Thoughts from the workbench of Radical RC. The online retailer of electronics and kits for radio control aircraft. Dave Thacker shares his thoughts and knowledge of electronics, batteries, kit design and overall enjoyment of the hobby.
Part 2 in an ongoing series about being a good test pilot. These articals are less about step by step hand holding instructions and more about how to think. We continue….
I always conduct an interview of sorts to fill in the blanks of things I may not be aware of such as level of experience, how long the project took, what the MFG says about CG location, suggested weight, what does it actually weigh and etc…. What your fishing for anything that could be a surprise. After the crash, you don’t want to hear the builder say “I thought 1/2″ behind reccomended CG was close enough?!?!”. Your looking for any shortcuts or oversights in the model. Did they use the reccommended servo’s or at least close? Is the battery large enough? How old is it? If the RX is new, has it been run a while? If the RX has come from another model, was it flying fine or did it’s last flight end in a crash? Has the TX been performing well? Are there any used or harvested components in the systems?
Always check the CG against common sense and what the builder says it should be. NEVER trust that it is right. Hold the model up in the air and check it yourself. Measure if you must. There is NO excuse for crashing over a missed CG check.
Control surface throws: I’ve run into many first time builders that started with a few foamy’s, have built their first sport or scale model and they put throws in the model that look like the 3d foamy they’ve most recently been flying. Not realizing the throws apropriate for a 25-30mph ship will be grossly excessive in a 70mph aircraft. Besides asking about suggested throws, apply your own stink test. If it doesn’t look right, it probably isn’t right. I like throws for a test flight just a tad on the high side of suggested first setups. However, you can take this way too far and end up with an over sensitive model. A model that is way out of trim and also way too sensitive is a real handful. Don’t walk into any such traps. Also, if a throw such as the elevator is too low and the model turns out to have an incidence or nose heavy problem, you might not be able to land at a reasonable speed and hold the nose up. Too little therefor can be just as bad a mistake. Try to be reasonable about what’s correct for “this” model. Generally, the faster it flys, the lower the throws should be. Something else to aid here is look for similar level of throws. If the ailerons are deflecting 30 degrees and the elevator only 15 degree’s perhaps the throws will be “out of balance”. Out of balance controls would be one control being sensitive and antoher being soft. This is more difficult to process in your brain when your under pressure trimming out a difficult model. Consider it before proceding.
Testing a new model out is an important task regardless if it is yours or a friends. Many things go into a successful test flight. This will be the first in a series of articals on this subject. I consider it a high honor to be asked to test a new model and you should as well. Lets honor those requests by doing the job well. My writing will be mostly from the perspective of testing anothers model to simplify the language.
When a modeler brings you model to test fly, not only is he choosing you for your flying skills and experience, but also for your wisdom and judgment. Obvioulsy your trusted. Don’t shy away from telling the builder what they need to hear. If the model is not really ready to fly, say so. Your were choosen because you have the judgement and skills to make that deturmination as well as the skills to fly the model if it’s ready.
The first thing to do is size up the modeler and the model. If the modeler is known to you, is the complexity of this model in line with this persons experience and flying skills? For example, a pilot on his 3rd model presenting you with a multi engine, air-retract model could be reaching out a bit far. You’ll need to inspect every detail of this model very carefully as mechanical errors are more likely. Check every connection in the retract system. Look the servos over, are the appropriate for the model? Is the linkage up to snuff for the expected speed and performance? Is other hardware like wheels and landing gear mounting substantial enough to handle landing loads? Is the wiring done well? Are connectors properly safety tied where needed? Is wiring mounted or flopping around inside? Is the battery and RX secure? One of these loose in the model could lead to plugs opening up or severe CG changes. How is the antenna routed? Is it shadowed by wiring or other objects? Look at all the basics. If there is anything at all your not comfortable with, now is the time to discuss and address any problems.
This had to be the biggest hoot ever at a night fly. Heard the cheering from across the field, went to investigate and found alot of foam crunching fun going on. Had to be 200 spectators. It looked easier than it was, how could these guys miss so often?
Come to SEFF, learn that you can have more fun that you thought you could take. Stretch yourself.
This can sometimes be the most challenging part of the whole project. First, you need a budget. Try to get your group to approve about $1000 so you have wider options. There is nothing wrong with coming in way under budget. However, If you spend less than you should have, your whole event could go down as a disaster.
