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Author Topic: Motor/gearbox for big subs  (Read 7150 times)

FullLeatherJacket

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Motor/gearbox for big subs
« on: August 04, 2010, 09:26:29 AM »

I've had an enquiry from a chap in USA who is having overheating problems with the speed controllers in his large submarines (1/48 scale). The ESCs aren't our manufacture, I hasten to add! The problem is that the speed controllers have thermal cut-outs which trip after about 15 minutes of normal running. The ESCs then work OK when cooled off, but in three cases only in one direction. He's blown five of this make of ESC since May and is getting a bit disillusioned with that particular manufacturer. No names, no pack drill.

He asks if I know of a suitable motor/gearbox combination to run props up to 4" diameter on 12v low current draw seems mandatory to avoid overheating. Water-tight compartment is also 4" outside diameter. Can anyone suggest a suitable unit from their own experience, please?

FLJ
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Patrick Henry

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Re: Motor/gearbox for big subs
« Reply #1 on: August 04, 2010, 09:45:54 AM »

You have yourself a pm, boss..
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RonP

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Re: Motor/gearbox for big subs
« Reply #2 on: August 04, 2010, 09:49:08 AM »

An easy answe to this one is to split the propshaft near to the motor housing but outside in the free flood, secure a 15 tooth gear to the drive end. You will need to make a counter shaft
that will carry a 30 tooth and a 15 tooth gear below then put another 15 tooth gear on the other end of the propshaft Bingo 2:1 reduction on a crossover rather like a car gearbox.
If this is not clear give me a holler and I will put a sketch together for you.
RonP
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Tug-Kenny

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Re: Motor/gearbox for big subs
« Reply #3 on: August 04, 2010, 11:10:10 AM »


Just a thought. I would think about bonding the speed controllers to the hull where they can conduct their heat into the water.  It must be very cramped and air tight where they are, with no air flow.

Ken

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FullLeatherJacket

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Re: Motor/gearbox for big subs
« Reply #4 on: August 04, 2010, 11:18:43 AM »

Ken
At the suggestion of the ESC manufacturer the customer actually hung them outside the WTC to cool in the water (they are allegedly totally waterproof) but they STILL tripped out. Methinks a motor overload problem is the cause rather than a hot sweaty installation, hence the call for suggestions for a suitable motor/gearbox combo. A 4" scimitar prop is going to take a lot of torque to swing it, albeit at pretty slow RPM I'd have thought.
Keep 'em coming, chaps - that's what this forum is all about!
FLJ
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Subculture

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Re: Motor/gearbox for big subs
« Reply #5 on: August 04, 2010, 01:58:06 PM »

Can be tricky giving recomendations for a motor when just a props diameter is mentioned, as the blade area of a prop affects RPM just as much as diameter. A 720bb motor would be a good start, high torque low revving motors, although you may well have to go for even lower RPM.

Andy

sheerline

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Re: Motor/gearbox for big subs
« Reply #6 on: August 04, 2010, 02:08:28 PM »

FLJ, Whats needed is a 720BBTorque fitted with a 5:1 ratio gearbox. This is an exceedingly good setup as that particuar motor is a low current, low rpm, high torque machine and when hooked up to 5:1 reduction box is unstoppable and should turn his prop at decent rpm without caning the speed controller and batteries to death. Because the motor is lightly loaded, the watts go down and everything runs much cooler. (why am I telling YOU that... sorry chief)
 If he is trying to run his setup as a direct drive he will be unsuccessful because the load on the motor will be excessive. I wonder how many amps he is drawing ?


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FullLeatherJacket

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Re: Motor/gearbox for big subs
« Reply #7 on: August 04, 2010, 03:47:16 PM »

I wonder how many amps he is drawing ?

Enough to cook five speed controllers on the trot, and I'm blowed if he's gonna do that to one of my babies!! Is there a commercially available 5:1 gearbox which could be fitted to the 720BB Torque?
Thanks for this info - I'll pass it all on and maybe the man will sign himself up here - I couldn't recommend anywhere else more highly.
FLJ
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sheerline

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Re: Motor/gearbox for big subs
« Reply #8 on: August 04, 2010, 04:19:27 PM »

re the gearbox FLJ, he's going to have to hunt one down I'm afraid, the last pair I got came from Dave Keogh at Subtech (now gone) and he got those in for me specially. They were all metal planetary types, ruddy expensive as hell and came from a supplier in Australia, I never knew the source. He could try the internet of course or the other option would be Hectaperm motor/box setup which would also work but may be a little greedier on amps, but not excessive. I have seen these used on many large subs and they work well.
.
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FullLeatherJacket

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Re: Motor/gearbox for big subs
« Reply #9 on: August 04, 2010, 04:23:50 PM »

Ah ha! I know that Oz supplier very well ('t is Sir John of Darke Horse legend). I'll get onto him and see what I can entice from him if he's feeling up to it. Poor old devil's a bit crook at the moment.
FLJ
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getemuphigh

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Re: Motor/gearbox for big subs
« Reply #10 on: August 04, 2010, 06:05:21 PM »

Is the ESC a BEC type, if so then maybe tha amps drawn to drive the servos etc is too high and overloading the BEC / overheating the ESC unit.

