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Author Topic: Propultion advice please.  (Read 2147 times)

boman

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Propultion advice please.
« on: August 24, 2013, 11:27:19 AM »

I have a dilemma. My tug, which is currently running 45mm props, Kort nozzles. 2x Silver can Tamiya motors, running through modified Tamiya planetary gearboxes. 6v supply. I have trialled Tamiya Digital speed controllers, only because I already had them.

I have found the speed controllers and motors get hot during a run. And have been perusing around the net looking for some better options. I need to stick with 6v supply, due to lack of room forward, where the battery goes.

I have found a 15a marine speed controller, on e-bay, an mtroniks brand.

Where would you knowledgeable people go? which direction. I am kinda limited for space, motor wise and battery wise.
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Shipmate60

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Re: Propultion advice please.
« Reply #1 on: August 24, 2013, 03:43:48 PM »

You need to find out what the motors are and what current they draw under load.


Bob
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Re: Propultion advice please.
« Reply #2 on: August 24, 2013, 04:18:40 PM »

Ok.
Your running 6volt.
Throwing numbers around for illustration .
If your motors require 200watt for efficient operation ,at 6v the motors would require 33 amps
If your motors require 200watts for efficient operation ,at 12v the motors would require 16amps
voltage can change ,but wattage remains the same ,more voltage less current, less voltage more current.
I would suggest ,you try running a 12volt system ,or what ever your ESC's can handle , and give it a go.
Heat is a good indication of excessive current use.
You can root around the internet ,its liklely ,very likely there is a 12volt battery with the same foot print as you 6v battery.
It wouldn't be that hard to just trial the boat with a 12v battery ,borrowing a battery from a friend, just for a look see.
from where im standing , excessive current draw will toast your battery ,as it will only discharge at a certain rate.,It will also have a larger voltage drop, less voltage ---more current ---because of the wattage.
or
Switch to 6volt motors,however 12volt operation ,these motors can stand.
http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=rs_540sh
 
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malcolmfrary

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Re: Propultion advice please.
« Reply #3 on: August 24, 2013, 06:30:37 PM »

If the motor is already getting too hot on 6volts, its going to be toast in minutes on 12 with the same load.  Best to find out what current is being taken, running the motor direct off the battery via an ammeter.  A bit hard to say what should be happening without knowing the motor characteristics.  I don't know, but Tamiya could produce a range of motors, all with silver cans.
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Colin Bishop

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Re: Propultion advice please.
« Reply #4 on: August 24, 2013, 06:57:48 PM »

Looks like the motors are overloaded so smaller props might be an idea. As the others say, you need to check the current draw.
Definitely don't up the voltage!
Colin
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Re: Propultion advice please.
« Reply #5 on: August 25, 2013, 03:08:04 AM »

Its possible that the motor is underloaded,.by voltage. for the same reason a starter motor ,or any motor can be burnt up with a lower voltage. It still demands wattage given the load.  the more load the closer the motor gets to stall ,the more current it will require ,until either the battery drops off, theres only so much current it can deliver before the motor become's a current sink and the battery drops out.You can burn the wire off underloading a motor,  and melt the brush carrierer's.
45mm prop on this motor isn't a tall order,
 assuming the gear head turns the shaft rpm down.
if you don't have an Ammeter ..the redneck way would be to start with a low amperage fuse, say 2 amp and work your way up,An ammeter by itself isn't going to tell you much ,if the voltage isn't known.. voltage current go hand in hand.
. this motor will require according to Mabuchi , 13amp at maximum efficiency running 4,8-7.2 volt. stall current (Motor shaft stopped at full power) is roughly 70 amp
At 4.8-9.6 it will require 9.5 amp..stall is 57
Its a really large drain for the little 6volt battery to offer up.
given your info, your left with two choices run it on 7.2 -12 volt (12v would be overdriving this motor). or reassess the motor choice.personally..I think that's to much motor for the battery unless you can gear it down some more and take a little more load of, recheck the linkage and make sure there is little binding in the shaft. prop size could be dropped ,or if your up to it reset the pitch of the propellor
Its not all bad.. Johnson make's some very good motor's
http://www.ebay.ca/itm/Johnson-Electric-6V-Motor-RC-Power-Wheels-Fan-Cooled-DC-Hobby-Motor-/270982055899?pt=LH_DefaultDomain_0&hash=item3f17ca07db
 

 
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nick_75au

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Re: Propultion advice please.
« Reply #6 on: August 26, 2013, 09:05:37 AM »

The motors look like standard 540 can motors that came stock with Tamiya buggies. They are quite high revving motors for scale boats even with gearing. Look to replace the motors with 45 or 55 turn rock crawler motors. Identical bolt pattern and you will not need to change anything else. this will reduce the amps and therefore the heat.


I don't think that this works the same way in a boat as the load reduces as the RPM reduces (motor RPM is directly related to voltage) unlike a starter where the load remains the same.
Quote
Its possible that the motor is underloaded,.by voltage. for the same reason a starter motor ,or any motor can be burnt up with a lower voltage. It still demands wattage given the load.  the more load the closer the motor gets to stall ,the more current it will require


the other issue is a gel battery is current limited so even if the load got to where the amps could be high the battery would not be able to supply the current. Unlike a car battery which is designed to deliver a high burst current.

Cheers
Nick
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tugboyben

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Re: Propultion advice please.
« Reply #7 on: August 26, 2013, 09:42:15 AM »

Boman
Just a idea these motor's from steve at modelboatbits will do the job the motor's are 555 am sure you will just have to do a swap your's


http://www.modelboatbits.com/shop/article_MBB-555M/555-HIGH-TORQUE-MOTOR.html?sessid=lHd95S8HhLIrZwyJIuWY0znZtXxqH9nxBDDu8nsR5scUf4fZ980Vqb8MaQBBrUhB&shop_param=cid%3D19%26aid%3DMBB-555M%26


Jason
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Re: Propultion advice please.
« Reply #8 on: August 26, 2013, 04:21:45 PM »

Nick, the difference in this case is the battery.It will only deliver so much current before it drop's out.
Now if the same battery could supply a larger current ,the motors may run outside the happy zone because of excessive current. The motor becomes a current sink,
I'll stand on my decision that this 540motor is to much motor for that battery, given there are two. its worse,
If both motors pull the same current at 6 volt it would equate to roughly 160watts. running properly loaded.
I made a variable power supply ,a while back , it would be interesting to know how the motors behave at 6volt with a 25amp current supply.
http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=rs_540sh
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malcolmfrary

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Re: Propultion advice please.
« Reply #9 on: August 26, 2013, 06:21:24 PM »

If the battery was being overloaded there would be a different set of symptoms described, mostly the motors stopping due to the ESCs giving up or behaving erratically and twitchy steering due to unstable voltage.  There would also be mention of the battery heating.
The answer is either swapping to the right motors, or ensuring good alignment or shaft lubing, or all of the previous.
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boman

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Re: Propultion advice please.
« Reply #10 on: August 28, 2013, 11:25:26 AM »

I can see I have promoted some good discussion on this matter. I will look at different avenues, and report my findings.
Many thanks to all who replied, and don't be shy to keep adding.
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