gordon205

I am building a A-10 warthog with two brushless motors and two ESC and have a question concerning the two esc's. Does anyone have any info about wiring both esc's together in parallel or useing a single battery to power both motors. I have heard of pulling one positive line out of one esc when useing multiple esc's useing a 2200-10c battery source.

motor 1500's

esc's 20c each

any thoughts will this work? or should I use a larger esc and run both motors with one esc?

Dr Kiwi

Using a single pack is best... then both motors should run at the same speed. With two ESC's you simply need a Y-connector from the pack, but you should sever the red wire on one ESC [in fact don't sever the wire... just use a short servo extension between one ESC and the Rx ...cut the red wire on that extension... then your ESCs are unmodified and can be used in future projects).

toywizard

Thats a great way to do that. I like that. Thanks for sharing!


What about if someone wanted to control the speeds of each esc so you could turn the plane
with the motors? How would you set that up?

Can you do it with the left/right stick ?

toywizard

Dr Kiwi
What about the two brushless motors with thier own esc's, how would you make them steer the plane using thier speed?
They do it on some of the back yard foamies like the intruder and I had a foamy airliner that did the turning using the motor speeds.

How would one do that using todays brushless setups?


Thanks

Dangaras

I have built a P38 and I have the same issue with managing the RPM sync of both motors. I am using a DX7/AR7000 combination. Initially I ran both ESCs off a Y-cable connected to the throttle channel.

I noticed a 70 rpm difference left higher than right. With Master Airscrew 3-blade 8x7 props I notice a significant  pull to the right on takeoff and during flight. The left ESC is the one where the BEC is disconnected and it starts up the motor before the right motor when the throttle is advanced from zero.

I am also running the right motor clockwise (when viewed from the front) basically counter rotation.

Now I know there is a way to slave one of the other unused channels to the throttle, I have tried /aux1 (flaps) and  /I am unable to get the DX7 settings correct.

Anyone able to provide pointers on this?

toywizard

Sounds sim to what I need to set up for an oversize Intruder. I have not had the time to experiment yet.

Dangaras

Here is some text that I posted in another thread.. I hope this is helpful. It got me 90% of the way, but I am still unbalanced under 300RPM and above 650RPM.. I am going to the next step of experimenting with a new ESC then motor.

I did discover what the stalling issue is on the counter rotating starboard motor, instead of swapping the Red & Yellow wires, I swapped the Red & Black. That appears to have cured the stalling around 500 RPM.

If anyone wants the particulars on my DX7/AR7000 setup to get the Throttle > Flaps slaving configured, let me know and I will post it all later on.

Considerations for a Twin Engine setup:

1. are you running both ESCs off 1 or 2 batteries?
2. are you running the ESCs of a Y-cable from the throttle channel or are you slaving an unused channel to the throttle channel?
3. are you running the RHS motor clockwise or both motors counter clockwise?
4. 2 or 3 blade props?


1.If you choose one battery, then the motors will most likely run at close to the same RPM. That is if the ESCs and motors are closely matched. Different batteries can introduce a different RPM value on one or the other and cause your twin to "pull" left or right. This speaks for using the slaved channel option. If you can get one 'fat' battery into the main body that is way better in terms of usability & safety than having to get at the nacelles to install 2 batteries.

2. No matter what you do for power, one of the ESC BECs will have to be disabled or disconnected. That means removing the red wire from which ever one is not going to power your receiver. That or you remove both ESC red wires and use a receiver flight pack. Either way, don't cut the red wire on the ESC, use a cheap extension cable and cut the red wire there, allows you to use the ESCs elsewhere if you move on to another model.

Also when connecting the batteries,connect the one with the disconnected BEC first, then the one that powers the rx second, that will initialize the ESCs together. Do remember to configure the ESCs (if doing so with your TX & RX)before disconnecting the BEC wire, it's a real pain to go digging around in the wings after everything is all assembled.

If you use a Y-cable off the Throttle channel to run both ESCs you most likely will find that the model will fly well with some minor pulling, I used a tachometer to determine which was at a higher RPM and used that knowledge to help me "remember" what trim was required on the maiden flight. I found it quite manageable and never changed to slaved channel until I went to 3-blades and counter rotation.

