Model Boat Mayhem

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: surabaya on June 07, 2008, 01:49:28 PM

Title: short run time
Post by: surabaya on June 07, 2008, 01:49:28 PM
hi all,
I have just been to my local river/canal to try out my just finished motor cruiser and I was pleased  :)apart from the time it lasted. :(
It is 50" long and I have 2 x 585 mabuchi motors  from one  50 amp Esc with a 12v 12ah sla battery and one servo for the twin rudders. It has twin props about 45 or 50 mm.
It cruises at a reasonable rate for what it is, Ie. cruiser, but the battery only lasts about 10 t o15 min.
I have two and they both do the same.
Any ideas on how to increase running time
Title: Re: short run time
Post by: Shipmate60 on June 07, 2008, 02:15:42 PM
surabaya,
There is something not right there. Those figures give you a current consumption of 24 Amps.
Do the motors or ESC get hot after the run?
I would certainly suggest changing at least the props to smaller ones as these would put a lot of load on direct drive.
In my opinion the motors are too small to power this size of model at a scale speed.
I would go for 550's or even 777's on 12 volts and a smaller prop.

Bob
Title: Re: short run time
Post by: Stavros on June 07, 2008, 05:01:11 PM
As you sau Bob there os something really wrong here as I get at least 10hrs out of a TID Tug with a 700 and a 3ins prop,but I must admit and you should remember I had Exactly the same probs with the fireboat, mfa motors pulling horrendous amps as bob says change the motors asap


Stavros
Title: Re: short run time
Post by: HS93 (RIP) on June 07, 2008, 05:05:46 PM
How hot do things get?

Hs93
Title: Re: short run time
Post by: surabaya on June 07, 2008, 05:39:30 PM
Hi,
After running, I checked the Esc and the motors and they were not even warm. I could reduce the prop size , but at the moment they look right. Much smaller and they would look too small.
Are the motors drawing 2x 12 v, they are running in parallel. or do they still take 12v and more amps.
I never get these motor numbers, is a 550 stronger than a 585 then.
What if I use a bigger motor with a gearbox. Maybe the batteries are naff?
I don`t want to lose any speed, in fact maybe she could do with a little more.
Title: Re: short run time
Post by: HS93 (RIP) on June 07, 2008, 05:46:52 PM
Borrow a battery of someone the same size or even less amps to try ,I think yours may be not as good as it should be.

Title: Re: short run time
Post by: Martin [Admin] on June 07, 2008, 05:58:28 PM
Can you show us a picture of the internals?
Title: Re: short run time
Post by: Shipmate60 on June 07, 2008, 06:26:33 PM
surabaya,
What I didn't make clear is that the 24 Amps is for EACH motor.
If that was the case the motors would burn out after a few minutes!! They are just not designed to take that sort of current for long.
If you want to keep the props I would suggest something like 550 motors on a 2 or even 3:1 reduction gearbox.
The speed pictured isn't fast so these should allow that type of speed with much reduced current therefore longer battery life.
If there is any doubt about the reliability of the batteries replace them, or borrow a known good one.
If on a good battery she handles as you want with nothing getting hot, problem solved.
As Martin has said pics of the internal and external layout would make it much easier to tell.

Bob
Title: Re: short run time
Post by: surabaya on June 08, 2008, 12:24:35 AM
Hi, These are a couple of pictures of the inside, pretty basic stuff.
2 motors, 1 Esc, 1 battery, acoms receiver, and a servo for the rudders plus some lead weights.
I have put the battery on charge over night to try again and I have a smaller 12v 4ah that I will try too.
If not I`ll nick the battery of of the Mrs car ;D. Only joking  ::)
Title: Re: short run time
Post by: banjo on June 08, 2008, 04:47:17 AM
I have put the battery on charge over night to try again and

