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Author Topic: Electric Wright Stuff trial event for Div. B or C?  (Read 2056 times)
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Little-Acorn
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« on: April 15, 2018, 07:54:57 PM »

I've been coaching a (rubber-powered) Wright Stuff team at my local Middle School (Div. B). Lately I saw an "Electric Wright Stuff" competition at the SoCal State competition at Caltech last week, for Div. C (high school), where the planes had an electric motor and were powered by a 5F 3V supercapacitor. Apparently this event has been called "Capacitor Wright Stuff" in the past.

It was listed as a "Trial event". Does anyone know if this might be an event for next season, either "trial" or "main" event? I looked at the schedule for July's SOSI meeting, and didn't see any mention of it for either Div. B or Div. C.

For kicks and grins I picked up a few supercapacitors and small electric motors (Vapor motor/gearbox/prop, small quadcopter motors etc.) and have been playing with them.

Anybody know of a forum where Electric Wright Stuff is discussed? I'd love to hear what components people are using, what results they're getting etc.
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frash
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« Reply #1 on: April 15, 2018, 08:50:01 PM »

Look at http://www.hippocketaeronautics.com/hpa_plans/details.php?image_id=9801. This is in the HPA Plans section. This is Chuck Markos' article from a NFFS Sympo report.

I do not know about any forum with much discussion yet on Wright Stuff capacitor planes for Science Olympiad.

Fred Rash
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ceandra
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« Reply #2 on: April 16, 2018, 10:45:58 AM »

It does seem to be on the Summer Institute schedule. It is listed at 1pm on Tuesday as "Gliders or EWS?". EWS being Electric Wright Stuff. Interestingly, gliders are also mentioned at 9:50am same day.

With the question mark, it is not clear if this is still in the decision process.

Chuck
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Little-Acorn
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« Reply #3 on: April 16, 2018, 12:23:28 PM »

Hmm, ceandra, the schedule I saw had simply "EL Gliders" at that time.

Is there a more recent version of the schedule than this?

https://www.soinc.org/sites/default/files/uploaded_files/2018_Schedule_032618.pdf
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ceandra
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« Reply #4 on: April 16, 2018, 01:58:18 PM »

Your schedule looks far more recent (mine was dated 1/19/18 at the bottom). I'll have to let our coach know!

Your schedule shows Wright Stuff Tuesday 7pm. I would assume (though we know how good that is) that this would be EWS, since we have done rubber WS 4 years now (2 C, 2 B).

Chuck
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calgoddard
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« Reply #5 on: April 18, 2018, 11:54:32 AM »

I am sorry to learn that the powers at the SO National organization are pushing e-Wright Stuff again. I thought this event was dead due to the following reasons elloquently explained by an expert indoor flier, LeoP, a few years ago:

"Having started indoor flying by being a coach for SO Wright Stuff, I , too, would be glad to see Wright Stuff back in the event list.  However, I am of the very strong opinion that the only power used should be rubber and not electric in any way.  The reason I feel this way is because of fairness issues.

When the capacitor powered planes were first proposed, I built several and ran a great deal of tests.  I found that the nominally specified capacitors could differ in capacity (which equals flight duration) by nearly a factor of two depending on manufacturer and manufacturing tolerances.  This led to some (richer?) SO teams buying a large number of capacitors and selecting for the ones with the greatest capacity.  I had already seen a similar thing in the AMA battery powered indoor class (both free flight and radio controlled) as small LiPo cells of the same mAh rating could vary by 50% or more in storage capacity.  I think this makes for very unfair competitions.

Some will say that the same is true for rubber powered planes as there is a difference between poor and excellent rubber.  However, the difference in energy storage capacity between the very best rubber (Tan II 5/99 or 3/02, for example) and the currently available Tan Super Sport is less than 20% (and more like less than 10% for the better batches of the current Tan SS).  A well built, tuned, and flown rubber powered plane using Tan SS will be competitive.  However, for electric powered planes, only those students who have selected the best storage cells or capacitors from a large number will be competitive at the state or national level.  I think this unfair and biased toward the richer schools.

LeoP"


I have a great deal of respect for Leo's opinions.  He is very rigorous in his application of science and engineering to our hobby and has a great deal of experience. 

