Axle Hung Motor Gearbox (AHMG)

[Peaky 556]

Phil,
Thanks for that drawing. Could you just clarify if the motor body outlines will overlap on the 8'9" wheelbase you use as an example? It looks very close call, but what I am wondering is if two sets of gearbox plates can be "nested" together with the motors just clearing each other.
It hadn't dawned on me that the units were so long. With my "Peak" at an 8' wheelbase it is clearly going to be impossible to fit three drive units, as I had hoped to do.
One further question on the gears which you state will be metal. Have you ruled out the cheap plastic hostaform ones that Ralph had promoted?
Happy New Year to all,
Tim

[classicdelights]

Hi Tim

I am afraid that with Ian's current design it is 1 gearbox/motor unit for a Bo-Bo and 2 for a Co-Co, each bogie that is.  I imagine that the unit is going to be pretty powerful so 2 motors/gearboxes for a Bo-Bo and 4 for a Co-Co locomotive should do the trick.  Your Peak diesel would have 4 motors, it would probably pull a house down!  I built a Class 40 in gauge 1 with 4 motors and it was very powerful, I don't see why this one in gauge 3 should be any different.  You also avoid the wheel slip problem that 3 motors on a Co-Co installation would probably create; it would require some very delicately adjusted springing to get them all working together.

What I have offered to do is build the first units to make sure that they can be put together and probably write some build notes for members.  At the moment with Ian's design the use of metal gears is preferable as some have to be metal anyway, plastic not being available.  We do not have a design for the gears Ralph suggested, it would probably not be the same as this design.  Cheap plastic gears also throw up the problem of how you attach them to the shafts/axle.  The gears would almost certainly have to be pinned, you cannot rely on gluing them.  There is also the issue of how a plastic gear would be secured to the motor shaft.

Regards

Phil

[classicdelights]

Further to my last, I am attaching a picture of a Co-Co bogie, this is the Bulleid diesel that has an 8' wheel spacing.  I have outlined what would be 3' 9" wheels, correct for a Class 45.  You will see that there is no way that another unit will fit on the centre axle.  There is another issue in that the unit has to be restrained somehow.  I have indicated tension springs that fit around the rear spacer of the gearbox unit and onto a main bogie chassis spacer.  I used this method successfully on my gauge 1 diesel.  It allows the gearbox unit to move slightly whilst still being restrained.

Regards

Phil

[cabbage]

I really do feel sorry for you....

As to the problem of cheap plastic gears being attached to metal shafts -the problem was solved in 1925. It is called an allen grub screw. If my 12 year old niece in Yr7 can drill a 3mm hole through the boss of a delrin gear with an wheel brace and then tap it to M4 -then I believe the majority of the readers of this forum should be able to do as well -if not better.

As to securely fixing the drive spur onto a motor use an interference fit. This can either be a length of heat shrink tube or simply drill the central hole 0.1mm smaller than the drive shaft in the gear and wang into place with a hammer. The former method is used by AUDI and the latter method used by Chevrolet to secure plastic gears to fix plastic gears to metal shafts.

My Peak variant has 12 motors -two per axle. There is no wheel slip. There is actually no suspension either -unless you count the small amount of foam packing above each axle box that stops the rattling.

<moderated>  Give the specs to me and I will find them for you. I know an awful lot about the use of plastic and metal gears in gearbox systems -I wrote at least 25,000 words on this subject as part of my 2nd Masters thesis.

Yours Respectfully

R.Brades B.Ed. B.Sc. M.I.A.A.P. M.Sc. Ph.D.

Post Scriptumn: I only use the "scrap metal" when I am really annoyed....

[cabbage]

The first JPG shows the 2 SME motors (80p each) either side of the bull gear H60M0.6 this gives a drive ration of 1:5. The motors are stuck to a piece of polycarb with superglue. The three "engine mounts" are then M3 bolted to a 6mm spine (it was the first thing out of the bits box). This spine is then mounted is then cable strapped to two spacers. The slack between the bar and the plate is taken up with two squished rubber washers.

There is noticeable reaction on the system as the motors are in opposition and the bull gear slides vertically between the teeth of the motors -there is no suspension on either the axles or the motors.



This shot shows the underside.



The bull gear is bolted through the wheel to provide connection. Additional "belt and braces" is provided by a small flat hand filed onto the the axle and an M4 allen grub screw locked into it. The drive spur gears are fitted to the motor shafts via the AUDI method -precision placement was ensured by putting the two parts between the jaws of a vice and winding in.

There you have it -an axle mounted gear box. The big bull gears are about two quid and the small ones about 30p. All of it done within the 8 feet axle spacing of a class 45 (or 97 in this case). Lateral axle slide is circa 3mm. Would somebody tell me what is so hard, costly and mechanically difficult about doing the above?

QED

ralph

[classicdelights]

Ralph

Thank you for your erudite explanation as to what is required.  Why don't you design a gearbox unit to take the motors that many of us have purchased, you would be able to do it much better than Ian has done and clearly your advanced engineering methods are far above my experience levels, personally I have never used glue on steam engines so am ignorant of the latest techniques.

We all look forward to a great design for a really cheap gearbox - when can we expect to see something in print?

Kind Regards

Phil

[cabbage]

The time is now 12:02 GMT. Sunset is in 4 hours. It shouldn't take me too long as the raw data is already in this thread. Constructional drawings will be presented in PNG format.

