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[Lortel]

I'm interested in using a motor like the Graupner Speed 900BB but i'd prefer a cheaper or better equivalent.

I suppose I should own up and say that I am not using these for a boat but I found this forum and have spent many hours reading all the excellent info on here and you guys seem to know these motors better than anywhere else i've found. I'm using them for a 5" gauge loco and but Maxitrak www.maxitrak.co.uk already use the 900BB in all their electric locos to good effect. I was thinking of using the MFA RE 850 which seems similar in spec (and cheaper) but if anyone can suggest any other options i'd be most grateful.

Many Thanks

[Shipmate60]

The MMB is a direct equivalent for the MFA 850, but being a large multi pole motor has good torque and low current consumption.
Just check out MMB in the traders Section.

Bob

[Lortel]

Thanks for that Bob.

In case it is of interest there is a good writeup about motors, gearing and control on the www.maxitrak.co.uk website in the Articles section. Direct link http://www.maxitrak.co.uk/grabarticle.asp?article=What you need to know about Electric Locos.pdf&title=What you need to know about Electric Locos

Thanks

Barry

[stallspeed]

I have yet to see an equivalent to the Graupner speed 900BB
Check the caldercraft 900

The Torpedo 800 can't be considered an equivalent and the Torpedo 850 is nowhere near unless someone can convince me otherwise with reliable figures.

This one or a Torpedo 800 geared 2:1 would be close to the Graupner 900.If you are operating the 900 well within the power limit you could step down to a geared 500 size on a ratio of 6:1 or more.

[Marks Model Bits]

Quote "I have yet to see an equivalent to the Graupner speed 900BB"

Well all that is about to change Stallspeed!!!

Specs for the Graupner 900BB torque...........
Nominal voltage 12 V Operating voltage range 6 ... 40 V No-load rpm 6500 min
No-load current drain 1,1 A Current drain at max. efficiency 8 A
Length of case, excl. shaft 85 mm Shaft diameter 6 mm Weight 645 g

Specs for my MMB 900 Motor................
Body: 52mm dia  85mm long
Shaft:  single end 5.0mm dia ballraced
Commutator: 12 pole,
Voltage:  12- 24v DC
No load RPM: 6500 1.1A on 12 volts
Max efficiency: 5250rpm, 1500g cm, 80w, 8A, efficiency 55%

Not exactly the same but so close it makes no difference I only rate my motors to 24 volts (they will take a higher voltage but how many modellers use more than 24v) Plus the shaft diameter is different.

Almost forgot the other difference................... The price!!!!!

Mark.

[stallspeed]

Usinng your figures,Mark,I reckon the MMB 900 on 12v would have on test,
stall current 31.1 amp
stall torque 534 mNm

at the maximum power point
Power out  91 watt
rpm         3250
efficiency  47%
torque   267 mNm

The Torpedo 800 has a stall torque of 470mNm and the M5-RS775-12 I just linked to is 431.5mNm
I worked out both the Caldercraft 900 and Graupner Speed 900BB,on 12,to have a stall torque of 1,000mNm with their other data being available.
Was it £20,Mark?
If so,why buy any more Torpedo 800s at £28

[Shipmate60]

stallspeed,
The MFA 800 on a gearbox would run too slowly.
Here are the 800 Specs:

http://www.mfacomodrills.com/motors/800.html

No load is just over 5000 rpm.

Bob

[stallspeed]

To get to the same operating point of a Graupner 900BB, an 800 would have to be geared down 2:1 and run at a slightly higher voltage

[Shipmate60]

stallspeed,
You sure you don't mean the MFA 850 which has no load speed of just over 9000.

Bob

[stallspeed]

Nope.
I took what data was available on the 800,850 and 900 and filled in the missing parts some time ago.


edit
850 on 1.5:1 would replace a Graupner 900BB on same voltage

[Marks Model Bits]

Was it £20,Mark?

Well that depends on how many you want to buy off of me!!

[stallspeed]

I just remember that figure £20I got more high torque 540 and 600 motors than I needed from someone in the auto trade.

If you have several pallets and get the full performance data you are sitting on a cash mountain.

[Lortel]

Theres some very interesting info coming out of this so I thank you all. But, I've been given differing opinions regarding how relevent the stall torque is to the overall practical performance.

Also the maxitrak article sheds doubt on using motors such as are discussed here  at 24v instead of 12v and they now sell all their Graupner 900BB powered locos set to run on 12v as they say there is no practical advantage to running them at 24v. Would you all agree ?

Thanks
Barry

[stallspeed]

   I don't think there has been a difference of opinion here.Four motors nearly match the Gr 900,and have the same power capability.With an alteration by gears,and a touch more voltage for an 800,775 and MMB 900 ,whatever is being driven by the existing Gr 900 will react the same way.(The Caldercraft 900 is the same motor.)
That seemed part of what you asked for?

You could get a drop in replacement for your 900 but you need to hunt one down outside the model trade and possibly buy hundreds to better the price.

 I haven't managed to see the article through your link but I tested motors many moons ago and can do the arithmetic on a fag packet.Don't take my word for the relevance of stall torque over a salesman.Get some rpm and current readings off the 900 in service and with reliable performance charts you can predict what a different motor will do in its place.

 Twelve to 24 is a huge jump. Upping an 800 from 12 to perhaps 14,with gears,will emulate a 900.If you have power to spare,there is no need to change the voltage.If you are presently running the 900 at > 80% of the no-load rpm then you could get away with directly replacing it with the lower torque alternatives.

[Lortel]

Thanks Stallspeed thats a very interesting appraisal. I've been doing a lot of research and you have nicely put it all in perspective. If as you suggest all these motors can do a similar job of work I would assume that in practise I won't notice much if any difference in practical performance.

As i'll be powering my machine with car or motorcycle lead acid or the gell equivalent batteries I can go 12v or 24v and will be using a  4qd or equivalent controller. It seems that apart from Maxitrak the model engineering fraternity have not noticed the advances in small high power motors that has been going on in the model boat and car world (yes I have dabbled in both in the past and no I don't consider myself a model engineer....i'm a bodger and proud of it !). The small size is a big advantage in allowing the motors to be axle hung in my application so more room for BIG batteries because the wieght aids traction.

So the next question that comes to mind is reliability and lifespan. Should I expect them all to be equally as reliable or are there some with a better reputation than others. And as an aside (I know too many questions !) have you guys any experience of the motors available from Distel http://www.distel.co.uk/DC_motors_1.htm which seem good value for money.

[andygh]

Have you seen this?


http://quantrum.co.uk/redbankmodels/graupner-speed-p-759.html

[stallspeed]

There are two important parameters.Motor stall torque and the load torque being placed on the motor.
If the load torque is 1/5 to 1/2 of the motor stall torque then you are in the ball park.If at,present,you are doing >90% of no load rpm with the 900 then a lower torque motor is actually a better fit.

You actually can predict if the others will do the job with an rpm reading of your 900 motor against data or no-load motor rpm measurement at running temperature.You can further predict which one of the alternatives is the best match.
To get the rpm, back calculate the working 900 motor rpm from its full throttle speed, 2 x Pi x R and gearing

How many motors do you need?
If it is many then it is worth the hassle to do some tests and arithmetic for the few pounds difference.

Where have I seen that supplier on Mayhem before?

[andygh]

Where have I seen that supplier on Mayhem before?

Dunno, I use them alot

[Lortel]

Have you seen this?


http://quantrum.co.uk/redbankmodels/graupner-speed-p-759.html

No wonder they're out of stock at that price........ Worth keeping an eye on though !