Let me just add that in my personal experience, May 99 TAN II rubber is probably only about 5% better in terms of energy storage capacity than the better batches of TSS rubber that have been sold during the last few years since Leo voiced his opinions set forth above. Some outdoor fliers say that June 2016 TSS rubber is as good as any batch of TAN II rubber ever made. Even if May 99 or March 02 TAN II rubber are still 5% better than current TSS rubber, it is very unlikely that WS fliers will be able to obtain any of the former. 
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ceandra
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« Reply #6 on: April 18, 2018, 03:10:31 PM »

Cal:

I concur, and was aware of Leo's discussion you quoted. As a coach, I am simply trying to get things lines up for next year. If they do go with EWS, there could be a run on certain items. I do note that EWS was changed to Wright Stuff in the later agenda, so maybe there is hope. However, the sequence has changed. It appears elastic glider will be in B, instead of heli, and WS will be in C, instead of glider. I am with you, hoping it is rubber, but preparing in case it isn't.

Interesting on the June 2016. Our batch for WS this year is that date code. It has worked well (I don't think we are at a high enough level to see dramatic impacts, but we are going to be at least competitive at Nationals). However, when cutting to less than 1/16" (from 3/32 stock), we have noted difficulty in maintaining loop length for the given 1.5g. I thought it was our skills in running my stripper (Harlan). We would get a short piece (2-3") to the g/in we wanted, then cut a loop, and be off by a cm or more. Cut another loop, its off in the other direction. Even on half loops (24-26 cm, 0.75g). Last week I cut some from an older batch (cannot recall date) of 3/16", and every loop was identical, and predictable from the small sample! Anyway, thought it was interesting that you identified it as good rubber, I'll keep that in mind as we prep for Nationals. I can work around the density variation, just means we need to cut more loops to get the size we want (and running out of that batch).

Chuck
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piecost
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« Reply #7 on: April 18, 2018, 04:39:39 PM »

Chuck, that is an interesting observation about june 16 rubber. I have some of two different thicknesses of that date and had not noticed such a problem myself. I did struggle to match the target g/m but put this down to making thinner motors than usual.

Do you thing that the density was changing rather than the thickness?
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calgoddard
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« Reply #8 on: April 18, 2018, 05:02:22 PM »

Perhaps I am getting a bit off topic by adding to the discussion about June 2016 TSS rubber.  Its praises were sung in the outdoor free flight community, and as I recall, the F1B fliers.  In that class an enormous torque burst is apparently desirable as the model is thrown straight up, and after a delayed prop release, it climbs vertically for at least 15 seconds.

I have a friend who is a true expert in outdoor rubber powered free flight. He did very scientific pull tests on June 2016 TSS rubber and told me that the quality of that rubber varied a great deal within the same batch that he tested.  He made up some P-30 motors from the middle of the batch and observed that they could tolerate a very high level of torque without breaking. My friend said that he considers this part of his batch to be exceptional.

This does not necessarily mean that June 2016 TSS rubber would be optimum for WS models.
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ceandra
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« Reply #9 on: April 18, 2018, 05:07:18 PM »

Pie:

Yes, it may be density rather than thickness, I have no suitable means to measure thickness. All I know is the finished loop length varies a lot in sequentially-cut loops without changing settings, and the other batch did not.

Cal:

I agree. Within the limitations of WS, it is most important to match the rubber you have with the prop, especially with the low ceilings like last year. But I do believe the rubber varies more across the batch (or even within the box) than other rubber I have tried.

But (wrapping back to the original topic), probably not nearly as much as 5F capacitors!

Chuck
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Little-Acorn
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« Reply #10 on: April 18, 2018, 08:34:10 PM »

Many have expressed concerns over the wide tolerances of the 5V 3F supercaps we power these planes with. These concerns are well founded, even according to the capacitors' data sheets.

One of the common ones is the AVX SCCR25E505SRB. See its manufacturer's data sheet at https://www.mouser.com/datasheet/2/40/AVX-SCC-3.0V-1128335.pdf

Indeed, the datasheet itself says that the capacitance values can vary up to 10% lower then the advertised 5F, and up to 30% higher than 5F. So it should be possible to find one marked "5F", whose capacitance is actually 6.5F. A student flying a plane with a capacitor whose actual value is 6.5F, can certainly glean a significant advantage over one with a capacitor that's actually 5.0F. I don't know if other manufacturers' supercaps have similar wide tolerances, but it's certainly possible.

There doesn't seem to be much that SciOly officials can do about that. But I don't see cancelling the entire event as the only recourse.

