Need advice about RC options for ultralight paper airframe project

Discussion in 'RC Aircraft & Watercraft' started by liftline, Sep 29, 2010.

  1. schorhr

    schorhr Member

    Heh. I am sure we will. It will most certainly fly earlier then my new stuff, if I continue at this pace.

    Brushless motors: Trial and error ;-) If it runs the wrong way, change two wires- done.

    Beer cam: Hehe. I used to make macro vidos through a kid's magifying glass... If it works, its legit.

    1. Free wood! Great ;-) Why buy balsa if you can have a delicios snack instead?

    2. Looking good! What where those mounts now? From HK?

    3. Looking good as well. Yes, programmable gear solves so many issues...

    4. 5. Can't wait for seeing the finished project! :D

    You should get a $8 Spycam + Jelly Macro lens ;-)
    ,,,Or a $4.70 webcam off ebay (incl. shipping) with a manual focus... not the best image sensor, but decent:

    I am now getting the "old" Canon 450D since my girlfriend upgrades to the 550D- fun. Can't wait to shoot a HD Stop Motion animation film. It's also awesome for macro/close ups with a cheap inverter adapter or adapter rings and $8 lens.
  2. liftline

    liftline Member

    Bit more progress. The motor has been fitted with a folded paper ITM (Insanely Tiny Mount) that slides over the popsicle stick lug epoxied to the shaft.

    The motor and mount fit inside the upper cowling with plenty of room to spare. Looks like the ESC may fit up front too. Every bit helps with the CG.

    Couldn't resist fiting the prop. Nice!

    Getting ready to fire the motor up for the first time. I'm working on the assumption that the motor leads follow best servo practice...positive lead in the center, negative and signal to either side?

    Attached Files:

  3. schorhr

    schorhr Member

    ITM (Insanely Tiny Mount) :mrgreen:

    Motors have no signal cable?

    The ESC powers the coils to cause the motor to spin.
    Here a three pin example diagram: Winding Diagram1.jpg
    So ->Red-Blue-Green-> would cause a clockwise spin.
    If you change two wires, eg. Blue-Red-Green or Red-Green-Blue it starts to rotate counter clock wise.
    So if it runs in the wrong direction, just swap two wires... done ;-)

    Or do you mean the ESC?
    Then the setup should be similar to the servo plugs, I am not sure which is "up" on your reciever type... :)
  4. liftline

    liftline Member

    I meant motor, but I was just plain wrong about a signal lead...not sure where got that idea. Anyhow, doesn't look like anything on the motor can get fried. The ESC is plainly marked, so no problem there. Thanks!
  5. schorhr

    schorhr Member

    Nope, no worries!
    The only problem is determing which direction it will turn, but just try before soldering and no load... even though it does look nice with prop installed ;-)
    Perhaps use a bit of tape to better see the moving direction. Or hold+run slow.
  6. liftline

    liftline Member

    More progress to report. I got the ESC and motor up and running this (snowy) evening. Had planned to just cram bare leads into the plugs before committing to a configuration, but that they wouldn't stay put without soldering. I made a hash of that- the pins on those little plugs that come with the ESC are tiny and move every which way as you try and solder...even with my jury rigged clamps. Still, everything worked right the second try...the first didn't really count because I connected the ESC to the wrong channelwall1.

    The motor runs smoothly and has pretty impressive torque for something so small. So far I am very impressed. I never really opened up the throttle much and kept the test short to avoid overheating.

    My test was an impressive testimony to those little micro lipos. I hadn't charge the battery in 6 weeks, but it was still full of juice. I've never had the chance to even run it through one cycle. Think I should discharge it?

    If the weather were good I would make a proof of concept model with just rudder and throttle and take it outside for a spin. I'll need a bit more than just that to test fly in a confined space.
  7. schorhr

    schorhr Member

    No real need to cycle lipo batterys in, as it was with nicd...
    They will have more power after a few cycles, but just using them out of the box is fine :)
    Or just charge it up again. LiPos have (almost) no memory effect.
    The only things not good for them is too high discharge rates, charging them too fast (the slower, the better), and the last ~20% charging is one of the causes they age (that's why laptop computer batteries tend to get worse if you keep them on the ac/dc adapter all the time).

