rwolfe9

In addition to the last question, I did find a 4PDT relay rated at 20amps@120V and 2.72oz that would work if the contacts are big enough.


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Vertical3-D

My Feedback: (20)

I would probably hook up a single fan, ESC, and battery through a watt meter then you will know the continuous draw at WOT and know what relay you need, I'd go a bit bigger then needed to be on the safe side, the same reason I run a 60 amp ESC on my plane thats drawing 25 amps on a 4s, plus if you ever want to upgrade the power system you can without a huge cost

cyclops2

Hi wolfe

I used BARE soild wires in my 4 engine China Clipper. The wires have the ribs as spacers and also provide cooling air. Not really needed. I stripped off all insulation. Used regular white plastic #14 guage. I did use insulated # 16 to each 400 BRUSHED motor, stranded wire. Leave a loop in there to pull the drives out if needed.

#14 = 15 amp............# 12 = 20 amp..........#10 = 30 amp.........Those values are way too conservative for us.

Remember !!!! You WILL NOT be switching the relay contacts with current flowing under a heavy load. That prevents burning of the contacts & problems. Closed contacts can carry 5 times rated current easily. That is you.

I soldered all connections with about a 1/2" of the 2 wires soldered together.

Piece of cake! If I fail to post here, send me P Ms .

Rich

mjbennett9

I never tried it, but how about throttle to throttle mixing set to a switch on the RX. at a certain point of throttle, and/or setting a switch, the throttle end point, or something would be set for negative? just a thought

jdhughen

My Feedback: (1)

I'm thinking of trying this on a single EDF. Where did you find relays that you handle the amp draw we are talking about that use a solenoid that works at 4.8-6v ? How are you controling the voltage to activate the solenoid on the relay ? @ almost 2.5oz for the 4DPDT would it be less weight with just a micro switch/ micro servo arrangement ?

Joel

nexxa

Here a simple build to make a reverse with a standard ESC. Need a extra servos and channel. The drawing only shows the logic.
Instead of using plastic servos arm to redirect the power, cut an arm in a aluminum or copper.
Instead of making contact on the side of the connector, bolt thought the plywood, and makes the aluminum or copper arm to pass on. Hard to explain and unfortunately don't have enough time to draw another one!

But it works, can handle a lot of AMPS, depend on the quality of contact.
Need to be switch forward to reverse and vice versa when throttle if off and turbine has stop turning.

nexxa

A simple version

Important, use a wood, fiberglass or plastic arm to transfer the power. Each side of the arm as different power from ESC.

cyclops2

Joel

What are your EDFs maximum amps ? How long do you stay at WOT in seconds & how many times in a minute.

Rich

jdhughen

My Feedback: (1)

Last time I put a meter on it it was around 80 amps @ 14.8 volts at peak. looking at some of the example of this being done I would think that the required braking action could be done in burst of less than 10 sec and no more than 2 or three would be needed. If reversing the fan would actually slow the plane I would think a 10 sec burst would be about the limit of it. On the flip then closed on the "forward" side the contacts would be required to carry the full load of all forward flight. I found a DPDT micro switch rated at 20A @120/240v. Given that the "switching" would be done under a "no load" situation and the closed contacts should easily carry the above draw, that switch should work. I can actuate it with a micro servo. I couldn't find a relay that would work with a 5v control voltage that would carry that kind of amp load. ???

Joel

cyclops2

Sounds like a car / truck ESC with a adjustable time & force brake & reverse . Only safety thing I would do, is to put a swing hook that would stop you from pulling too far back, before you are in final approach to the runway.
14.8 is close enough to their ESC voltages.

