Brushless for Slow-boat

[patmat2350]

OK, I'll admit it... every time I see the "-less" after "brush" in threads here, my eyes glaze over and I fall into a stupor... so let me start from scratch here (instead of researching other threads... :rolleyes: ).

If I want a big "slow" brushless outrunner that has the torque to direct drive, say, a 4" prop at 5000 rpm in a tug, what should I look for? Let's see, if I stick with 12v, that's a Kv of around 415. Don't care about lipos or lightness, it's a tug!

And controllers? Reversible of course...

[der kapitan]

Pat, I'll admit that I know virtually nothing about brushless motors, except that they can make a boat go really fast---. :o

So I hope this thread will develop into a learning tool---. :)

[Hoghappy]

My first question is why?

Why do you need a brushless motor in a slow boat?

Speed/weight/power comsumption are the reason behind the brushless set up and that is not a concern in a big tug...is it?

I know.....it's a just because! ;)

Capt. Crash

[patmat2350]

My first question is why?
...
I know.....it's a just because! ;)

Capt. Crash

You got it!
Don't want to be left off the technology bandwagon...

[toesup]

If I want a big "slow" brushless outrunner that has the torque to direct drive, say, a 4" prop at 5000 rpm in a tug, what should I look for? Let's see, if I stick with 12v, that's a Kv of around 415. Don't care about lipos or lightness, it's a tug!

And controllers? Reversible of course...

Seeing as i 'do' cars (brushless) as well as boats, i will start the ball rolling.

Brushed = slow.
Brushless = fast.

All the car boys go to brushless as the RPM for a brushless motor is way higher than a brushed motor.
Putting a brushless motor in a tug would be like putting a Ferarri V12 in to a Chevy truck... interesting, but a waste of time and effort.

Reversible ESC's ARE available (as well as forwards only from the fly boys) as well as complete set up's, motor - ESC as a matched 'item'.
Forwards / reverse ESC are from the likes of Mamba and Novak
Forwards only from Castle.

Sorry Pat, to learn more you are going to have to delve in to the Car and plane forums... :eek:

[pkboo]

Pat, I´ve also had good experience with these guys elemodeldotcom, which offer a little more in reversible ESC´s. They are from China and not so pricey as to what Toes indicated. As far as i could/can gather the quality is OK. Boo.

[Kmot]

Pat, you can buy a complete RTR brushless system designed for "slow" from Novak:

http://www.teamnovak.com/products/brushless/crawler_system/index.html

[blckgnx]

I gotta jump in here too. All of our info put together should get us somwhere! Toesup in correct for his usage, however, us Rockcrawler/Tugboat guys prefer Brushless because of the "Low" end power, durability, and "less"power consumption. Kinda like a Lathe motor vs 7 turn brushed motors. Like Kmot recommended, go the the Novak site, lots of info there!! My two bits worth, now I can go get my coffee. Ron

[Hoghappy]

Pat, you can buy a complete RTR brushless system designed for "slow" from Novak:

http://www.teamnovak.com/products/brushless/crawler_system/index.html

That's pretty cool! :cool:

Is 2700 enough revs? ....oh wait....bigger prop! :rolleyes:

Capt. Crash

[Shaun Hendricks]

Brushless is the way to go for efficiency, light weight and little to no maintenance. Outrunners are just less expensive to manufacture than inrunners and have the bonus torque to turn large props or tires easily. They lose the rpm race in larger sizes but in some micro sizes they scream and power turbine blades with them.

Anyway, you can go cheap or go expensive or just well made middle of the road. I'll start you with the latter because they also do great data sheets (not geared towards boats but you can get a good picture of what they can do from them.)

This motor is the equivalent of a .40 - .60 nitro motor:
http://www.allerc.com/product_info.php?cPath=7_76_77&products_id=1911

This one has a little more torque but lower Kv (405) so it would be in the .60-.80 nitro replacement class:
http://www.allerc.com/product_info.php?cPath=7_76_77&products_id=1914

The same site has cheaper options and more expensive ones. I tend to value the Hyperion line because they give attention to detail like the high-end guys but have a nicer price point.

