Model Boat Mayhem
Technical, Techniques, Hints, and Tips => BRUSHLESS Motors and Speed Controllers => Topic started by: Richard Houston on July 14, 2019, 02:04:24 pm
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I have a 48"(4Ft) Perkasa torp boat its fitted with twin Torpedo 800 motors, now it runs via 2x 12v batteries one per motor, can someone please tell me how long roughly a 12v 3.2Ah battery would last in that please... I know its a hard guestimate but I need to know as with SLA there is size limitations of the side area for the batterys.
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That's an interesting choice of motor / battery for an mtb. The motors are rated at around 5 amps each in normal use, but, and it's a big but, it depends on the propellor size, and hence the current drawn.
a guesstimate for around 10 amps drawn using small sla batteries would be only a few mins of sedentary performance.
If I might make a personal observation based on a lot of models made, the Percasa cries out for a decent brushless motor and lipo battery set up. It would run well, not silly fast ( 'though that is achievable) and it could run much longer and be much lighter in weight.
A basic rule in model boating is that sla batteries are great in ships etc, and darn near useless in anything not designed to crawl along.
Chas
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The model is 16 years old, it was not my choice I'm just the new owner who has already cashed out £180 moving from 40mhz to 2.4ghz on futaba.
Ok I will make the move as above but I need 2x Brushless motors(PLEASE HELP ME WITH THIS), 2x ESC's for Brushless and i'm guessing finally What size of batteries to got for.
I would appreciate any and all help on this one.
And this is it currently sitting in Dry dock!!
(https://i.imgur.com/wX64R0c.jpg)
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Error
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Not sure what jmac wrote, the text isn't coming up on my screen.
Richard, start by typing perkasa brushless into the search box, a lot of info there to get you started. If confusion sets in come back with some questions.
If you start wanting to compare motor specs etc, you could look at the hobbyking web page, ( you don't have to buy from them ) the comparison facility and filter settings make it easy to narrow down alternatives.
They do a lot of lipo packs too.
Chas
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Not sure what jmac wrote, the text isn't coming up on my screen.
Richard, start by typing perkasa brushless into the search box, a lot of info there to get you started. If confusion sets in come back with some questions.
If you start wanting to compare motor specs etc, you could look at the hobbyking web page, ( you don't have to buy from them ) the comparison facility and filter settings make it easy to narrow down alternatives.
They do a lot of lipo packs too.
Chas
Amazing help Chas very much appreciated mate
Also heres what he typed above you ...
I replaced 3 x 850's with One Turnigy 3648 1450kv outrunner operating on a one 3s lipo to run a 5' S-Boot and it equals or betters the 3 (using one 3s Lipo)but as you have only two props you're stuck with 2 motors . I would try a Lipo first ignoring the Duration time I though the 800's are for not for planers
I've looked at hobbyking but am still lost, the brushed 800 specs is below, so I need 2 brushless motors as a replacement to the below if anyone can help here.
Torpedo 800:
Approx motor diameter: 50mm by 70mm long.
Operating Voltage 12 volts.
Current approx. 5.28A at max efficiency.
RPM at 12.0v – 4289 at max efficiency.
Weight 595g (approx)
Shaft Diameter – 6.35mm
Someone tell me if this is correct the way to work out the difference between a brushed and brushless is take the brushless x12v get that number and get it as close of a RPM to the brushed ?
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co-incidence or what, I've just ordered the same Turnigy motor for my next project. I've had 2 of the Turnigy outrunners so far, 1 is a smaller 2836 1450kv in a 38 inch lightweight rttl. It goes beautifully for around 45 mins on an old 3300 nimh pack. I'd recommend them.
Re brushless motors in general, the only way to feel confident is to read up on them and understand the numbers. It is far from complicated, if my ancient befuddled mind can suss them out after an hour or so, anyone can.
Chas
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Whilst I can’t deny that brushless is the way forward with electric boats that you want speed out of, my first change would be to ( if budget is an issue) replace the SLA batteries with Lipo cells.
Using the biggest capacity 3 cell ( 11.1 volts-ish) lipos you can afford you will probably get enough power, at twice the capacity into the motors for half the weight of the current battery pack.
Performance will be better and if still not up to your wants, then go brushless.
Whilst you’re buying the lipos , buy some low voltage alarms at the same time, not expensive but could save the batteries..
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Whilst I can’t deny that brushless is the way forward with electric boats that you want speed out of, my first change would be to ( if budget is an issue) replace the SLA batteries with Lipo cells.
Using the biggest capacity 3 cell ( 11.1 volts-ish) lipos you can afford you will probably get enough power, at twice the capacity into the motors for half the weight of the current battery pack.
Performance will be better and if still not up to your wants, then go brushless.
Whilst you’re buying the lipos , buy some low voltage alarms at the same time, not expensive but could save the batteries..
It has ZERO batteries when I bought this boat it came battery less, thus the confusion over getting a setup that works, will the 3S be enough to power the boat safely ?
and
The boat would normally hold 2 batteries, one on each side powering a motor each
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Sorry about the Error post I get P****d off with the Shrinking this lot does.
