newbie

[Graeme LinskeyParticipant @graemelinskey75588]

Hi there,

First post been lurking for a while…….couple of questions I did buy of the bay a Tug boat it went cheap with all the gear so ok give it a go have been into RC of and on for 40 years but now have a bit more time and some extra tools etc ..so my first question is I am after a motor called the MMB 900 but cant find one any where.. so what is the next best? and also how do you guys measure your prop speed under load?

The Tug is 7KG scratch built came with a speed 600 and a 4 blade 60 mm prop TUG is 830 mm long 200mm widepowered by 6v 12 ah sla seems all under powered to me tried looking for the mmb 900 but no luck unless they come under a different name

all the best

Graeme

IOM

[Graeme LinskeyParticipant @graemelinskey75588]

couple of questions 🙂 mmb 900 etc

[Amy jane SeptemberParticipant @amyjaneseptember49770]

Hi there Graeme,

Sorry I can't answer your questions, But I can bid you welcome to the forum!

Some one will know , and hopefully be along soon!

Amy jane

[Dave MilbournParticipant @davemilbourn48782]

You won't find any of these left on the market unless you drop across one on E-Bay. They were a particular type of Johnson 960 motor which were imported for golf trolleys. This is the nearest you'll find to it although it isn't as fast as the original MMB900. **LINK** Jotika also list the same motor. The alternative is to use good old faithful MFA 800 or a geared motor such as the MFA 919D type. All of these motors I've mentioned should be run on 12v, not 6v.
The Speed 600 is totally inappropriate for this type of model as it revs far too fast and doesn't have the torque for a prop of that size. I've no experience of measuring prop speed under load; all my measurements are taken on the bench with a cheap Turnigy optical tachometer.
Hope this helps.

Dave M

[lnvisiblemanParticipant @lnvisibleman]

Hi and welcome,

I have a slightly bigger tug and it is powered by one of these that I bought very cheaply. Loads of torque and low power consumption. It also revs at the right sort of speed for a chunky prop. I made the mount from a piece of 3mm ali sheet in about 10 minutes using very basic tools, i.e. a drill, a mallet and a Goscut.

**LINK**

Mike

Edited By lnvisibleman on 27/07/2014 09:31:42

Edited By lnvisibleman on 27/07/2014 09:32:44

[Gareth JonesParticipant @garethjones79649]

Hi Graeme,

Marks Model Bits website still advertises the MMB motor but I dont know if they still have them in stock. **LINK** I have used a Graupner Speed 900 motor in a similar sized tug and it was very effective driving a 55 mm prop, in fact way overpowered really.  However the Grauper Speed 900 is pretty well unobtainable mowadays.   I suspect you will need to operate on 12 volts though, whichever 900 sized motor you obtain.

To measure prop speed I have used a laser tacho to good effect. The one that I use is this type **LINK** You just need to measure the speed of the prop on the bench at full throttle and then again with the boat tethered in the water. The loaded rpm should ideally be around 80% of the unloaded rpm. However if you are not going to use full power for long periods of time its possible to go down to a figure of around 50% but you will need to watch for signs of the motor overheating after periods of high power operation.

Gareth

Edited By Gareth Jones on 27/07/2014 09:33:34

[Dave MilbournParticipant @davemilbourn48782]

The original MMB900 was rated at 6000RPM no load @ 12v i.e. just about the same as the Speed 900 and a bit too fast for a 60mm prop in a tug. These later types are half that speed but arguably more suited to a big tug prop on 12 volts. The difference really comes when you run one of the originals on 20 cells with an X55 prop in a Perkasa……..
DM

[nomustangmarkParticipant @nomustangmark]

Hi Gareth, the link you posted to my old 900 motor must be a very old out of date cached page,… That page was removed from my site ages ago,

Mark. (MMB)

[Gareth JonesParticipant @garethjones79649]

My apologies Mark, I should have checked your current website rather than just Googling the motor part number. It just shows how easy it is to get misled by the web. Anyway, that rules that motor out I guess.

Gareth

[Graeme LinskeyParticipant @graemelinskey75588]

Thanks for all the replies and help…Going to settle for a MFA 800 and keep an eye out for a MMB 900 as my next boat will be a huntsman or a perkasa…so if anyone has a spare mmb motor and would part with it then let me know

cheers

graeme

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