What sort of charger are you using, what charge and for how long?
Title: Re: short run time
Post by: surabaya on June 08, 2008, 07:56:30 AM
It`s a multi voltage charger. It can be switched to  2, 6, or 12v at 600Ma and when charging is complete, it switches to trickle charge.
And you have just given me an idea, maybe it was not on long enough or I may have set it to 6v by mistake. ::)
Title: Re: short run time
Post by: FullLeatherJacket on June 08, 2008, 09:24:11 AM
Mabuchi don't list a "585" so I think you must have 385 motors. These are best on 12v but those props do look a bit large for such motors. You might consider some "soft" 540-sized ones or, as has been suggested, geared motors. This would enable you to fit some decent-sized props e.g. 45mm 3 or 4 bladers without overloading the motors.
Having said all that I reckon it's a duff battery or faulty charging that's the real problem.
Keep us posted.
FLJ
Title: Re: short run time
Post by: surabaya on June 08, 2008, 09:40:57 AM
Hi,
Sorry, I made an error regarding motor`s ::)

They are 540`s, RS540Sh to be precise.

FLJ : What is a "soft" 540?
And what motor would you reccomend?  ( keeping cost down)
Title: Re: short run time
Post by: surabaya on June 08, 2008, 09:43:51 AM
Also, does anyone know how to work out charging time for a 12v 12ah battery with a 600MA charger?
Title: Re: short run time
Post by: wombat on June 08, 2008, 09:52:16 AM
Assuming the battery is totally flat charge time will be greater than 12/0.6 = 20 hours - so a good 24 hours to get the thing up to full power.

If it is 385 motors in there, I can't see them taking 25A each for 15 minutes without combusting - I would guess that if you didn't burn out the windings, you would burn out the brushes.

I would suspect either a duff battery or a discharged battery

Wom
Title: Re: short run time
Post by: surabaya on June 08, 2008, 10:02:03 AM
They are definitely 540`s and I am beginning to suspect the batteries more.
As for charging, am I right that you just Divide the V by the output = hours of charge.
Title: Re: short run time
Post by: John W E on June 08, 2008, 10:19:50 AM
surabaya hi there

First comments; the batteries you are using - they are the same as I have in my model of HMS Leeds Castle - they are huge things.   Those batteries are a heavy sort in fact very heavy.      Your comment about the boat not performing fast enough for you, well with these weight of battery in you will find it extremely difficult to make your model perform at any reasonable speed.

As for, your charging time; I use a PowerTech multi charger  which is 600ma charge.   It takes anything between 24 hours to about 36 hours to put a full charge in these batters REMEMBER THOUGH WHILST CHARGING THEM KEEP A CLOSE EYE ON THEM - JUST IN CASE THEY OVERHEAT.

I have one battery which is a bit naff - one half of it stays cold and the rest of it becomes warm whilst charging - this is indicating naff plates on the inside.   This battery I just keep as balast for models or when I freshly instal new electronic systems in a model I will sometimes check it out using this battery.   

Your motors, can you attach an amp meter directly between the battery and the motor? just to give some indication of what amperage they are pulling whilst the model is out of the water.  540s / 585s should pull in the region of between 1.5 amp and just a little over 2 amps.  Whilst, as I say, free running.   Anymore amperage than this whilst the model is out of the water and we have some problem with alignment or friction in the drive between the motor and the propeller.  This may be the cause - very doubtful though, if you are saying there is no heat generated in the motor.

aye
john e
bluebird
Title: Re: short run time
Post by: Shipmate60 on June 08, 2008, 11:04:59 AM
surabaya
If the motors are genuine 540's there is a problem.
Genuine 540's are basically car motors and as such designed to run on 7.2 volts.
Some however will run higher voltages but id is usually printed on the can.
These motors rely on rpm to give power so they would struggle on the props you are using.
As an example the smaller Fast Electric boats use 540's.
As Bluebird has rightly said the weight of the battery will always slow her right down as they are very heavy.
For out and out speed 2 x 700 BB turbos will have her planing easily, but your run times will be very short.
This can get expensive so can you tell us what you want to change?
The size of props will not allow you to use most of the faster motors as they are designed to give power by rpm, which the props wont allow.
You can however keep your set up and just change the motors but the compromise will always be speed.
2 x MFA 850's will power her along quite well but these motors are about 25 each.
For speed you will need lighter batteries, faster motors and racing props.
The decision is yours!!

