Two Brushed motors and 1 ESC

[HaigParticipant @haig]

In my latest Vosper MTB (1/24 scale), I have the following set-up

Power Supply – battery pack 9 x NiMH 9Ah D Cells into 1 MTroniks TIO Marine ESC (with the BEC disabled) and through to 2 x Graupner Speed 600 Brushed 12V motors (in parallel).

Radio is Futaba Tx 10CAG 2.4 GHz, / Rx R617FS

My problem is that at speed the motors exhibit a pulsing sound that resembles engines that are 'missing' – Sort of "HMMMm, HMMMm, HMMMm " etc. The power also drops momentarily at the 'miss' but is not noticeable.

I have several similar setups on my other models, but at lower speeds such as in ships with no problems. I have written to MTroniks but have not received a reply. Any thoughts!

There are photos of the boat in this album

http://www.modelboats.co.uk/albums/member_album.asp?a=42550

Regards

Haig

[HaigParticipant @haig]

Engine ‘Missing’ sound

[Dave MilbournParticipant @davemilbourn48782]

Haig

I've not handled this particular ESC but I have some experience with their 20A brushed marine speed controller. It too makes the motor "hunt" noticeably and also has a very wide band at low speed i.e. 3/4 of full stick goes up to maybe 1/2 speed, then it ramps very quickly up to full speed. This has happened with three separate controllers on different occasions so it seems to be either inherent in the thing or they all came from the same batch (unlikely). I'm surprised the company haven't replied to you.

BTW I've also handled the 10A Micro and 15A Viper and not had any such problems with those. Have you tried testing the ESC with just one motor connected?

Dave M

[HaigParticipant @haig]

Dave,

Thanks for your response.

I have not run this boat with only one motor but can do so tomorrow at the sail day.

I think the problem maybe related to the twin motors, as this has also happened with an identical setup on another patrol boat. and its own identical ESC. I have written to MTroniks on an earlier occasion and not had a reply then either.

In my Fairmile D (1/24 scale) I have two separate drive systems, each with this same type of ESC and identical power supply, but running a Graupner 700BB 12V each. For that boat I have set up a separate radio channel for each system, one acting as a slave to the main channel. This boat runs well with no hunting or 'missing'.

[Colin BishopModerator @colinbishop34627]

An interesting point. I suppose it depends on the electronics of the ESC whether some sort of feedback interference can be caused by two motors running off the same ESC supply. The motors may be nominally identical but will still have some electrical differences I would imagine and are part of the same circuit.

My ongoing fishery cruiser has only been tested in the bath but the setup there is that there are two ESCs which can either be controlled independently (tank steering) or switched from the TX so that a Y lead from one RX channel controls both ESCs on a single TX stick. Each motor thus retains its independent power supply. It works OK in the bath anyway!

Colin

[Dave MilbournParticipant @davemilbourn48782]

I would never use just one ESC for twin motors, but some folk insist on it. To my mind you should have two of everything, unless you're using a P94 which is designed to perform as twin ESCs anyway. It makes tracing faults that much easier in that you can try out the suspect items in the opposite circuit. It also means that if one motor is stalled then it won't blow the speed controller for the opposite motor, so you can get back to base.

But suit yourselves anyway…

DM

[ashley needhamParticipant @ashleyneedham69188]

And I do, with the majority of my boats being single ESC/twin motors, BUT the boats have nothing powerful in them. My Titanic has three 385`s on 7.2v all on one Mtronics 15A esc and this has been ok for years.

​I should probably go for twin ESC with 600 if it was well loaded if nothing else to prevent having overheating issues with larger currents thro a single unit. I know it is difficult to disperse this heat adequately without a good flow of air through the boat/fans/water-cooling.

​I have has issues with the Mtronics units if the receiver is not getting a decent signal….they hunt at a distance, becoming steady as you get closer. Twiddling with the wiring or Ariel layout has always fixed this. You have 2.4 gig of course, but these can be affected by being mounted too low in the boat.
​Ashley

[Malcolm FraryParticipant @malcolmfrary95515]

If more than one ESC is being fed by one ESC, separate fusing is a GOOD IDEA. About the only time that a fuse between motor and ESC is a good idea.