[patmat2350]

Is 2700 enough revs? ....oh wait....bigger prop! :rolleyes:

Capt. Crash

That's Kv-- 2700 rpm per volt... and it only takes up to 7.2v (not 12v).
Say I use a 6v gel cell, then it would run 6 x 2700 = 16,200 rpm... needs 3:1 reduction for a 5000 rpm 4" prop... so it fails the direct-drive test.

[Hoghappy]

That's Kv-- 2700 rpm per volt... and it only takes up to 7.2v (not 12v).
Say I use a 6v gel cell, then it would run 6 x 2700 = 16,200 rpm... needs 3:1 reduction for a 5000 rpm 4" prop... so it fails the direct-drive test.

See...hang out here long enough....ya learn something! ;)

Capt. Crash

[Umi_Ryuzuki]

My confusion has been how to match motor and batteries.

Charging seems to have become hi-tech computerized.(except the flower pot or bar-b-que)
Motors seem to be random choice.
ESC seems to be match the amp draw of the motor(look for auto voltage sensor)

Am I missing everything here?

:confused:

[Hoghappy]

Am I missing everything here?

:confused:


Rip.......$$$$$$$$$$$$$$$$$.... :eek:

Capt. Crash

[patmat2350]

Well, cross battery complexity off the list. ESC and motor don't care where the electrons come from... so except for those who need excessive lightness (racers and micro-RC), same old gel-cell and/or NiMH chargers apply...No need for expensive LiPo. Smart chargers are still a good thing.

And just like brushed, brushless motors have a Kv value (how fast do they spin, unloaded, per volt), and a max current capacity. So you still need to know how fast to spin your prop, and whether you need gears or not.

Choosing an ESC seem to boil down to three things:
1. Current capacity... I believe ESC makers use a random number generator here, most ratings are highly suspect;
2. Reversible or not
3. Some kind of logic/sensing matching to motor? (see the wikipedia article on Brushless). ESC needs to know where the rotor is relative to the poles in order to energize the correct poles next (for proper rotation, acceleration). Some motors have sensors built in that report position back to the ESC... other ESCs infer position from the changing back-EMF on each pole.

And there are probably many finer points beyond that!

[pompebled]

How's this for direct drive?

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=2102&Product_Name=TURNIGY__50-55A_400kv_Outrunner_(Eq.4120/18)

Still looking for a matching ESC...

Regards, Jan.

[pkboo]

My confusion has been how to match motor and batteries.

Charging seems to have become hi-tech computerized.(except the flower pot or bar-b-que)
Motors seem to be random choice.
ESC seems to be match the amp draw of the motor(look for auto voltage sensor)

Am I missing everything here?

:confused:

Umi in what I've learned from it so far is what Pat says, batteries don't matter. Because the ESC is the expensive part, most of the times, always have that one on a higher amp than the motor. Cool as far and as much as you can (FE tend to watch for weight here) :cool: Magnets count, those neodynium or...something magnets have gradation in the quality, it seems that the Czech's (Axi) are one of the best the reason why their motors are so expensive. You get more torque, speed and max rpm per weight compared to brushed motors. As with brushed you will have to test your prop that go with the motor and that's where I'm at at the moment. The motor is worthless now but it only cost like €5. Boo

[Umi_Ryuzuki]

So is there any concern for over discharging a
battery too quickly these days?

I have been trying to understand the "C" ratings... :confused:

[tsenecal]

Having actually done this (check out my "Brushless Mr. Darby thread" )

http://www.rcgroups.com/forums/showthread.php?t=888430&highlight=brushless+darby


here is what i have found:

1) castle creation makes two really nice ESCs, the sidewinder micro, and the mamba micro pro. they replace the original mamba. they are called micro, but they can handle a 3 cell lipo (12 v) and 30 to 35 amps. they have forward and reverse, and are fully programmable using the castle-link software and usb connector.

2) patmat is right. you basically have to match the original RPM with the new. I bought motors that have a 615kv rating, I should have gone down into the 400-500kv range. even with that, I will say that I am still using the same belt drive that I used in the boat in its original brushed form (i would need a motor with a 120-150kv to go direct drive).