3. I got my hands on some master airscrew 3 blade 8x7 pushers for the RHS motor. In order for this to work properly, I switched the RED & Yellow (my motor's wire colours are red, yellow & black) wires to get counter rotation (clockwise rotation looking from the front). Then I tested the RPMs and noticed the difference was the same. On my first flightwith the new props I really had to push up the throttle to get the similar performance as 2 blade props. This really cut my flight time. As opposed to flying for 10 mins now I can only reliable get 6 mins.

My configuration DX7/AR7000, 3 cell, 1500mAh LIPOs in each nacelle (I sometimes parallel two of these in each nacelle), 40 amp ESCs &1100KV AXI type outrunners. I also noticed a pronounced pull to the right that was not there before.

I also uncovered an odd behavior, the counter rotation motor would stall occasionally on my takeoff run. I had to do a few static full throttle "warm ups" beforethe problem went away. I can still hear the motor 'missing' when Ithrottle up from zero.

To deal with this I have gone to the throttle slave route. I am all connected and preliminary testing looks positive I am planing to test the configuration tonight to determine just how much tweaking I need to do to get balanced RPMs through the entire range.

4. 2 blade props like 9x7 will give you far better efficiency than 3 blades like my 8x7. I however, like the look of the 3 blades and the counter rotation...

toywizard

Ahhh
Sounds like some progress for sure.
I would be looking for one battery, two esc's, no Y cable so I can have each esc on a seperate channel so I can use the motors to turn using
the rpms like the back yard flyer Air Hogs Intruder.
So how would I set that up on a Hitec Eclipce 7 ?

Dangaras

I use the SpektrumRC DX7, cant tell you how it's done with other transmitters. I did spend hours screwing around to get the DX7 config to where it is now.

As you can see however, there is just as much screwing around with the TX as there is with the ESCs & motors. I am still not satisfied & am planning to test with new ESC and motor that are the same type, rating and brand hoping to get a better match. I may also have to mess around with the ESC programming....

toywizard

Well, I appreciate your efforts for sure.

Seems like there should be some kind of standard to do this. I mean this is not that new. lol

I will work on the set up tomorrow and see what I can come up with too.

Keep up the good work and thanks for your help.

Dangaras

Here is the DX7 config;

[PROG.MIX6]
     THRO-> FLAP    ON
       RATE:   +108%
                          0%

     SW:ON
     OFFSET:  -82


    
My Flap switch is set to position 2 for this config to be ON. My upper throttle range is at 108%, low end is at 0% and the Flap offset was set at -82 to get the FLAP output down to zero and to follow the main throttle with a bit of a lag.

I still plan to experiment some more with the throttle range settings. I will update with more details later.

Hope this helps.

toywizard

ahh, our TXs are not that much differant..............that makes sense...-82 ? no kidding? hmmmm
That might be the diff I need.

TommyWatson

My Feedback: (1)

I have just been helping a friend with a large C130 Herc. It has four motors. I have wired it so that the inner motors are run from one battery and the outer motors from another battery. I have extended the wires from the ESC to the motors and kept the battery wires short. The batteries and the esc's are in the fuse.I have "Y" leads from the four esc's to the throttle channel.
He has chosen to use a seperate RX battery and disable the BEC by removing the red wire on the last of the "Y" Leads.

My question is, why not use the BEC on all of the ESC's via the "Y" leads. if the BEC is limited to 3amps at 5V as it says on the label, then four bec's would give a current capacity of 12 amps, surely enough to power all the servos?

Will there be any interaction between the BEC's?

Also another question regarding reversing the direction of the motors so that the port motors run in opposite direction to the starboard motors. Is this a good idea, and as pusher props wil be required on one side, will the pusher props be exactly the same thrust at the same rpm as the normal props?

Dangaras

The problem is a BEC is a simple DC voltage power supply. They are not designed to share current into a load (the receiver). There is no guarantee that each BEC is going to have the same output voltage as the next one, and that can lead to all sorts of power source &sink issues. One BEC might supply power to the RX & to the other 3 BECs because is is 0.5 V greater than the other 3, then it runs too hot, cuts out (or the other cut out) &you lose it (them) plus the motor(s). Then the others can go into a crazy source- sink oscillation, who knows what happens then.....