Look to your membership first:
Does somebody in the group belong to a civic group with a meeting hall? I’ve been to swap meets in Churches, VFW Halls, Union Halls, Corporate Cafeteria’s, High School Gym’s, Grade School Gym’s, Vocational School Cafeteria, Convention Centers, Sports Arena’s, Civic Center Halls, Grange Halls, and even a Plumbers Garage. Yes, it is a big garage. The point is to think out of the box. Your membership probably has at least a few connections to facilities such as these. Rarely they will be free, but often becasue your member is part of that association there will be substantial discount, often 50%. Look into each one of the opportunities with an open mind.
It’s never a waste of time to visit your local city officials for some assistance. They are often favorable to support events that bring visitors and revenue to the community. You can never predict what might be offered or suggested. During the years we held our event at the Convention Center, which is managed by the City of Dayton. They were exceedingly helpful in making sure we could both afford the venue and had what we needed. It’s a feather in their cap to have another event in town. And, being a civic group working in a city park didn’t hurt at all.
What makes a good room for our new swap meet?
What your looking for is a heated/conditioned space that is reasonably clean and big enough 80 tables or so. (You need about 7200 square feet or more to do this.) It’s very important to have a room with 2 entrances. You want a front entrance for the public and a back or side entrance for your vendors to load in. I’ll cover these subjects in later articals. Just realize you need to control the “Sneaker In-ers” to protect your event profit and the first step in this security is seperating the vendor entrance from the public entrance. Things to watch out for is a vendor loading entrance with bad auto traffic flow like back in a corner of the lot will be a problem. Also, it needs to be an entrance a dolly can go through, no steps.
Why 80 Tables?
Just from experience, I’ve learned the meets with less than 80 tables seem to wallow around in the 40-60 zone. They never are very busy or crowded. The ones around 80 tables or larger just seem to be stonger. In times of economic failure like these, people who like to go to swaps perhaps decide with higher fuel costs they are going to cut out the smaller ones and just do the bigger ones. You want to be one of the bigger ones. It’s OK to start smaller, but don’t get stuck, make sure your adding in 10-20 tables a year, and make sure you advertise how many tables your event it. It makes a difference.
How do you get tables and chairs?
Very good question! Although I’ve been to meets where the club rented tables from local party rental companies, this is expensive and often means you’ll be managing a pickup truck brigade to get them to your site. It’s alot of work and money. Expect table rental from sources like this to be $5 to $8 a unit, chairs about $3 a unit. It’s best to look for a hall that has tables already for a modest rental fee or perhaps included. We’ve negotiated that as part of our rent for our event. Our crew sets up the tables and at the end we fold them up and put them back on the carts to be stored. You’ll need 4-10 more tables than swap meet tables you plan to rent. If the room is a bit short, it’s no big deal to get members to bring some folding tables for a few things like vendor check it and other places you’ll need them for your staff.
The Midwest Model Rama’s first location:
The first Model RAMA shows were in a local UAW Union hall. A club member had access to the hall at a discount rate. As I remember, it cost the club $400 to rent the hall. The hall was just big enough for what I considered the minimum size successful meet. And, that was 80 tables. The hall size is 120′ x 60′ or about 7200 square feet. We sold the hall out completely the first 2 years and moved on to something even bigger.
We went from there to a large room in Hara Arena. We’ve had our event at Hara several times and even the Downtown Dayton Convention Center a few times. Currently it’s held at the Montgomery Country Fairgrounds. We’ve spent anywhere from $400 to $2400 on room and tables each year. We’ve always made a profit. However, at the high point of rental, we didn’t make much for our group and that had to change. Our current location is about $1300 and lets the county rent a room in the winter when there are no customers and lets us make a decent profit. All our procedes are spent improving our model airport “Wingmaster Field” in Dayton Ohio. Home of the Dayton Wingmasters Model Airplane Club. The field is in a public park and is open to the public. What a great deal a local model airplane club can be for a city. It’s probably the only public park in the area maitained by a civic group. What a DEAL for the taxpayers! And, we are happy to do it, it’s one of the country’s most beautiful flying sites.
A Hard Date:
Make certain your deal with your venue is a hard date. Meaning, it’s your date. We once almost rented an indoor college practice field. But then they told me if a coach needed the room they might have to move our date. I asked how much notice and they said, “Oh a week or so”. I said, no thanks! You need 6-12 months to plan one of these things. You can’t have somebody flipping over the applecart on you. A real rental hall with give you contract that barring Tornado or Fire, it’s your room on the agreed date.