I just bought some small multimeters on Amazon.com for $9.97 each, that are advertised as having the ability to measure the capacitance of a capacitor. Whether they can measure capacitances as high as 5F (or 6.5F), remains to be seen. They're supposed to arrive tomorrow, then we will see.

If such meters are available and accurate, then perhaps the rules can be modified to read, "The capacitor must have a maximum measuredcapacitance value of 5.0F, and will be measured by the judges before the flight at the same time they weigh and measure the planes." Or maybe the maximum value should be specified as 6.5F, or whatever value the officials find suitable, so that commonly available capacitors can be purchased.

The caps cost around $2 each, every team should be able to buy a number of them, and buy their own meter as I just did, and measure their values until they find capacitors that are genuinely at 5.0F or slightly less. Or whatever the rules' stated maximum is. This is not a great expense.

Let's not deep-six the entire EWS event because a component has wide tolerances. There are simple and inexpensive ways to take such things into account and level the playing field for everyone.

I'll post what I find out about those meters, and if they can accurately measure a capacitor around 5 to 10 Farads.
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ceandra
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« Reply #11 on: April 18, 2018, 09:27:16 PM »

You intend to report as to how "accurately" the $9 DVM can measure capacitance? How do you determine accuracy, if the caps you measure vary by 40%? Or do you have a reference capacitor?

Unlike the scales we use, which can be checked with a reference weight, how do you resolve the difference between my cheap $9 meter (or free with coupon at HF) vs. the ES's $9 meter, without a reference cap?

I hear you on giving EWS a chance. But Caps are generally not tightly toleranced, and a 40% range of variation is quite wide.

Perhaps the ES needs to have 5 caps that are measured and matched, and loan them to each team? Assuming you could get ES's anymore. Our State tourney has a hard time finding a scale the does finer than 1g increments. This year it showed a 1.5g rubber at 3g. We loaned them a scale.

Perhaps the National organization would be able to sort and test caps, and distribute them to sanctioned events?

I don't know if there is a good answer.

Chuck
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calgoddard
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« Reply #12 on: April 19, 2018, 09:31:04 AM »

Ceandra brings up an excellent point about the practical difficulties of accurately measuring capacitance at an EWS contest.

Even assuming that a viable technical solution could be found, in my own personal experience the flying event committee of the National SO organization is not open to outside suggestions.

After years of coaching WS, last year I wrote rules for an alternate SO flying event called Rubber Powered Airplane (RPA).  See http://www.socalstatescioly.org/downloads/TrialEvent-RubberPoweredAirplaneC.pdf

Basically under the RPA rules any rubber powered airplane was legal so long as it fit within a large FedEx box and weighed a minimum of 5 grams. There were no restrictions on the size of the prop or the rubber motor. There were no restrictions on the configuration of the airplane.  It could have any size wing and stab and it did not have to be a tractor monoplane. It just had to fit within the box in a ready-to-fly condition (with or without the prop).

The main goals of my RPA event were to: 1) ease inspection of airplanes and rubber motors at check-in; 2) inspire creativity in design; and 3) promote experimentation regarding the optimum size of the prop and rubber motor for a chosen air frame design.  I was confident that flight times of RPA airplanes would be limited to a maximum of around 3 minutes in a typical HS gym, even for the very best fliers, which seems to be a big concern of the committee at the National SO organization. Note also that students could use free and readily obtainable FedEx boxes to safely transport their models to a practice site and to a competition. In the process FedEx received free advertising and good PR for supporting STEM education in our country's youth.

RPA was run as a trial event at the SoCal State SO tournament that was held at Caltech in 2017. I was the ES for the event.

After a very successful trial run in 2017, my RPA event went nowhere with the flying event committee of the National SO organization.  I received zero feedback from the committee.

I did receive many favorable opinions from WS coaches at the trial run of RPA. In addition, many favorable opinions about my proposed RPA event were expressed on this HPA web site. The variety of the airplanes at the RPA trial run was impressive.  One team in particular stood out for its ingenuity.  Its airplane fit in the FedEx box sideways to maximize the wing span. In other words, the wing of the model had a span slightly smaller than the length of the FedEx box. In addition, the wing had a high aspect ratio that minimized drag.

However, NIH (not invented here) appears to be the overriding philosophy with the flying event committee of the National SO organization. This philosophy almost certainly applies to any suggested rule changes for EWS proposed outside of the committee. The unfortunate reality is that EFS will be an unfair event. The winner of many EFS competitions will be the team that bought and tested lots of 5F capacitors and used the one that with the highest capacitance, or the team that got lucky and unknowingly used a capacitor marked 5F which actually had a capacitance closer to 6.5F.

