Hot hot hot

[Chris HoverdParticipant @chrishoverd48135]

Hi all, I'm not talking about the fantastic weather we have been experiencing, it's more a problem with my motors and speed controller set up I have recently installed in a Drumbeat of Devon.

I have installed twin graupner speed 600 motors, with two mtroniks 15amp speed controllers each supplied by their own 8.4 5000mah NIMH battery packs. The throttle command is through 1 channel via a Y lead, and as specified, I have removed one of the leads that would supply power to the receiver so that only one speed controller is powering the receiver via the BEC. I cannot understand why the motors and speed controllers are getting extremely hot, even to the point of melting the vac formed motor mounts installed in the hull. I would appreciate any advice given, thanks!

[Chris HoverdParticipant @chrishoverd48135]

[Tim CooperParticipant @timcooper90034]

Chris

As someone will be able to tell you there are Graupner 600 of differing kinds. I have 2 600 Eco in a Tamar lifeboat running on 9.6 v, I did install 2 computer fans above the motors.. Another boat uses 2 Graupner 600 12v BB motors.

What size are the propellers.

Tim

[Charles OatesParticipant @charlesoates31738]

Hi Chris, if things are getting so hot, dangerously hot in fact, I'm sure your installation is drawing too much power / amps. The most likely reason is that the props are too big or too coarse a pitch for the motors or both. I'm assuming that everything is freely running and that nothing is binding which would put extra load on the motors. Everything should be easy to turn with your fingers.

It is possible to cool the motors and maybe the speed controllers, but this should not be an option untill the cause of the overheating is addressed.

Can you tell us what size props you are using so we can offer some advice.

Chas

[Chris HoverdParticipant @chrishoverd48135]

Hi both, thanks for your replies. The props are 38mm four blade, I'm not sure if the pitch is course or not😬. Everything is free running, in fact I have just replaced the prop shaft bushes and re greased the tubes.

[Malcolm FraryParticipant @malcolmfrary95515]

The common rule of thumb regarding props is "diameter no more than the motor can diameter, no more blades than the motor has poles". Right on the limit regarding diameter, possibly 2 blades too many. Cheapest thing to try is probably a pair of same diameter two blade props.

[Chris HoverdParticipant @chrishoverd48135]

Malcolm, thanks for your advice, that makes perfect sense to me. I will follow your advise and get some new props to try👍

[Glynn GuestParticipant @glynnguest59245]

Oh dear, "re greased the tubes" is often the sign of a problem?

Grease filled prop tubes can create significant viscous drag when the motor turns at speed.

This might be part of the problem. I'd be inclined to measure the current drawn when running the props out of the water then flush the grease out, refill with oil and retest. You might find a significant reduction in the current.

Glynn Guest

[Charles OatesParticipant @charlesoates31738]

That's all good advice, years ago I changed away from grease and had no problems, it's been a hot discussion point on here in the past.

If it were my model I'd buy a few cheap plastic props, 35 mm and 37.5 mm and do some testing. As Glynn says there is no substitute for measurement and numbers.

Chas.

[Chris HoverdParticipant @chrishoverd48135]

Thanks guys for your input. I'm glad I posted! So regarding the grease issue, what (if anything) should be used for lubrication? I thought that greasing the tube helped to stop water ingress via the shaft?

[Charles OatesParticipant @charlesoates31738]

Re grease, as I said this has been much discussed in the past, with some people being in favour of grease an many, probably a majority against. To stop water coming up the tube, a decent shaft and bearings, together with properly adjusted prop / locknut and coupling at the top should be fine. Any decent light oil is ok in my opinion.

Other ideas and opinions are readily available, but this has worked for me on over 60 models…….. I'm old!

Chas

[Chris HoverdParticipant @chrishoverd48135]

Thanks Chas, I shall put your advice to good use!

[Dave MilbournParticipant @davemilbourn48782]

Chris
The clue to the main problem is the word "Speed". The whole range of Graupner Speed 600 motors is essentially for electric flight – even the ECO 600 has a no-load speed in excess of 10,000 RPM at 7.2v. This being the case then they need to be combined with racing props in an appropriate hull when used in a model boat. Drumbeat is not an appropriate hull, and four-blade props of that diameter are far too much of a load. I wouldn't use them with anything less than a Speed 700 12v, and two of those would vastly overpower Drumbeat.
Your most cost-effective solution is to change the motors for two Mabuchi 555's – less than a tenner apiece . They have the same mounting holes as the Speed 600 range and the same diameter shafts. They will turn at about 3500RPM no load on 8.4v and should draw a low single-figure current on load, even with those big props. An alternative is the MFA 540LN, which is also a 5-pole motor and has similar performance. I have used both types and was very happy with their overall behaviour.
Links are here **LINK** and here **LINK**

Dave M

[ashley needhamParticipant @ashleyneedham69188]

Chris. Just put my penn`orth in, a summation of good practice as per previous posts really.

I would purchase a wattmeter ASAP They are cheap from (not the only supplier) a well known auction site, easy to use and show what's going on in a way that cannot be seen by simply running a boat.

​Secondly purchase a bunch of twin bladed plastic props in 35 40 45mm diameters, X and S pitch (course and standard). Cheap as fried pommes de Terre (diced appropriately) and great for experimentation. Despite that usually the x pitch are used on very fast boats, I have found them to be good at low engine speeds for slower boats.

The MFA LN are great motors and do not pull many amps or get hot even when moderately overloaded (just in case).

​Shaft lubrication. Hot potato subject. Packing with grease will increase drag, has to. May be ok for very powerful fast motor setups when the grease will go soft/melt and lubricate bearings. My favourite combination is nylon bearings/stainless steel shaft. Bottom bearing water lubricated, upper by odd drop of oil. No one will agree on that of course.

Ashley

[Chris HoverdParticipant @chrishoverd48135]

Ok Dave, thanks for your input, i do like the sound of the 540LN's. So you are saying I could keep my current setup (4blade 38mm props)? Chris

[Chris HoverdParticipant @chrishoverd48135]

Excellent advice there Ashley thanks! Guys, the motors in this Drumbeat have been installed using a cradle and elastic band method🙄

I'm looking to replace this with an aluminium mount, but I need to know what thread is in the motor casing, and if so body could provide a link to some suitable bolts (preferably hex head) 👍

[Dave MilbournParticipant @davemilbourn48782]

Chris

You can start with the current props but, as Ashley says, you might choose to experiment. I'd start at 40mm dia x 3-blade if the model was mine.
MFA and Component Shop can supply a suitable ali mount – it's the same for the 540LN and the 555 – and the Speed 600! You can also obtain a moulded glass-nylon mount. Model Boat Bits [Steve Tranter] can supply both types **LINK** I favour the glass-nylon type as it doesn't flex at the bend.
The motor mounting thread is M3. I buy all of my model boat fixings from this supplier **LINK**
The 540LN has a very short shaft so if that might be an issue with the length of the couplings – especially if you use a glass-nylon mount – then the 555 might be more suitable. There's not a great deal of different in performance. The links I posted should show these dimensions.
Finally here's my choice of watt-meter, although others are available **LINK**

Dave M

[Chris HoverdParticipant @chrishoverd48135]

Thanks for the links Dave, and thanks to all of you for your invaluable advice! 👍😀

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