Weak Bachmann Lyn motor

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metalmuncher
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Re: Weak Bachmann Lyn motor

Post by metalmuncher » Tue Mar 02, 2021 7:56 pm

ge_rik wrote:
Tue Mar 02, 2021 6:55 pm
If the worm wheels are standard size, then maybe a motor with smaller diameter worms might give more thrust. I'm hoping that assumption is valid.
With worm gears, the gear ratio is dependent on the number of starts of the screw, not the diameter of the worm. E.g. a single start worm used with a 40 tooth worm wheel has a ratio 40:1, no matter the diameter of the worm. Most of the worms I've seen on models are single start, but I can't really tell if the ones on your motor block are single or multi start. If it is multi start, swapping the worms for same-diameter single start versions would increase the gear ratio, giving more torque and less speed.

Since most worms are single start, to get more torque your best bet is to increase the number of teeth on the worm wheel, but for simple arrangements where the worm wheel is on the same axle as the wheels, your number of teeth on the worm wheel is limited by the size of the wheels, otherwise the worm wheel can foul the track.

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Re: Weak Bachmann Lyn motor

Post by gregh » Wed Mar 03, 2021 5:45 am

Have you tried the Bachmann spare parts page? A quick search gave me this...
https://estore.bachmanntrains.com/index ... 3vmdta3l11

I think I mentioned before that I used two of the motor blocks in my red Garratt with no problems. I bought them in 1997 but they were labelled as Spectrum types so may be better quality.

If you apply finger pressure to the loco, do the wheels spin or stall? From the video it seems to stall.

The different operation in forward and reverse MAY be due to 'slop' on the main drive shaft allowing the worm gear to be pushed to one end and bind. I had to put a small brass shim behind the worm to hold it in place.

Can you measure the armature resistance with your multimeter? It could help determine if the motor is damaged. Expect resistance to be around 4 or 5 ohms. I can measure mine if it helps. And measure the milliamps the motor takes when running with its wheels in the air.

And the obvious - how much does it weigh and is the weight over the drivers or unbalanced at one end?
Greg from downunder.
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ge_rik
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Re: Weak Bachmann Lyn motor

Post by ge_rik » Wed Mar 03, 2021 9:06 am

metalmuncher wrote:
Tue Mar 02, 2021 7:56 pm
ge_rik wrote:
Tue Mar 02, 2021 6:55 pm
If the worm wheels are standard size, then maybe a motor with smaller diameter worms might give more thrust. I'm hoping that assumption is valid.
With worm gears, the gear ratio is dependent on the number of starts of the screw, not the diameter of the worm. E.g. a single start worm used with a 40 tooth worm wheel has a ratio 40:1, no matter the diameter of the worm. Most of the worms I've seen on models are single start, but I can't really tell if the ones on your motor block are single or multi start. If it is multi start, swapping the worms for same-diameter single start versions would increase the gear ratio, giving more torque and less speed.

Since most worms are single start, to get more torque your best bet is to increase the number of teeth on the worm wheel, but for simple arrangements where the worm wheel is on the same axle as the wheels, your number of teeth on the worm wheel is limited by the size of the wheels, otherwise the worm wheel can foul the track.
I can see that I'd get the same reduction ratio regardless of the diameter of the worm, but how about the amount of thrust on each tooth. Say, for example, the worm was a metre in diameter. Wouldn't amount of effort needed to push each tooth be greater than if the worm was only 5mm in diameter - or will the amount of thrust remain the same? Sorry if I'm getting my forces terminology mixed up.

