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Author Topic: Converting brushed tug to brushless  (Read 4082 times)

clockworks

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Converting brushed tug to brushless
« on: September 02, 2019, 04:00:33 pm »

Another "what motor" thread.


I have an Anteo tug, 3 foot, about 10kg. I bought it secondhand, after a bit of fettling it's working nicely, but is underpowered. Most of the time I'm using full throttle, and it's just about reaching a nice cruising speed - eventually. Previous owner told me that he found it a bit sluggish too.


It's currently fitted with a torpedo 800 motor and a 2:1 O-ring pulley reduction. I need to stick with the pulleys, as the propshaft is very low in the hull, with bulkheads that would get in the way of a direct drive motor. Running on two 8-cell NiMH packs in parallel, turning a 50mm 5 blade brass prop.


Motor spec suggests that the shaft will be turning at around 2000rpm on full throttle - which I guess explains why it's a bit slow. Raboesch prop is rated up to 7000rpm.


I'm guessing that if I fitted a motor that turned twice as fast, the tug would in theory go twice as fast. Drive losses probably mean a bit less than that at full speed, but twice the power when manoeuvring, and maybe 50% more top speed, would be about right I think?
That means I would want the propshaft turning at 4000rpm, so the motor turning at 8000rpm. I'd switch to using a pair of 3s LiPos in parallel, so a motor around 680kv would be suitable - right?


What physical size motor should I be looking at, and have I got my kv calcs right?
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Tug Fanatic

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Re: Converting brushed tug to brushless
« Reply #1 on: September 02, 2019, 05:37:19 pm »

I agree that 2000rpm on a 50mm prop for a 36in tug does sound a little underpowered.

Might I suggest the easiest thing first. I know nothing about your controller but your motor will take rather more than the 9.6v that you are giving it. Do you have access to a 12v battery (or 3S Lipo) to see what difference it makes?

The prop might be rated for 7000rpm but that would be fitted in a planing hull. In a tug half of that will be a better sort of revs to consider.

Do you know how many amps you are using because a larger prop (if it will fit) or reduced gearing might be good alternatives? How warm does the motor get is a very poor substitute but better than nothing.

Your existing motor has a 6.35mm shaft which will be difficult (impossible?) to find a brushless motor to match. You will either need a sleeve or a new pulley to fit your new motor.

No the tug will not go twice as fast if you have the prop turning twice as fast. A  displacement tug hull requires very little power to reach hull speed and then vastly more power to go any quicker. You will however get a much more impressive wash (which is where all that extra power goes) which might be all you need for "satisfaction". Without seeing the model it is difficult to be more specific.

More power is also useful if you want your tug to work to earn its living.

Have a think about some of the above before leaping into anything dramatic.
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clockworks

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Re: Converting brushed tug to brushless
« Reply #2 on: September 02, 2019, 06:12:59 pm »

Thanks for the reply. Although nominally only 9.6v, the NiMH packs peak at just over 12v. Probably somewhere between the 2 under load. 3s Lipo would give me a bit more voltage, so probably worth a try. I've got a couple of smaller 3s LiPos that I could try before I spend any money. I think they are 2100 or 1800mAH, should be OK for testing if I connect them in parallel.


The motor doesn't get very hot in use. I'm using a 30A mtroniks ESC, although the model came fitted with a 20A fuse which I've left in place.

I've got a wattmeter somewhere, left over from my days. I'll see if I can find it.

Got a lathe, so making a new pulley or sleeve wouldn't be a problem.

I didn't know that there was a steep jump in power requirement for a little more speed, so that's good to know. A little more prop wash could well be all I need - the impression or speed/hard work, rather than an actual increase.
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BrianB6

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Re: Converting brushed tug to brushless
« Reply #3 on: September 02, 2019, 11:52:37 pm »

Sounds as if you need a bigger prop.   A geared 800 motor should turn 60 or 65 mm easily   More pitch if there is limited space
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malcolmfrary

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Re: Converting brushed tug to brushless
« Reply #4 on: September 03, 2019, 09:39:20 am »