Excuse me I have to get back to writing someones letter for them.

ralph

[jamiepage]

Quote 'Cheap plastic gears also throw up the problem of how you attach them to the shafts/axle.  The gears would almost certainly have to be pinned, you cannot rely on gluing them.  There is also the issue of how a plastic gear would be secured to the motor shaft.'
Unquote.

How were they secured in your G1 traction motors, and indeed the ubiquitous Fosmotors,  you described and photographed earlier in this thread then?

[andrewfoster]

I've taken time out lately and am catching up on this interesting thread. I don't pretend to be an expert, not having attempted anything like this myself, but a few details I've picked up along the way in gear and gearbox design may (or may not!) be relevant, while bearing in mind this project doesn't fly passengers or aim weapons and such like.

- Nylon and Delrin gears work best in mesh with metal gears, as two less rigid materials in mesh are inefficient and will wear more. This allows you to work without wet lubrication in many circumstances. (Printers have plenty of Delrin gears in mesh with each other, but they don't haul trains).

- In a metal/Delrin pair, the metal gear should be the smaller one if possible, as the smaller gear wears more (same reasoning as you would apply to a steel/brass mesh). In the case of a worm, generally better if the worm can be the harder material.

- The most important features of the gears are the centre distance, which must be accurately maintained to minimise wear and noise, and the concentricity of the gear teeth and shaft.

- Where possible, it's better to pin or clamp a gear to a shaft than use a set screw, especially with plastic gears, as the radial force tends to distort the gear (clearly not always possible, but always desirable).

- Bolting a Delrin gear to a feature such as the wheel is excellent as long as the face of the wheel is true and perpendicular to the axle. Avoid countersunk bolt heads if possible, to avoid distortion.

I probably don't deserve to have this post read, as I'm not building a motor bogie (yet!).

Andrew

[cabbage]

4:11 GMT -sign on.

ralph

[cabbage]

4:42 GMT uploaded.



ralph

[cabbage]

Quote:

when can we expect to see something in print?

Unquote:

According to the date stamp on my FTP client 16:42:19 02-01-2016. If you want a DXF or DRG you will have to wait until I get home. I did the above using my Blackberry on the train home.

ralph

[Peaky 556]

Ralph,
Good work, especially when taking the Hogmanhay hangover into account!

I don't suppose these gears come with anything finer than 1.0 MOD do they?  If not, never mind, the prices look great!

Andrew's point about using metal for the smallest gear seems to be intuitively correct to give long life, but does your experience tell us the difference is irrelevant for our duties?

I make your overall gear ratio 7.2:1, which should be perfectly OK. My opinion is that we will not be sensitive to gear ratio, as something equal or higher than 10:1 will achieve the 747 rpm necessary to achieve a scale 90 mph with wheels of diameter 3' 9".  Not sure where your "circa 11:1" came from, but that would be too low a gear ratio. You will recall that John's Sentinel has an ultra-low 30:1 ratio and will run flat out at a realistic 25 mph I think.

I am assuming that your schematic showing three vertical stacks is not actually proposed?  I would be very interested to know how compactly the three gearing axes could be brought together as a triangle, to allow the Peak's 8' axle spacing to be achieved when using three AHMGs, with "nesting" as required to minimise the vertical height. Hope that makes sense!

Regards, Tim

[cabbage]

OK... After a few hours on my futon, some food and a large cup of RR coffee. The Sabre engine of my mind begins to fire!

Tim,
You could use lower MOD gears -but why would you? The strength of the teeth of the gear would be lower and the teeth being smaller would be more heavily subject to fouling, (leaves grass etc). You could easily replace the nylon Gear One with a steel one for £4.20p (part number 4910-110). I prefer to "sacrifice" my primary gear to ensure quick replacement. The nylon primary gear on my mill being a good example. Non of the "Pocan" primary gears on "Lady Jane" have suffered wear -but I haven't seen small Pocan gears retailed in some time? Pocan is a glass nylon composite -the only people I still know sell them are IP Engineering.

In order to "collapse" the arrangement to a smaller volume I need to know the type, size, and position of the front fixing point for the motor. It is no good designing a gearbox if you cannot get at the nuts and bolts easily. To continue I would need some form of photo or dimensioned doodle of the front of the motor -sorry but someonelse is going to have to do the leg work for this part...

Phil,
Although I am now retired you will have gathered I have spent quite a lot of my working life either Teaching, working for either Siemens Transdata or Siemens Power Systems -oh and I worked for 6 years in the design dept for a company called "ZF Gmbh"...

regards

ralph

[classicdelights]

Indeed, good work Ralph.  If you look at the plan view of Ian's design you will see how the motor fits and how the gearbox frames are configured.  Ian's design is much smaller being just 93mm overall length where yours is 130mm.  That is not a problem if you were to configure the motor vertically as you suggest but I am not sure if this is practical in use.  In my experience it would be better to try and keep the whole AHMG unit within the bogie frames as much as possible as most space within the locomotive body is required for the other works. Just to refresh, the motor sits in circular cuts outs within the gearbox frames and is clamped into position, the frames being slit into the cut out and having a small clamping block added.  There are no fixing points at all on the motor.

Your design also throws up the question of how the gearbox frames are located.  One frame needs to be at each end of the motor but you have a problem with the gear 2 hub sitting where the shaft bearing should be.  If these issues can be sorted out perhaps we have the option of 2 designs for our gearbox. 

Once again, a good job Ralph, it will be an interesting option once sorted out.

Phil