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Author Topic: Running time guestimate...  (Read 334 times)

Richard Houston

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Running time guestimate...
« on: July 14, 2019, 02:04:24 PM »

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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chas

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Re: Sorry for the mixed question but here goes
« Reply #1 on: July 14, 2019, 02:44:49 PM »

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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Richard Houston

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Re: Sorry for the mixed question but here goes
« Reply #2 on: July 14, 2019, 03:11:51 PM »

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!!


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jaymac

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Re: Sorry for the mixed question but here goes
« Reply #3 on: July 14, 2019, 03:34:14 PM »

Error
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chas

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Re: Running time guestimate...
« Reply #4 on: July 14, 2019, 03:43:07 PM »

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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Richard Houston

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Re: Running time guestimate...
« Reply #5 on: July 14, 2019, 03:46:29 PM »

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 Ė 4289 at max efficiency.
Weight 595g (approx)
Shaft Diameter Ė 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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chas

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Re: Running time guestimate...
« Reply #6 on: July 14, 2019, 04:26:17 PM »

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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grasshopper

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Re: Running time guestimate...
« Reply #7 on: July 14, 2019, 04:58:58 PM »

Whilst I canít 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 youíre buying the lipos , buy some low voltage alarms at the same time, not expensive but could save the batteries..
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Richard Houston

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Re: Running time guestimate...
« Reply #8 on: July 14, 2019, 05:15:38 PM »

Whilst I canít 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 youíre 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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jaymac

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Re: Running time guestimate...
« Reply #9 on: July 14, 2019, 07:51:14 PM »

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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Richard Houston

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Re: Running time guestimate...
« Reply #10 on: July 14, 2019, 07:56:10 PM »

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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grasshopper

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Re: Running time guestimate...
« Reply #11 on: July 14, 2019, 09:58:07 PM »


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 batteryís 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, itís a lot quicker and actually a bit mental.


Just dont forget the LV alarms, itíll save you trashing the lipos by overdischarging them!
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jaymac

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Re: Running time guestimate...
« Reply #12 on: July 14, 2019, 10:37:14 PM »

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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canabus

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Re: Running time guestimate...
« Reply #13 on: July 15, 2019, 07:58:00 AM »

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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Richard Houston

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Re: Running time guestimate...
« Reply #14 on: July 15, 2019, 01:10:35 PM »

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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canabus

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Re: Running time guestimate...
« Reply #15 on: July 15, 2019, 01:23:52 PM »

Hi Richard
What size props and number of blades are on the boat??

Canabus
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Richard Houston

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Re: Running time guestimate...
« Reply #16 on: July 15, 2019, 01:56:47 PM »

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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canabus

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Re: Running time guestimate...
« Reply #17 on: Yesterday at 07:05:53 AM »

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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Richard Houston

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Re: Running time guestimate...
« Reply #18 on: Yesterday at 07:25:11 AM »

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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Richard Houston

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Re: Running time guestimate...
« Reply #19 on: Yesterday at 06:32:32 PM »

2 blade, 30mm from single blade to centre so total 60mm, pictured below ...


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canabus

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Re: Running time guestimate...
« Reply #20 on: Today at 08:08:44 AM »

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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