Replacing Mashima motors

[Pebbles]

Many years ago I attempted to build a Finescale J39 with the MRRC motor mounted horizontally on a sub frame that meshed with the lower open part of the boiler. The drive was via a MRRC 3:1 bevel gear driving a vertical shaft that then engaged  a Hornby 13:1 gear on the rear axle. I gave the whole thing up as being far too noisy. I concluded that whilst a worm gear may not be very efficient - I say this in the context of Romford gears where the worm diameter is needlessly oversize - it is more effective in dampening transmission noise and can take up much less space.

[Michael Edge]

Geoff Helliwell (who has done a lot of work on this in 3mm scale) abandoned bevel gears because they were nigh impossible to mesh in small scale locos. He did however report that meshing crown and pinion gears was easier than meshing worm and wheel. He has also produced a kit (sold within the 3mm Society) for a motor bogie and for a drive for small tank locos (OK GW panniers). These will go down to 12mm gauge. I have taken one of his motor bogies and modified it for 9mm gauge by making it outside framed. The main issue for 3mm scale use is that the smallest available crown wheel is 8.5mm diameter which only just fits in a bogie using 9mm diameter wheels. However my limited experience is that crown and pinion is the easiest of the drive turning gear trains to set up as well as the one that puts least drag on the motor. I forget who it was, Iain Rice possibly, who said that putting a worm drive in a small scale loco is like driving with the hand brake on.

 

I've had no problem meshing bevel gears so far - and all Portescap motors have them (but on the input side, which makes the whine a lot worse).

[Izzy]

Straight cut spur gears will mostly be noisy/whine when run at higher speed due to the on/off loading transfer from one tooth to the next. This can be overcome by using helical cut teeth, but they need decent widths and angles to be effective in this respect along with good side thrust bearings to minimise frictional power loss through this aspect. I agree with others who feel worm gears get a ‘bad press’ simply due to their alleged inefficiency. It’s a generalisation that has so many caveats that it becomes meaningless in many respects since one gear train design may have quite different primary needs and objectives to another. Little mention ever seems to be made for example of the materials from which gears are made or their size relative to the power input/output.

 

Izzy

[AndyID]

Just received motors - six pole armature 10mm x 10mm square about 15/16mm long with 1mm shaft. Supposedly rated at 7.2/9 volts, but even at this voltage displays very good torque at reasonable revs. I think something place inline to limit the voltage would be useful.

 

The problem with using a resistor to reduce the voltage is that the voltage drop across the resistor will increase as the load on the motor increases (longer trains, curves, inclines, etc.) The motor will slow down and tend to stall.

 

An alternative to a resistor is to use silicon diodes. The voltage across a diode varies a lot less than a resistor with changes in current - it will be approximately 1 volt. You'll need two diodes connected in parallel facing in opposite directions to allow current to flow through the motor in either direction. You can string pairs of diodes in series to "drop" more voltage.

[whart57]

Surely there is a heat aspect as well. If the motor is drawing something like a quarter or an amp and you are dropping four volts across a resistor then thats a watt of heat being generated. At the least it means you have to use the chunkiest resistors

[burgundy]

Some way back in this thread, I made the point that one of the real advantages of the Mashima range was that they were a well documented product. This applied not only to the physical dimension but also to the performance. I still have the set of performance sheets that were developed for the EMGS by J Douglas Smith of Weybridge, who used a common process to measure the torque and speed of Mashimas and other motors that were on the market during the 80s and 90s. From this, it was easy to derive the suitability for a particular loco and the likely required gear ratios. I have a feeling that similar (or possibly the same) data was published on one of the magazines - probably either MRC or MRN.

Does anyone have the skills, time and inclination to repeat this process on some of the currently available motors? Or are we living in a age where batch production means that successive lots of motors, that come onto the market, may well have slightly different characteristics?  