The ESC gives its output as a quite high frequency series of pulses. If the two motors are not in perfect sync, there will likely be times when the back EMF from one motor interferes with its mate, especially if the power being demanded is anywhere near the capability of the supply. As each motor turns, its electrical "appearance" changes as the coils are connected and shorted, and with a PWM controller, have power applied and switched off.

The simplest mitigation for this is one ESC per motor. With something like a 1:24 MTB, the economy of one ESC is hard to justify.

[HaigParticipant @haig]

Thanks for all the comments.

I have previously tried 2 ESC's to 2 motors through one radio channel with its' own set of problems. I have a thread on that subject from about 5 years ago. Please also refer to my Fairmile D reference above.

I also have a few ships that use a single MTroniks ESC to twin motors from 385 to 550 size that work very well. These are nominally 6 Volts except for my Z39 destroyer that has 2 x 385s & 8.4V.

I also ran the MTB on a single engine and there was no hint of the 'missing' effect.

The ESC in in the MTB is rated at 30amps. It would be helpful if MTroniks responded to my query.

[shipwrightParticipant @shipwright]

If you have a servo tester try that instead of the Tx/Rx control. If the problem persists then my money is on a faulty ESC (assuming that all wiring, batteries and connectors have been checked and that the ESCs have been installed as per manufacturer's instructions). I have only ever used Mtroniks ESCs (both brushed and brushless) and have never encountered any problems (maybe I have been lucky !)

[HaigParticipant @haig]

Hi Shipwright,

Thanks for the response. Please refer to the 3rd post in this thread,

"I think the problem maybe related to the twin motors, as this has also happened with an identical setup on another patrol boat. and its own identical ESC."

The ESC is not faulty, and neither is the other in the other boat. This appears to be a characteristic of the design and its use with the twin motors running at full or near full speed.

[shipwrightParticipant @shipwright]

Thank you for that info. I look forward to hearing what Mtroniks response is to your query. BTW I had a setup of a 40 Amp Mtroniks ESC with two Mabuchi RS- 555PH-3255 motors driven in parallel from one ESC without encountering the problems that you have described.

[HaigParticipant @haig]

Unfortunately I have not got any response from MTroniks, Hence my requests from this forum.

The boat's motors 'sound effects' are only at high speed under load on the water. The Vosper MTB has 2 Graupner 600 12V motors. My other boat had two Johnson 550 size motors, also running at the same 12V. Both exhibit the same effects.

The only thing I can add is that I have set up the motors to be opposite hand, so the props rotate left and right handed propellers.

[Dave MilbournParticipant @davemilbourn48782]

With respect, Shipwright, the only things in common between the 555 and the 600 are the diameters of the cans and the shafts. Chalk and cheese. Your 40A ESC will hardly be aware of the 555's; I run them on 5A ESCs. I think Malcolm's theory is probably nearest to the cause of the problem.

As regards MTroniks' lack of communication you can only draw your own conclusions from it and take those into account when you next purchase a speed controller. Theirs may be popular but they aren't the only ones available out there.

Dave M

[Ted MarecakParticipant @tedmarecak97283]

Hello Haig:

I am wondering if you ever got this issue resolved as my first large scale model boat scratch build (1:12th scale Tyne Class lifeboat) is exhibiting similar problems. Here are the details I have:

12 volt – 12Ah lead acid battery; 2 – Torpedo 500 motors (geared at 2.5:1); one Dual 25 amp ESC from Dimension Engineering in USA, 72Mhz Futaba radio and receiver.

First test worked well until near full throttle when power to both motors was cut then restored, cut then restored cut then restored etc… so never reaching full throttle speed. ESC was sent back to manufacturer who bench tested it and confirmed it was functioning as it should.

My build is 47" long and weighs in at just over 30Lbs and the torpedo 500's were working too hard as they were drawing over 6 amps each, fine for the ESC which can handle 25 amps per motor but the torpedo 500's are not supposed to draw more than about 2.85 amps each , so I ordered two new Torpedo 800 direct drive motors. Installed the new motors and they draw about 6 amps each under full load which is within specification for these motors, however the pulsing issue is the same at or near the full throttle setting which still points me to the ESC but the manufacturer claims it is working correctly……. frustrating.