I have heard of this happening and the cure is a separate higher amp rated BEC, this is what is fitted to my static dive 6ch sub which had the same problem.
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FullLeatherJacket

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Re: Motor/gearbox for big subs
« Reply #11 on: August 04, 2010, 07:20:57 PM »

Nope - they considered that and a separate Rx battery pack has been installed but the problem persisted. As I said earlier, I'm 99.9% sure it's too small a motor on direct drive, hence the request for motor/gearbox suggestions. A pigeon has been despatched to Brisbane to see what Dr John can provide.
FLJ
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Windsorsub

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Re: Motor/gearbox for big subs
« Reply #12 on: August 04, 2010, 08:21:13 PM »

Good afternoon,

   As per the thread of POSTS below, I am at a loss as to why I am having this issue. The current set up for all 6 submarines (ranging from 5 to 9 feet in length) is as follows...

- Single Mabuchi 550 Motor connected to a 3/1 gear reduction system exiting the WTC bulkhead with a 2 inch manufactured stuffing box.
         There is minimal to no drag on this set up, and the shaft can easily be turned with your fingers.
- Each WTC contains 4 servos (Rudder/Aft/Forward planes/Ballast Tank) plus a maufactured (40A) Speed Control witha 20A fuse
         The BEC capability was removed based on suggestion from the manufacturer support team and replaced with a nicad pack
- The ESC (one each per WTC) is inside a 4" OD cylinder which is 9 inches long
          As per suggestion from manufacturer, one ESC was rewired to be outside the WTC and completely immersed in the water
- The ballast system is Propel, the props range in size from 2" (for the twin screw subs) and 3 to 4" (for the single screwed boats)
- All six subs used to work flawlessly when thety were "dry hulls", but since changing to a WTC sytem, I have had this problem
         
Because the set ups are the same, I have swapped out every mechanical part with my surface flleet (servos/speed controls/motors/batteries/and Radio Contol) with no change.

Using one sub as a guinee pig, the latest modification is that the ESC BEC has been disables with a Nicad pack installed, The ESC is now running the the water, all four servos have been changed, a new 40A ESC has been installed, a new 550 motor has been installed. Same problem.

FLJ, Thank you for leading me to this Forum !
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Patrick Henry

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Re: Motor/gearbox for big subs
« Reply #13 on: August 04, 2010, 09:27:34 PM »

That is weird...my SLEC Patrick Henry had a stock 540 motor running off a 6volt 10a/h gel cell and never gave me any problems, either with an esc or when it had just two micro switches. The PH used to turn a 70mm 7 blade scimitar prop.

U117, my all wood 9foot U-boat had two 540's in it to start with using Tamiya mechanical speed controllers, it worked perfectly but was down on power, so we changed the motors to two Decaperms minus the gearboxes but retaining the Tamiya controllers, it never gave me any trouble. Prop shafts were 24" long (if I remember correctly) turning 4 blade brass props of 50mm diameter.

Does the wtc heat up inside?



Rich
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Windsorsub

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Re: Motor/gearbox for big subs
« Reply #14 on: August 04, 2010, 09:41:26 PM »

Hi Rich,

    I never verified the inside temperature, but when the subs "shut down", and I open the WTC, the ESC's were really hot to the touch. What I don't understand, is that even now with the ESC IN the water, it still shuts down after 15 minutes or so. The ESC is NOT hot in the water, and I have a 20A fuse installed, that does not blow....

Dwayne

 

   
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sheerline

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Re: Motor/gearbox for big subs
« Reply #15 on: August 04, 2010, 10:16:59 PM »

I still wonder what current is being drawn by this setup. It is possible that particular motor may be giving problems and they could be intermittent. I am beginning to think you should stick this boat in a test tank, place an ammeter in series with the battery and monitor the current at full throttle. I would be inclined to leave it running flat out whilst monitoring the current drain. I wonder too if the motor is fully supressed and if it is possible for large motor spikes to destroy the output stage of a speed controller, especially if the motor commutator is dirty and it's being worked hard. Perhaps you could clarify that point FLJ as I don't know how susceptible these things are these days.
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FullLeatherJacket

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Re: Motor/gearbox for big subs
« Reply #16 on: August 04, 2010, 10:42:29 PM »

It's that "550" that bothers me. Remember those horrible Johnson things that flooded the market a while ago? Designed to work high-ratio gearboxes but sold as suitable for model boats. It is possible for high back-EMF to whack the MOSFETs in a speed controller, but the type Dwayne used are genarally considered to be bomb-proof in that respect.
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Shipmate60

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Re: Motor/gearbox for big subs
« Reply #17 on: August 04, 2010, 11:47:15 PM »

Dave,
If it is one of "Those" 550's they run fine on 6 volts but not on 12 or above, what voltage is being used?
Is he using the 12 volts now?