To avoid any intentional rules violation and/or moral dilemma based on knowingly using a capacitor with a capacitance greater than 5F in an EFS competition, a team could simply test fly the same airplane with a number of different capacitors marked 5F and use the one in competition that consistently yielded the longest flight times in practice. This team would never actually measure, using a multi-meter or other testing device, the capacitance of any of the capacitors used in test flights.      

Little-Acorn, I admire your dedication and your willingness to coach students in flying events.
« Last Edit: April 19, 2018, 10:18:45 AM by calgoddard » Logged
jdpsloflyer
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« Reply #13 on: April 19, 2018, 11:14:54 AM »

Notes from a wet finger flier:

Having less resources and $$.

We do not cut our own rubber,  I get it pre cut and am at the mercy of whoever supplies the "widths" (and lot dates) I order.  I do however use a caliper to check sizes.  When balancing a plane for trim/rubber/prop, we do use different loop sizes (widths) to get the best times.  Once the best combination is found, that team uses it for tournaments (unless a crash causes recalibration in practice).

The same would go for EWS, I would buy a batch of supplies and we would experiment to see what works best (unscientifically with only fundamental tools).

Luckily our teams have placed high in regional and state tournaments, and placed at Nationals in 2017.  Maybe our luck will hold.

Jerry

Personally, I like gliders or rubber power airplanes.
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Little-Acorn
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« Reply #14 on: April 19, 2018, 04:21:06 PM »

Got the little $10 DMMs in. Actually they're almost as big as my old Fluke 77. Four digit display. The lowest three digits can display 0-9, the highest order digit can display 0-6. Don't ask me why. They came with a User's manual, lead set, a plugin for semiconductors and capacitors etc., a (cheap) 9V battery, a warranty card, and even an inexpensive Phillips screwdriver to open it and replace the battery and fuses. The plastic case of the meter is wrapped in a Fluke-like rubber sheath.

https://www.amazon.com/gp/product/B072PVKP4M

Went immediately to the User Manual (teenyweenie type font, had to use a magnifying glass) and looked up the capacitance-measuring section. Bad news: It says (Page 08) that it can measure three nanofarad (nF) ranges, three microfarad (uF) ranges, and two millifarad (mF) ranges. Highest value it can measure, is 60 millifarads... which is two orders of magnitude lower than what we need for these 5 Farad supercaps. Aw, sh*t.

Well, I got them mostly to set up a capacitor/charge/motor test bench, so I could read current flow, voltage at the motor terminals, voltage at the battery terminals, etc., all simultaneously. Should be pretty good for that: In the 600mV DC range, accuracy is 0.8% plus the 3th-digit rounding error (which I think means that only the highest two digits are used, hmm); in the 6V DC range, accuracy is -.5% plus the 5th-digit rounding error, which hopefully means all four digits are used. DC Current accuracy is similar: In the 60mA range the resolution is 10 uA; in 600mA range it's 100uA, at the 10A range it's 10mA. DC input impedance is listed as 10 Megohms. Haven't yet found an input impedance for the current measurements, often these meters (including my Fluke 77) can't be used to measure currents directly since they put many Ohms of resistance in the path. I usually measure current by putting a 0.1 Ohm 10W resistor in the circuit and measuring voltage drop across it.

But it would have been nice to be able to measure the capacitance of these 5F supercaps directly. With this meter, no dice.

However, it should be pretty simple to have the team members (and later the judges) charge a capacitor to 3V, put it across a known 1% resistor, and see how long it takes to drop to 2.5V or whatever a good value is. The longer it takes to drop, the higher the capacitance is. If it takes more than a certain number of seconds to drop to the target value, the capacitance is too high and that supercap is disqualified.

The formula is simple: (Capacitance) = (Current) divided by (Rate of Voltage change).

