Overheating motor

[Alasdair AllanParticipant @alasdairallan37423]

[Alasdair AllanParticipant @alasdairallan37423]

Hi – a problem I have not had before (prob because I am more used to using motors that are geared down for paddles, rather than motors for propellors).  My (possibly overpowered?) puffer is racing well beyond scale speed for about 30 seconds and then cuts out, with the motor noticeably hot to the touch.  Once it cools down, it works again. I don’t think there is any reason why I would need to install a mechanism to cool the motor. I notice it only does this in the bath, and not on the work bench, presumably because it doesn’t like the resistance of the water.  I am using a 7v nimh battery with an ungeared motor (see picture).  With the usual apologies for my ignorance, but am I using the wrong motor?  It certainly should not be overheating!  Thanks!

[Alasdair AllanParticipant @alasdairallan37423]

Or, as I rather dread, is it because I need to put grease on the propshaft again?  I put some in when building it, but had so much bother with the rudder structure that I decided to make that fixed at that end.  I can still remove the prop shaft if necessary by unscrewing the prop and pulling the shaft into the hold to grease it there, but would be keen to know if there is likely to be another problem I am not understanding! thanks

[Colin BishopModerator @colinbishop34627]

Alastair,

Sounds like your ESC is becoming overloaded and activating the thermal cutout. Looking at your photo it doesn’t appear that the nut on the inboard end of the shaft is actually doing anything. You should have a locknut on the propeller to stop the shaft tightening itself up and locking everything solid.

If that is the problem then it would account for things working on the bench as the prop is only pushing air. In the water it will literally want to screw itself up!

Have a look at this article and the diagrams at the end which explain everything.

Drivelines

Colin

[Alasdair AllanParticipant @alasdairallan37423]

Thanks Colin – will investigate!

[Alasdair AllanParticipant @alasdairallan37423]

So when you say the inboard nut is not doing anything, you mean it is not protecting the motor from friction/ direct force when going astern? the locknut at the propellor end does seem to work as does not have any tendency to unscrew itself. Anyway, I will read through this very helpful article, but just to check what it was exactly you saw in my photo!  Many thanks

[Colin BishopModerator @colinbishop34627]

It may just be my screen resolution but it looks like the upper nut isn’t screwed hard against the collar. If it is then the motor is being overloaded by something. Is that a 540RE motor? If so, it is a low drain type and shouldn’t overheat unless almost stalled. What size is the prop? What ESC are you using?

Colin

[Alasdair AllanParticipant @alasdairallan37423]

HI – just to check  I am reading your helpful comments right, plus the para below from the article you sent:

 

“if the coupling insert is threaded to match the propeller shaft, then it too must be secured with a lock nut. The method is just the same as described for fitting a propeller but this time two spanners must be used, one for the nut, the other for the coupling.”

So I do need the nut, but one that is jammed against the coupling so it doesn’t move.  Aft of that, I need a small space between that nut and the washer on inboard bearing of prop tube? Sorry am slow on the uptake here.

[Alasdair AllanParticipant @alasdairallan37423]

it may be that I am stalling it by running it at a low speed (to prevent boat going at speed boat speed). The ESC is a viper 25

[Colin BishopModerator @colinbishop34627]

Basically, if the motor is not connected then there needs to be a lock at both ends of the tube to prevent it moving backwards or forwards but with a minimum clearance. This means tighten it up at both ends and then slack off the top end fractionally so there is only a tiny amount of fore and aft play and it spins freely. Then connect up the motor coupling which only then has to provided rotational force and not absorb longitudinal force from the propeller.

If you are still then experiencing problems then it suggests that the load on the motor applied by the propeller is too much which seems unlikely if you are using a 540 size motor and a prop no bigger than 40mm diameter. Alternatively if you have stuffed the tube full of grease then that is likely to have strangled the motor! You only need to grease the bearings at each end and maybe introduce a bit of light oil into the tube to prevent corrosion.

Running the boat at slow speed simply supplies less voltage to the motor and cannot result in it overheating.

Colin

[Alasdair AllanParticipant @alasdairallan37423]

thanks Colin. basically the nut in question is gradually screwing itself to the inboard end of the tube, however much I try to tighten it against the coupling. I am going to take it out as the coupling seems to hold itself to propshaft with grub and it is difficult to get in a spanner to tighten the offending nut much more. Will see what difference that makes!

[Richard SimpsonModerator @richardsimpson88330]

Alastair, is the splined insert with the grub screw threaded or plain?  The idea of the lock nut is to lock it against the splined insert if the insert is threaded.  If the insert is plain, as the grub screw would tend to suggest then you could be locking the grub screw against the thread on the shaft, which could damage the thread, and it won’t hold to it very securely.  Ideally if the insert is plain it is best that the grub screw locates on a flat on the shaft for the best security.

The trouble is that currently the nut is free to move around and so it is tightening up on the end of the stern tube.  You can’t stop the nut from moving around though because tightening the nut against the splined insert only pushes the splined insert further up the shaft.