3) the advantages I have been able to see are the following:
using the castle-link, I am able to tailor the throttle curve and other parameters of the ESC/motor combo so that the tug has incredible low end speed. I can literally watch individual blades rotate as the propeller(s) spin(s). I am also seeing much greater efficiency. I have not completed all my tests, but in initial water trials at the pond, average cruising speed on the boat draws between .5 and .7 amps per motor (yes, less than one amp). For comparison, the Dumas 12 volt motors that were in it before drew about 1.5 amps at the same speed. My 45 amp (nominally rated) 12v battery could run the boat for more than 25 hours straight. As far as further testing goes, the rock crawler guys seem to think that the brushless outrunners have an order of magnitude more torque than the original lathe motors they used before, so I am definitely going to do more testing to see what kind of bollard pull vs amp draw this thing has...

4) downsides:
all of these brushless motors in the 400-600kv range are made for .90 size airplanes, so they have stout shafts. I searched to find a reasonably priced motor with the smallest shaft I could find, and I still had to replace the drive shaft components that were originally bought for the 1/8th dumas shafts with 5mm stuff for the new shafts. some of the brushless have 6mm, or 8mm, and some go as high as 12mm (12mm is 1/2"!!!!!) nobody makes a u-joint for a 12mm shaft!

[boater_dave]

I have only just begun to use Lipos in my stuff, but I know that when an ESC says it is Lipo capable they refer to a low voltage cutoff so the battery doesn't burn if discharged too far. A sticky problem with Lipos, as I understand. Some ESC's are programmable, and that low voltage feature can be turned off if powering with an SLA. One more advantage of a brushless motor is the adsence of armature arcing and less radio interference. Be careful of the term reversable in brushless ESC lingo. Switch any two of the three motor wires and the motor spins in the opposite direction. Many new ESC's have true reverse, but read the specs carefully.
As for matching batteries to motors, the battery C rating should be at least that of the max draw of the motor, maybe even twice. More doesn't help so why pay for it? Most of the time the C value is way higher than scale boats need anyway. My tiny PCF has a 7.4v/500mah Lipo pack rated at 5 amps max discharge (10C). The boat uses about 1 amp stalled (both motors total). I am using it because it is light (this boat falls into the micro catagory).


Dave

[Shaun Hendricks]

C ratings are fairly easy once you get used to the concept.

C is the discharge amount in amps equal to the amp rating of the battery. Stay with whatever the rating is in.

A "5C" battery that has a 2400mah rating can only safely discharge (2400*5=12000mah or 12amps). Same battery with a 20C rating can discharge (2400*20=48000mah or 48amps), big jump.

Where it gets complex is that cheap battery companies give you a max peak rating for the C rating, and good (read: expensive) battery companies give you a max sustained rating for a C rating. Good batteries can usually peak higher than their C ratings for short periods- important in planes, not so important in boats.

So, realize that if you get a battery from "Joe's LiPo Shop" you can probably only safely run at about 75% C rating for a continuous state. Get something from Thunder Power or another company that guarantees its C ratings as continuous state, you can run them at that rating.

A lesser known fact is that generally speaking, a battery can be fast charged at 1C but not recommended for LiPo. Fast charging also degrades life of the battery. Best charge rates are at .5C or lower for longer life of battery. Always stop charging at Delta-V and charge again just before use for max juice.

Those are the tips taught to me and seem to work really well.

[nick_75au]

Hi Patmat,
Im a convert to brushless, every new boat I do now will be unless it to be a real cheapy, brushless controllers are around the same price as brushed ones these days, the motors as well.

Your calculations are good, my Springer uses a 1000kv (KA22-20l) in direct drive on 6 volts and turns 6500 rpm unloaded and draws 3.5 amps maximum on a 40 mm prop holding the boat back, the motor is rated to 21 amps speculating here but I think it will turn a 65 mm prop and still be well under the amp rating (25% bigger prop double's the amps?)
The motor is less than half the size of a 550 and draws just under half the current of a 27 turn long can motor and has more power.

The speed controller is a Pulso brand but there are 3 or 4 other brands that are the same controller. Its rated at 40 amps, I don't water cool it in the Springer even though its provisioned for it.