Rik
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Re: Weak Bachmann Lyn motor

Post by ge_rik » Wed Mar 03, 2021 10:18 am

gregh wrote:
Wed Mar 03, 2021 5:45 am
Have you tried the Bachmann spare parts page? A quick search gave me this...
https://estore.bachmanntrains.com/index ... 3vmdta3l11

I think I mentioned before that I used two of the motor blocks in my red Garratt with no problems. I bought them in 1997 but they were labelled as Spectrum types so may be better quality.
Thanks for this comprehensive reply Greg
I've now investigated the parts needed to replace the motor block. I'd also need a new wheel set as the gears on the new block are different. The total comes to £98 with shipping to the UK and I'd then need to pay 20% VAT so it would be nearly £120 overall. I think I'll see if there's a cheaper solution.
gregh wrote:
Wed Mar 03, 2021 5:45 am
If you apply finger pressure to the loco, do the wheels spin or stall? From the video it seems to stall.

The different operation in forward and reverse MAY be due to 'slop' on the main drive shaft allowing the worm gear to be pushed to one end and bind. I had to put a small brass shim behind the worm to hold it in place.
Yes, I can stall the loco with finger pressure. Something which is very difficult with my other locos. I'm going to try playing around with the block in its half assembled state to see if I can spot any sloppiness or binding. I'll give it a jolly good degrease and cleanup as well.
gregh wrote:
Wed Mar 03, 2021 5:45 am
Can you measure the armature resistance with your multimeter? It could help determine if the motor is damaged. Expect resistance to be around 4 or 5 ohms. I can measure mine if it helps. And measure the milliamps the motor takes when running with its wheels in the air.
Armature resistance is 6 ohms and it draws around 100 mA on tickover and around 180mA on full power with wheels in the air.
gregh wrote:
Wed Mar 03, 2021 5:45 am
And the obvious - how much does it weigh and is the weight over the drivers or unbalanced at one end?
I've placed the original weights from the Lyn in the side tanks. Slightly biased towards the cab so I might try adding something to the front end as per the Lyn.


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Re: Weak Bachmann Lyn motor

Post by ge_rik » Wed Mar 03, 2021 6:33 pm

Well folks! Thanks very much for all your kind thoughts, suggestions and contributions - both in words and, in one case, in posting me a replacement motor - which I maybe won't need to use. I think I have identified the problem and fixed it (let's hope that's not famous last words!).

By cleaning everything up and then closely scrutinising all the bits I figured out that the motor which was installed in the motor block was actually a replacement to the original. The original mountings for the motor had been filed away and the corners of the motor had also been filed to clear the worm wheels.
Merged_document.jpg

BY watching carefully, I discovered the motor twisted slightly (by only a couple of mm) when under power. This was sufficient for the motor can to rub against one of the worm wheels. I inserted a self-tapping screw through the clamshell housing to engage with a slot in the side of the motor can. This seems to have done the trick. The loco now runs as well (or as badly) going forwards as it does in reverse.



My next task is to design and 3D print a bespoke clamshell housing which include lugs to hold the motor more securely. The plastic of the original housing is so brittle that all the pillars for the self-tapping screws holding it together have either split or completely disintegrated.

Many thanks again to all those who contributed to the deliberations in this thread. To my mind, this sort of discussion is what a forum like this is all about.

Rik
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philipy
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Re: Weak Bachmann Lyn motor

Post by philipy » Wed Mar 03, 2021 7:06 pm

Well done Rik. That looks fine ( weird as an 0-4-0 ) but fine. :D

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Re: Weak Bachmann Lyn motor

Post by ge_rik » Wed Mar 03, 2021 10:19 pm

philipy wrote:
Wed Mar 03, 2021 7:06 pm
Well done Rik. That looks fine ( weird as an 0-4-0 ) but fine. :D
It reminds me of one of those Hornby tinplate clockwork locos which I used to have running at full pelt on the sitting room carpet as a kid .... My first train set! :D

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Re: Weak Bachmann Lyn motor

Post by GTB » Thu Mar 04, 2021 9:15 am

ge_rik wrote:
Wed Mar 03, 2021 6:33 pm
I think I have identified the problem and fixed it (let's hope that's not famous last words!).
I thought that thing looked like it had been butchered to fit a different motor. You're more patient than me, I'd have long since given it a burial at sea by tossing it off the end of the local pier.......

