motor size

[ernest2]

hi! i have a problem with my boat. it is powered by a 540 stock mabuchi with a mini jet drive from graupner. well its a bit disappointing. although i am not expecting it to be very fast, i am at least hoping it will just plane, but i cant. its is only powered by a 6cell pack. i dont want to upgrade because that would also means upgrading my esc which at this moment, i dont have money for.

will making changes for the motor helps?

i am thinking of buying a graupner 400 or 380 size. will this helps? because i observe that the 540 doesnt turn too many rpm. will a 400size motor rated 6 volts turn faster when i power it with 7.2 volts compare to 540 motor powered with same battery pack?

thanks!

ernest

 

[brooks93]

what you need is a better 540 size motor

a 380 or 400 will have more rpm but, not more torque. So you would actually do more harm then good

maybe try a 19 turn stock motor or a good 27 turn.. the silver can you have now has nothing on a good 540 stock motor

 

[himmelman]

Hi Ernest

A 540 stock motor is quite low powered and very low rpm when compared with modifieds, but it should still have more torque than a regular 380 or 400 motor. A 380 or 400 may look impressive on paper with its high rpm per volt figures but it doesn't have the rotational force to spin a descent sized propeller, or in your case, an impeller.

A large prop would be required to produce a large thrust cone to move most boat hulls at a decent speed. The boats I used to run with the stock 540 and 550s would get up to 12-14 mph tops.

How large is your boat? Most 540 motors are great with a small hull 17 - 22 inches. When I tried, it wouldn't push my Kyosho Jet Arrow (27 inches) any more than 12 mph.

Is there anyway to adjust the thrust angle on your boat? Do you have trim tabs? Even moving some weight towards the front might help.

It would be nice to tune the hull properly to take full advantage of the lower power, and then we could work on upgrading some stuff.

Feel free to ask more questions, its nice to see so many people interested in model boating, and your questions are great.

Greg

 

[ernest2]

in a boat that is 20" long and weighs 1.2 kg. (about 2.65 lbs), will torque matters much? please bear with me, this is my first boat so experience wise, not much.

i really thought that the jet drive needs more rpm on it, that i didnt get from my 540. my problem with upgrading to a better motor is that the esc is limited. it is only rated up to a tamiya 540 sports tuned motor, which i dont really know how many turns. but its the only motor upgrade, apart from the graupner thats available for me.

 

[himmelman]

A 20" boat should get on plane without a problem. I don't have any experience with jet drives so I'm not sure what is required. It soulds like you're right about the rpm - maybe the jet is a little less efficient with moving water and requires a higher rpm.

A stock Reedy or Trinity with ball bearings should be fine with your ESC and should give more power. I've been very happy with my 19 turn Trinity - but it may hurt your ESC.

I'll see what I can find out for you -

in the mean time...Does anyone out there know jet drives?

Greg

 

[ernest2]

yes, jet drives are less effecient than props and requires higher rpm.

heres a pic of it running.

 

[Andrewg]

Ernest hi

first thing is remove all the weight you can. The boat needs less power to plane and as it is pushing less water and lifting less weight it will be faster and handle better. This means cut you esc and pack wires as short as possible. Remove any brackets not being used and if possible replace steel screws with aluminium.

2nd the biggest power increases with a 540 come two ways - first by running it in to reduce drag from the bushes and the match the comm and brushes so the motor can use more power. All you need is your motor a glass of water and some brasso & light machine oil. First put brasso in the bushing on each end of the motor - put the motor in an electric drill hold the motor and run it till the brasso is black - wipe out the dirty brasso and do this again. This polishes the shaft and bushes for a better match and less drag

Put the motor into a large glass of water - just enough to cover the motor when it is running. Run it using either the drill as before or a penlight cell. Do this till the water turns grey. The water softens the bushes and lets them shape to the comm without damage and cleans out the brasso. Put in fresh water and repeat this. Dry the motor as best you can witha rag and hairdryer and oil the bushings.

You will find the motor runs faster by 1k-2k rpm under load

3rd add 1 cell to your pack. This gives a minimum 15% extra power and rpm.

4th remove the impellor and very carefully sharpen the leading edge with 600 grade wet and dry dont change the shape just sharpen it - make sure the jet surfaces are smooth and match up well - if you have a guard over the inlet remove it.

5th sharpen the transom where it meets the planing surface. This needs to be sharp so the water breaks away easily. The sharper it is the slower the speed at which it will break away. You can add body filler. The best and lightest way is to scuff the roounded edge and then put tape across the transom so it hangs past the planing surface. This will create a triangular gap between the tape and the curve where the transom meets the planing surface. Fill the gap with CA so it is a little overfull - zap it or let it harden and sand it down so it is flat with the bottom of the hull and with the transom - it should make a sharp edge.

good luck

 

[ernest2]

thanks for those tips andrewg. tips no. 4 & 5 are certainly to be done, i didnt think of that. however, this is an old motor from a rc car, so i dont know if tips 1&2 still applies. what is brasso by the way? and tip 3 is out of the question because my esc can only handle 6 cells. thanks a lot, i will certainly do tips 4-5.

ernest

 

[Andrewg]

ernest brasso is metal polish

try it in the bushes (once only) and give it a 5 minute water dunk it cleans the motor up

 

[ernest2]

ok i'll try that. thanks a lot.