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[john44]

Hi guys, would 540 geared 6-1 ratio motors be o/k for the Billings Smitt Netherland
Also would the same motors be suitable for the Krick Düsseldorf fire boat.


John

[RST]

No experience with that model personally. I built mine on the smaller vac formed hull and scratch built with 2 385 motors.


But "540" is very generic to the "physical size". Why not a 545 or the other MFA derivative I forget would for slower tuning and higher torque?  The non-uk guys mention 80T 540 "crawler motors" but I think that's less common here.


Personally I don't use gearboxes or reduction drives unless absolutely necessary. There's usually a better motor to match as-is.


Not sure if that helps, plenty of debates on this on here already without the brush less options!


Rich

[unbuiltnautilus]

6:1 would be fine if running 12v, but a bit slow for6v/7.2v/7.4v. If so I would suggest their 2.5:1 units instead.
I cannot yet comment on the high turn crawler motors, although I am tempted to try one direct drive on a 50mm brass prop at 6v. My 'old school' brain is screaming at me saying don't do it, but talk on the forum, and my own attempted stall testing of one of these gives me some hope it could be an alternative, even with  a big 2" prop..

[roycv]

Hi I agree 2.5 : 1 is a good reduction.  Hi unbuilt... what about finding a cheap big motor like an 800 and run a big prop on a low voltage?  As a for instance you can run a biggish prop on a standard 540 but on just 2 - 3 volts and it works fine.
I do much the same but I run at a relatively low power on my model boats.
regards
 Roy

[unbuiltnautilus]

Hi I agree 2.5 : 1 is a good reduction.  Hi unbuilt... what about finding a cheap big motor like an 800 and run a big prop on a low voltage?  As a for instance you can run a biggish prop on a standard 540 but on just 2 - 3 volts and it works fine.
I do much the same but I run at a relatively low power on my model boats.
regards
 Roy

I am coming at this from a 'don't know, need to know' viewpoint. My current setup works but I am keen to know the limits of these high turn motors.

[Shipmate60]

If you are using the kit props you need about 5000 rpm.


Bob

[DaveM]

I've used the geared MFA motors and my main memory of them is the noise they make! They cost about twenty quid, too. I'm with UBN on this and would try something like this one first https://www.modelsport.co.uk/rc4wd-540-crawler-brushed-motor-80t/rc-car-products/401163
This motor has built-in RFI suppression and also appears to have pre-soldered leads and bullet connectors - what's not to like? The RPM at 7.2v is almost smack on Bob B's suggestion, too. Do note that there's a decimal point in front of that No Load current spec!
DaveM

[john44]

Thanks guys, I think the way to go is with the motors from Modelsport as Dave put a link to
Thanks Dave, at a good price as well. 


John

[DaveM]

John
I think many people will be interested in what you find out when using these motors in this model. Please keep us all informed.
DaveM

[GG]

Having used "Crawler" motors for several years now, I can say that they can be a good match for direct drive in suitable sale models.


Some results of motor testing have been found in my files and may be useful.  Have to say that the load tests were simply made by making a prop, shaft and motor rig, then lowering the prop into a bucket of water.  Not perfect but, as our American cousins are want to say, it gets you in the "ballpark", and further testing in models showed good correlation.


The results are shown in Tables 1 and 2.  The propellers used were the 2 bladed plastic "P" types which have a pitch/diameter ratio of, I think, about 0.8.  The currents drawn were modest even on the large P50 (2 inch diameter) props which would have seriously distressed the usual 27 turn motors on direct drive.


Another 70 turn motor was tried with four bladed brass propeller with a diameter of 2 inches.  Even with a relatively course pitch, more suited to a steam engine, it only drew 4 Amps on a 6 Volt supply and really churned the water around.


Having praised Crawler motors it must be said that even they can be overloaded with too large a propeller and still need a smooth drive line to work well.
Glynn Guest

[unbuiltnautilus]

Very interesting data there. They look like a good practical solution to the relative lack of geared motors out there, without going down the more expensive, low kv brushless route. The only thing to check now would be heat generated over say a five minute sustained run. Low current alone is a good sign, but the motors may still be being overloaded, generating an excess of heat. Time to retrofit the corvette again maybe?!

[Subculture]

A general good rule for electric motors is to run no lower than around 75-80% of unloaded RPM. Below that and the motor is badly matched.

[Tug Fanatic]

Having used "Crawler" motors for several years now, I can say that they can be a good match for direct drive in suitable sale models.


Some results of motor testing have been found in my files and may be useful.  Have to say that the load tests were simply made by making a prop, shaft and motor rig, then lowering the prop into a bucket of water.  Not perfect but, as our American cousins are want to say, it gets you in the "ballpark", and further testing in models showed good correlation.


The results are shown in Tables 1 and 2.  The propellers used were the 2 bladed plastic "P" types which have a pitch/diameter ratio of, I think, about 0.8.  The currents drawn were modest even on the large P50 (2 inch diameter) props which would have seriously distressed the usual 27 turn motors on direct drive.


Another 70 turn motor was tried with four bladed brass propeller with a diameter of 2 inches.  Even with a relatively course pitch, more suited to a steam engine, it only drew 4 Amps on a 6 Volt supply and really churned the water around.


Having praised Crawler motors it must be said that even they can be overloaded with too large a propeller and still need a smooth drive line to work well.
Glynn Guest

Glynn

Something very odd here.

The 75 turn motor should have a lower kv than a 65 turn but yours appear to be the other way around. More turns should equal a slower spinning motor. Using your data as posted:
75 turn = 5831 / 6 = 971kv
65 turn = 5044 / 6 = 841kv

I would normally expect a 65 turn 540 sized motor to be around 930kv and a 75 turn around 800kv. Yours results are transposed.

I am also very surprised that the 75 turn motor has both a higher free running current and a higher stall current. But then when you put a prop on them the results are as expected with the 75turn using less amps . Hmmmmmmm.

Were they similar motors?

[GG]

Tug Fanatic,
                 Yes, the motors were of a different makes.


You have noticed that the stall currents, both on a 6 Volt supply, were different with the 75 turn motor being significantly higher than the 65 turn one.  So, despite having a greater length of wire around each pole, the 75 turn motor must have a lower armature resistance.  Assuming both motors use copper wire, the wires in the  75 turn one must be a larger diameter.  The magnets may also be of different strengths along with the variations in any mass produced product and I'm not surprised that they don't behave perfectly.  As if to illustrate this, later tests with a different make of 70 turn motor did not produce results that fit in-between these two!


It was not unknown in the early days of electric RC car racing for keen (or maybe desperate?) people to buy many standard 27 turn 540 motors, test them to find the small percentage that were "Rocket Ship Motors".  That is the perfect combination of materials, assembly and balance that would out perform apparently identical motors.


The main point of this posting was to illustrate that that "Crawler Motors" are available and can make suitable direct drive systems. With of course the usual proviso of a suitable propeller and good alignment.


Thanks for taking the trouble to write.
Glynn Guest