Richard prior to going brushless I ran the 3 x 850's on one 3s no probs as comparison with a meter the volts will droplike a stone on nicad or sla but not on the lipo. Physically on my PT598 3 brushed motors I could hold her at the waters edge (waist level) flat out on Nicad but the lipo nearly pulled me in.
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Lipo nearly pulled me in.
Oh lets not be having a water-boarding with a model shall we :-))
So One 3S at 5000 mah or 2 ... one for each motor
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So One 3S at 5000 mah or 2 ... one for each motor
If you can stretch to one for each motor and you can fit them in that would certainly be my preference.
The 800 motors may have enough grunt for your boat. It only if you have a power source that deliver enough current, lead acids are capable but the weight penalty negates a lot of the advantages.
Lipo battery’s tech' is a huge leap forward in capability and may not require the motors to be changed..
I have a plastic RTR speed boat (Helion challenger) brushed motor and an 850mah Lipo battery, goes well enough...recently bought a replacement battery (for convenience) but a 1300mah, same voltage...the difference is immense, it’s a lot quicker and actually a bit mental.
Just dont forget the LV alarms, it’ll save you trashing the lipos by overdischarging them!
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I would try one first and if that suits and you are ok with the runtime Sorted or 2 for more runtime
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Hi Richard
Converting to brushless.
First the 3S lipo is 11.1 volts but charge above this.
So on you motor RPM 4300 divide by 11.1 which gives you a kv number of 388kv( say 400kv).
The number on brushless motors, the first two are the diameter and the second two are the length(generally).
The power rating is on the maximum voltage and amps, so dropping to a lower voltage drops the power.
Hobbyking gives you a lot more info(including ESC requirements).
I wish the other sellers did the same.
Shaft size for that size motor is generally 6mm, so new metal coupling will be required.
The plastics one do not handle that power.
As for batteries two 5000 to 5800mah with a C of40 plus.
Also you will require two ESCs with a Y connector cable.
Canabus
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Thanks Canabus,
You'll have to excuse myself I know next to nothing about lipo and brushless, but what I do know is the boat is 48" long fibreglass hull and dual props, so if anyone would like to help me by suggesting which brushless motor to go and buy and ESC and batterys I'll just go get them.
I'm sorry to be a pain but I defer to people who know more about this subject than I do, I'm not so worried about the money side of things, so what ever I need for Motors / ESC and finally Batteries, please tell me so I am not left sitting here semi confused and no clue who to buy, at the price point of some of the items I dont want to waste the cash buying the wrong thing.
But in the end I dont want to sit with a new to me boat in dry dock
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Hi Richard
What size props and number of blades are on the boat??
Canabus
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Very good point, I'll be back at the model on Wednesday its in my club house, how would I know the prop size ?
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Hi Richard
Count the number of prop blades and measure one blade from blade tip to the centre of the shaft.
Double that measure and you have the prop diameter( mm's please( that's Mickey Mouses as my daughter calls mm)).
Canabus
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Hi Richard
Count the number of prop blades and measure one blade from blade tip to the centre of the shaft.
Double that measure and you have the prop diameter( mm's please( that's Mickey Mouses as my daughter calls mm)).
Canabus
Canabus I have my own keys to the club house, i'll nip in after work today and get that prop measured for you and will make sure to snap a few pics of the prop as well for good measure, just in case.
Many Thanks
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2 blade, 30mm from single blade to centre so total 60mm, pictured below ...
(https://i.imgur.com/mV6lomm.jpg)(https://i.imgur.com/qD9UWj6.jpg)(https://i.imgur.com/7Pu0SIb.jpg)
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Hi Richard
The closest I found are Hobbyking SK3 4250-350kv( SK-4250-350) which have a 25mm apart bolt pattern.
Shaft 5mm, max load 53Amps with max power 1190Watts on 5S.
Voltage range is 4-5S Lipo's with a weight of 266grams.
Would require two 70 plus ESC's.
The rpm unloaded 5180 which you car trim back on the throttle.
Lipo's 4S Zippy Compact 5800mah 40C(SKU9067000064-0).
The car 100Amp ESC's I use are not available at present.
Knowing Hobbyking they may have drop it from their line as with a lot of other products.
I do not like their water-cooled ESC's as they have no on/off switch.
As for run time depending on the driver good 1/2 to 3/4 hour.
It's a dam good looking model by the way!!!
Lucky Duck.
Canabus
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Ok so help me out here the idea was change from brushed to brushless because height in the boat is at a premium and nothing bigger than a 2x 3.2Ah SLA would fit so go brushless and lipo but your telling me that 2x motors running on 2x5800Mha 4S wont run much past 30 minutes.
I also noted you said 70A+ ESC's .... looking at this HobbyKing 80A ESC 4A SBEC obviously x2
I need the boat to be in the water for between 1.5 and 2 hours which is a normal boating session on our pond, just saying I don't want to be towed back to shore ;)
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Hi Richard
I am only questimate the run on flat out throttle and each boat and setup may vary !!!