Now thinking of scraping this ESC and getting two separate ESC's but stumbled onto this thread and wondering if you ever determined what the issue was?

Look forward to hearing back from you.

Ted M

[ashley needhamParticipant @ashleyneedham69188]

Ted. Hello and welcome to the forum .

Haig has not posted for 3 years, so unlikely he will comment now.

I have a similar sized boat with twin 800s and have used two different esc I have not had a pulsing problem..

Do we take it that you have the motors wired in parallel, so both motors receive 12v? And do the motors actually pulse on/off, or just sound as if they do? And is this when running out on the pond, or being run in the bath or being held by the pond side

Ashley

 

 

Edited By ashley needham on 11/05/2021 20:49:11

[Ted MarecakParticipant @tedmarecak97283]

Hi Ashley and thank you for the welcome to the forum.

The ESC I am using is designed to power two brushed motors and each can draw up to 25 amps. Each motor connects directly to separate terminals on the ESC. Here is a link to the manufacturers website for the ESC

https://www.dimensionengineering.com/products/sabertooth2x25

So yes both motors receive the same voltage directly from the ESC and the motors actually had been shutting down at or near the full throttle setting (and then they would power up again to near full throttle and then shut down and power up and shut down etc….) as the boat would never reach full throttle speed. And yes while in the water and under load. I had a hard time getting the issue to occur on the bench.

Doing more bench testing yesterday I noticed that the issue was very present with the motors running full throttle in reverse and then providing a rudder input…… so I changed out my rudder servo and could no longer get the issue to happen on the bench. HA! I got it…… or so I thought. Back to the pond today and while the issue is much better it still happens once in a while so my next step is to eliminate the BEC connection from the ESC to my receiver and provide a separate power supply for the receiver to see if eliminating that connection to the ESC eliminates the issue.

At least the ESC manufacturer has been supportive and providing suggestions for troubleshooting. They have not left me in the dark at least.

I must say it was so very nice to see the motors actually run at full throttle and the boat planing!! Makes the last 6 months of work seem worth while…… I just need to see now if eliminating the BEC connection from the ESC to the receiver completely resolves the issue. I have also had experience where a servo extension wire was causing interference issues (not with this model) and I have a few servo extensions in this model so that might be another trail to see if that helps.

It has been so darn windy here the last few days that I had to hunt for a small pond to test today! I live near the Bay of Quinte in Ontario Canada and have not been able to get out on the bay with the crazy wind we have had the last few days. I hope that stops soon as I have more testing to do as you can see from above.

Thanks again for the welcome to the forum and I will keep this thread updated with my progress. Happy to hear back from you again with any thoughts now that I have provided some further details for you to ponder.

Ted M

[Charles OatesParticipant @charlesoates31738]

Hi Ted, your problem sounds like something commonly referred to as brownout. If I'm correct, what's happening is that the voltage from the battery is dropping when you use full throttle. When the voltage drops below a certain point, the esc stops working, then as the motors stop, the battery recovers a little and it starts again. The lead acid battery you're using is far from ideal, they are very prone to this effect when used with larger motors.

There are two simple ways to check if I'm correct. Firstly you could put a voltmeter across the battery, and check the voltage when the motors are on load, in the water. A check of the voltage without the load won't tell you anything. Second way is to substitute the lead acid battery for a nimh or lipo pack and try again. These batteries work quite differently, and don't suffer voltage drop in the same way.

It's a surprisingly common problem and can easily lead to misinterpretation as a fault with other bits of the installation..

Let us know how you get on, good luck.

Charles

[Malcolm FraryParticipant @malcolmfrary95515]

While the ESC might be happy providing the current that the motors want, the battery might not. Lead acid bricks, even fully charged ones, are good for providing low levels of power over a long run time and ballast. They can only support high currents briefly. NiMH or LiPo does a much better job with continuous high current.

Lead acid were only in common use because back in the day they were almost the only game in town. When alternatives became easily available, their use declined, but old designs and their associated specifications were never updated.

[HaigParticipant @haig]

Hi Ted, I may have not posted anything here for a while, but I see the system sent me the 'Batman' light in the sky. I don't claim to be an expert in any of this, but can give my observations.

