Possible motor problem with Bachmann Lyn

PhilP said:
So I was probably answering the wrong question? :(

AND..............

I got both answers wrong!! :oops::wasntme:

PhilP.
(Sir, as we are not doing exams (again) this year... Will this affect my grade?) :)
Click to expand...
I'm just hoping I've interpreted the calculator correctly :wasntme:
I'm sure somebody will put me right if not ;)

Rik
 
I suspect we are mixing up the theoretical mechanical advantage of the worm gear mechanism with the increased frictional forces generated by the larger contact surface area between the gears. In your "larger diameter screw or bolt" analogy the increased force required is due to the increased friction of the increased area of screw thread in contact with the threaded hole. The bigger the worm gears are the more surface area and sliding across the facing surfaces there will be. But it's a long time since I studied this at Uni so I may be misremembering!
 
idlemarvel said:
I suspect we are mixing up the theoretical mechanical advantage of the worm gear mechanism with the increased frictional forces generated by the larger contact surface area between the gears. In your "larger diameter screw or bolt" analogy the increased force required is due to the increased friction of the increased area of screw thread in contact with the threaded hole. The bigger the worm gears are the more surface area and sliding across the facing surfaces there will be. But it's a long time since I studied this at Uni so I may be misremembering!
Click to expand...
I suspect you are right. I'd like to think that my suppositions about the mechanical advantage (or disadvantage) have some bearing (no pun intended), but I consulted a mechanical engineering mate of mine and shared some of our discussions. These were his conclusions .....

Interesting, but note that if you quadruple the radius, it only increases the torque by around 25% (not by 300%, not 4-fold). I still maintain this is chiefly about friction. A bigger diameter worm will offer more contact face area leading to increased friction. I think most of your bloggers are mostly right in what they say, including you. Your views are more relevant to start-up than steady running. Once you get a flywheel revolving it is easy to keep it revolving.

A smaller diameter worm weighs less, will offer less friction and reduce thrust bearing and worm-wheel wear (unless chosen sizes are ridiculous). One downside is that it limits thrust bearing size which is why worms in heavily loaded gearboxes feature large diameter shafts (also for the shaft to cope with the load / torque). It can become a compromise.

Of course, being a mate, he might be trying to let me down lightly and steer a middle course - but it does look as if friction is a key factor. I tried tinkering with the calculator by reducing the coefficients of friction to see if that made a difference. Reducing them to zero led to somewhat confusing results suggesting that friction is a key factor (drat!!).

Rik
 
Well, it's taken me a while - several re-designs and a few duff prints - but I think I now have a workable clamshell for the re-motored Lyn. As was suggested, I've moved the axles outwards by a couple of mm to bring the worm wheels more central to the worms - and also to help prevent them rubbing against the motor casing. Of course, it will mean having to extend the connecting rods but that's a small price to pay for what I hope is increased reliability.

Many thanks to those who offered observations, advice and suggestions. This has been an "interesting" build... :think:

Motor block x 3.jpg

Rik
 
Greg Elmassian said:
Great! have you run it yet?

Did you build in a lug to secure the motor rotation?

greg
Click to expand...
Hi Greg
I've run it on the bench but not yet on the track.
Definitely included the lug - visible in the first photo

Thanks for your input in this thread.

Rik
 
Looks like you're just a step away from one heck of a solution. The forum input was not only enthusiastic but very technically entertaining throughout. Of course, the final result (a NEW one of a kind motor block which you designed and made through what I maintain is still a sort of "miracle" process of 3d printing) is such a fitting conclusion. Kudos are due all around! Extremely well done.
 
Thornmini said:
Looks like you're just a step away from one heck of a solution. The forum input was not only enthusiastic but very technically entertaining throughout. Of course, the final result (a NEW one of a kind motor block which you designed and made through what I maintain is still a sort of "miracle" process of 3d printing) is such a fitting conclusion. Kudos are due all around! Extremely well done.
Click to expand...
Yes - I see this as very much a team effort ....... :)

Rik
 
ge_rik said:
I suspect you are right. I'd like to think that my suppositions about the mechanical advantage (or disadvantage) have some bearing (no pun intended), but I consulted a mechanical engineering mate of mine and shared some of our discussions. These were his conclusions .....

Interesting, but note that if you quadruple the radius, it only increases the torque by around 25% (not by 300%, not 4-fold). I still maintain this is chiefly about friction. A bigger diameter worm will offer more contact face area leading to increased friction. I think most of your bloggers are mostly right in what they say, including you. Your views are more relevant to start-up than steady running. Once you get a flywheel revolving it is easy to keep it revolving.

A smaller diameter worm weighs less, will offer less friction and reduce thrust bearing and worm-wheel wear (unless chosen sizes are ridiculous). One downside is that it limits thrust bearing size which is why worms in heavily loaded gearboxes feature large diameter shafts (also for the shaft to cope with the load / torque). It can become a compromise.

Of course, being a mate, he might be trying to let me down lightly and steer a middle course - but it does look as if friction is a key factor. I tried tinkering with the calculator by reducing the coefficients of friction to see if that made a difference. Reducing them to zero led to somewhat confusing results suggesting that friction is a key factor (drat!!).