Something deep down suggests that an O ring pulley system might not be the best way to go with a motor like an 800.  It mght well be that, unless the ring is tensioned perfectly, slippage is happening that restricts the power at the prop when the prop is under load.  Of course, too much tension reduces slippage but puts wear on the bearings, both motor and shaft.  Is a toothed belt option available? Or multiple O rings to increase the contact surface area? Or a 1:1 pulley?  If the motor is not able to spin fast enough in the first place to turn the prop as desired but has enough grunt to drive it direct, that could be a simple answer.
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Re: Converting brushed tug to brushless
« Reply #5 on: September 03, 2019, 01:25:41 pm »

Something deep down suggests that an O ring pulley system might not be the best way to go with a motor like an 800.  It mght well be that, unless the ring is tensioned perfectly, slippage is happening that restricts the power at the prop when the prop is under load.  Of course, too much tension reduces slippage but puts wear on the bearings, both motor and shaft.  Is a toothed belt option available? Or multiple O rings to increase the contact surface area? Or a 1:1 pulley?  If the motor is not able to spin fast enough in the first place to turn the prop as desired but has enough grunt to drive it direct, that could be a simple answer.

I have used O rings with 3.5 inch props & car heater motors for years with no problems. It all depends on the thickness of the O ring, how many you use in parallel (I normally use 2 or 3) and the material that the pulley is made from / how well it grips the O ring. I suspect that they are much more tolerant of slightly out of line pulleys than belts and much more tolerant than the single universal joints favoured by most.
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Shipmate60

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Re: Converting brushed tug to brushless
« Reply #6 on: September 03, 2019, 07:23:24 pm »

If you need 4000 rpm from an 800 motor why not just go direct drive.
I have 2 of these motors in a 6 foot destroyer and on scale props gives "sufficient" speed.




Bob
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clockworks

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Re: Converting brushed tug to brushless
« Reply #7 on: September 03, 2019, 07:51:27 pm »

I made a mistake about the size of the prop, got confused with the boat I'm currently building.  It's actually a 70mm 5 blade prop.


The pulleys are nylon or a similar plastic, with aluminium bosses. They had definitely been slipping when I bought the boat, as there were traces of rubber stuck to the pulleys. I cleaned them up, and put a bit more tension on the belt. No more deposits on the pulleys since. The belt could still be slipping under load though, but seems fine out of the water.




I can't fit the motor directly onto the propshaft, as the shaft is very close to the keel, and there's a bulkhead where the motor case would have to go. It would take major surgery to cut the bulkhead, with limited access through the hatch.


I guess I could fit a 1:1 pulley system, or maybe 1.5:1?  Toothed belt would mean much less chance of slippage, but are they not a bit noisy and less tolerant of maladjustment?
Where is a good place to buy suitable pulleys and belts? Are pulleys available for using more than one o-ring belt?
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Shipmate60

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Re: Converting brushed tug to brushless
« Reply #8 on: September 03, 2019, 09:11:16 pm »

Toothed belts arent noisey unless running at silly rpm.
1:1 toothed belt or 1.5 :1 toothed belt would eliminate the slipping.
My destroyer props are Prop Shop Scale Warship 60 mm props.


Bob
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coch y bonddu

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Re: Converting brushed tug to brushless
« Reply #9 on: September 03, 2019, 09:45:38 pm »

SHG supplies for toothed belts and pulleys




Dave
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clockworks

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Re: Converting brushed tug to brushless
« Reply #10 on: September 04, 2019, 09:25:05 am »

SHG supplies for toothed belts and pulleys




Dave


Looks like I should be able to get everything I need from there - thanks.


Might be a bit tricky working out what pulley and belt combination I need to fit the existing motor and propshaft, as there's not much adjustment on the mount.
I guess the easiest way is to make a scale drawing of the pulleys and measure the belt length with a piece of string.


Would the plastic pulleys be OK, or should I get aluminium?
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Tug Fanatic

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Re: Converting brushed tug to brushless
« Reply #11 on: September 04, 2019, 10:05:07 am »

So have you decided that all you problems are belt slip or are you changing the gear ratio?

What profile pulleys/ belts does SHG supply?
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clockworks

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Re: Converting brushed tug to brushless
« Reply #12 on: September 04, 2019, 11:51:42 am »

So have you decided that all you problems are belt slip or are you changing the gear ratio?

What profile pulleys/ belts does SHG supply?




I'm still trying to decide - so many options!


I could just try a bit more voltage by using 3s LiPos. That might give me about 20% more rpm. Free to try with the small packs I have, but would need to buy bigger ones for a decent run time.