I also think if you drive current into an ESC that is not designed to do this, you can kill the ESC. Castle has a BECdesigned for Twins. I have also seen a hybrid at one of the LHSs which drives 2 motors but looks like a singe ESC

otrcman

As a person who knows just enough about electronics to be terrified of its mysteries, your explanation makes a lot of sense. On the other hand, I am flying a twin with both BEC's feeding the receiver without a problem. When making my installation, I contacted the manufacturer (Scorpion) and was assured that running both BEC's would be OK, although I couldn't expect to see the full combined current rating of both BEC's. Lucien Miller (Mr. Scorpion) said that he was working from actual experience with multi-motored installations in his own models.

I wonder if Castle is just being more conservative or if there is some design difference in ESC's ?

Dick Fischer

Dangaras

My 2 cents;

That's the problem exactly. No manufacturer has actually performed tests to determine the effect of paralleling BECs. If they have, there is no publication on it and you have to go hunting to get any sliver of information. Even then, I have never got anything in writing. Liability issue???

Most people who parallel the BECs and have no issues are lucky that the BECs are pretty closely matched. Most electronics are built with tolerances from 5% to 10% for standard consumer applications & ESCs are consumer electronics, that means wide margins on output V-I specs. That may also be why your BECs will never give you full power, one is always pushing current into the other one and feeding the receiver & it's loads. When it drops, the other one did take over without issue.

Now imagine a larger model with heavier current requirements, if you had a sudden demand on your system for power, all servos active & retracts active for eg, and both BECs browned out, you would be looking at a potential bad ending.

I suspect that lighter models might get away with it or if you use one battery you might be safer, however, in general, I like my models & prefer to spend a few extra $ on a separate BEC or matched ESCs at least.

dumorian

My Feedback: (6)

Actually, Castle has a publication from 06 which states using both BECs on the Phoenix line is preferable. Here's a link.

[link=http://www.castlecreations.com/media/castle_scribe_archives/Castle%20Scribe%20CE-03-Mar2006.pdf]Castle ESC Setup for Twin Engines[/link]

Dangaras

Here are items for consideration for those who desire to fly twins, the cost versus the time tinkering is at the forefront. Understanding the construction and resulting flight dynamics is critical.

One can purchase ESCs from HobbyKing for less than $40, the same pair of ESCs from Castle or E-flite will be over $100. Matching ESCs are great (and probably greatly expensive also) but one can work with the transmitter (like a Spektrum DX7) to drive the 2 ESCs separately by slaving one of the Aux outputs to the Throttle where adjustments can be made through the low & high rates to advance or retard the offending motor RPM. However, they will never match 100%, one should care about 1/3 power to take off power to stop the model from experiencing a yaw or roll effect.

Messing around with ESCs & paired BECs versus cutting a wire on an extension cable, hmmmm wonder which is more efficient?

Also consider that motors are also slightly unbalanced and this can add to the unbalanced RPM issue. Great motors for less than $15 at HK compared to $80+ elsewhere.... The design of the models can also contribute to flight dynamics.

The Nitro P-38 that I fly has both engine mounts designed for standard rotation, there is a "down-right" adjustment to compensate. I think the expectation is to fly the model with standard 2 blade props and standard rotation. However, being the adventurous individual that can't leave well enough alone, I have switched the starboard motor to counter-rotate and this has added a whole world of excitement.

There is a definite tend to rotate the model while flying and this forces me to aggressively manage the flight with aileron input. The roll is definitely more present with more power applied and lessens as power is backed off. One could hack the mount apart and adjust the motor mount angle or use washers to position the motor to down-left to help remedy the situation.