Bob
Title: Re: short run time
Post by: surabaya on June 08, 2008, 11:26:56 AM
Hi, Firstly, even if I reduce the size of battery, I then have to increase the ballast, so that is not really an option for me.
It does sound like I need to replace the motors with something a little stronger, but not faster.
Like you say, the motor I have are trying to turn the prop  too fast and if I use something with more torque but less rpm I maybe getting there.
Any other reccomended motors, other than the 850s?
I have heard someone mention a 777 somewhere?
Title: Re: short run time
Post by: Shipmate60 on June 08, 2008, 11:30:31 AM
I did,
I run 777's in a gunboat on 12 volts with about 45mm prop shop props.
On full power she is too fast but the motors do get hot.
I am reducing to 9.6 volts, but haven't run her on that yet.
Duration doesn't seem bad though as I run her on a 12 volt 5 Ah battery.

Bob
Title: Re: short run time
Post by: malcolmfrary on June 08, 2008, 11:56:45 AM
As neither motors nor ESC are getting hot, the first suspect has to be the battery, either not getting fully charged, or not holding a charge.  I would check the voltage at the battery terminals.  Fully charged, you should see over 13.5 volts.  Swich on and spin the motors, the reading should not change by more than a very small percentage.  Or apply a test load such as a car headlamp bulb.
For motors, a couple of 15 volt 545s are a fairly cheap drop-in replacement, and should have a more suitable power delivery.  Looking at a web search for rs540sh, it seems a popular stock motor for cars - it is intended to rev freely, whereas you are needing torque.
Title: Re: short run time
Post by: John W E on June 08, 2008, 12:05:03 PM
hi there Surabaya

Please can you confirm how you have your motors wired up?    Looking at your photograph it looks as though you have them wired up in series?  If they are, they may be contributing to your performance of the vessel.

I have included a little scribble to show what I mean about the wiring up.

If the motors are maximum voltage 6 volt;  to run them off 12 volt, you would have to wire them in series.   However, if the motors are 12 volt - 18 volt, you would be better off having them wired in parallel.

Having said that, if the motors are only 6 volt, you could get 2 x 6 volt x 10 amp batteries which would give you the equivalent of your 12 volt - 12 amp batter and then all you would have to do is wire your batteries in parallel to give you 6 volt 20 amps.

aye
john e
bluebird

Title: Re: short run time
Post by: surabaya on June 08, 2008, 01:40:58 PM
Hi, Bluebird,
Your "scribble" is exactly how I have the motors set up. Is this the best way . If I did it the other way, would they draw 12v each, therefore try to take 24v from the battery? andwould the Esc take it?
 Shipmate, the 777`s sound a little quick, what are your thoughts if I used the 555`s?
Ray
Title: Re: short run time
Post by: Shipmate60 on June 08, 2008, 01:58:48 PM
My thoughts are to go with the 777's and wire them in Parallel, so each motor gets 12 volts, if she is a little fast you could always not use full throttle, water cool them or go for smaller props.
What is happening with your boat now (well spotted John) is that basically you are running 2 racing motors on 6 volts which is a run down racing pack.
There are always alternatives to get the required result, just depends on how much you want to spend.
If it was me I would try the 777's on the present props, check the performance and bring her in after a full power trial and check the temp of the motors.
I would also fit the fuse in the red lead FROM the BATTERY, not where it is now.

Bob
Title: Re: short run time
Post by: John W E on June 08, 2008, 02:07:59 PM
hi there all

well Bob, you can type faster than I can do a scribble  :D  as Shipmate 60 has said, in your set up now each motor is receiving 6 volts.  Now, if they are 12 volt motors, they will only be revving at approximately half the revs.  The thought is then if they are a 6 volt motor; they will be at their max rpm obviously.

Try setting them up in parallel as Shipmate Bob has described; be careful though of the amperage drawn from your motors wired in parallel, ensure that your speed controller can handle it.  In parallel say - if one motor is drawing 15 amps the other motor will be drawing 15 amps as well, so it will be a total of 30 amps.

aye
john e

I have included a scribble  O0
Title: Re: short run time
Post by: Shipmate60 on June 08, 2008, 02:19:52 PM
John,
If they are true 540's they will only take 7.2 Volts so 12 might burn them out.