Best wishes

Eric  

[whart57]

We are living in an age where a DCC chip can be programmed to take account of small differences in motor performance

[AndyID]

Some way back in this thread, I made the point that one of the real advantages of the Mashima range was that they were a well documented product. This applied not only to the physical dimension but also to the performance. I still have the set of performance sheets that were developed for the EMGS by J Douglas Smith of Weybridge, who used a common process to measure the torque and speed of Mashimas and other motors that were on the market during the 80s and 90s. From this, it was easy to derive the suitability for a particular loco and the likely required gear ratios. I have a feeling that similar (or possibly the same) data was published on one of the magazines - probably either MRC or MRN.

Does anyone have the skills, time and inclination to repeat this process on some of the currently available motors? Or are we living in a age where batch production means that successive lots of motors, that come onto the market, may well have slightly different characteristics?  

Best wishes

Eric

 

Sagami motors came with a comprehensive datasheet. Sadly the company ceased when Mr Sagami died. I still have some of his excellent motors salted away along with all the datasheets.

[AndyID]

Surely there is a heat aspect as well. If the motor is drawing something like a quarter or an amp and you are dropping four volts across a resistor then thats a watt of heat being generated. At the least it means you have to use the chunkiest resistors

 

Alternatively you can use multiple lower wattage resistors in parallel. The heat still has to go somewhere of course.

[Jol Wilkinson]

We are living in an age where a DCC chip can be programmed to take account of small differences in motor performance

 

Not if you prefer to use DC. 

 

Even so, it helps when choosing a motor for a particular application to know what the performance characteristics are. The EMGS data referred to by burgundy is/was most useful.

[whart57]

Of course you can choose not to live in that age

[asmay2002]

We are living in an age where a DCC chip can be programmed to take account of small differences in motor performance

And a DCC chip helps you choose the gear ratio how exactly?

[whart57]

And a DCC chip helps you choose the gear ratio how exactly?

 

It doesn't but it does allow you to set maximum speed, start voltage and a speed gradient. It's not the only answer but the question was on matching motors from different batches, and DCC is a means of doing that.

 

I don't know why mentioning DCC causes such snappiness.

[AndyID]

 

I don't know why mentioning DCC causes such snappiness.

I suspect the editorial "we live in an age" had something to do with it.

[whart57]

I'll bite my tongue on that

[Pebbles]

Geoff Helliwell (who has done a lot of work on this in 3mm scale) abandoned bevel gears because they were nigh impossible to mesh in small scale locos. He did however report that meshing crown and pinion gears was easier than meshing worm and wheel. He has also produced a kit (sold within the 3mm Society) for a motor bogie and for a drive for small tank locos (OK GW panniers). These will go down to 12mm gauge. I have taken one of his motor bogies and modified it for 9mm gauge by making it outside framed. The main issue for 3mm scale use is that the smallest available crown wheel is 8.5mm diameter which only just fits in a bogie using 9mm diameter wheels. However my limited experience is that crown and pinion is the easiest of the drive turning gear trains to set up as well as the one that puts least drag on the motor. I forget who it was, Iain Rice possibly, who said that putting a worm drive in a small scale loco is like driving with the hand brake on.

 

A copy of MRN March 1953 a letter from a Mr L Hudlass "Worm v.Spur Gearing". Do times ever change?

[whart57]

Geoff Helliwell does have a party trick though where he shows how hard it is to stall a loco with spur gears by pressing down on it compared to a worm driven loco

[asmay2002]

It doesn't but it does allow you to set maximum speed, start voltage and a speed gradient. It's not the only answer but the question was on matching motors from different batches, and DCC is a means of doing that.

No it wasn't. Burgundy's point was about using the data sheets to select gear ratios.

[whart57]

No it wasn't. Burgundy's point was about using the data sheets to select gear ratios.

 

This is what I was answering from Burgundy's post

 

"Or are we living in a age where batch production means that successive lots of motors, that come onto the market, may well have slightly different characteristics? "

 

Mentioning DCC clearly triggers the same sensitive spot as suggesting the wrong shade of brown for a 1930 GWR coach.

[burgundy]

This is what I was answering from Burgundy's post

 

"Or are we living in a age where batch production means that successive lots of motors, that come onto the market, may well have slightly different characteristics? "

 

Mentioning DCC clearly triggers the same sensitive spot as suggesting the wrong shade of brown for a 1930 GWR coach.

