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[BlueWotsit]

Im just going to connect two motors together, to then link in to one speed controller in my MTB.

I understand that the best method of propulsion is to have the 2 motors turning the props into each other / away from each other.

Looking at the motors I see each has a red spot by one of the terminals.

Two questions

1. Am I right in thinking that to achieve the propulsion mentioned above, the wire from the red terminal on one motor, needs to connect to the NON red terminal wire on motor 2.

2. For the connections, can I bridge a wire between the 2 motors, as in (1) above, and just run the other two wires to the speed controller - or do I need to have 4 wires coming down to the 2 on the speed controller


thanks
Andrew

[Shipmate60]

Andrew,
Correct in both.

Bob

[BlueWotsit]

cheers Bob, makes a change for me to get one correct   

[dougal99]

Raising my head above the parapet. I'm assuming you want the motors to ratate in opposite directions. If so, you will need to connect either both red terminals together or both non-red terminals together. If you connect red to non-red then the battery leads will also be connected to a red and non-red, thus the current will flow through both motors the same way and they will turn the same way. To turn the motors in opposite directions the current needs to flow through the motors in different directions, so the motors need to be connected to the battery by the opposite terminals. That is the red terminal of one motor should be connected to the positive battery lead and the red terminal of the other motor should be connected to the negative battery lead. Of course connecting your motors this way will give you half your battery voltage across each motor.

HTH

[Peter]

Dougal99

What BlueWotsit has decribed is correct for the contra rotation of the motors.
He is connecting them in parallel across the esc output, with one reversed to the normal red/red and black/black.
Thus each motor will receive the full voltage, but rotate in opposite directions.

Your description seems to be for conecting the motors in series, but still giving contra rotation.

The limiting factor in the parallel case may be the current capacity of the esc, otherwise it will be ok.

Peter

[RaaArtyGunner]

It helps us non electrically noused to understand if it is possible, to draw a little sketch.

If both motors are powered independently for whatever reason then, wouldn't the comment that one motor has to be wired opposite to the other apply.
That is the black lead to the red dot and the red lead to the remaining terminal and then check that each prop is turning in the right direction.

[Peter]

dougal99 - I owe you an apology, I misread the initial comments, and you are entirely correct in what you say. A 'senior moment' on my part

RaaArtyGunner - Your comments are correct, and made me reread the original text. Hence the apology to dougal99.

In BlueWotsits original descriptions - if he connects red/non red of each motor, and takes 4 wires to the esc,he will have contra rotating props with full voltage applied to each motor, at full esc output.
If he only connects red from one motor to the non red of the other motor, and takes the other two wires back to the esc, then he will have the same rotation on each motor, but with half the voltage.
As dougal99 correctly pointed out.

It teaches me that I should take note of the ever increasing occurrence of 'senior moments', and play safe by keeping my comments to myself

Peter

[RaaArtyGunner]

Peter,

We All have Senior moments,  some of us are more Senior than others,  but wouldn't keep comments to oneself otherwise ya wouldn't know it was a "senior moment"

[Peter]

RaaArtyGunner,

Very true comment there.

It was all the more frustrating though, when I had reread the posts several times, before making my initial post.

Your comment re sketches is very true.
I had a college lecturer, in another lifetime, and when UK still had a Navy, who always tried to emphasise the point that 'a sketch is worth a thousand words.'

It is also more difficult to misread a sketch, 'usually' that is.

Thanks for the encouragement to go on ---------

Peter

[RaaArtyGunner]

RaaArtyGunner,

Very true comment there.

It was all the more frustrating though, when I had reread the posts several times, before making my initial post.

Your comment re sketches is very true.
I had a college lecturer, in another lifetime, and when UK still had a Navy, who always tried to emphasise the point that 'a sketch is worth a thousand words.'

It is also more difficult to misread a sketch, 'usually' that is.

Thanks for the encouragement to go on ---------

Peter

 

 

[dougal99]

Peter,

apology unnecessary, but thanks anyway. I have to admit I hadn't considered motors in parallel and it is unclear (to me anyway) from the original post what was intended. I will produce a diagram, and post it here later, of both the series and parallel situations.

Doug

[malcolmfrary]

I assumed parallel, as well, until I re-read it properly, however -
assuming the same motors and battery,
2 motors in series puts out half the total power of one motor, but takes half the current.
2 motors in parallel puts out twice the power of one motor, but this arrangement takes twice the current, so the ESC needs to be able to handle the increase.

[dougal99]

Here's the diagram (I got a D in art) which I hope explains/shows the required connections for series/parallel set ups. I've used green to show the inter-motor connections just for clarity, there is no other significance. The power supply leads could, of course, be reversed if required.

Malcolm I bow to your superior knowledge on power output, but would the power of 2 three volt motors in series running on a 6v supply be half that of one 3v motor running on a 3v supply?

[BlueWotsit]

Ouch........my brain hurts NOW I know why I prefer sail - its so much less complicated.

Ok if I am now understanding things correctly looking at dougal99's excellent diagram.

The picture on the left is similar to what I intended - ie 12v source in, equating to contra rotating propellors, motors running at 12v each BUT consumption of battery quicker.

The picture on the right - would see the 12v source, being split as 6v to each motor - less power but longer consumption of the battery.

What I dont understand on the picture on the left is why both motors need the green bridging line, can this not work with just one green line, and the 2 wires to the ESC going from the remaining connections on each motor

 - thanks guys


Andrew

[malcolmfrary]

Malcolm I bow to your superior knowledge on power output, but would the power of 2 three volt motors in series running on a 6v supply be half that of one 3v motor running on a 3v supply?