Of course, as a capacitor discharges, its voltage steadily drops, which means the current through the resistor isn't constant, but drops just as steadily. So the above formula isn't as simple as it looks. I'll have to get out my old E=IR textbook (untouched since I was 20, a LONG time ago) and get the exact formula. I sense an integral in my future. :-(

But these meters are useful $10 voltmeters with 4-digit accuracy for voltages of 6VDC or less (excellent for E-WrightStuff planes), plus other ranges. And have lots of other functions. I may get some more for when I build a wind tunnel to test propellers and motors. And maybe entire planes, though that tunnel would have to be at least 3' by 3', storing it could arouse the ire of my boss. Amazon.com only lets you buy three at a time.
« Last Edit: April 19, 2018, 05:15:31 PM by Little-Acorn » Logged
Little-Acorn
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« Reply #15 on: April 19, 2018, 04:57:52 PM »

BTW, a few days ago I measured a current of 380mA through a Vapor standard motor with an Ember gearbox and 5-7/16" propeller. Power source was two AA Eveready Energizer alkaline cells in a battery box in series, when the motor was running they showed 2.88V. Tachometer showed a propeller RPM of 4,140 in still air.

Then tried it with one cell, current 190mA with 1.55V from the cell, prop RPM was 2,500.

That motor at 2.88V and 4,140 RPM seems to present an ESR (Equivalent series Resistance) of around 7.5 Ohms. With one cell, ESR was around 8.2 Ohms.

Of course, if it's powered by a supercapacitor, the voltage will continuously drop as the capacitor discharges. So the current will decrease, the motor will slow down, and the ESR will change accordingly.

I also tried an old 7mm x 3/4" motor from a U816A quadcopter with its 2-3/16" direct-drive prop. At 2.815V it turned 16,170 RPM (wow!) and drew 710mA. At 1.487V it turned 9,950 RPM and drew 280mA. And that was probably a pretty cheap motor, I saw an ad for that copter for less than $30 including radio at Walmart.

All this was in my garage, in still air.

Looks like Energizer AA's don't like discharge currents of 380mA. Next time I'll try two Energizer D cells instead.

Would also be nice to list RPM vs. voltage vs. current when driven by the decreasing voltage of a supercap. Or a variable DC power supply.
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Re: Electric Wright Stuff trial event for Div. B or C?
« Last Edit: April 19, 2018, 06:23:09 PM by Little-Acorn » Logged
Little-Acorn
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« Reply #16 on: April 19, 2018, 05:24:09 PM »

Hmm, Amazon.com has an ad for a dedicated Capacitance meter that says it can measure up to 10 Farads with 5% accuracy for $58 with free shipping. That accuracy isn't particularly impressive, but if the ad is accurate it might let EWS people measure their 5F supercaps directly, at least, and tell which caps have more capacitance.

https://www.amazon.com/Supco-MFD10-Digital-Capacitor-Accuracy/dp/B000LDF97U
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ceandra
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« Reply #17 on: April 19, 2018, 06:22:49 PM »

IMHO, I do not think that a discharge measurement at the sign-in table would work out. Tech inspection is already a holdup. You would need to first charge to make sure the cap was fully charged, and then discharge. I think you would be better served to have standard caps that are handed out to participants. Of course, it is most likely that at most events these woudl be purchased caps that have never been tested by anyone, while the desire would be caps that had been qualified and compared to each other.

I don't know how other states are, but in my state we are lucky if the ES has read the rules ahead of the event, and if they have, have they comprehended them. I usually try to meet the ES in the morning and, being very friendly, offer my help, tools (measuring, scales), etc., in order to gage their understanding of the rules. Moreso this year with the 3,6,9 prep rules (nope, none were aware nor understood them, none had enough stopwatches, etc.). This was both at Regional and State. ES's also were not even aware of FAQ's, so in WS we had 6 rubbers prepared (three for primary, three for backup which had a different prop), so that they could respond to the first flight. In both cases, the ES only allowed two to be checked. At State we had printed the FAQ, which helped. In Heli at State, the kids launched first flight, started winding immediately. Got 2:52 first flight, immediately hooked up first rubber, and were starting to wind second rubber, when ES told them their time was up. The kids argued, then packed up to leave. We sent them back to find out what time was up. "Your 9 minute clock expired". This was the preflight. They had never started an 8-minute flight clock.

All this is to say the check-in and ES responsibilities have to be kept as simple as possible. Many ES's are college students from the institute that is hosting. I think qualifying caps, at the check-in or prior, will be beyond the capabilities in many cases. Cal's approach to the RPA I think goes toward this, as it reduces ES workload.

If we have EWS, I suspect it will indeed be "by the label", and if so, I would be buying at least a few dozen caps. It will still come down to good construction, and matching a prop to the cap/motor combo. I think more advanced teams will be working with various gearboxes as well as testing numerous motors. But, 40% variation in caps will indeed separate the (rich) men from the boys...