    GOod that the connecting worked out :) Can't wait to see the little sucker pull a plane ;-)
    I just have the 5 gram brushless, and boy, these litle motors are really amazing, aren't they? They pull 30+ times their own weight... sort of like ants :))

    If you want a concept model, you could buy a sheet of 3mm depron to give it a go outside in the snow :) Just a minimalistic delta or a smaller version of the "little twin" or something.
  8. liftline

    liftline Member

    I really would fear for the electrical components in our slushy winter weather. I live about 12 miles from the Wright Brother Mansion. There is a reason they did there winter tests in South Carolina, and not just the strong steady winds. They wanted out of Dayton! Things were primitive in 1903..they had to lose their own luggage.:twisted:

    Would it be OK to mount the motor and prop on a test stand and do a brief throttle up? Just to get a feel for thrust and torque and to see how hot that little can gets.

    I'm leaning towards testing the model indoors with just throttle, rudder and elevator. Can the motor really pull this beast? There is a large indoor sports arena in my area which hosts a few electric fly-ins this season. I used to test stuff there on the sly a few years back. There is a lot of airspace above the seats, but air currents can get tricky - the architects move a lot of ventilation above the heads of the crowds.

    Now that I have the engine wiring down I'm going to have to put longer leads on the engine and esc. The ESC with plugs is a bit too long to fit next to the motor. wall1 The best place for the ESC is the battery box space under the RX, but the stock leads are too short. Another option is to bury the ESC in the lower wing root. Any option is tight.

    As you suggested way back when, I'm looking to cut weight. I currently connect leads to the RX using E-flite 3 pin female plugs from 3 inch servo extension kits. Pricey, a bit heavy and bulky. I cut the plugs apart with a utility knife and the little crimp tubes inside would be near perfect. It's tight up at the RX pin box, but nothing actually touches. Given the low voltages, maybe just a coat of varnish would given adequate insulation safety margins. I think Hobby King may sell similar connectors, but it's hard to tell, I don't know what the industry calls these things.

    I also like the idea of ultimately using bare wire strands coated with varnish. I could make my own customized wire guides by gluing strands to sheets of paper. Spray a little varnish over the top. Would go a long way towards curing the spaghetti factor which is becoming a real problem.
  9. schorhr

    schorhr Member

    Sure, water and snow are the enemy of electronics, but if it's all covered up, little can happen- usualy...

    Mount it and test the little motor ;-) Nothing can go wrong. At those dimensions and power rates, not much can happen. Probably stings when holding your finger into the prop, but not as bad as on a 10" prop... those don't sting, they chop!

    Some indoor toys just have rudder and throttle. And with such a light weight, there usualy is not any damage at all, if you do not crash it too bad.
    How much does the thing weigh now?

    If all fails, remove as much as you can, and solder directly.
    paint coated wire is ideal for low power connection such as servo or data.

    Well, I am sure you'll manage to get this thing flying... good luck ;-)
  10. liftline

    liftline Member

    By the way, I think FlySky sold a LOT of RX/TX units this Holiday Season! I went to the MyCoolHelicopter site to have a look at the manual (which I forgot to save the first time) and downloads were impossible. I sneaked in this morning before the rush, but it looks like traffic is still really high.
  11. schorhr

    schorhr Member

  12. liftline

    liftline Member

    Weight is currently pushing 40 g, with 4 servos rather than 3. This includes the plastic RX case, which adds 3 g, but also provides CG necessary ballast (if I believe my center of lift estimate from glide tests). The Royal Aircraft Factory configured this thing to take a heavy engine! If the engine & prop can deliver 20 g of thrust I figure the model will actually be a bit hot for me to handle. But who knows how much thrust I'll actually get. Flying with just 2 axis control is more a simplicity thing than a weight thing at this point. I don't insert components into this model, I build the model around the components. I hope to get past this at some point, but things are quick and dirty right now. You would be correct in saying I am a lot better at the dirty than the quick!

    Interesting thing that prop... looks identical to the ones I have on an airhogs RC toy. At this scale I bet you could flip it and it would work just fine. But I've got mine rotating as intended, right hand rule thumb is pointing back at me.
  13. liftline

    liftline Member

    Yes, that's it, and it downloads in seconds. I initially thought the slow download was due to changes I made in my Internet service - bit lower bandwidth but way, way lower price. Thought the new Malware/virus filter might be to blame. Nope, just lots of happy hobbyists.
  14. schorhr

    schorhr Member

    I downgraded to 2 Mbit and at the family there's only 1 MBit available, so I am used to "slow" broadband, but even with 16 mbit or more, usualy the problem is clogged servers.