Bob
Title: Re: short run time
Post by: John W E on June 08, 2008, 02:53:04 PM
hi there

Bob; I wonder if these 540 motors that have been supplied by RS are the ones they were 'selling off' not so long ago; as a 6-18 volt 540.  They were originally made for the battery-operated drills; I do not think that these 540s have the fan in the commutator end.   In actual fact, they were a 12-18 volt motor; cheap and nasty things from a foreign source.  Maybe wrong....but, .... maybe right  O0

aye
john e
bluebird
Title: Re: short run time
Post by: FullLeatherJacket on June 08, 2008, 05:57:53 PM
Have a look at this, chaps - straight from Mabuchi's own website. BTW the RS is a manufacturer's nomenclature and nowt to do with Radio Spares/RS Trade.

http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=rs_540rhsh

Looks pretty hot for direct-drive on 12v, doesn't it? Still, it shouldn't be drawing umpty-squat amps. I've still got my money on the power supply or charger being crook.

Surabaya - you asked about "Soft"; the 3-pole Sun 540 which we stock is rated at a nominal 7.2v; RPM at Max Efficiency is 8390 and current 4.04A. Torque is 223g.cm. It's all relative, but that's pretty soft for a 3-pole motor in this size of can.

FLJ
Title: Re: short run time
Post by: Martin [Admin] on June 08, 2008, 06:46:50 PM
Can any you clever cloggs give me a brief guide to reading these motor charts please....... :'(
Title: Re: short run time
Post by: HS93 (RIP) on June 08, 2008, 06:55:48 PM
if you go to the original link and play in shockwave. it's interesting to see the efficiency drop as the temperature goes up

Hs93
Title: Re: short run time
Post by: John W E on June 08, 2008, 07:57:05 PM
hi Surabaya

Looking at the link - the one that the Man from DelMonte has put on here  O0 - your RS540 SH motors in your model are from 6 to 12 volt & they do 17thousand&something ....  :) rpm at 12 volt so therefore, with you having yours wired in series - they will only be doing 8000-9000rpm each.  This will account for the slow performance.
Also, I think you may not have charged your battery fully, giving the poor performance on duration.

So...fully charged battery - anywhere between 24-36 hours - at 600 ma 

rewire your two motors into parallel - ensure that your speed controller can handle, because, at 12volts under load, they say about 6 amps per motor.   So, to be on the safeside, let us hope your speed controller can handle 20-24 amps.

To be really, really safe, fit a fuse of say either 10 or 15 amps between your speed controller and your battery.

aye
john e
bluebird
Title: Re: short run time
Post by: surabaya on June 08, 2008, 10:06:18 PM
Hi, all.
Martin, now you`ve really gone and done it. That`s not a "scribble", thats a page out of a fizzysist type book. ??? :-\ :o I get confused with the beano. ;D
I think I am going to go the route bluebird suggests. Sounds like a safe bet.
Plus I like the "scribbles"
Thanks to all for the help and I will let you know next weekend if it sinks or swims so to speak.
Ps I do no ow to spewl  :D
Title: Re: short run time
Post by: surabaya on June 16, 2008, 10:34:16 PM
Hi,
I rewired the boat motors in parallel as suggested and tried it. It did not seem much faster, but after a few minutes it slowed, so I brought it in. When I checked inside, the battery was very hot and the Esc warm. I tried the motors, still in the water and they almost stopped due to low battery, I think the battery is naff.
I thought I would change the wiring back and give the other battery a try, it is a 12v 4ah.
This time I had more success. I stopped to check and all seemed fine, so I continued and had a good 30 - 40 Min's before it started to set a little slower.

