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Author Topic: Drumbeat of Devon electrical issues  (Read 528 times)

ChrisH1981

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Drumbeat of Devon electrical issues
« on: November 29, 2019, 03:58:22 PM »

Afternoon all, can anybody help with some issues im having regarding my electronics setup in my Drumbeat of Devon model.


I have 2 x MFA 540/1 motors driving 40mm 4 blade propellers.
i have 2 x 12v 3700mah NIMH batteries wired in parallel and a p94 mixer unit for speed control


The issue i am having is im getting no longer than a few minutes (4-5mins at best) duration from the batteries. The motor casings become hot too.
Now I know this points towards the motors drawing lots of amps, but I cant understand why. I have tried different motors but im still getting similar results.
I usually have the patience of a saint, but im now at the end of my tether!

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Shipmate60

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Re: Drumbeat of Devon electrical issues
« Reply #1 on: November 29, 2019, 06:32:38 PM »

Can you confirm the motor current draw with an ameter?
A pic might help to confirm the wiring.
On 12 volts the motors give 14500 rpm which is far too fast for this model


Bob
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DaveM

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Re: Drumbeat of Devon electrical issues
« Reply #2 on: November 29, 2019, 07:35:25 PM »

I'm with Bob B. The motors are being seriously overloaded due to a poor motor/prop/battery combination. In truth I can't think of much else that woud be worse.
Solutions would be:
Reduce the props down to 35mm x 3 blade AS A MAXIMUM.
If you want to keep those big props then switch to Mabuchi 555 or 70T rock-crawler motors.
Reduce batteries to 7.2v AND cycle discharge/charge the batteries several times, especially if they're new, at no more than about 500 mA.
Finally don't put the P94 in Mode 3 (100% mix) until you've sorted the other problems out. Mode 4 (50%) is kinder to everything, including your tether...

DaveM

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unbuiltnautilus

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Re: Drumbeat of Devon electrical issues
« Reply #3 on: November 29, 2019, 07:35:38 PM »

I would agree. Despite the rating of the motors going up to 15v, I think the prop size and voltage combo is putting too much strain on the motors.
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RST

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Re: Drumbeat of Devon electrical issues
« Reply #4 on: November 29, 2019, 07:40:33 PM »

Well if motors are getting hot it kind of points towards watts drawn. Have you done the usual...


Disconnected the shafts from the motors and run the motors unloaded?
Have you tried feeling resistance on the shaft with no motor connected?
How are your shafts aligned / connected to motor?


An ammeter is always great to have. Be weary though if you're using a multi meter. Cheap ones can have ratings /  5a fuses, decent ones still often have 10a fuses.


You've said you've changed motors but what's the driveline like?  Are the shafts threaded both ends?  I hate this, they thread more end than necessary so they can be way too easy to bind when the nuts and couplings are tightened.


Sorry if pointing out obvious.


Rich



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justboatonic

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Re: Drumbeat of Devon electrical issues
« Reply #5 on: November 29, 2019, 11:28:36 PM »

I ran my Drumbeat on the brass upgraded props supplied by MSW. I think they were 4 bladers (might have been 3) but cannot remember the diameter. It was powered by twin MFA geared motors running on 6v SLAs through an Action dual motor mixer unit (sorry Dave, cannot remember which one!).
I never had issues with it and went at a scale speed as far as Im concerned. It didnt 'plane' or throw lots of spray about the place either. Nice boat and gutted I sold it (and the Envoy tug!).
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unbuiltnautilus

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Re: Drumbeat of Devon electrical issues
« Reply #6 on: November 30, 2019, 03:22:27 AM »

Replacing with geared 2.5:1 MFA motors may well be a good fix, while still retaining the 12v setup. Sounds like a good plan :-))
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tica

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Re: Drumbeat of Devon electrical issues
« Reply #7 on: November 30, 2019, 07:56:45 AM »

My set-up on Drumbeat is 2 Speed 900BB with either 45 or 50mm 4 blad props with a 12V 7.5Ah Lead Gell cell

Smooth running, almost no noise / vibration and enough power to get away if needed and sail time of 1½hour.
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unbuiltnautilus

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Re: Drumbeat of Devon electrical issues
« Reply #8 on: November 30, 2019, 08:17:33 AM »

Pity they are no longer available, they were really good motors. Closes equivalent at the moment are the Caldercraft 900 motors.
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malcolmfrary

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Re: Drumbeat of Devon electrical issues
« Reply #9 on: November 30, 2019, 08:54:30 AM »

Re-quoting the old rule of thumb for direct drive - "the prop should not be of larger dianeter than the motor can, and it should not have more blades than the motor has poles".  As you get nearer to the rated voltage of the motor, this gets truer. 
[/size]Too much prop being turned by not enough motor is the classic recipe for overheated motors and short run times.  That's without considering the possibility of driveline problems such as badly done locknuts self-tightening in use and binding the system.
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DaveM

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Re: Drumbeat of Devon electrical issues
« Reply #10 on: November 30, 2019, 10:08:07 AM »

I have one of these in the workshop which I haven't fitted into anything yet. It looks like it might be a very good motor as half of a twin installation in a model like Drumbeat. https://www.componentshop.co.uk/775-dc-motor.html
DM


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coch y bonddu

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Re: Drumbeat of Devon electrical issues
« Reply #11 on: November 30, 2019, 10:11:30 AM »

Been toying with the idea of throwing a pair of them into a Mersey lifeboat I have or should I go the whole hog and bung a pair or rocking horse dooh dood's a Pair of Marks Model boat bits original unused 900 the ones that will take 24v MMMMM