I could try a different ratio by fitting a bigger O-ring pulley to the motor. I might get away with that without sourcing longer belts. Need to find a supplier for compatible pulleys and belts


I could replace the O-ring setup with a toothed set.


I could keep the existing pulleys and go brushless. Expensive as I'd need to replace motor, ESC and batteries.


Leave it alone and just take it easy - until the motor or batteries die of old age. The motor is a bit rusty, and NiMH packs don't last forever.




If I was starting from scratch and building the boat myself, I'd use a direct drive brushless. My other 2 boats are brushless, as is the one I'm currently building and the 3 I've got ready to build.


SHG only supply toothed belt components - around 20 for a set with plastic pulleys, double for ally.
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SailorGreg

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Re: Converting brushed tug to brushless
« Reply #13 on: September 04, 2019, 01:45:59 pm »

If you are looking for a selection of smooth and toothed belts, pulleys, and similar stuff, try Motionco.

Greg

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Re: Converting brushed tug to brushless
« Reply #14 on: September 04, 2019, 04:55:57 pm »

If you are looking for a selection of smooth and toothed belts, pulleys, and similar stuff, try Motionco.

Greg
That is why I asked about the size that SHG (& anybody else) would recommend. So many widths, so many pitches etc etc  {:-{
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Subculture

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Re: Converting brushed tug to brushless
« Reply #15 on: September 04, 2019, 10:05:15 pm »

You can GT2 pulleys and belts for beans on ebay. They're used a lot for 3d printers amongst other things. Fine for scale electric use. The pulley holes usually need bushing, but not a problem if you have a lathe.

Hurric123

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Re: Converting brushed tug to brushless
« Reply #16 on: September 05, 2019, 02:57:30 am »

Hi that Motionco site looks great I was wondering what joint I would be able to use for my 1.45m cabin cruiser. I just stripp the old JAP engine out and will have a big brushless in there joined to the 1/4" shaft.
Sorry to but in.
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clockworks

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Re: Converting brushed tug to brushless
« Reply #17 on: September 05, 2019, 08:40:48 am »

Having "slept on it", I think the most sensible thing to try would be a bigger motor pulley and slightly longer belt. 50% increase in diameter will potentially give me 50% more rpm. I'll have a search on eBay first, failing that, Motionco.


I think that O-ring drive makes more sense than toothed, as it will slip if the prop gets jammed with weed. Our lake tends to get a bit clogged at the start of summer



If that's not enough, I'll try the 3s LiPos. I'm going to need some bigger packs for a future build anyway.


I'll go brushless if the motor dies.




Thanks for all the ideas guys.
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Subculture

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Re: Converting brushed tug to brushless
« Reply #18 on: September 05, 2019, 11:35:44 am »

If you have a lathe standard pulleys for prints are easy to machine. Plastic metal or even wood are suitable materials.

chas

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Re: Converting brushed tug to brushless
« Reply #19 on: September 05, 2019, 12:31:18 pm »

I've followed this thread with interest, low mounted prop shafts can be a real problem in some models.
  I definitely agree that trying a different pulley is a first step, and that making one is a doddle, I've had no problem even without a lathe, and the test will cost next to nothing.
   A couple of things to think about, firstly, if the new pulley gives the performance you want, consider a further modification to use double pulleys and 2 belts, as was said earlier this is a good simple and cheap way of doing it.
  Last thought, I had a similar problem in a model a few years ago and I used a slightly larger prop direct coupled to a geared 540 motor from MFA motors. The output shaft is set very low down so I had no problem connecting it.
   The motor is geared 2.5 to 1, slightly lower than your pulleys, but the motor can run from around 4 volts up to 15 volts so I had loads of power on the 12 volt SLA that I used. Also the motor didn't use much current, the gears increase the torque hugely without putting much load on the motor.
Cost is around 20.00 from Cornwall model boats, and you can see the specs on the MFA Como website.
Chas

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Martin [Admin]

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Re: Converting brushed tug to brushless
« Reply #20 on: September 07, 2019, 06:08:41 pm »


.... not helpful.... but funny.... sort off!

            Skip through to: 6:52


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clockworks

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Re: Converting brushed tug to brushless
« Reply #21 on: September 09, 2019, 10:58:59 am »

I've ordered a 1/4" coupling (propshaft universal joint type) to use as a boss, and some 30mm diameter plastic rod. I'll make a larger motor pulley.
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