Author Topic: Twin motor matching speed  (Read 891 times)

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Toby

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Twin motor matching speed
« on: April 13, 2018, 16:52:41 »
I am working on a model with twin props and have several other models in the yard which will also have twin props.

When using the motors direct to battery with the polarity one way the motors operate at a certain pitch to the ear. With the polarity reversed the pitch its lower indicating that the motors are running slower.
This presents no problem until that twin power is installed in the boat to power counter- rotating props when then one motor will be running slower than the other. This likely will cause the vessel to tend to veer to either port or starboard depending on direction.

My set up will be to have each motor with its own esc and channel so that the motors are controlled by both tx sticks.

Whilst I may not want to run on full sticks,  if I were to, then the vessel would veer off course because of the motors; one slower because it is going anti to its main/ norm direction.

I cannot be the first to encounter this and, albeit that I have been searching through this forum, I have not found anything to date.

I shall be using the Viper Marine esc and it may be that the set up of that enables the setting of full forward and full reverse on the sticks of the tx.

Any thoughts anyone?


Toby
 
« Last Edit: April 13, 2018, 16:56:04 by Toby »

des

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Re: Twin motor matching speed
« Reply #1 on: April 13, 2018, 21:57:16 »
Hi Toby

First of all, I wouldn't rely on the sound that a motor makes as being at all indicative of its speed - there are many reasons why it may sound different in each direction, even though with the same applied voltage and hence the same nominal speed.  On the other hand, there are also reasons why it may indeed produce different output speeds in each direction for the same applied voltage - it all depends on the motor.

Try to get your hands on an optical tachometer (as used by auto technicians) - you can then produce speed vs voltage curves for your motors, in each direction.

Once you've got these curves you can then calibrate the outputs from your transmitter's throttle sticks to obtain the same output speeds from each motor, port and stbd, and forward and reverse.  That way you will know that for the same throttle movement you will get the same motor speed for both motors - but the trick will still be in producing the same throttle stick movement on each side.

Have you considered using something like the ACTion Electronics P94 dual esc / mixer?  That way you get the ease of use from using only one throttle stick, but also with mixing so that one motor slows in turns.  If you find you don't like how the P94 works then you can change it to two-stick control without changing any motor wiring, so you don't have to throw it out.

Des.

sea monkey

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Re: Twin motor matching speed
« Reply #2 on: April 14, 2018, 11:34:28 »
I have used the 2 motor/1 battery/1 ESC set up on several models and have had no problems, with no noticeable difference in motor power, or steering. Has only been for tugs at scale sort of speeds but has worked fine.