Chuck
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Little-Acorn
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« Reply #18 on: April 19, 2018, 06:53:51 PM »

Chuck, you may be right about discharge testing at the judging table not working out. In that case, if the rules remain as stating the capacitor must be advertised as 5F at 3V, then the teams will essentially have a choice of capacitors up to 6.5F. Those that know that, might well buy many of them as you pointed out and cull out the 6.5F ones among them, and use those in the contest.

Those capacitors go for around $2.40 each from outlets like Digi-Key. Teams could buy two dozen for around $50-$60. I don't know how many above 6F they would find, they might even have to buy more before they got lucky.

Teams that didn't know this, would buy far fewer, of course. But the variance between units isn't a secret. It's right there in the manufacturer's datasheet in black and white.

There are a lot of other variations many teams don't know about: The advantages of dihedral, different densities of balsa wood, CG placement and stability, and many other such things. Teams that study harder, find better info sources, and learn more, will likely do better in contests. That's part of the event. Variances in supercap capacitance are another bit of information that someteams might not know... but again, those that look up sources and learn more are more likely to win. The difference with the supercap issue is, as you have pointed out, that it usually takes money (maybe $50 or more) to take advantage of it. In addition to the usual studying, understanding, and patience (5F 3V Supercaps with lower capacitance can be used as "practice caps", but how many of those does a team really need?)

In this last (rubber powered) Wright Stuff event season, we spent more than that for Ikara props as my six teams hit the floor, hit a wall etc. during long testing. Excellent props, but fragile. Supercaps aren't cheap either, but they are less likely to be damaged through the season - once you've got a few 6+ F caps, they're yours and you need no more (how long does a supercap last after dozens or even hundreds of flights?). Multiple teams from the same school can even trade the good ones around among themselves, not every team needs three good ones each, unlike Ikara props.

As has been pointed out, a team can "test" its supercaps for maximum performance, simply be charging and running them, one after the other, on the same motor and prop, and timing them. The ones that run the longest are the highest capacitance. Testing need not cost anything, once the capacitors are bought.

EWS indeed wouldn't be a "perfect" event. Are its disadvantages sufficient to cancel an event that also has a great many advantages?
« Last Edit: April 19, 2018, 07:33:23 PM by Little-Acorn » Logged
frash
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« Reply #19 on: April 19, 2018, 09:35:48 PM »

Hip Pocket Builders' Forum > Indoor Free Flight Forum > General Discussion > Topic: Electric Indoor FF Sport Duration

Above topic contains 4 charging or discharging curves for a capacitor in Replies 11-12 and 15-16.

This was done with a very old meter that could log voltage or current with time and plotting resulting data with Excel.

Fred Rash
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Little-Acorn
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« Reply #20 on: April 19, 2018, 10:47:22 PM »

Fred, that is a GREAT thread! And the graphs are very handy. Thank you!
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Little-Acorn
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« Reply #21 on: May 06, 2018, 02:50:59 AM »

I threw together a test set for EWS motors, gearboxes, props, and capacitors, using an old tach from my (bigger) model plane days, some panel voltmeters ($6 each at Amazon.com), a 0.1 Ohm resistor to sense current, and a "clothespin" with two D cells to charge the capacitors. Then ran a Vapor motor, Ember gearbox, and Vapor propeller through its paces to see if it would work. So far so good. I've got other motors, gearboxes (if any) and props waiting their turn. Plus lots of capacitors.

See the pics, including a printout of the dataset from the test runs. I'll graph it soon, when I find out how to put multiple lines with different scales on the same chart in Excel.

I ran the tests before putting the labels on and the tach mount. The first photo shows the board AFTER I finally put them on. At the left side of the board is the motor, prop, and tachometer. At the bottom of the board is the clothespin and D cells. At the right is a choice of power sources: A capacitor, a variable regulated power supply (LM317, TO-220 case), or some AAs to run the LM317 (and light up the digital meters).

Did you more experienced folks get data in this range with your planes and tests? I hope I'm not too far out in the weeds with these. Thanks for your help!  :-)

The photos show (in order I hope):

1.) Overall look at the test board with labels
2.) Charging the capacitor. See voltage readings on the meters.
3.) After charging, unhooking the clothespin
4.) Running the motor
5.) Still running the motor, see changing voltages and current
6.) Printout of Excel spreadsheet showing results. Left side (pink) shows raw readings, right side (green) shows derived data (more useful).