Over the years at various venue’s we’ve had indoor flying after the meet. If your ceiling is tall enough inside it’s always a great hit to allow some flying. Most of the time, your rental is for all day. You’ll find swap meets run strong in the morning but by noon or 1pm they are fizzled out. Only the very largest meets can hold a croud as late as 2 or 3 pm. So, if the building permits, soon as everything fizzles out, tear down the tables and start flying. If your going to do this, be sure to put it in your AMA ad and on your flyers. This will attract even more people than would come out for “just a swap meet” and adds an extra level of fun in the day. A location with flying potential is worth more to you.
The Tight Wad Failure
I’ve seen events that never really grew to meet with the clubs dreams because they got intoxicated with the cheapness of a free or low cost hall to hold the event. Once on the needle of cheapness they just can’t find a way off. Don’t make this mistake. It’s ok to start out this way. However, if your venue is full, you need to move on, look onward and upward to achieve your potential.
For many of us there is a winter storage season. How do we bring our fuel powered models out of storage confident our RX battery packs are up to snuff? Were they nearing the end of life at the end of last seasons flying? Did they survive being in the trailer or garage ceiling for a number of months? Here are important steps to greatly reduce your risk of shouting “I Ain’t Got It!” when you hit the field this spring. These recommendations are intended for NiMH and NiCad packs although the similar principals apply to any mission critical TX or RX pack regardless of chemistry.
1. You should have cycled your packs and noted the value on them when you put the model in storage. Did you do this? A simple round of cycling in the fall will help weed the weakest packs from the herd.
2. Check the purchase date on your pack prior to model reactivation. Did you date your packs? Noting the purchase date in permanent marker should be a routine with new packs. Has this pack made it 3 seasons already? If it has made it 3 seasons, it’s time to replace it with a fresh one even if it’s still cycling well. It never seems like a good deal to “squeeze one more season” out of a pack if a model is lost doing so. There are no battery experts in the industry, nor any magazine writers that are willing to dare recommending using packs beyond 3 years. Most recommend only 2 years. The incident of surprise failures increases with each season. It’s much cheaper “not” to find out how long it will take to have a failure. Think about it.
3. Similar to a new pack, a pack having been in storage for some time is in need of a slow “forming charge.” A forming charge is a simple full-to-overflowing charge on a non-peak detecting charger like your factory wall wart. While in storage the cells slowly discharge. Not every cell will discharge at the same speed. After a few months, you could have one cell at 80%, one at 60% and two at 50%. When form charging, It’s important the charge rate does not exceed 10% of the packs mili-amp-hour (mah) value when doing this procedure. This type of charge allows all the cells to fill fully and the first cells to fill won’t be overheated by the ongoing charge. The danger of peak charging a pack that has been in storage is the best cell (the 80% full one) can be ruined as it’s overcharged while the other 3 are still filling up. Also, your pack may false peak meaning that although the charger reports it is full, it really might not be. Re-equalize the cells with a good long slow wall charger charge prior to any peak charging to avoid most problems.
4. Test for Capacity. Discharge the pack on your favorite charger (with discharge function). For the purposes of this kind of test, the correct rate to test against factory rating is 20% or 1/5 of the rated capacity. It’s ok if you can’t get that setting exactly, just get it close. Example: A 1000mah pack would be tested at 200mah discharge. Most chargers will display this as .2A. Your pack should test at least 80% of it’s rated capacity. If it does not, then a few more charge / discharge cycles are in order. If you can’t get the pack to test above 80%, it’s time to replace it. Although it might seem like a money saver to succumb to temptation and overlook marginal packs, one crashed model will pay for a great many replacement battery packs. And that’s to say nothing of the risk to others when a model goes out of control. Good pack or no go!
5. When you recharge the pack after your final discharge test, check the charger input mah. Did it put in about the right amount? A pack that’s been in storage, particularly if you’ve skipped the step of re-forming it is very prone to a false peak. A great pack that tests perfect but only takes 50% of the expected recharge amount could cause some unwelcome excitement.
6. Test your Switch. First, use a loaded tester to check your fully charged pack directly. Note the value then test it through the switch harness. If it tests good directly but marginal through the switch, it might be a sign the switch is getting dirty internally, worn or perhaps some connectors are going south. Like battery packs, finding out how long a switch will last is costly knowledge to acquire. It’s a good idea to replace the switch with every other new battery just to avoid trouble. Load testing your pack with and without the switch harness looking for any substantial difference is a good way to detect a problem before starting the season. Did you notice what I omitted? After checking the battery through your switches charge lead or charge jack, unplug it from the RX, turn the switch to the “ON” position and check it again. Is it load testing similar to the charge jack/charge pigtail? The most important place for your pack to deliver it’s energy is to the RX. Make sure it’s solid to this point, not just the charge harness.