Dave
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unbuiltnautilus

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Re: Drumbeat of Devon electrical issues
« Reply #12 on: November 30, 2019, 07:21:34 PM »

I have one of these in the workshop which I haven't fitted into anything yet. It looks like it might be a very good motor as half of a twin installation in a model like Drumbeat. https://www.componentshop.co.uk/775-dc-motor.html
DM


They look a pretty good buy, do you know if they are three or five pole? Makes little difference looking at the spec, just nice to know.
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DaveM

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Re: Drumbeat of Devon electrical issues
« Reply #13 on: November 30, 2019, 07:51:38 PM »

They look a pretty good buy, do you know if they are three or five pole? Makes little difference looking at the spec, just nice to know.
Curse you, Mr T! I've now got to go out to my freezing workshop, dig the damn motor out and count the ruddy poles! It's as well that I have a bottle of JD out there to help ease the cold.... %)
More soon.
DM
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DaveM

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Re: Drumbeat of Devon electrical issues
« Reply #14 on: November 30, 2019, 10:46:30 PM »

UBN
It's a 5-pole motor.
DM
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Andyn

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Re: Drumbeat of Devon electrical issues
« Reply #15 on: November 30, 2019, 11:23:53 PM »

UBN
It's a 5-pole motor.
DM

Dave spent just shy of three hours in the shed with that JD ;)
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unbuiltnautilus

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Re: Drumbeat of Devon electrical issues
« Reply #16 on: December 01, 2019, 04:11:32 AM »

They look a pretty good buy, do you know if they are three or five pole? Makes little difference looking at the spec, just nice to know.
Curse you, Mr T! I've now got to go out to my freezing workshop, dig the damn motor out and count the ruddy poles! It's as well that I have a bottle of JD out there to help ease the cold.... %)
More soon.
DM


I thank you for your dedication to your fellow modellers, we have suspected it all along, despite your best efforts to hide the fact! Will put a couple of these on the Christmas List now, just for stock, at the moment!
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DaveM

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Re: Drumbeat of Devon electrical issues
« Reply #17 on: December 01, 2019, 08:21:04 AM »

Dave spent just shy of three hours in the shed with that JD ;)
Nothing that dramatic, Andy. I went into the lounge first and dozed off in front of theTV.
DM
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ChrisH1981

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Re: Drumbeat of Devon electrical issues
« Reply #18 on: December 03, 2019, 09:07:16 PM »

Good evening gents, thanks for all your replies. Sorry for not updating sooner, but ive had a busy week.


I have followed your advice and checked that all the shafts are free to turn by hand and that non of the locking nuts are binding.
 
I have checked using a multi meter the amps being drawn by the port motor. Connected to the shaft and running on the workbench im getting between 3.5-4 amps. When running at full speed in the water this increases to 7 amps. Obviously these figures are doubled because of two motors, so 8amps on the bench and 14amps in the water.


With the batteries wired in parallel their total amperage is 7400mah (7.4ah) so i can now see why the batteries are getting a thumping. What I don't understand is why the motors are rated as 2.75ah no load by the manufacturer, but im getting a reading of 3.5-4ah.


Also I am wondering what the discharge rate of the NIMH packs could be, what I mean is, how good are they at delivering the power? Please understand that although I have been building model boats for many years, my understanding of electronics is basic.


Would changing the propellers make a big difference if much at all?
Im willing to give it a try, but one snag is that the Drumbeat appears to have M5 shafts and the range of 3 blade props in the 30-40mm range is non existent, apart from prop shop, but im a bit reluctant to spend £30-£40 on a new set if the problem still exists after.


I have tried to attach some photos for clarification, but unfortunately they are too large to upload and I don't know to resize them for the forum, but i will try.


Anyway guys, i enjoy reading all your comments so please give me your thoughts.


 :-))   
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coch y bonddu

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Re: Drumbeat of Devon electrical issues
« Reply #19 on: December 03, 2019, 09:44:49 PM »

message sent...are you sure your motors are perfectly aligned,even a couple f degrees out will give you a higher amperage reading




Dave
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ChrisH1981

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Re: Drumbeat of Devon electrical issues
« Reply #20 on: December 03, 2019, 10:01:40 PM »

Thanks for helping to post the pictures Dave, yes the shafts and couplings all seem inline, but im going to strip down and check now you've mentioned it.
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coch y bonddu

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Re: Drumbeat of Devon electrical issues
« Reply #21 on: December 03, 2019, 10:15:25 PM »

Posted on behalf of Chris


IMG_1596 by David jones, on Flickr

IMG_1595 by David jones, on Flickr

IMG_1594 by David jones, on Flickr

IMG_1593 by David jones, on Flickr

IMG_1592 by David jones, on Flickr

Dave
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unbuiltnautilus

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Re: Drumbeat of Devon electrical issues
« Reply #22 on: December 04, 2019, 07:32:08 AM »

Same suggestion as previously, to much prop area for the voltage being put through the motors.
Options are;
 Replace the direct drive motors with 2.4:1 ratio versions of the same and keep the voltage as it currently is.


Replace the direct drive motors with motors with more torque and keep the voltage the same. See the Component Shop 775 motors as listed above.


Reduce the supply voltage to the system. 7.2v/8.4v should be withing the spec of those motors with those props, just about.


Internal layout looks fine, if the propshafts turn over easily by hand, you can rule out thick grease causing problems.


My choice would be the 775 motors, they are about the same price as a pair of brass props which you suggested changing. I wouldn't, short of much shallower pitch props of the same diameter, any option that would help your problem would have to involve smaller diameter props which would just look silly!
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