Attached files Thumbnail(s):
Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
Re: Electric Wright Stuff trial event for Div. B or C?
« Last Edit: May 06, 2018, 03:19:16 AM by Little-Acorn » Logged
frash
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« Reply #22 on: May 06, 2018, 10:11:30 PM »

I like what you are doing and expect to learn from it.

Did you log all data points manually or use some type of data logger? I only did a little of this and much simpler than you. My "data logger" was an old (Radio Shack discontinued special for $20 in 2000) Metex ME-11 multimeter. It can log current or voltage at time intervals, but not both, to a .csv file for import into Excel. Obviously, you have a better system and/or more patience and perseverance.    

Keep up the good work.

Fred Rash
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Little-Acorn
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« Reply #23 on: May 07, 2018, 01:37:36 PM »

Thanks, Fred. I wasn't finding too much data on EWS planes, probably because the event hasn't been run very often. Most people seem to plug a cap into their plane and hope for the best. So I'm trying to create my own data, hopefully accurate enough to share. Fumbled around with test leads for my Fluke 77 multimeter, and could never measure simultaneous voltages and currents, so finally decided to put together a dedicated test set. It could still use improvement (a lot), but it's a first step.

As you pointed out, the biggest logjam now is data recording. I presently do it by aiming an inexpensive digital camera at the board from about 18 inches above it, and letting the test run. Then download the resulting mp4 file to a PC, and I can fast-forward, reverse, or pause it all I want. Then with every freeze-frame, I type the numbers into an Excel spreadsheet on the same computer (big screens are handy sometimes :-) .
 
Your mention of a data-logging multimeter is very interesting. I don't have such a thing, yet. Looking at some more gadgets on my favorite high-tech sore (Amazon.com), they have some dongle-shaped USB toys that have an LCD or LED display that apparently can show voltage and/or current. Most say that they can be used on a USB charger, say for a cell phone, I guess to measure the charger's output voltage and current.

I wonder if that's all they can measure? Do any have a place to plug in test leads, that we can plug into an EWS plane's motor or capacitor or current-sense resistor? And can they record whatever readings they get on a file in the host computer?

Some examples, chosen pretty much at random:
https://www.amazon.com/gp/product/B019RHJRM8/ref=ox_sc_act_title_3?smid=A2Z6I2H487OQGL&psc=1
https://www.amazon.com/gp/product/B077PZF8B8/ref=ox_sc_act_title_2?smid=A2JJP3F6PC8TJO&psc=1
https://www.amazon.com/gp/product/B073R7YRM9/ref=ox_sc_act_title_1?smid=ANGHDKZZ80XV6&psc=1

I'll look into these further, hoping to see if any of them can be used as a data-logging multimeter (or at least voltmeter with good enough resolution) as yours did. (And, can I plug four of them into my computer at home, maybe using one of those one-output-four-input USB hubs, so the computer can read all four separately?)

One thing I want to do with the present board, is measure various capacitors for their actual capacitance. As we've already discussed, AVX's datasheet says the tolerances on their supercaps are -10% to +30%, which is astonishingly wide. I have a dozen AVX 3V 5F caps here, pretty new. I wonder what variance there is among them? Pretty small sample, but you have to start somewhere. Will the large majority of them be within 5% of 5F, with maybe one or two outliers? Or will they be fairly evenly distributed from 4.5F to 6.5F?

Instead of connecting them to an EWS plane's motor, I'll connect them to a 10 Ohm 5W resistor from my junk box. The one motor I've tested so far, shows an equivalent series resistance around 7 to 10 Ohms (varies with RPM), so this resistor should be at least similar to a load the capacitor will usually drive. If I can figure out the rate of change of voltage across the cap while also measuring current, capacitance in Farads should be pretty clear. Same resistor for all tests, and warm it up before starting so its resistance won't change (I hope) from capacitor to capacitor.

Well, that's the plan. It may or may not give me garbage, but you never know till you try.
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« Reply #24 on: May 07, 2018, 02:33:07 PM »

Little-Acorn,

My eyes are glazing over a bit.....  I am sure there is some Middle Schooler or High Schooler who can rig up an Aurodino board to act as a data-logger.  It would be a nice "science project" for them to complete for you.  I would like to see this EWS event at SO.  Maybe someone will put Snoopy in the cockpit going against the Red Barron?  My son would like to do this for DivB, if not then we will build for fun.

Lee
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