Axle Hung Motor Gearbox (AHMG)

[IanT]

Hi Gavin,

Sorry I was (slowly) typing my previous post when you replied.

I'll certainly check these brushless motors - a very interesting approach.

Regards,

IanT

[Peaky 556]

Ian, I'm pretty disappointed to hear these HQ7P motors with drive gear will not fit within the 58mm BTB space.
Are we a long way off? Can anything be trimmed back a smidgen?  Any chance of a photo of the mismatch (pictures say a thousand words etc).
Thanks and regards, Tim

[IanT]

I'll see what I can do Tim - but sat here I've (quickly) just measured the HQ7P and the one in my hand has a 'main' body length of (a smidgen under) 50mm - but with two circular bosses which extend the overall length (without shaft) to 55mm. I don't think it could be easily shortened.

However, I don't think it's the end of the world. The G3 "between wheel bosses" dimension (given as 'H') is 76.2mm and that begins to define the inside face of any external frames. So whilst the motor will not sit right between the wheels, it may still be possible to have it sit above the wheels but off-set. I haven't done the CAD yet, so I may be talking complete nonsense (and often do).

However, I've looked at this problem (of AHMGs) in the past and the issue has always been finding a suitable motor, one small enough but with sufficient 'oomph' to do the job. The HQ7P looks like it should have the right kind of power available (again I need to do some static tests on one of mine) so we (just) need to find a way to make it fit.

I've had a look at Gavin's 'brushless' gimbal motor by the way and was pleasantly surprised by the price (not as expensive as I expected). They are also quite small but I don't know enough about them at this time to comment in any way. They seem to be defined by their "kv" (revs/volt - not Kilo-Volts) and the motor Gavin is using has a very low kv - 114kv in the version I found. I don't know too much about their other characteristics (such as current draw for instance). Gavin is probably much more advanced in his knowledge of these devices and hopefully can help us get up to speed.

In the meantime - I have bunch of HQ7Ps and that's what I'd like to use for my current 'bogie' loco project. Let's see what's possible.

Regards,

IanT

[Peaky 556]

Ian,
What you are saying is that the 55 mm length, when added to the length of a spur gear, would exceed 58mm.  So if the boss at the back end of the motor was reasonably small in diameter, and the spur gear on the drive end had a bigger diameter, then this boss could overlap the wheel flange?
Not sure if I am explaining my idea clearly enough, but it does depend on the rear boss being fairly small, and it may result in a non-ideal gear ratio as the spur gear on the motor shaft would have more teeth than ideal, in order to push the motor axis far enough away from the axle axis.
I don't know the viability without seeing a pic.
Cheers,
Tim

[IanT]

Hi Tim,

Yes (kind of) - the 'body' is 50mm + 3mm 'boss' + (say) 6mm Spur gear = 59mm. So use a thinner spur gear? - maybe but I suspect the gear ratio might be low. Not checked it.

I've just done a very quick draft of a 2-stage spur box using the off-set motor model. The motor fits (just) inside the frames - it's 1.5mm over but there would be some kind of bearing between the wheel hub and frame I assume - so probably not a problem. I'll try to dump it to JPeg and post it here. It may be difficult to understand it - as it is a quick "think it out" drawing.

Let's see .....

[IanT]

Ok - that worked better than I expected...

To explain - I just grabbed a "wagon" wheel set and added 0.75 MOD (HPC Steel) gears to it. The second stage is 12:60 ratio and there is a 50 tooth gear on the first stage (but no gear on the motor spindle. The horizontal red lines are simply to show me where a scale 4ft wheel (and flange) would be. The vertical red lines are the side frame/motor clearance (if you see what I mean).

Too late to go any further tonight, my brain is seizing up. So I haven't explored the other projection - as the motor is obviously also offset in the other plane as drawn here. Needs some thought and more work - but I think hope remains that we can sort something viable out.  :-)

Regards,

IanT

[Peaky 556]

Morning Ian,
I was still along the track of a single stage gearing for simplicity, not to mention low cost with gear wheel costs at HPC, and avoiding the intermediate shaft and bearings. As you will appreciate the costs of a AHMG are multiplied up by four or maybe six, per loco.
Can you give the diameters of the rear boss and the shaft please and I'll have a think about a layout in parallel to yours. It'll be tonight before I can get onto this.
When you state "I suspect the gear ratio may be low", do you mean low as is first gear in a car, or numerically low such as only say 3:1 instead of a desired say 5:1?
Regards, Tim

[classicdelights]

Ian

When I made similar motor arrangements for a gauge 1 Class 40 I set the bulges at each end of the motor into holes in the sub-frame that held everything in the correct place.  The wheels run in bearings in the bogie side frames and the sub-frame was prevented from rotating by a coil spring that fixed onto a bogie frame spacer.  I have attached some pictures of what I did plus a drawing of the Fosmotor system that is widely used in gauge 1 and also a picture of the Fosmotor.  The Fosmotor used standard coach wheel sets as did my system.  Most people are not bothered that the wheels are not exactly the correct size as you cannot see most of them anyway.  You just set the bearing position so the ride height is correct.

The gauge 1 system just used cheap MFA £3 motors, the best arrangement was 2 motors in a Co-Co bogie, 6 motors causing lots of wheel slip.  The gauge 1 Class 40 easily pulled 14 heavy coaches, all on a combined effort of 4 motors costing £12.  The motors we have should be much better.

I hope this is of some help.