I use the same controller for a 3200 kv (KA450H) motor turning a 35mm prop and 2.7:1 reduction on 12v (10 cell NiMH), and 25 kph maximum speed in the Miami Crash boat hull.
Regards
Nick

[Umi_Ryuzuki]

C ratings are fairly easy once you get used to the concept.

C is the discharge amount in amps equal to the amp rating of the battery. Stay with whatever the rating is in.

A "5C" battery that has a 2400mah rating can only safely discharge (2400*5=12000mah or 12amps). Same battery with a 20C rating can discharge (2400*20=48000mah or 48amps), big jump.

Where it gets complex is that cheap battery companies give you a max peak rating for the C rating, and good (read: expensive) battery companies give you a max sustained rating for a C rating. Good batteries can usually peak higher than their C ratings for short periods- important in planes, not so important in boats.

So, realize that if you get a battery from "Joe's LiPo Shop" you can probably only safely run at about 75% C rating for a continuous state. Get something from Thunder Power or another company that guarantees its C ratings as continuous state, you can run them at that rating.

A lesser known fact is that generally speaking, a battery can be fast charged at 1C but not recommended for LiPo. Fast charging also degrades life of the battery. Best charge rates are at .5C or lower for longer life of battery. Always stop charging at Delta-V and charge again just before use for max juice.

Those are the tips taught to me and seem to work really well.

Shaun,

Thanks, I have read a lot of lipoly tech sheets, and that is the clearest
explanation and math I have seen yet...

[pkboo]

Umi, as far as I know you don't need to worry about your discharge rating on a NiMh or NiCad's pack. As long as you don't overheat these in the discharge, like the charge, you're OK :) What you need to know is if you can discharge at the rate the motor needs you to discharge. I'm using 4500mAh packs at 70A CC, that's like having a turbo on your carb, you need the speed you get the juice :D instantly! Boo

[Umi_Ryuzuki]

Yes, but it is the Lipoly packs I needed help understanding.

I never worried about how fast I discharged Nicads.

Lipoly will lose up to 300 grams out of the boat in just battery weight.

:)

[Shaun Hendricks]

Well, NiMh is more sensitive to discharge rates than NiCd. I *have* vaporized some NiMh AA's with over drain. I've also overheated a 6cell SubC NiMh pack to the point of damaging it. I've yet to damage a NiCd pack with over drain but dead short one and find out it can be done!

Lead acid can be tricky. Many gell cells actually have very low discharge rates compared to their storage capacity, fractions of "C" value. Liquid acid batteries tend to have large discharge rates by comparison to their storage values. Your standard car battery can dump 500 amps to a load until it's 30000mah (30amp) capacity is drained.

All batteries are dangerous when over drained. They overheat and can 'blow up'. LiPoly gets the majority of the fingerpointing but it's only the most sensitive chemistry. I've seen a video of a sealed lead acid gell cell detonating because it was over drained. It was actually far more explosive than any LiPo detonation I've seen.

[Rex R]

my .02. working on converting a brushed boat over to brushless 380 12L w/ cc barracuda 80 esc...the other night I reprogramed the esc and couldn't resist plugging everything together and trying it out (bench test) forward...check, reverse...check. note the rotation check was done at low speed(had to, prop shaft isn't connected yet :)). is the 80amp sc overkill...perhaps but it will give me some fudge factor in case of weeds. usuall rule of thumb is not to run things over 80% of capacity if you want things to live a while.

[nick_75au]

I GPS-ed the Brushless springer today (6 volt) a massive 4.2 Kph (2.6 Mph) max speed ;)
Regards
Nick

[LtDoc]

"a random number generator"... Oh, I like that! Wish I'da thought of it. Unfortunately, it's closer to the 'truth' than most people think, I think.

Since I don't really have a need for 'fast', I haven't gone brushless. (Being cheap also figures into that.) But you've opened up another way of thinking about it, so I'm not real sure I still like you anymore Pat (remember the cheap part). Now I'll have to figure a way of fooling my wallet...
- 'Doc

(good topic, by the way!)