The only problem is that when I brought it back in, the motors were red hot although the Esc was still only warm.
I have a feeling that the answer maybe to dump the old battery and change to a little bigger motor.
Any suggestions? not too costly. 850`s seem a little pricey for a pair at the moment.
Title: Re: short run time
Post by: Shipmate60 on June 16, 2008, 11:53:35 PM
The cheaper option would be to go for 550 motors, but the original Mabuchi, not the Chinese ones.
And certainly NOT the Jonson motors.
Unfortunately these days they are like hens teeth to find but will happily run on 6 or 12 volts.
What size props are they on her?

Bob
Title: Re: short run time
Post by: Shipmate60 on June 16, 2008, 11:59:36 PM
here is a pic of my old gunboat at about 3 feet long running on 1 x 550 and a 3 blade 35mm prop shop prop.
She is running on 8.4 Volts on 2Ah cells which used to run for about 30 mins.
Bob

Title: Re: short run time
Post by: malcolmfrary on June 17, 2008, 01:04:09 PM
If it performed OK with a good batery, but the motors got hot, why not consider water cooling the motors rather than changing them?
Title: Re: short run time
Post by: John W E on June 17, 2008, 03:32:22 PM
Surabaya hi there

Just reading the results of your last trial of the boat.

It has brought me to a couple of conclusions:

If we take it one at a time:

Look at your actual model - it is actually based on a sort of leisure/broadstyle cruiser.  The original boat is Not really designed and built for speed.  We should then be looking for a speed slightly quicker or just around walking pace, not that of a 'blistering' fast MTB or an offshore power boat  ::)

So next we will look at how your model was made.   It looks to be of a fairly heavy construction - frames made from thick plywood; and so forth.   So, the hull itself will weigh a fair amount.   Plus the hull shape does not lend itself to be one of a fast boat.   What I am getting at now is, by increasing the motor and propeller size is not really going to gain you much in the way of speed.

You have said that you went to a 12 volt 4 amp battery and also, you rewired your motors from parallel back to series.  You got a better duration time from this set up.  To me, this indicates that although the motors are rated between 6 and 12 volts; they are at their happiest running at a 6 volt because that is what you are doing when you wire them in series from a 12 volt battery - each motor is receiving 6 volts.  So, with this in mind, why not invest your money in 2 x 6 volt batteries - of either 4 amps or the 8 amp variety.  Where you could place 1 battery between your propeller shafts at the rear half of the hull and this would dispense with some of the lead weight that you have been putting in that area and also, place the 2nd battery forward where your original battery was situated.   Then, wire both batteries up in parallel giving you 6 volts but double the amperage if you used 2 x 4 amp batteries it would give you 8 amps.   If you use 8 amp batteries it would give you 16 amps.

As well as doing that, rewire the motors up again in parallel so that each motor individually receives 6 volts - this should give you the same or better running time for less cost than it would be to re-motor it, and add new props on.

To be honest with you, I don't think you are going to improve much on the model's performance.  If you really want a model to perform as a speedboat they tell me they are selling Concorde's engines off pretty cheap.   Downside to that though, fairly large consumption but boy will it make your boat go.

Have you ever thought about building a new cabin cruiser from a set of plans or one of the semi-kits you can purchase.

I know there are several people on this Forum now who have said they couldn't manage to build from plans, but I know they are well on their way building now.....and it was not as difficult as they thought it was.

This would give you the opportunity to build a model with a higher speed performance than your existing one.

aye
john e
bluebird
Title: Re: short run time
Post by: surabaya on June 17, 2008, 11:09:27 PM
Hi, All.
After the run on sunday, I was reasonably happy with it.
You are right, it is more of a broads type cruiser, I just worried about the motors getting hot and thought that maybe a little better motor would run cooler and longer plus give me a little extra speed just to have that bit in reserve.
 I run it at the local canal/ river and some people have got bigger boats than me, 30 foot bigger, Most are very nice and stop to talk or look, but some can be a little unfriendly.
I have found a couple of matching car aerial motors that I will test for amp`s.
But I think the twin 6v batteries and water cooling will help too.
If any one has a plan of a cruiser, I would be grateful ::) , but it needs to be the type that you just copy onto wood and cut out, if you  know what I mean. Has this type of plan got a special name?