Integrate these practices into your seasonal routines and many common pitfalls are avoided. Don’t forget to scrutinize your TX battery in similar fashion. Ongoing TX function is every bit as important as RX functionality.
I wrote previously on the subject of “Confirmation Bias”. Sometimes it is difficult to discover the answer to a technical problem because the person bringing you the problem has a hitch, assumption, or faulty logic step in their diagnostic process. Often people draw conclusions from spotty evidence. For instance a customer shows me a receiver and say’s “This receiver is bad.” I ask: “Why do you think it is bad? The answer almost always comes back something like “I plugged it in and it does not work.” The person is saying from that one test or measurement they have drawn a conclusion. It seems reasonable doesn’t it? But, really it’s pretty silly when you think about all the things that can cause an RX not to respond to a TX. You see, the real and only conclusion you can draw from the customers test is this. “In one trial, the RX produced no apparent response.” That is quite a bit different from “This receiver is bad.” Understanding the difference in those two conclusions is why some people are good at diagnostics and others are not. To be good at figuring out a problem, you are greatly advantaged by not making any assumptions or broad conclusions.
In the case of a receiver, lets go over many measurements and tests that you might perform to decide if it is in fact “Bad”.
1. Has it ever functioned successfully?
2. Does it really match the Transmitter? (is it talking the right language DSMII vs DSMX or PCM vs FM vs AM and etc…)
3. Is it on the same channel? (in the case of non-2.4ghz gear)
4. Besides looking at the stickers, did you actually look at the tags on the TX and RX xtal?
5. Is the shift the same? For example, a positive shift JR TX is never going to drive a negative shift Hitec or Futaba RX.
6. Have you driven the servo you used on the tested RX with a servo tester to make sure it actually wiggles?
7. Have you load tested the battery your driving the RX with to see that it is high enough to actually turn on an RX?
8. Are you using a switch between the battery and RX? Plug the battery in directly so your not actually testing if the switch is good.
9. Can you demonstrate the TX driving another RX to establish that your testing with a working TX? One might complain, “I flew it a week ago!” However, we’re not testing the troubled RX a week ago, we’re testing it now. 😉
10. Have you plugged a voltmeter into an empty servo port to see if there really is voltage finding it’s way to the RX?
11. Is the crystal really fitting tightly in the socket or is it loose and wobbly?
12. Does the TX have the capability of being on for programming without broadcasting?
13. Is the meter on the TX a voltmeter or RF Output indicator? What does it say?
I’m sure a sharp thinker can come up with some more things to consider. Many of the things above we’ve found at one time or another to be the cause of a non-responsive RX. Assume nothing.
Recently we had an A123 RX pack returned by a customer. He said it tested poorly, only a few hundred mah. The customer appeared to be correct, it was testing bad after several charge/discharge cycles on our bench. And, the charger would increase in voltage rapidly when we applied charge current. Strange. However, even after several trials, a good mechanic still hasn’t drawn any conclusion. He may be moving towards condemning the battery but all tests were not complete. He cut the shrink off the pack. The tabs all looked fine. He re soldered the tabs anyway just in case there was an unseen cold joint. Note: He had originally built the pack, but without emotion, he redid his original work anyway. Many people fail at this step because “they couldn’t possibly have done anything wrong.” (yea right!). The pack was cycled again with the same poor result. Now, finding a bad battery pack is rare, exceedingly rare. We know this to be true from many years of experience. So, we keep looking. I examined the pack under magnification (even though it had been re soldered by a respected pro) and all looked good. I looked at the plug under magnification and found a thin transparent film on the plastic shell. The more I looked, the more I saw this film all over the shell. Is this paint? We decided to solder a second lead onto the pack and test again. The pack tested good. What was the problem you wonder? We can only conclude the film on the plug was thin CA the customer had somehow accidentally allowed to come into contact with the plug. It had a high resistance because one or more connector pins was evidently coated in glue. After replacing this plug, the apparently bad battery pack was proven that it was always as good as new.
So, if a battery pack fails a discharge test or an RX fails to respond, is it bad?
To read about The Texas Sharp Shooter Fallacy, check out this wiki link. Reading it is what inspired me to write today’s article. It describes in somewhat technical language a common way to foul up a test. “Texas Sharpshooter Fallicy” Wiki Link.