Thats why I said the SAME motors and the SAME battery.  If 2 of 3 volt motors are run in series on a 6 volt supply, then each is getting 3 volts worth, so each would give the same power as one 3 volt motor on a 3 volt supply.

It might help understanding the left drawing if you imagine the black wire just going to the top motor +, and the red wire just going to the lower motor +.  The green links can then be seen to extend the ESC outputs, both black and red, to the appropriate motor terminals, each motor, of course, needing two connections for the current to flow through. 
Thats the difference between series (like a string of sausages) and parallel (like the rungs on a ladder)

Incidentally, I really hate it when ESC makers use red and black for the output - it makes it far too easy to connect the battery into the wrong end, which always results in the magic smoke coming out.  This applies even with appropriate connectors fitted.

[tt1]

Excuse me for jumping in Bluewotsit, but for someone like me having an extreme weakness in the electrons side of the hobby, this is an EXCELLENT forum thread -  Glad you asked the question Andrew  Have learned so much from it.
          Looking out for the next answer now! - Peter? R.A.G.? Malcolm? - well done guys - keep it simple though! 

[tomo55]

Interesting thread , as a relative newbie to boats (from aero)the wiring of motors as described was a eye opener I did not realise that motors had to rotate opposite ways.
I intend building a Tug twin screw in fixed Korts, does it make a difference which way they rotate?also am I right in thinking that I will need a left and right Propeller?
My only other boat was a ASRL from deans single screw which was simple forward and reverse.
Chris
 

[RaaArtyGunner]

Dougal,

Thank you for the diagram.

Malcom,

Thank you for the clarification.

Andrew,
If I understand it correctly, you need both "green" jumpers as you will only then need two battery connections, negative and positive.
If you only used one green jumper, say only the one on the right then  you would end up with two remaining motor connections, a positive and negative both to be connected to the negative on the battery,
The layout as drawn and explained is neater and simpler.

[BlueWotsit]

Excuse the "poor" picture as Ive not mastered these Art software programs - not been drinking honest  .

Is there a reason why the connections could not be made as in the attached revised picture.

Im just wondering as sometimes its not always easy joining several thicker cables together into a connector

 

[dougal99]

Hi BlueWotsit,

Your circuit is the same as the right hand circuit in my diagram except the motors are both connected the same way that is positive supply to positive motor terminal. So you have the motors in series and both turning the same way, not what you want I suspect.

[Shipmate60]

Andrew,
Connecting that way will give each motor 1/2 the voltage so will run slow.
One problem is that the motors and shafts have to be almost identical for drag and speed as 1 motor tends to "grab" more of the load so uses more voltage and current.
This speeds this motor up (higher voltage) and slows the other.

Bob

[Colin Bishop]

Bob is correct, you will very likely have problems with one motor taking more power than the other and giving unbalanced thrust. And it's not only the motors that must be exactly balanced but the whole drivelines as well. If one shaft is a bit stiffer than the other (which is quite common), or one prop has a fraction more pitch than the other, then you can get the situation when one motor may hardly run at all or refuse to start up. It is always better to give each motor an independent share of the power from the battery/ESC then they will both run at pretty much the same speed irrespective of minor differences in electrical or physical resistance.

Colin

[BlueWotsit]

Sounds good to me guys.

This leads me to my next question linked to this  - often the wiring cables from the motors are reasonably thick.

Bearing in mind each set of these two wires  have to be joined together, then a single connection from each combined pair, to the ESC wires - are there any good tips on how to connect them.

In the past past I have tried squeezing the pair of wires into terminal blocks, brass connectors and so on, but unless I have used a really big terminal block, I have often found this difficult.


cheers
Andrew

[malcolmfrary]

Unless you are using truly GIGONORMOUS cable, 30A connectors should be very adequate.  To connect 2 cables to one (say, 2 motor leads to 1 ESC lead, take a 3 section strip.  Make a W shaped piece to be a good fit (with insulation between the ends) and fix it in from one side so that all three parts are connected.  The trade know this a a "bus strip" or "bus-bar".  Connect each of the three wires into one of the holes and the job is done.
Usually, after stripping stranded wire, I give the bare end a twist, so that there are no fuzzy bits to create annoyance.  If the force is with me, I can stop pulling the insulation off before it clears the wire, and apply the twist with it still on.  After the insulation is finally pulled off, it leaves a much tidier twist, and, importantly, no little holes in my finger ends.
Soldering is a very viable alternative, and hiding the join within heatshrink tubng.  Halfords sell boxes with short lengths at a fairly extortionate price, across the trading estate (or nearby) there is often a Maplins, where they sell metre lengths of it at a much more attractive price.  Scotchlocks work, as well, but are not pretty.
I wouldn't be at all surprised if one or other of the ESC manufacturers didn't have some sort of distribution board with the donkey work already done.

Colin made the point of matching the two loads - series does work with reasonable care, but it is a GOOD IDEA to make sure that both motors are happy with the full supply voltage.  If one gets stalled (big lump of weed, feather from moulting wildlife etc), that motor will suddenly have a very low resistance, and the other will cop the lot and increase its power output.  Steering will be affected, but you can still drive it back on the unstalled motor.

[dougal99]

Assuming you want to go the parallel route, you only need to run two wires from the ESC output to one of the motors. Provided the motors are wired together as shown the positioning of the input form the ESC can be anywhere along the 'green' connector, even at the end (motor terminal). The connection point does not have to be mid way as shown diagrammatically.

HTH