Rich

Jag Fan

would it not be simpler and easier to just build a clam shell system for reversing thrust? it's very simple to build and only requires one servo per side to operate. you could do it on the inboard pods only , since that should be enough power to stop and/or reverse the plane, if that is your intention. if you want an idea of how to do it, fo to rcgroups and check out the DC9 (SAS livery) build thread and there's some very detailed pics and video on how to do it. they look cool and they work. not quite scale on this plane, but they will work.

rwolfe9

If it helps, the 4DPDT relay I am using is for 2 EDF's for a lockout feature. You could accomplish your goal with a 2DPDT relay. The control voltage I was going to use for the relay coil was going to come from the main batteries, not from the BEC output. You should be able to find a relay with a 12V coil, or something similar. I haven't really looked into how to control the big relays with the #6 channel. I think that there is a switching unit that could be used for the purpose, or if I need to use the 5V BEC circuit, I could use a smaller relay to run the larger ones. Let me know what you think. Also, I am putting a reverse lockout on the stuff that will make the reversing avaliable only when the landing gear is down. Then I will have to use #6 to reverse the thrust.



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jdhughen

My Feedback: (1)

After looking around and comparing relays, switches, methods of control, and weight of components, I think I'm going to go with DPDT lever micro swicth and activate with a micro servo. It seems to be the simplest solution for me electricaly and weight wise. I'll post my results when done

Joel

rwolfe9

To get the micro-switch you need, look around for an electronics "junk" store in your town. I have one near me that has thousands of them in a bin 3 for $0.99. If you can't find exactly what you need, you could gang-up identical switches to get the ampacity you need, just make sure to keep the paralleled wires the exact same lengths. This could save you from ordering online and getting something that won't work.



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spete2000

When I was a kid, some of us had go karts and mini bikes. One of the guys had an old Briggs and Stratton 7 HP gas engine and was going to build his own cart frame. He didn't have a welder, didn't need one because he figured out a better way. He made his frame out of electrical conduit and fittings. Testing it, he started off slow and increased power and speed. It really was fast for our go carts. After he hit a thick tar strip at maybe 30 to 35 miles per hour, the frame did a slow collapse with it folding first under the seat, then moving towards the steering and folding the front wheels, and then finally twisting the rear end so far out of shape that it jammed the throttle cable wide open. (Remember the older cars in the 60's that would allow the engines to lift when a motor mount would break pulling the throttle linkage wide open?) I do. Many times. Too many times. He was kind of lucky as the older cars had higher frames and while the rear wheels hit the rear wheels of the car, he ducked and slid under the parked car and only banged up his head and arms and legs and stuff.

Anyway, using relays or homemade 2P2T switches to reverse the fan engines seems somehow familiar, especially considering using your own memory to wait till the engines stop turning before switching the polarities. Also, I don't think the motors and / or ESC.'s will like intermittent current demands even in regular flight without using some kind of buffer system to protect them.

Not really trying to knock your idea, but that is a big beautiful wing that looks very nice. If the rest of the plane is planned to have the same high level of quality construction, I would hate to see it turned into a 1950's go cart built of conduit. Scale brakes are not that expensive, nor, if you are mechanically inclined, that difficult to manufacture. Also the full size aircraft uses clam shell reversers which can slow down or possibly stop the plane by themselves. You will not see a 747 use it's reversers to back around the airport. The mirrors would have to be too big. You will also never see a 747 popping chutes at the airport.

I am sure that with your skills you can build a more true to scale plane that will function perfectly without trying to experiment with "stuff" that has questionable reliability, functionality, or cost savings.

You might consider one of the previous members mentioning using a carbon fiber tube for a main spar for the wings. If you want to do it again, you may want to use a carbon or aluminum tube for a wing spar as they are much lighter, stronger, and can be useful should you decide to make the wings removable. You may want to build new wings if there is a minor inconvenience in the air concerning the operation of the motors.