I know that my 37" Perkasa's do not like turning over 1/2 throttle as they pull the bow down hard.
I have played with the balance point and changing the rudder angle, but not found a great fix.
Very fast in a straight line and wide turns !!
Canabus
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Thats why I was looking for some serious insight, but were you serious that twin motors on 2x 5800 lipos only has a run time of 30 minutes
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Ok taking the plunge and may god have mercy on my soul, cause this boat is a black cash hole as canabus says:
Items just now ordered:
All HobbyKing keeping it simple.
2x SK3 4250-350kv = £60.00 roughly
2x HobbyKing YEP 80A sBec = £80.00 roughly
2x Zippy 6200mah(SKU9067000069-0 = £106.00 roughly
I deal in roughly's so thats about £250 roughly
I hope for more than 30 minutes.
Will stay in touch as the boats refurb goes on.
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Hi Richard, I refer you to my third post, understanding these things will save you money and heartache later. Anyway you seem to have placed an order so here's hoping you're happy with the result. Four things come to mind immediately.
1. You don't mention a lipo charger, I presume you have some way of charging them when they arrive.
2. I hope you checked delivery is from UK or European warehouse, you might get hammered for tax otherwise.
3. Propeller size, since you seem to be aware of how brushed motors work, it's just the same for brushless. I.e a large prop needs more power ( amps) to turn it. So reducing the propeller size will reduce the power needed and give a longer run time.
4. Did you read some of other peoples ideas and installations from the search box I mentioned? There's a lot of good ideas and experience there.
Lastly, and not related to your order, making a Perkasa turn well can be addressed by experimenting with rudder shape, but most effectively by using a mixer to allow the motors to help. But that's for later, if you feel you need to go down that route.
Chas.
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ok, lets begin ...
1. Yes I own a HTRC HT100AC/DC Smart Charger is brand new so all good for lipo charging, I also got a stand alone balance board for it as the one that comes with it is ok but a bit flimsy I thought.
2. Everything is from the UK apart from the Motors, both of them are from Hong Kong and yes I got stung on import duty tax but more money than sense so no big issue motors will be here tuesday ... See below.
3. I'll change this if I need too but as its got a nice sized racing prop on right now i'll try this first and will change if need be.
4. a few I have read but what I'm struggling with meantime is power cables and gauge to buy, I have 3m of the following sizes available to me on hand 14awg, 20awg for internals and 24awg for lighting, but since its gonna be 2x 4S lipo running the motors and ESC's If i need better gauge like 8AWG i'll get that, 14.4v
5. Something not really touched on just how big of a ESC would this setup require
(https://i.imgur.com/4XUUDQP.png)
As another poster posted, Moving from Torpedo 800's to the 350Kv is one thing but I noted its going from 6mm shaft to 5mm shaft would I need to order new Couplings to be on the safe side and do they just come in one size fits all ?
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Wire size - look at the battery wire. Thats as heavy as you will need.
Coupling size. One size does not fit all. Various size options are available, with different ways of getting the combination needed depending on the make. Some are rigid one piece items with the right size hole at each end, some are three or more pieces with a selection of end pieces to match motor and prop shaft, with your chioce of bendy bits in the middle. Some are closely related to the solid type, but have the end pieces selected to order with the flexible bit in the middle ready fixed.
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There is a large list of prop and motor details over on the other site https://www.modelboats.co.uk/forums/postings.asp?th=45505&p=4 (https://www.modelboats.co.uk/forums/postings.asp?th=45505&p=4) scroll down about 4-5 posts. Richard you may already know this but scale speed on your boat is only about 10 mph.
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What will be interesting is the run time of 2x 5000mah 4S 40C Turnigy lipos through a 2x Turnigy Marine 70A ESC running to 2 of these motors ... 2x Turnigy Aerodrive SK3 - 4250-350KV
I know 60mm 2 blade Sports Prop
Just a guess would be nice as the boat is still in the building phase
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Richard I think you're asking a good question. For me your props are just huge for that hull (surprised nobody else commented) and I worry why one is painted green and 'tother red but hey ho. If it were me I'd knock them back to something more like 40mm'ish.
I just did a similar thing to you in as much as bought 8.4v Ni-MH 5Ah sticks for my Sangsetia. I bought motors for it so long ago I can't remember now but it was based on 12v SLA which was too heavy. I'm old school brushed though. I will put it in the bath and do a test to see how it goes, nobody can really give a definitive answer -I think you can wait for a week or a month if you don't try yourself. Trying for yourself is part of the fun. And If you're lucky enough to sail with the guys in Duthie Park, sure they'll let you re-charge batteries betwen sailings.
Rich
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Port and Starboard props hence red and green, they came like that so I wont forgot which was which.
Also to compensate for the weight change moving from torpedo 800 motors to lighter more powerful brushless motors and also moving from Solid lead acids to lipo's I've made a new bracket to hold the motors in place out of mild steel, so this very much does compensate the weight and also hold the weight more centred in the boat
(https://i.ibb.co/tPkk6VN/bracket.jpg)