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[chrise]

I have been looking at some “model” motors that I might consider using in place of the car heater motors that I have traditionally used. Unfortunately my supply of these motors has ended.

The motors that I am considering for 2 different models are:

Graupner Speed 900BB approx £36
http://www.cornwallmodelboats.co.uk/acatalog/graupner_6373.html

MMB900 approx £30
http://www.action-electronics.co.uk/pdfs/MOTORS03.pdf

Caldercraft CEM900 approx £26
http://www.cornwallmodelboats.co.uk/acatalog/cem900.html

Graupner Speed 720BB approx £35
http://www.cornwallmodelboats.co.uk/acatalog/graupner_6372.html

MFA Torpedo 800 approx £25
http://www.cornwallmodelboats.co.uk/acatalog/mfa1114_1.html

MMB755 approx £15
http://www.action-electronics.co.uk/pdfs/MOTORS03.pdf


There has been much discussion of these motors over the years but never, that I can find, have the following questions been answered – or perhaps they have & I just don't understand the numbers!

From my perspective the relative price difference between these motors is not significant compared to the time that building a model takes.

For use in tug type full displacement hull models at 12v & with direct drive & which will be used for towing:

1. What is a good guess for the largest (best thrust) sensible size prop/number of blades to buy for each motor without overloading the motor?
2. What current will that motor/prop combination draw as a static load?
3. How much static thrust (bollard pull) will be generated?
4. Any comments on relative build quality & longevity?
 

[chrise]

58 viewers & no response.

Surely there are some suggestions out there?

[Andy K]

Hi Chris, I have 2 Graupner 720 Torque motors in one of my tugs. Brilliant motors but a tad expensive.

http://www.cornwallmodelboats.co.uk/acatalog/graupner_6372.html

Andy

[787Eng]

My Money is always on the Mobile Marine Models T12 and would not get anything else,
I have 5 of them in various tugs and have recommended them to club members and all have been very happy with the quality and reliability. Nice Nice motors with plenty of power. I along with other members of the club have never had to fit suppressors to the motors.

The motors are turning Propshop 4 blade 75mm props with ease and are just above ambient after a good long run. I used a data logger on board my Imara and average current consumption was around 2.5A @12V. As for bollard pull is this enough !
Mark

[Shipmate60]

Chris,
With the questions you ask there are just so many variables.
A small motor spinning fast can produce the same thrust as a large prop running slower.
The usual starting point is if you want a scale appearance out of the water.
Most do as the model spends most of its time out of the water.
This will give you a starting point, tugs do have large slow(ish) running props.
The same prop running at the same speed will give the same thrust in almost any hull.
If you were happy with the Car Blower Motors do you know what rpm they give?
If you know that you can find a motor that will give similar speed as long as its powerful enough to turn your prop.
The nearest to your blower motor is the T12 but the MMB900 comes very well quoted with other model tug builders.
There is a full spec on the MMB website. These are usually used on 6 volts for tugs and free running and 12 volts for towing.

Bob

[chrise]

I hear what you are saying about this being a difficult, or perhaps impossible question, but it is still a valid question.

We all face the same problem, & it is asked here regularily. I am building a model and I nee to know what motor/ prop to put in it. This is compounded by larger props being £20+ and a wild guess as to whether they will be any good. Add to this the uncertainty of whether the motor will be any good and it is a mess.

The motors that I have traditionally used are the Ford Cortina heater motor, which was a 2 minute job to remove at the scrapyard, drew up to 5 amps & worked well with up to 3" props and the larger black fully enclosed Smiths motors which with 4" props were about 6 amps. Unfortunately modern heater motors appear to be burried very deeply in the dashboard.

I picked a number of popular motors, specified 12v as being easy to supply, gave a tug model - low speed, lots of thrust & what I build - & asked for some comparative figures.

It would be useful to know what props are being used & what current they draw. I guess nobody has the "right" combination but surely as a group we could get a good working combination for each motor?

Shipmate60. I have looked at the MMB website & I don't see figures or prop recommendations for 12v operation in a displacement hull. To be fair prop recommendations & figures are pretty rare generally! It would be really useful if motor manufacturers gave a few "for example" figures for the sort of model that they expected their motors to be powering. A 49" Perkasa on 24v doesn't tell me much about a tug on 12v.

[Shipmate60]

Chris,
The Cortina motors would run free at 5200 rpm, so this gives you a starting point.
If these motors powered your tug as you like it use a comparative motor to this.
This will make the prop selection much easier as you will know the set up history in similar models.
Speed/power is also relative, some like their tugs to go over scale speed and almost all of us overpower our models.
For tug towing this seems overpowering by a massive amount by some.
It would be easier to ask about a specific tug or type as again there is the question about single or twin shafts.
Some swear by MFA800's some at them. The T12 are a fine motor but do you have the available room to fit these, but they are the closest to the Cortina/Smiths type motors you have been using.
Please remember I am trying to answer your question "cold" with only the information in your posts.
Bob

[787Eng]

The T12 are a lot smaller in diameter and length that a Fan blower and if my memory serves me correct they are only slightly larger than the MMB900

Mark

[chrise]

Thanks for the suggestions.

[justboatonic]

My Money is always on the Mobile Marine Models T12 and would not get anything else,
I have 5 of them in various tugs and have recommended them to club members and all have been very happy with the quality and reliability. Nice Nice motors with plenty of power. I along with other members of the club have never had to fit suppressors to the motors.

The motors are turning Propshop 4 blade 75mm props with ease and are just above ambient after a good long run. I used a data logger on board my Imara and average current consumption was around 2.5A @12V. As for bollard pull is this enough !
Mark

Jaysus, Mark. That's some pulling power! 

What sort of strengthening did you have to build into the boat to stop the tow hook ripping out?

[787Eng]

Tow hook is one that MMM recommended and its strong!
Glued a large piece of 1/4" ply inside the superstructure to spread the load and thats about it. Keep meaning to fasten the superstructure to the deck but seems to hold on well as is

The story behind the picture the boat's engine failed and they had no easy way to get it back, so as it was an open day for the canall trust and the media were there. one of the trust members asked if my tug would pull it... the picture is taken where I'm pulling the nose round to moor the boat up on the bank.... 

The public were very entertained and the trust members were shocked how well the toy boat performed!

Mark