If the shaft is threaded to the end then the splined insert should be threaded not held by a grub screw, so, if that is the case, you need to buy a new splined insert.

If you just remove the nut then there is nothing holding the washer in place on the end of the tube and you could find you are getting water ingress.  As Colin mentioned the two washers on either end of the tube should be a close fit with just enough clearance to allow free movement.

I would also question the use of grease.  Grease in a shaft tube can also put more load than necessary on a shaft and motor, causing the motor to take more load.  Oil is much better, preferably with an oil filling tube on top so you can top it up as you will loose a small amount over time.

[Colin BishopModerator @colinbishop34627]

That would seem to account for the problem you are experiencing. Maybe substitute another nut for the collar which might give a more secure fixing.

I have just experienced something similar on my Silver Mist model where not screwing the shaft fully into the prop resulted in something similar. We live and learn!

Edit: Just seen Richard’s contribution – very good advice! Most of my shafts are threaded at the prop end and plain at the inner end which makes things a lot simpler!

Colin

[Alasdair AllanParticipant @alasdairallan37423]

[Alasdair AllanParticipant @alasdairallan37423]

Thanks for help. For the moment, a bearing is working better than a nut (when the boat is going in other direction, there is a gap between the steel bearing and the brass pipe of the prop shaft, though was not visible when I took the photo).  The motor is still warm, but significantly not the prop shaft this time and is no longer cutting out because of heat.  Will see how it works, out but the bearing option seems to be avoiding the issue of the nut tightening itself, and there was not much room to successfully lock the nut in the right place. The puffer is definitely over powered though – she practically hydroplanes, so I may seek out a smaller motor!

[Colin BishopModerator @colinbishop34627]

Or a smaller prop?

[Richard SimpsonModerator @richardsimpson88330]

Or a lower voltage?

[Alasdair AllanParticipant @alasdairallan37423]

thanks for advice – will investigate all of this and also have ordered a smaller motor to see if that makes a difference.

[ashley needhamParticipant @ashleyneedham69188]

If a large motor is overheating, a smaller motor is bound  to heat up even more!

There has to be a physical reason the motor is getting hot, barring the motor itself being faulty which would be unusual.

Is the boat ventilated? My sub 540 gets very warm but only because the interior is small and sealed up.

Ashley

[Charles OatesParticipant @charlesoates31738]

Hi Alasdair, what size prop are you using? This is the fundamental starting point in any installation.

 

[Alasdair AllanParticipant @alasdairallan37423]

OK – making progress on this one! Smaller motor is definitely an improvement and have managed to get the lock nut to sit against the bearing properly.  The new problem, alignment wise, is that the brass bearing at the motor end keeps working itself loose from the red universal coupling, and so pushing the whole thing back agains the prop tube. Don’t have any equivalent problem with the bearing at the motor end.  In answer to previous question re the prop shaft, it is threaded at both the properllor and inboard end. This allows for the jam nut but there is no thread (and doesnt seem a need for one) on the inside of the bearings on universal coupling. Not sure if that makes sense, but hopefully I can have another go and send you on a photo!

[Alasdair AllanParticipant @alasdairallan37423]

On Ashley’s point about ventilation, the previous overheating was happening with the hatches of, so I think this one definitely comes down to the forces that are getting placed on the motor until I get the drive alignment right.

[ashley needhamParticipant @ashleyneedham69188]

Personally, I cut small thrust washers from plastic milk bottles to use either end. A plain bit of shaft inboard is fine presuming the brass coupling is of the unthreaded but grub screwed type.

Just to reiterate….sequence of parts is…

Prop, locknut, plastic thrust washer outboard..

Inboard…plastic thrust washer and grub screwed collar (coupling?)

As an afterthought…the shaft should rotate freely in  the the tube

..if not…then the tube or shaft is bent.

Ashley

[Alasdair AllanParticipant @alasdairallan37423]

hi – finally have the motor working well, touch wood, thanks to people’s help. In the process, however, my radio link T8FB transmitter has suddenly decided that  the throttle  needs to be moved  left to right rather than the previous up and down to work. This is a bit counter intuitive (and new). The manual for the transmitter is written in a way that is indecypherable to me, and is probably meant for those types who are into model planes. Does anyone know how I get back to moving the throttle up and down, either via the transmitter or its associated app? Thanks!

[Richard SimpsonModerator @richardsimpson88330]

Some how or another you have the transmitter channels mixed up with the receiver channels.  The only way you can do this is by plugging the wrong plugs into the receiver.  I assume with all the playing around you have been doing with the motor and speed controller that you have removed the speed controller plug from the receiver and have plugged it back into the wrong location.  Easily done as the pins are not always perfectly lined up with labels.

I would check that the plug for the speed controller is plugged into the correct set of pins before doing anything else.  It us usually channel 1 but that is not guaranteed.  Channel 1 is then usually the left stick up and down.

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