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[cassf1]

Hi all

I am new to RC and have a few questions i hope someone can help with, i have decided to use a old drill motor for my build its from 18v dewalt drill so i think should have plenty of power to run bait boat I'm building.

One question is if i use with 12v lead acid battery how many amp ESC do you think i will need. (speed controller and battery from drill not available)

Also i plan on using 6v battery for the receiver as i been told not good idea to use 12v for this (RX has BEC), am i right i thinking that all i would need to do is cut the red wire from the ESC before this plugs into RX

thanks for any help Craig

[OMK]

"Also i plan on using 6v battery for the receiver as i been told not good idea to use 12v for this (RX has BEC)..."

If you intend running the receiver from 6 volts, I'd recommend that you remove or by-pass the on-board drop-down voltage regulator (BEC) from the receiver itself.
If you intend to run the receiver from 12 volts, then leave the regulator intact since its job is to reduce the 12v input down the Rx's working voltage of 5 or 6 volts. (Bear in mind that the BEC itself needs as many as 2 or 3 volts from your battery, which means a BEC receiver needs at least 8 or 9 volts in order to operate... which in turn means your 6-volt battery would not be enough juice unless the BEC gubbins is by-passed first.)
The major downside to using an Rx with BEC is that the receiver will become useless once your main 12 battery is depleted, whereas a separate four-cell or five-cell battery supply for an Rx without BEC will at least allow you to still work the rudder if you should get into a bit of a pickle.

As to the DeWalt motor, it's pretty difficuly to recommend any particular ESC since it's hard to guess how many amps it might pull when under full load. You will have to load the motor first then measure the current with an ammeter in series with one of the 12v supply leads. And being that you are driving an 18-volt motor from a 12-volt supply probably means that the motor will not be operating at full efficiency anyhow. Therefore, you might get away with a cheapo bog-standard ESC... I'd take a guess of one rated at least 15 to 20 amps.

[barryfoote]

Hey thanks for that PMK and cassf1, I am thinking of running my latest tug off an 18 volt drill battery.......Now I have the answer without asking the question....

[OMK]

Morning, Baz.
I take it that you are now well familiar with using your multi meter, then?
I guess you must be, because we haven't heard any tales of you electrocuting yourself, or smoke coming out your ears, etc..... 

Would be interesting to learn how much current those 18v drill motors pulls. Perhaps you will keep us posted on that one.

[FullLeatherJacket]

BUT

Read the section on Bad 540 motors here; check the motor you are proposing to use, and be absolutely sure you know what you might be letting yourself in for.

http://www.modelboatmayhem.co.uk/Common/Electrics/How%20Fast.htm#Fast%20motors

Frankly I've never understood why some folk will happily pay umpty squillion quid for scale model kits and fancy radio sets and then either butcher dead drills or scour scrap-yards for cheap motors. "Yes - I'd like a Ferrari 308GTB, but can I have a Lada 1400 engine in it 'cos it's cheaper and I've heard they're better at low revs....?"
 
(And with that can of worms well and truly opened, M le Jaquet retires for a relaxing weekend in South Shields.............  )

FLJ

[OMK]

Blimey!... That Mr. Jaq-yoo-ette is bang on the money... again.

I hope you're ear-wigging, Messrs Footski and cassf1, and reading that piece which FLJ mentions, because right there at the bottom of the page, the very last sentence... "Personally I wouldn’t install it in anything but a wheelie bin"... pretty much says it all.
Which brings me round to another question....
I thought DeWalt gear was supposed to be the cat's whiskers, meant to be the best gear since ever. So how come I'm hearing about all these defunct DeWalt drills of late?


Note to FLJ:
Here's to a well-earnt rest, oop North in sunny S. Shields....... the land of Bluebirds and brown ale, wye-aye.

[barryfoote]

Well I guess that puts me in my place. Looks like I am going to run my new boat on one of FLJ's motors...

That is such a shame as I was so looking forward to keeping PMK posted on amperage and current draw........

[catengineman]

Nothing stopping you building a test bed and carrying out those tests to satisfy yourself and the good man!

Project in the making of future knowledge 

R,

[cbr900]

Dewalt gear used to be excellent, some of it stillis,
but there has been a lot of failors for some reason.
One of the mates is a gyprocker, he bought a dewalt
and two batteries so he could use one and charge the
other, but it only lasted 9 months, it was also the dearest
so he went back to Makita, they seem to last for two years.......

Roy

[OMK]

I bought a couple Makita drills shortly after Makita started making a name for itself here, but oddly enough I just couldn't get on with them. One was 240-volt (which died after just three months), and the other was a cordless jobby - and that too died in less than a year from purchase. Of the DeWalt gear I've used I've never had any problem, other than needing to replace the batteries a couple times. It seems good, reliable gear and stands up to the abuse it gets from British electricians. That's why I was surprised to hear of people having problems with their DeWalt stuff........... or were they just stripping the motor from a perfectly good drill in the hope of finding the ultimate power plant for their models? 

[ray123]

hi all  ive installed a 18volt ''old'' drill motor (slighty bigger size than a 540)  in my springer tug   & on 12volt it draw's 1.2 amps (no load) it's very smooth & quiet & also has fan inside (didnt even get warm) for about 4hrs  running   
regards ray

[Roger in France]

I have some great De Walt gear. Particularly my radial arm saw which gets used and abused for all kinds of jobs. Super, do not know how I could get on without it.

I was also a fan of Elu gear (I have a router, a belt sander and and a plane) but since Dewalt took them over I find it difficult to obtain spares. I have just broken the dust extractor attachment on the belt sander and I cannot find a replacement. It is currently on the bench being stuck with epoxy and so I am keeping my fingers crossed for tomorrow.