 

Can Burgundy perhaps comment on what Burgundy thought he meant?

I think what I am seeing on e Bay is a batch of motors being built for a particular purpose and surplus stock then being "remaindered" for other purposes. When the next batch of motors comes along on e Bay, they may have been built for a different purpose and therefore possibly with different characteristics (physical size, performance or whatever). This contrasts with the Mashima model where a 1220 was a 1220 and, subject to marginal variations, you knew what you were getting. What I personally feel that we are missing in the "post Mashima era" is a standard product, where you know what size it is, where the screw holes will be, what diameter the drive shaft will be, how much gearing it will need and that it will be available for a foreseeable length of time.

Less serious points

- it is as much as I can do to get a motor into locos like these without messing around with chips and speakers  

- if you really wish to hit a sensitive spot, just describe Mr Stroudley's Improved Engine Green as yellow (see Wave above). By comparison, the shade of brown on a 1930s GWR coach is trivial.

Best wishes

Eric      

[cctransuk]

Can Burgundy perhaps comment on what Burgundy thought he meant?

I think what I am seeing on e Bay is a batch of motors being built for a particular purpose and surplus stock then being "remaindered" for other purposes. When the next batch of motors comes along on e Bay, they may have been built for a different purpose and therefore possibly with different characteristics (physical size, performance or whatever). This contrasts with the Mashima model where a 1220 was a 1220 and, subject to marginal variations, you knew what you were getting. What I personally feel that we are missing in the "post Mashima era" is a standard product, where you know what size it is, where the screw holes will be, what diameter the drive shaft will be, how much gearing it will need and that it will be available for a foreseeable length of time.

Less serious points

- it is as much as I can do to get a motor into locos like these without messing around with chips and speakers  

P1010028.JPG

IMG_4968.JPG

- if you really wish to hit a sensitive spot, just describe Mr Stroudley's Improved Engine Green as yellow (see Wave above). By comparison, the shade of brown on a 1930s GWR coach is trivial.

Best wishes

Eric      

 

..... well, it ain't green !!!

 

Regards,

John Isherwood.

[whart57]

- it is as much as I can do to get a motor into locos like these without messing around with chips and speakers  

P1010028.JPG

  

 

Is that a Sharp Stewart single as rebuilt as a tank for the WC&PR? I'm getting the bits together for a SS single but in 3mm scale. It will have a tender though and that is where the bits and bobs will go.

[burgundy]

Is that a Sharp Stewart single as rebuilt as a tank for the WC&PR? I'm getting the bits together for a SS single but in 3mm scale. It will have a tender though and that is where the bits and bobs will go.

 

The full saga is documented at 

www.rmweb.co.uk/community/index.php?/topic/63652-a-small-problemnow-in-the-paintshop/

The set of castings are by 5&9 Models for a small Sharpie, based on drawings of one delivered to the SER. The Brighton were very good customers of Sharp Stewart in the early days and rebuilt a number of tender singles into tank locos.

I shall look forward to a 3mm version - with DCC and sound. No smoke unit?  

Best wishes

Eric    

[Pebbles]

As its unlikely to be continually run at full power have tried a 8.2 ohm resistor for the small 10mm square motor. Torque still seems to be there; must now look for an appropriate model. All this agonising over motor speeds etc, these small motors hardly break the bank and are worth a try. My only reservation is brush durability, to be on the safe side always buy more than you need.  

[whart57]

The full saga is documented at 

www.rmweb.co.uk/community/index.php?/topic/63652-a-small-problemnow-in-the-paintshop/

The set of castings are by 5&9 Models for a small Sharpie, based on drawings of one delivered to the SER. The Brighton were very good customers of Sharp Stewart in the early days and rebuilt a number of tender singles into tank locos.

I shall look forward to a 3mm version - with DCC and sound. No smoke unit?

Best wishes

Eric    

 

DCC probably, no sound and no smoke unit though. To me the main advantages of DCC are no need for section switching and full voltage to the track. I like sound on diesels but not on steam. As for smoke