I was also forced to swap out the ESC on the counter-rotation as it would mis-fire right int he middle of the power range, take offs were risky. During one landing approach the ESC sputtered as I backed off the throttle and the motor died!!!!!!!!!!!!!!!1 That was when I learned I could fly the model on one engine. Gave me enough to cut power to the ESCs and restart them. After that the ESC had to go. I swapped in a new one, same make and model, and have flown without issue.

speedy72vega

One thing to think about here.........on the subject of running a short extension to disable the second BEC. Whenever you increase wire length, and/or introduce additional connections, you are building added resistance into that circuit, even if it's a small amount. This increase in resistance will alter the signal to that ESC, resulting in slightly different throttle inputs to each ESC. The better way to go is to just remove the red wire from the connector and tape or heat shrink it back to the harness, then plug the ESC harness direct without an extension. That way you are making sure the signals reaching the ESC's are the same, without built in resistance.
This is easily done using a small pick or similar tool. There is a tab on the terminal that locks it into the plastic connector housing, all you have to do is push the tab in while pulling the wire out of the connector. It is very simple, costs nothing to do, and is completely reversible.
I'm sure some will argue that the effecrt is minimal, but whenever you're working with electronics, the smallest amount of resistance can make a difference.

As far as running both ESC power wires, you're talking about Direct Current, so as long as the leads are run parallel ahead of the rx, such as with a Y connector, there will still be the same voltage at the rx. However, if you decide to run the second ESC off of a slave channel, you will need to disconnect one of the BEC leads, because you would then be feeding 2 different circuits with battery power, as opposed to just the one if running a Y cable.

Dangaras

That would be a real concern if these systems were not pulling such high currents. Voltage=Current x Resistance.

Basic law of electricity, the more connections you add and the more differing materials in contact will cause more resistance. However, we are talking about 3 different connections here, the power conns from the battery to the ESC to the Motor, the ESC-BEC to the Receiver (RX) and the signal back from the RX-Throttle to the ESC.

The Power connections are gold plated with multi stranded, heavy gauge wire, so there is no significant loss there.

The ESC-BEC to the RX is one line to the RX, with an additional extension added the muti stranded wire with the gold connectors will not add any significant resistance in a circuit of this type, granted you should use the heavier 22 AWG wire and for the extensions and not the light 32 AWG. There would be a difference as 3 ampos through a 32 AWG wire is not as efficient as a 22AWG...

The Throttle &servo signals are very low current, high frequency pulse trains that will not suffer any degradation unless the the connectors are oxidized for some reason.. Being gold plated that should never happen. The power line out to the servo will require only the max current required at 4.8 or 6V for a standard servo (depending on your servo). If there is excessive current draw or bad contact then the pins can start oxidizing as gold plate is a poor choice for high current applications where ther is repeated make-break contact with power flowing. Silver-Indium plating is far better (and far more expensive).

Considering the low cost of extensions, Icut my power wire from one of the ESCs and did not worry about messing around with removing a pin from the plastic housing..

Dangaras

Here is a really good diagram that shows how to connect 2 ESCs with an additional external BEC courtesy of Merlin from RCGroups

Link is here http://www.rcgroups.com/forums/showp...&postcount=179

reyn3545

I have a 12x radio, with plenty of available channels available. If I have two channels set aside for throttle, can I just run the 3-wire connectors to each channel and not use the BEC? Both ESC's have built-in BEC's (ICE 75's).

Dangaras

Not advisable. The +Ve wire (and pin on the receiver) is common across all the connectors plugged into the rx. It would be the same as plugging both ESCs into a Y cable.

No matter what you do, you should cut one of the red wires. Isuggest you use a short extension on one of the ESCs and cut the red wire of the extension so the ESC cable stays virgin.

There have been several instances of people running ESCs together and experiencing unexpected landing events (hard crash). Castle makes a apecific series of ESCs from what Ihear, that are designed to work in parallel.

If you consider a 10Amp BES from Hobbyking is $10, what is that cost in comparison to the cost of your model?

reyn3545

Thanks for the info. I've never tried multi motors, and I certainly don't want to scrap a $2000 plane for not using a $10 component. Learning more every day.

dealwithit

My Feedback: (55)

hmmmm im having a similar issue with a new brushless setup on my plane, im gonna try and slave one of my extra channels over for the second esc. mine are way off, like 3 clicks apart from when one starts to when the other starts, when they are simply linked with a Y.