final design

    • John - Current design uses STM32 instead, software from STM32 will be ported over to Backplane BRAIN board

• Wellin - is this required for the competition, what happens if we decide not to use it?

  • Yev - not required, if we dont arm it it's just dead mass

• Will M - How is this system armed? Is there some kind of hardware/software safety or is it purely acceleration-based?

  • Yev - Planning on using screw switches

• Matt - Are there any design provisions to allow for fine balancing of the wheel to reduce oscillations?

  • Yev - going to balance the wheel manually and apply epoxy putty manually to balance

• Matt - Any plans to add another factor for fin angle error to the model?

  • Yev - not at the moment, good idea

  • Yev - bulk of spin comes from boost

• Will M - Any thought to doing some kind of software simulation or HITL (Hardware In The Loop) testing? Specifically for the tilt requirements and other off-nominal cases

  • John - simulating in matlab, can do a lot of tests on the ground, can't test everything on the ground (like vibration from rocket motor)

• Will M - Can your control loop tolerate variance in latency when getting your measurements over Ethernet on the backplane?

  • John - Good question, have to do more research, could be mitigation plans for latency

• Joe - what's the frequency of the control loop

  • John - currently 155Hz but can be increased to 1000 Hz

  • Wellin - why is that so low

  • John - currently based on the measurement rates

  • Yev - looking into sensor fusion to increase frequency of sensor data, also Kalman filter

• Wellin - how does this increase simulation accuracy (as you stated in slide 2)

  • Yev - OpenRocket assumes no spin in the simulation

  • Wellin - so you're not really improving your simulation, you're improving your observance of the simulation

  • Yev - yes

• Grace & Jim - why is aluminum considered harder to manufacture than steel?

  • Difficult to mill due to size of part and size of stock

  • Wellin - "manufacturability" is poor choice of words

  • Carter - length makes it hard to machine

  • Wellin - Why is that difficult tho

  • Alan - Hard to plunge 4" in to mill

  • Matt & Wellin - Not too hard, do different ops

  • Grace - some confusion, will look further into

Payload

• Brahm - How is this an airbrake?

  • Nate - It uses air to slow yourself down

  • Nate - "it's not a parachute if it's made of metal"

  • Nate - airbrake is not slowing the payload down, that's the streamer, this data will be used to build a larger future system

  • Brahm - what does this actually give you, besides maybe Cd?

  • Nate - getting force at different opening percentages, will use that data to program future system

  • Brahm - this doesn't get you anything besides Cd

  • Grace - this payload is in early stages, difficult to answer these questions at this stage, CDR will be in future, we don't have electronics

  • Nate - We do have most of the electronics

  • Grace - Brahm is saying we need live data, we don't have that

  • Alex - Gaining experience in building an airbrake system, difficult to sim accurately

  • Matt - this system lacks maturity, would be best to review this at a later time

Recovery

• Brahm - why no OSCALC

  • James - hard to use

  • Brahm - what is weight of rocket at apogee

  • James - dont know off the top of my head

  • Brahm - is it 100lb?

  • Will B - 73lb w/ payload and motor so dry mass is less

  • Jake - empty mass is around 53 lbs

  • Brahm - streamer is overspeced, we are going to drift a lot more than we should

• Brahm - why the streamer and not a parachute?

  • James - 2 reasons:

    • reduces risk in payload deployment (if payload impacts streamer, it does not get caught)

    • we also want to gain experience with streamers, they are used for high altitude flights so we want to gain experience

• Will M - How is deployment testing going to be performed? Does it just validate BP calcs or will the computers be vaccuum tested?

  • James - IREC requires that they are vaccuum tested, we will be doing that

• Yev - do streamers cause less drift

  • James - that is my understanding, drift is caused by horizontal winds acting on the streamer and it has less horizontal surface area

• Brahm - is it really safer to use a streamer

  • James - yes, but we have no sims

  • Yev - "compare putting your groceries in a bag and putting your groceries in a shoelace"

Overall

• Forgot OpenRocket overview (velocity off rail, expected apogee, weight, stability, basically all the core stuff)

• Forgot wiring diagram for avionics bay