    Flip the prop? Won't do any good :D

    While Hobbyking claims 36g thrust on 1s, 16 gram stock, 19g balanced, or 20g with a moded prop seem to be what people mesure on the comments.
    Roji_w posted his 40g foamy flies well outdoors with the little motor.
    If all fails, get the 5g motor ;-) Or fly with three servos, either control height by throttle and ailerons or use a single servo for rolls instead of having full controll with two wing servos...
  15. liftline

    liftline Member

    Pity Zealot doesn't support video announce1, but the motor just spun up beautifully on the test plank. :thumb: I didn't bother to secure the engine lug (popsicle stick) to the motor mount, figuring friction might be enough, and it began to pull itself out of the mount (aggressively :eek:) at about 1/2 throttle. Ok, need to work on a "toothpick JC Nut." :rolleyes: For now, held it in place with my finger and took it full power. Balance is excellent, vERY smooth at full throttle. Nice hum, lot of breeze. Not quantitative, but encouraging for a guy used to capacitor driven pager motors :cry:

    I've Googled the same reports from the field and have tended to assume worst case thrust at 16g. So long as all up weight stays below 48g the model ought to fly reasonably well. If I get near 20 I'll be thrilled.

    Partial aileron control are an option I hadn't consider. I'm assuming you mean just fit ailerons to one side (pair of wings) and live with high yaw. Good idea. I've also thought about running one servo to a bell crank driving torsion shafts on both lower wings. Might be a bit sloppy and Since my servos just weigh 1.7 g, the weight savings of a bell crank might not amount to much either. You can see why I'm hedging on ailerons a bit.

    As new as I am to this micro stuff, I just want to see if I can get it up in the air under reasonably good control. I figure refinements will come organically with experience (crashes & near misses). It's all fun.

    Attached Files:

  16. schorhr

    schorhr Member

    That's what youtube is for, hehe.
    Back when we had our public station TV show, it was allways hard to find a free/cheap webspace to host videos... seems so long ago.

    Sounds like the little motor really has power! Great! As you probably do not want to go vertical, I am sure the little thing will pull the plane just fine :)
  17. liftline

    liftline Member

    The little beast got a little better for two reasons: 1) I was testing on a rather depleted LIPO battery. Charging the voltage up to 4.2 made a big difference. 2) I read the small print instructions on the ESC and set the top throttle limit. Top end went up a bit, based on higher pitch hum. Wish I still had a strobe light! There are a lot of other ESC functions that can be programmed from the transmitter and I'll look into those. Programming isn't exactly easy though, no PC GUI interface, just beep cues and stick response after within a specified number of seconds.

    So yes, looking good, smooth, nice throttle response (but it can "stick" when the voltage drops) and a sweet hum. My motor mounts work great.

    Roads are icy today and I don't feel like leaving home a second time. I'm going to see if I can't get a good estimate on prop thrust. My plan is to take the motor mount and put it on a lever arm connected to a pivot. At a right angle to the pivot will be a second lever arm pressing on an electronic balance. Engine thrust generated torque on one lever arm will be balanced by reactive torque from the balance on the other lever arm.
  18. liftline

    liftline Member


    Good news from the test lab. The 2g motor is performing about as expected given the stock prop. Thrust should be sufficient if I can keep all up weight under 45 g.

    Here is a pic of my thrust thrust stand. It's pretty similar to stands I've seen on the internet, but smaller. Not much to look at - a bit like a gibbet. The second pic shows the pivot. The pivot shaft is made from a carefully straightened paper clip and the bearing surfaces are small beads I picked up at a craft store. The stand is very easy to use. My balance is only accurate to grams, but good enough for these tests.

    The ratio between the motor arm to pivot and and the reaction arm resting on the balance to pivot is 2:1 At full throttle I get a bit more than sustained 30 g static thrust on the scale which works out to 15 g equivalents of thrust (just in case there are any sticklers for correct units of thrust reading this). I can get 1-2 second bursts of 16g thrust initially.

    I'm currently running the ESC in default mode which uses middle advance timing according to the ESC manual. The manual recommends high advance timing for a high KV outruuner, so I'll try reprogramming to that setting next.

    Attached Files:

  19. schorhr

    schorhr Member

    Wow fancy!
    I allways ment to build one, but the internet provides most info I need and for bigger models I just attach a pull-scale ;-)
    I am sure it will work, especially if the wing/weight ratio is good on that little plane :)

    Well, it's model building, not flying, isn't it? :)
  20. liftline

    liftline Member


    Woooo Hoooo!!!

    Programming the ESC is a bit retro without a card, and takes some practice, but the motor pulls much better when you change the advance timing to HIGH. Twenty, yes 20 honest grams of thrust equivalent with a fresh battery at 4.2 V. Drops a bit pretty quickly as voltage comes off the peak, but nice to be able to have that much for take-off.

    I can't get complacent about weight creep, but things are looking pretty good right now. Time to put my feet up for the evening and just smile.

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