Phil

[IanT]

Morning Tim/Phil,

Phil - my first reaction was to do a version of a 'traction' engine (as shown in your photos) and I see that your photos involves a motor that does seem to sit within the wheel set. I was hoping to use the HP7P in this mode but it's size is an issue.

Tim - I was referring to a gear ratio that did not 'down-gear' enough and I agree that the cost of a 2-stage gear set would be very expensive with multiple drives (in the range of £50/set for HPC steel ones!). However, I will finish this draft CAD model simply to see if it is viable, before I look again at a single stage design along the lines you have suggested. If we can find viable designs then it might also be possible to 'cost-reduce' them.

It may be that for axle-hung - the HQ7P will not be viable on grounds of 'fit' or cost - but I'd like to examine the possibilities before taking a final view on that. There are other options (e.g. find a shorter motor) and Gavin's brushless approach may be a very good one. I was quite surprised at the lower costs of these motors now - probably due to the growth in 'drone' technology.

Of course, the HP7P can clearly be used with a worm gear set-up = which would be required for other model types anyway. One objection to them is that they lock, causing an engine to halt abruptly but an electronic flywheel could resolve this issue.

I do have another G3-related project that I'm trying to stay focused on at the moment but will try to do more work in this area when I can. I also have family demands on my spare time at the moment that have to come first of course.

Regards,

IanT
 

[Peaky 556]

Ian
If you could just give me those two diameters requested, then I will have a look at a single stage gear in parallel with your other time demands!
Cheers, Tim

[IanT]

Hi Tim, sorry just got back.

HQ7P motor dimensions (rounded up to nearest 0.5mm) are as follows:

Main body  - Length = 50mm ; Diameter = 29mm
Front Boss - Depth = 3mm ; Diameter = 17mm
Rear Boss -  Depth = 3mm ; Diameter = 12mm
Shaft  -  Length = 20.5mm (from face of front boss); Diameter = 4mm

Note - electrical connections are on both sides of the rear boss 18mm apart - and will need clearance/access.

Thanks - be in touch

IanT

[Peaky 556]

Hi Ian,
Taking my Peak wheels as an example (3'9", scales to 50.5 on the tyre, 54.5 over standard G3 flanges), and moving the non-drive end boss of the motor outwards to lie just outside the flange, the biggest crown wheel that can be fitted is 70t, and the smallest pinion is 26t. The shaft centres needs to be a minimum of 33.5 mm so the motor boss does not touch the flange. The above teeth numbers assume moulded Muffett 'Hostaform' gears with 0.7 M, which are promoted by Ralph as being 'value for money'. The ratio is a not very impressive 2.69:1, and this cannot be improved upon with the desirable single stage gearbox.
Before writing this off as impractically high for a gear ratio, we need firstly to understand the power against speed characteristic of this motor (I will try to do this when I collect mine), and secondly the bright sparkies in the society could think about ways of electrically modifying this characteristic to give lots of torque at low revs.
I have said in another posting that extant ESCs may well give us an acceptable performance with a ratio like this.
I think that's all we can do for the moment, so time for a glass of red.
Regards, Tim

[Gavin_B]

Work is progressing on a though axle motor with no gear box.  The wheels are 3'1 wagon wheels.  need to fiddle with the electronics a bit more but am hoping to have it running at the weekend.

Hopefully there is a picture attached!

[IanT]

Very interesting Gavin, this may be the best way forward in this area, so please keep us all informed!

For the existing HQ7P 'owners' out there, I've been trying various arrangements for the  gearing, trying to find something that might work. There are several usable two-stage options available but the costs do rise a bit. Technobots are a bit cheaper than HPC (and their prices include VAT whereas I think HPC does not) but they have a more limited range - although they might consider a special if we wanted a few?.

So at the moment - my best "gear" solution is a combination of a large (84t) gear from HPC together with two (15t/40t) gears from TB - one of them used as an idler. This gives a 1:5.6 ratio - which might just about be OK - frankly I don't know. I'd have to build one to see.

Just to be clear, this is not a "design" solution yet, I'm just trying to find something that fits and might be affordable. I decided that this was the only way to approach it. Once I had something 'possible' then I can try to figure out the actual 'mechanics' involved. Currently, the three gear set would cost (1-off) £23.12 (inc VAT) so a gearbox 'kit' for about £30 might be possible.

For anyone interested, I've dumped the CAD to a .Jpeg and will post it below. As before it's just for "thinking it out" purposes. This design should work for wheel sets between 3ft 7" & 4ft (which are drawn). I've used MOD 0.5 gears and the 3ft 7" really decides the maximum size of the main gear. I could squeeze a few more teeth in but clearances would then be very tight. The choice of the 15t motor gear was decided by the fact the motor spindle is 4mm - the smaller TB gears (10t & 12t) are 2.3mm bore and anyway might be a bit fragile. You can see that the distance between the axle C/L and the outer curve of the motor is just under 60mm (4ft 6" scale). However, the unit could be angled upwards to effectively shorten the wheelbase if required

I'm afraid I've not been able to give this too much time at the moment as there is a lot going on elsewhere. Anyway b- that's where I've got to thus far. Any thoughts?

Regards,

IanT

[cabbage]

Try replacing the gears with these...

Muffett Gears

0.7MOD Spur Gear

12 tooth s0.7 012h
40 tooth s0.7 040h
64 tooth s0.7 064h

That will (see above) give you the required 6:1 ratio.

regards

ralph