Bob
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sheerline

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Re: Motor/gearbox for big subs
« Reply #18 on: August 05, 2010, 12:23:21 AM »

OOPS!Had a re-read and  I didn't inwardly digest the last bit about the motor being replaced, albeit with another 550 :embarrassed:.
 So, now the plot thickens and I have to agree about those motors, they may not be suitable in this particular wtc setup.  Low current drain is the submariners God ,somebody get a meter and start putting some numbers up, without numbers  we can't do anything other than guess.. interesting problem this.
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Sub driver

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Re: Motor/gearbox for big subs
« Reply #19 on: August 05, 2010, 02:45:28 AM »

just a thought. have you checked all the bearings / bushes to ensure the are not binding , a binding bearing will feel relatively free until it is run at high speed then will heat up and grab the shaft . strange it all worked fine in a dry hull but when your set was transferred to a wtc it all went wrong. should make no difference. does it all work ok out of the water for a long time.
regards sub.

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derekwarner

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Re: Motor/gearbox for big subs
« Reply #20 on: August 05, 2010, 06:58:04 AM »

Sub driver may have a point here....what material are the prop shaft manufactured from? ......certain synthetic materials [nylon] absorb water and swell dimensionally................... <*<

This could explain a number of points raised here..........Derek
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nick_75au

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Re: Motor/gearbox for big subs
« Reply #21 on: August 05, 2010, 08:44:53 AM »

I Know Dr John will have the answer,
Whatever motor is driving the prop should be no more than 2500 RPM at the output with no load to keep the amps down, on a 100 mm prop.
Have a look at the Raboesch data on their props and for a displacement vessel work on no load speed of around 3/4 of the maximum recommended.

I have run a 100 mm prop on direct drive, but it was a 24 volt motor designed for diaphragm water pumps, it draws 5 amps at 24 volts, so expect 10 amps on a 12 volt system providing the no load speed is 2500 RPM

Nick
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Windsorsub

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Re: Motor/gearbox for big subs
« Reply #22 on: August 05, 2010, 05:16:29 PM »

Morning gents...

In answer to Sheerline: The 550 is fully supressed, no spikes on the bench OR while I put pressure on the shaft (to simulate load)
     I will try the AMP exercise....Do I connect the meter to the positive or negative side of the battery?
In answer to Shipmate60: According to MABUCHI support, all their 550's can work at between 6 ad 17 Volts....
     Does this make sense to you, or should I purchase another 550 type somewhere else
     The subs are on 6V, but I can change this....
In answer to Sub Driver: The bearings on the shafts (1 on each side of the WTC, 1 on each side of sub to shaft) do not heat on the bench
     They don't make any weird sounds either (that might identify binding/heating) I am guessing they are OK in the water but will check today
In answer to derekwarner_decoy: Props are made of brass, shafts are made of stainless steel
     
Question for nick_75au: Where can I get access to the Raboesch data you refer to..

You guys are GREAT !
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Mankster

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Re: Motor/gearbox for big subs
« Reply #23 on: August 05, 2010, 05:33:46 PM »

So how many Amps are you pulling in the water with your current set up? That should help someway in tracking down the problem.

Skip Asay

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Re: Motor/gearbox for big subs
« Reply #24 on: August 05, 2010, 05:51:30 PM »

Hello all.

As most folks on this side of the pond know, I'm a firm believer in small motors w/gear (or tooth belt) reductions. I have a 30 year old 56" long 1/24 Type XXIII which has worked absolutely fine with a Dumas/Pittman motor since it was launched. Just to prove a point, I recently replaced that motor with a little Mabuchi 385 sized motor with a 9:1 compound belt drive which drives a steeply pitched 2 3/4" 3 blade prop which was originally designed for steam power (LOTS of torque!). Max current draw is ONE AMP at full speed and full speed is fairly substantial. I'll venture a guess that at 9:1 ratio, that motor is generating more torque than some of the motors you guys are so enamored of. Now I'm not necessarily saying that 9:1 is the optimum ratio across the board but for the bigger props it certainly could be. It's a start, though.

Just a suggestion.

Skip Asay
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