Firstly my problems with the MTroniks ESCs is they were built for max of 12V. Pretty dumb really as fully charged 12V batteries are always over this and the ESCs don't seem to be too happy around 12V, especially if you are using one ESC for two motors. Now they build 24V versions too. I never got any response from the company. I know many people using MTroniks ESCs and many that have now gone elsewhere.

I read about your DimensionEngineering ESC and it seems to be a top end item, with the rated Amps and the voltage is 6-30V. If they have checked it then we need to look at another issue. Their manual is very comprehensive.

I never use BEC. It was designed to save weight in model aircraft. Try a separate power source for your radio receiver.

If you have only one 12V 12AH SLA battery then it may not cope with your current draw. What you haven't mentioned is the size of your propellers. Can you connect up an ammeter to one of the motors while the boat is in the water and get some real amps draw. I did this when I first started using brushless motors and was scared by the very high amps draw quoted for these motors so needed a test. I was pleasantly surprised and the Amps used nothing like the numbers quoted in the specs.

For my 1/24 scale Fairmile D, I use 2 x Graupner 700BB brushed motors, each with it's own MTroniks 30A Tio ESC and each going to a separate radio channel. The batteries are 2 separate x 9 cells x 9A/H. This works very well except some days I have to re-calibrate the ESCs as they lose their setup.

Summary (my opinions/suggestions)

– Check the amps draw in the water (even if the boat is stationary). Don't forget to get the size/blades of your prop.

– Strongly suggest another battery type. I use NiMh. If you use SLA then DE mentions an 18 A/H battery in their spec.

– I would use an independent battery supply and not the BEC.

I now use Brushless motors in my newer boats. Each motor requires its own ESC.

 

Edited By Haig on 12/05/2021 10:23:40

Edited By Haig on 12/05/2021 10:27:11

[Ted MarecakParticipant @tedmarecak97283]

Thank you everyone for the valuable feedback. Lots of ideas here to ponder and try. The propellers on my model are 4 blade 60mm diameter brass, which are scale for the model. The torpedo motors are each drawing right around 6 amps each at full throttle and under load which is within spec for the new bigger 800 motors.

I will keep the thread updated with my test results as I sort through this issue.

Thanks again,

Ted

[HaigParticipant @haig]

Hi Ted,

Your battery is the main problem. It is just not able to provide the necessary power supply.

Also a 4 blade x 60dia prop is a big load for a brushed motor on direct drive. I think that in the water that may use more than 6 amps and you have 2 powered from the same battery.

I suggest you also try a separate power supply to your receiver.

[Ted MarecakParticipant @tedmarecak97283]

Thanks Haig!! I measure the amp draw on the motors in the water and it came in right around 6 amps so I thought that would be okay for the motors….. but maybe not the battery so I have emailed the ESC manufacturer to get their input on changing to NIMH battery packs and have asked for their recommendation on # of cells, # of packs, Ah for cells etc…..

Thanks and stay tuned…..

Ted M

[Charles OatesParticipant @charlesoates31738]

Hi Ted, everyone is glad to help. What I didn't make very clear is your battery capacity. It's easy to suppose that a 12 ah lead battery will last for 1 hour if you draw 12 amps. Not so, the capacity is quoted assuming a minimal current draw, perhaps 1 or 2 amps. Drawing 12 amps will reduce it's capacity hugely, plus there's a strong chance that the battery has been over discharged. That would reduce it's capacity even more, in plain English, it's probably stuffed.

The rest of the setup sounds fine, probably similar to many models on here. Do the checks, then assuming we are correct, change the battery, a nimh battery would be my choice for that model.

If you're interested in the technical stuff, the internet has lots of info.

Charles

[Malcolm FraryParticipant @malcolmfrary95515]

SLA are usually quoted at their "10 hour" rate. So in theory a 12AH battery can give 1.2A for 10 hours. As Charles mentions, pulling 12A will not give a 1 hour run time, in the real world, under 1/2 hour. And that is assuming one in top condition.

A member of my club, many years ago, built a lifeboat model and, because it was all he had experience of, ran it on a 12 volt SLA. It chugged around like a tug, had a short run time and a hot motor. Changing to a "7.2 volt race pack" transformed it. It was able to semi plane and ran longer. Less weight, battery able to sustain the load.

Edited By Malcolm Frary on 12/05/2021 17:39:46

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