The butchery was presumably to replace a cooked Mabuchi motor, but possibly also in the vain hope that fitting the same motor that LGB use will make it run like an LGB loco. Not likely with Bachmann gears......

That's the early Lyn chassis, the current one is a better design with metal gears. Bachmann supposedly designed the early drive in the belief that the large worms would act as flywheels, but they aren't heavy enough, or large enough in dia. for that.

Greg also touched on balancing the loco. 0-4-4 tank locos are notorious for losing traction, as they are hard to balance properly. When running funnel first, the load of the train transfers weight off the drivers onto the rear bogie. They run better bunker first, as the weight is then transferred onto the drivers. Try and get as much of the weight as far forward as you can.

Graeme

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Re: Weak Bachmann Lyn motor

Post by ge_rik » Tue May 04, 2021 10:56 am

Well. It's been a while.....
After no end of unsuccessful searching, discussions with Bachmann and contacting several gear manufacturers I eventually tracked down a set of gears which were by no means perfect, but I felt I could use.

The worm has a 3mm bore (the Bachmann motor has a 2.5mm shaft) and the worm wheel has a 6mm bore (the nylon 'axle' on the loco is around 7.75mm).

I used a piece of 3mm copper tube, reamed out to around 2.4mm which is a force fit on the motor shaft. I 'removed' the moulded gear from the axle and turned it down to around 7.6mm (in the chuck of my drill using a flat file) and opened out the hole in the worm wheel to 7.5mm and force fitted it to the remains of the axle.

I redesigned the motor block to reposition the motor and to take the larger worm wheel.

It sort-of works! The gears grind horribly in one direction but are reasonably OK in the other direction, so I've eased the mesh by around 0.2mm. I've also moved the motor 1.5mm towards the worm - there is space, despite how it looks on the photo. I'm not going to be able to centre the worm over the worm wheel unless I can extend the motor shaft somehow.

Getting nearer........
new block-merged.jpg
Any tips on meshing gears anyone?
Trouble is, I can't see inside the block once it's assembled and so having to rely on what I imagine is going on inside.

Rik
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Re: Weak Bachmann Lyn motor

Post by Lonsdaler » Tue May 04, 2021 11:47 am

Congratulations on getting this far Rik. I can't offer any expert advice on positioning/meshing of worm gearing, but from my model boating days, I used to extend motor shafts by fitting an 'interference fit' piece of brass tubing over the exposed motor shaft, and then used the OD of that tubing to size other necessary components. Not sure if that would be any help to you, but I look forward to seeing your progress :thumbup:
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ge_rik
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Re: Weak Bachmann Lyn motor

Post by ge_rik » Tue May 04, 2021 12:29 pm

Lonsdaler wrote:
Tue May 04, 2021 11:47 am
Congratulations on getting this far Rik. I can't offer any expert advice on positioning/meshing of worm gearing, but from my model boating days, I used to extend motor shafts by fitting an 'interference fit' piece of brass tubing over the exposed motor shaft, and then used the OD of that tubing to size other necessary components. Not sure if that would be any help to you, but I look forward to seeing your progress :thumbup:
I might try that, using a longer piece of copper tube and then only reaming out half of it...

Rik
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Re: Weak Bachmann Lyn motor

Post by philipy » Tue May 04, 2021 1:32 pm

ge_rik wrote:
Tue May 04, 2021 12:29 pm
Lonsdaler wrote:
Tue May 04, 2021 11:47 am
Congratulations on getting this far Rik. I can't offer any expert advice on positioning/meshing of worm gearing, but from my model boating days, I used to extend motor shafts by fitting an 'interference fit' piece of brass tubing over the exposed motor shaft, and then used the OD of that tubing to size other necessary components. Not sure if that would be any help to you, but I look forward to seeing your progress :thumbup:
I might try that, using a longer piece of copper tube and then only reaming out half of it...

Rik
Or perhaps one of the expert engineers amonst our members might volunteer to turn you a nice extension sleeve, rather than relying on files and hand drills. :D

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