There are many reasons. Most clubs having expenses to maintain and improve their model airport have need of revenue. A model swap meet can make a terrific fund raiser for this or any other purpose. It can also serve as an off-season gathering for your regions pilots. A time to renew friendships and refresh interest in our sport.
Having managed one of the country’s largest swap meets for well over a decade, I speak from experience. The ModelRama has celebrated it’s 13th year in 2012 with a record setting 174 table reservations. Our first two events were 80 tables (filled the hall we were using) and the event has grown steadily ever since. It’s my major volunteer effort each year to support the Dayton Wingmasters and our Model Airpark “Wingmaster Field”. No one puts on an event of this nature single handedly. Our event has enjoyed excellent support from our club members every year. We’ll talk more about Volunteers in a later post along with many other considerations like date planning, setup times/hours, important positions you’ll need volunteers for, getting the vendors, getting the swappers, getting the modelers there, selling raffle and 50/50 tickets, holding an auction, walking sales, indoor flying and more.
If your already holding a similar event, perhaps you’ll find something here to improve your results. The suggestions and ideas that follow where not arrived at out of thin air. For about a decade, Radical RC (my family business) attended 25 or more club swap meets per year. I’ve witnessed much good and some bad and have tried to combine all the best idea’s in one “Super Swap Meet”. We make adjustments every year and are always looking for a better way to do everything.
We may alter these posts at any time as knowledge and opinions evolve. Consider these a series of articles suggesting current best practices. You can rest assured however, that if you follow these guidelines, you’ll have a successful and profitable event. It will be the most popular event of the year and probably the least amount of work per $100 earned of anything your group has ever done. Give it a go!
Look for these posts to accumulate within “How To?” sub category “How: A Successful Swap Meet”.
Hi Dave, I just assembled for the first time a plane I’m just finishing up and discovered I somehow ended up with the tail assembly sitting with one side lower than the opposite side by 3/4″ from side to side on an 18″ wide tail. At 3/8″ each side it didn’t even show until I pit the wings on and could see the difference. That said, it’s cocked so, is there any kind of epoxy solvent (softener) I might be able to use so I can remove the tail and square it up ?
I can’t access it either front of back to saw it apart. I don’t know how something like this could even happen with a SIG kit plane EP-20 Four Star when it’s all laser cut. I blocked both sides up even (I thought) with blocks each side until the epoxy set hard when I placed the tail on the fuselage.
Ted, I’m not aware of a chemical for that. Get your heat gun out and warm it up stearnly. Perhaps you can get it to soften enough to pull apart. Then when it cools and hardends, you can machine it off.
To get it off a flat surface, take a T sanding bar and cover all but center 1/3 with masking tape, Now you can slide it back and forth on the surface and only the glue above the surface will be cut off.
I usually will glue a stab on like this by proping it up with two block exactly the same height, then I square the fuse to the bench. Us your flat bench as the jig in this way. (I did not know it was covered when I sent my suggestions)
Hi Dave, Thank you so much for suggesting use of the heat gun. That worked and I was able to just raise the low side without removing the whole tail assembly, then let the epoxy cool and the tail is even both side perfectly now.. I had to replace some Monokote in the area that melted but you can’t tell now unless one looks for seams on the covering.
Lucky I melted the covering as I found I had broken one of the tails internal wood cross members and was able to replace it. I must have done that trying to raise the tail in my earlier efforts.
Thanks so much. I attached a shot of it on my work bench so you can see where I build my toys 🙂 .
Humans are built to want answers. We seek to eliminate all uncertainties. Giant institutions are constructed and survive on our desire to know. To comfort ourselves, when diagnosing a problem we often look at one or two points of evidence and decide the “cause”. Once we’ve reached a conclusion, there is a tendancy to interprit all future evidence in a way that confirms our conclusion. Such is an example of confirmation bias.
To effectively diagnose any problem, we must first desire above all to know the answer. One must not be married to any particular conclusion in order to observe the facts objectively. We look at the facts and begin to focus in on everything that could be responsible for something not working. As we check each thing out fully, we slowly eliminate possible causes. We begin to zero in on a theory of why something is not working. We then look for other things to measure and observe what would be true if our developing theory is correct. If we then aquire evidence not consistant with the theory, we back up and reconsider all prior evidence and seek a new conclusion in harmony with all the facts. It is only by repeating this process without bias to any particular conclusion that we can finally arrive at the truth.