Rik
Click to expand...
The coefficient of friction=force of friction/normal reaction suggests the area would not affect the forces caused by friction.
According to Mr Sheddon in those 'mechanics of machines' classes all those years ago.
Ben
 
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And so the saga continues ...... :(

After reassembling the loco, I gave her a test run. Still very disappointing in terms of pulling power. Even with a standard load of eight goods wagons the loco really struggled up my 1:40 gradients which my other locos gallop up. It also slowed appreciably on curves; the curve on the gradient brought it to a snail's pace on full power. I discovered the gauge on the drivers was slightly wide, but pushing the wheels tighter on to the gears to bring them to gauge made minimal difference. I stripped the motor block down to see if my clamshell was rubbing on anything. Nothing evident but I filed possible pinch points just in case. I reassembled and found there was very little improvement.

In desperation, I assembled the motor block which JimmyB had kindly sent me - which looks almost new.

Another test run and exactly the same outcome! Too little power to cope with a standard train!!

I can only assume that, for whatever reason (friction and/or my leverage theory), the large worms seriously impede the motor's ability to transmit power.

My next resort is to see if I can replace the worms with smaller diameter versions. I've ordered a gear puller and have found out how to calculate the mod value of the worm wheels. I just hope I can find a couple of replacements somewhere......

I will not be defeated!! :eek::wasntme:

Rik
 
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Very silly question, have you tried pushing the loco with out the motor in place? It may not be the motor block causing the problem, or even tried the motor block on it's own?
 
According to this online calculator,

Gear Size Calculator

Gear size calculator
www.technobotsonline.com www.technobotsonline.com

..... it's a Mod 0.5 gear on a 2.5mm shaft. Reassuring that it's note something more obscure.

Rik
 
ge_rik said:
My next resort is to see if I can replace the worms with smaller diameter versions. I've ordered a gear puller and have found out how to calculate the mod value of the worm wheels. I just hope I can find a couple of replacements somewhere......

I will not be defeated!! :eek::wasntme:

Rik
Click to expand...
Hi Rik
Right then, We know the make of the motor, but do you have any idea what it came from? It's possible that it's just too low powered for your application. As an example The motors in (LGB) Toytrain locos ( OTTO etc.) whilst being from the same manufacturer as for example an LGB stainz had considerably less pulling power.
Also smaller diameter worms will mean reducing the distance between motor and axle cogs, which would probably then require moving the wheels and worms further apart to clear the motor body.
Also what diameter are the wheels and axles?
Paul.
 
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ge_rik said:
And so the saga continues ...... :(

After reassembling the loco, I gave her a test run. Still very disappointing in terms of pulling power. Even with a standard load of eight goods wagons the loco really struggled up my 1:40 gradients which my other locos gallop up. It also slowed appreciably on curves; the curve on the gradient brought it to a snail's pace on full power. I discovered the gauge on the drivers was slightly wide, but pushing the wheels tighter on to the gears to bring them to gauge made minimal difference. I stripped the motor block down to see if my clamshell was rubbing on anything. Nothing evident but I filed possible pinch points just in case. I reassembled and found there was very little improvement.

In desperation, I assembled the motor block which JimmyB had kindly sent me - which looks almost new.

Another test run and exactly the same outcome! Too little power to cope with a standard train!!

I can only assume that, for whatever reason (friction and/or my leverage theory), the large worms seriously impede the motor's ability to transmit power.

My next resort is to see if I can replace the worms with smaller diameter versions. I've ordered a gear puller and have found out how to calculate the mod value of the worm wheels. I just hope I can find a couple of replacements somewhere......

I will not be defeated!! :eek::wasntme:

Rik
Click to expand...
Hm sounds like a job for a new scratch built chassis.
 
Not wishing to chuck a grenade in here, but replace the motor block with an LGB block..........

(Ducks for cover) :)
 
Paul2727 said:
Hi Rik
Right then, We know the make of the motor, but do you have any idea what it came from? It's possible that it's just too low powered for your application. As an example The motors in (LGB) Toytrain locos ( OTTO etc.) whilst being from the same manufacturer as for example an LGB stainz had considerably less pulling power.
Also smaller diameter worms will mean reducing the distance between motor and axle cogs, which would probably then require moving the wheels and worms further apart to clear the motor body.
Also what diameter are the wheels and axles?
Paul.
Click to expand...
The two motor blocks (original and modified) give almost the exact same performance so I don't think it can be the replacement motor which is the problem.

I've worked out that if I reduce the diameter of the worm I'll probably need to put an idler gear between the worm and the worm wheel on the axle to clear the motor casing. I've found single start mod .5 worms and worm wheels on eBay but the have 6mm holes so I'm looking for bore reducers.

The diameter of the axles is 8mm and wheels 37.3mm. Each wheel and stub axle slots into the worm wheel with a square end section (see previous photos)

Rik
 
How much is your time worth?
Plus the cost in 'bits'...

For £35 you could buy a new LGB twin-ended motor.. :nerd:
 
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