Just like FLJ I find some of this cannibalising perplexing. Why, decent motors are cheap enough and are known quantities? I think it is like the classic answer to "Why climb mountains?"......"Because they are there".

Roger in France

[OMK]

Ray, just out of curiosity, did you put your Springer in the bathtub to get a reading of the current with the motor loaded? If so, how much current does it pull with the prop' in the water and motor running flat-out?

[ray123]

  hi pmk no sorry  i didnt get a reading of the amps on the motor ''loaded''   i have a 35mm prop (brass)  direct drive  i only wished i had more of these motors   regards ray

[nick_75au]

Ive found most drill motors are high stall current high speed motors with around  27 turns of wire like R/C buggy motors, and buggy motors need to be geared for useful duty in anything.
I put one in a Springer on a 40 mm prop and it draws 10 plus amps,r emoved it promptly, put in a  motor designed for low rpm same size and it draws 6 amps, the drill  motor got very very hot, the 6 amp jobby got warm enough that I watercooled it. It remains in the boat, I prefer the brushless in my other but the local supplier here in Aus. John Darke has also a very suitable motor with similar performance.

http://www.robotmarketplace.com/products/BP393111-01.html

These are the specifications on the "old style" motor I assume you may have, check out the stall current

Nick

[cassf1]

Hi all

Thanks for all your replies, just to put some of your minds at rest this drill was stripped because it has been sat i the shed for over a year now as the battery died. I also have a 24v Bosch which seems to be enough for what i use it for.

I thought about using it because i thought this motor would have plenty of torque and because of dewalt reputation, i have also seen that these get used in RC robots and yes main reason its there.

Now a quick question i know you guys can answer in a flash, i have a  Futaba R136F 6 Channel Receiver 40MHz how do i bypass the BEC so i can run motor on 12v is it just a case of removing the red wire and plugging into channel 1.

Thanks Craig

[cassf1]

Sorry PMK i build deisel engines machanical is more me than wires they can burn out instantly lol.

heres what i was thinking.....

12v battery connected to ESC (does the ESC need BEC)
ESC connected to motor
Plug from ESC into channel 1 (does red wire need removing/cutting)
Receiver Futaba R136F 6 Channel 40 MHZ FM plugged directly to 4.8v 700mah Ni-Cd

Is this correct?

Also how do i test motor for amps, as multimeter only has 10a rating as do most i have seen.
I will keep you posted as i get info and time to test

[OMK]

On reflection, rather than remove the BEC regulator, maybe it's easier just to leave it there after all. As long as you stay at 6 volts maximim, then simply connect your 6 volt battery where the 4.8 battery would normally be. And yes, you are right about pruning the red wire. But rather that simply cutting it, an alternative way would be to lift the centre plastic tab on the plug itself, then just pull the red free. It means you only need to push the wire back into the plug if you should need the BEC again.

Re, 10A meter: Bummer about that, because in order to get your meter to read higher current means you would need a shunt resistor across the input wires. In other words, a resistor connected in parallel with the red and black leads, while at the same time connected in series between your battery and ESC. And not just any old resistor. Shunt resistors are usually big, bulky, cost more than a bog-standard resistor and dependant on close tolerance ratings. In other, other words... it's not the sort of component you can just grab from the shelf. Sure you make one, but the overall accuracy wouldn't be up to much. And HEAT, they burn up lots of heat. And when they get hot is when their internal resistance starts to go down, which ultimately means you end up with readings which are nowhere near accurate.

Sorry, bud. You should have spent an extra fiver and bought one with a 20A jack on the front panel.

 

[FullLeatherJacket]

It may be that the particular motor in that De Walt drill is OK, but my original post was to draw attention to the fact that a lot of power tools are powered by motors which are (IMHO) grossly unsuitable for direct drive on model boats.

Ref that shunt, here's a link passed on to me by David Harrison of Model Solutions. Just check out the exact wire diameter; the one quoted is AWG which isn't a direct equivalent of metric.

http://www.rcgroups.com/forums/showthread.php?t=393591

FLJ

[malcolmfrary]

All of the DMMs with a nominal 10A max that I have come across will survive a brief encounter with up to 19.99 amps, and read it accurately enough.  Strong emphasis on BRIEF.
Alternatives are to use a car ammeter as from a local friendly scrapyard, or to test via steadily increasing fuse values.  If the fuse blows, the motor is taking more, if not, less.

[cassf1]

Hi all

Thank you for the answers they have all been very usefull.
I had thought about finding the amps by using fuses and this looks to be the easy way.

[cassf1]

Hi all

Quick update i managed to test this motor, with no load it pulls 2.45amp i used pliers with felt and tried to slow the the motor which was hard as it just burned through and melted the felt so i tried to use folded over card this motor is very powerfull and hard to grip as only had a few seconds before it set fire to the card anyway with the most grip i could get on it which was squeezing tight it pulled 9.72amps

[stallspeed]

You can do the tests at reduced voltage and multiply your reading.

[cassf1]

Hi

Thanks stallspeed do you mean that will be easier to grip with lower volts then double the amps i read if 6v battery is used

[stallspeed]

I was thinking more like one or two high power nicad sub-c cells but yes, x2 your 6 volt measurement.

You can attatch a long arm ,like a servo horn, and get a weight measurement with digital scales if your that way inclined.
Torque = Force x distance.With dc motors the figure you get that way is inaccurate.It is done graphically with a motor-generator pair.

A stall torque and current figure with your no load current and rpm is all you need to define a low volt dc motor
It's all in the Mabuchi website. http://www.modelboatmayhem.co.uk/forum/index.php?topic=14273.0