All the best to you in the future and good luck with your plane. Keep us posted.

spete2000

When I was a kid, some of us had go karts and mini bikes. One of the guys had an old Briggs and Stratton 7 HP gas engine and was going to build his own cart frame. He didn't have a welder, didn't need one because he figured out a better way. He made his frame out of electrical conduit and fittings. Testing it, he started off slow and increased power and speed. It really was fast for our go carts. After he hit a thick tar strip at maybe 30 to 35 miles per hour, the frame did a slow collapse with it folding first under the seat, then moving towards the steering and folding the front wheels, and then finally twisting the rear end so far out of shape that it jammed the throttle cable wide open. (Remember the older cars in the 60's that would allow the engines to lift when a motor mount would break pulling the throttle linkage wide open?) I do. Many times. Too many times. He was kind of lucky as the older cars had higher frames and while the rear wheels hit the rear wheels of the car, he ducked and slid under the parked car and only banged up his head and arms and legs and stuff.

Anyway, using relays or homemade 2P2T switches to reverse the fan engines seems somehow familiar, especially considering using your own memory to wait till the engines stop turning before switching the polarities. Also, I don't think the motors and / or ESC.'s will like intermittent current demands even in regular flight without using some kind of buffer system to protect them.

Not really trying to knock your idea, but that is a big beautiful wing that looks very nice. If the rest of the plane is planned to have the same high level of quality construction, I would hate to see it turned into a 1950's go cart built of conduit. Scale brakes are not that expensive, nor, if you are mechanically inclined, that difficult to manufacture. Also the full size aircraft uses clam shell reversers which can slow down or possibly stop the plane by themselves. You will not see a 747 use it's reversers to back around the airport. The mirrors would have to be too big. You will also never see a 747 popping chutes at the airport.

I am sure that with your skills you can build a more true to scale plane that will function perfectly without trying to experiment with "stuff" that has questionable reliability, functionality, or cost savings.

You might consider one of the previous members mentioning using a carbon fiber tube for a main spar for the wings. If you want to do it again, you may want to use a carbon or aluminum tube for a wing spar as they are much lighter, stronger, and can be useful should you decide to make the wings removable. You may want to build new wings if there is a minor inconvenience in the air concerning the operation of the motors.

All the best to you in the future and good luck with your plane. Keep us posted.

rwolfe9

Thanks for the advice. You are probably correct about the wing/EDFs being able to take the strain. It does seem easier to make some scale brakes than to make all of the buffers that would be necessary to protect all the electronic stuff without letting the factory smoke out. I did however change the main spar in each wing a while ago to a 1" aluminum tube and added a piece of #4 bare copper wire to stiffen the wing. This also solved my problem of the power to all of the ESCs I will need. The Al tube will be the positive buss and the Cu wire will be the negative, since current flows from negative to positive. The arrow shafts were really not strong enough to support anything.

Just as a sidebar, if your friend would have made his gocart from IMC with steel fittings, it might have lasted twice as long. Sounds like he built it from EMT, which is thinner and easier to bend. There's still no substitute for welding.


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Tommygun

My Feedback: (2)

It's an interesting idea, but might be more trouble than it's worth. I'd wonder how much reversing action you'll even get from the fans. Real planes with thrust reversers have either a target door system or a sliding transcowl ring to deflect the thrust of the engines- these have the added benifit of adding drag (real B52s have neither). I work with full scale aircraft performance, and TRs really don't help reduce landing distance on the charted value as much as you think they would. Spoilers and braking action has a much more profound effect on stopping distance. Maybe with the model being overpowered and lighter per scale, it would work better, but I still believe pneumatic brakes would be better. Think about it, you'll have to wait until touchdown to even begin the reversing procedure (since you'll need to carry some speed on the approach when configured, more so if it's shallow or you have gusty winds/tailwind). Then as soon as the wheels touch, you'd need to go full low throttle, flip whichever switch reverses the ESCs, then give it throttle again. The fans have to wind down, then reverse, which takes time and eats up runway. Additionally, you have absolutely zero go around capability should you land long and fast and have to take it around. Let us know how it works out, sounds like a cool project.