Multiple motors on one speed control
 

I have a project that I am working on and there seems to be two ways to do it. Is one better than the other? looking at cost and time? I have ordered the motors and am now trying to decide if it can be done with a single speed controller, both of the following ways will need some soldering/parallel circuitry.

The Problem: Control 4 brushless motors so that they are rotating at the same speed, or at least really close.


Solution 1: connect all four motors to the same speed controller capable of delivering the necessary amperage

Solution 2: connect all of the motors to individual ESC's and send the same signal to each ESC.


In my search for an answer another post said it would not work(solution 1), I am not satisfied though because there was no explination of why. The same post also said that if you are using solution 2 you had to disconnect the positive wire(red one) from 3 of the esc's --> reciever connections. Again my curisoity becons the question of why.

Can anyone test this with their own equipment? Does it work? Can anyone explain why it won't/will work? Thank you for any and all input. Lets keep it clean!

RE: Multiple motors on one speed control
 

Solution 1: I haven't tried this and have always used one control for each motor. I guess if you had enough amp capacity from the esc you could do it, but I have also been told not to.

Solution 2: The reason you have to remove the power wire is so you don't provide too much power to the receiver. Each esc will provide about 5 volts to the receiver, so as you add escs to the system you also double the voltage each time you add one. I just use 6" sero extensions and cut the red wire that way I don't have to cut the wire on the esc.

Jeff

RE: Multiple motors on one speed control
 

Thank you for the response. At the risk of opening a can of worm I disagree with your reasoning on the removal of the red wire. If you open up and look at the circut board, all of the black pins are connected, and all of the red pins are connected. What this means is that the everything is in parallel. If you take two batteries and connect them the same way red to red and black to black you don't get double the voltage.
Granted I am no electronics expert, but my gut is telling me it has something to do with electronic noise feed back.

RE: Multiple motors on one speed control
 

Well I guess you can check the voltage using a meter on the reciever and see how much it's getting. I haven't played with that much, but have just gone with what works based on other's feedback. I can put two on my meter tonight and see what it reads. I have several twins and can see what they show.

RE: Multiple motors on one speed control
 

Solution 1 will not work because the motors will fall out of sync with each other and stop.

Some ESC's can be wired together, some can't, I have twin Thunderbird 18's in my GWS P-38 both wye'd to ch 3. Read the mfg's info.

Use 1 battery, 4 ESC's.

Dave

RE: Multiple motors on one speed control
 

One of my twin flying boats has two brushed motors, one ESC, one battery
The other has two brushless motors, 2 ESCs Y-ed to channel 3, the red wire is NOT disconnected. One battery.

RE: Multiple motors on one speed control
 

Thank you all for your practical input. Here is the response from a friend of mine that has been working with Brushless motors for some time.


As I understand it, option 1 will not work because the 4 brushless motors generally would not be in the same phase of their rotation at startup. The speed controller initially sends an input, which causes the motor to rotate, and the back-EMF of the motor is measured to determine position, so that the speed controller can make corrections and get the motor moving in the desired direction. If you have 4 brushless motors hooked up to the same speed controller, unless all the stators have the exact same orientation at startup they will all react differently to the initial input, and generate different back-EMFs, which will be superimposed and confuse the ESC. For most combinations of initial motor orientations, no set of inputs from the ESC could bring all the motors into phase (and they wouldn't be programmed to attempt to do so), which would be required for operation. Also, if the motors somehow managed to start rotating, any anomaly, such as a wind gust, or a period of powered down gliding flight might knock one of the motors out of phase, which would cause it to stall, or its back-EMF might confuse the ESC, and cause all the motors to react abnormally.
Option 2 will work, though you would have to be careful at startup, as some motors might spin up slightly sooner than others (depending on orientation). Once the motor reached the desired speed they should all spin at the same rate and react identically to changes in speed, since each ESC will analyze the back-EMF of the motor it is connected to, and attempt to match your desired rotational speed.

RE: Multiple motors on one speed control
 

That makes sense. I forgot all about the motor position on start-up. I see that all the time as some motors on my planes will start before the other. Also some motors are tighter and take more amps to get them rotating. Once the power comes up they are in sinc.

RE: Multiple motors on one speed control
 

I would have a 4-motored plane use two channels for each pair, rather than all four running from one, with the inboards and outboards separate.
Mixing to get both work with the throttle, but have the "not throttle channel" motors on a variable channel.
I've done this with twins using Futaba equipment, both mixed to channel, with the odd one on channel 6, which has a knob which permits controlling that motor separately.
This for exploring single motor flight.
I found that more than 40% power on the running motor would be too much for the rudder authority to let the plane be turned towards the running motor.

RE: Multiple motors on one speed control
 

sounds like you've got some good answers

I would put in my vote that #1 will not work for the above said reasons. Most brushless motors are sensorless meaning they rely on 2 conductors for power and 1 for a signal to come back telling the ESC that the motor has flipped over a bit and needs to change polarity and/or leads, so if you have 4 different signals coming back from the motors the ESC is gona get really confused really quick

about the red wire, it's the BEC, if you wire them together, you may or may not have a problem, but generally it's best to only hook 1 up just in case. The reason you could have a problem is different BEC voltages flighting against each other, and one might try to bring another to a different voltage, and in doing so might put out more that it is rated for and fry.

RE: Multiple motors on one speed control
 

BEC's in parallel: Some linear voltage regulators will oscillate when hooked up in parallel. Read the docs, some mfgs say theirs will work in parallel increasing the current available for more servos. If the docs don't say then you can test with a meter to see if the voltage remains stable when they are connected together, move the servos and throttle, if the voltage jumps up at all then don't use them in parallel.

RE: Multiple motors on one speed control
 

It's also practical to disable the BEC feature for both ESCs.
I cut the red wire in a 6" jumper from each, rather than mess with the basic cable from the ESC.
And then use a separate receiver battery for the radio and servos.