An international forum for garden railway modellers in all scales and gauges. It is free to join and is funded through voluntary contributions by its members. Many thanks to all those who keep it going. https://gardenrails.org/forum/
It sort of runs under gravity - but not quite. It moves but the slightest thing stops it.
It has ball races in the axles, but the wheels are solidly mounted on the axles.
How do I reduce the friction so that it runs even more freely?
Re: Gravity running on the RVOM
Posted: Tue Oct 06, 2020 12:19 pm
by Trevor Thompson
I suppose I have not framed the question correctly!
It should be where do I get small ball races which will fit into the hubs of the wheels, or on the axles?
What I have done is to use 2mm stainless balls running on 3mm diameter axles, and turned a loose bore or housing to take the balls - as a sort of home made ball race.
They do "all of the colours in all of the sizes" to quote Beattie!
Re: Gravity running on the RVOM
Posted: Tue Oct 06, 2020 2:03 pm
by 11thHour
Because of the light weight there will be no significant wear to worry about, will having the wheels a loose fit on a stepped axel, combined with a retainer on the outside work. Any standard bearing will produce a lot of friction?
Tim
Re: Gravity running on the RVOM
Posted: Tue Oct 06, 2020 2:17 pm
by GTB
Trevor Thompson wrote: ↑Mon Oct 05, 2020 6:39 pm
How do I reduce the friction so that it runs even more freely?
I suspect you are on a hiding to nothing.
I did a bit of playing around in the workshop with some of my stock this afternoon while I was waiting for some paint to dry. The testing was done with a length of track on a board, propping up one end to try different gradients. The rail was cleaned recently and was nice and smooth. I machine my own wheelsets out of bright steel bar and use plain bearings, lubricated with teflon grease.
Anyway......
I found that a recently machined wheelset with clean treads would roll freely on it's own on a 1:65 grade.
Fit two of them in a bogie and they needed a 1:60 grade to roll freely, so the axle bearings have increased rolling resistance by 8-9%. Add enough weight to simulate one of my four wheel open wagons and the bogie needed a 1:50 grade to roll freely.
Metal wheels that haven't been cleaned lately don't roll as well, so two wheelsets in a bogie needed a 1:50 grade to roll freely and a 1:45 grade to roll freely when loaded. Dirty rail would increase the rolling resistance even more.
On top of all that.......
As you've found, the starting resistance of a vehicle is higher than the rolling resistance, so a steeper grade is needed to start something rolling than to maintain that speed once moving. Which means that if the vehicle is on a grade steep enough to start rolling on it's own, it will then continue to accelerate once moving and some sort of braking system is needed to control speed downhill. This is why most of my four wheel wagons have working handbrakes, as although my track is flat, others aren't.
The other thing to remember is that the rolling resistance of rolling stock is higher on curved track than it is on straight track. It was higher on a 1200mm curve by a factor of about two when I did some testing a while back, so I developed a wheelset where one wheel in a wheelset is free to rotate on the axle. Wagons fitted with these wheelsets now have the same rolling resistance on curved track as they do on straight track.
If you have a hobby shop locally that specialises in r/c cars and buggies, they usually have a range of suitable size miniature ball bearings. I looked at making some ball bearing wheelsets a while back to minimise rolling resistance on curves and was going to use 3x8x3mm shielded bearings, but eventually used plain bearings.
A 1:60 grade may not be steep enough to do what you want, as ball bearings aren't friction free, especially when grease lubricated as most are. Adding them between wheel and axle will certainly minimise the effect of curves though.
To minimise rolling resistance you will also need to have metal wheelsets (if you aren't already using them) with squeaky clean and smooth wheel treads and rail.
The only way to know for sure will be to experiment and test each change you make until it works, or you find the optimum gradient. Personally I'd do it in the workshop with a length of track on a board, so you can control all the variables.
Regards,
Graeme
ps. What direction do your prevailing winds come from? Wind resistance from that sail may well override any improvements you can make to rolling resistance........
Trevor Thompson wrote: ↑Mon Oct 05, 2020 6:39 pm
How do I reduce the friction so that it runs even more freely?
I suspect you are on a hiding to nothing.
I did a bit of playing around in the workshop with some of my stock this afternoon while I was waiting for some paint to dry. The testing was done with a length of track on a board, propping up one end to try different gradients. The rail was cleaned recently and was nice and smooth. I machine my own wheelsets out of bright steel bar and use plain bearings, lubricated with teflon grease.
Anyway......
I found that a recently machined wheelset with clean treads would roll freely on it's own on a 1:65 grade.
Fit two of them in a bogie and they needed a 1:60 grade to roll freely, so the axle bearings have increased rolling resistance by 8-9%. Add enough weight to simulate one of my four wheel open wagons and the bogie needed a 1:50 grade to roll freely.
Metal wheels that haven't been cleaned lately don't roll as well, so two wheelsets in a bogie needed a 1:50 grade to roll freely and a 1:45 grade to roll freely when loaded. Dirty rail would increase the rolling resistance even more.
On top of all that.......
As you've found, the starting resistance of a vehicle is higher than the rolling resistance, so a steeper grade is needed to start something rolling than to maintain that speed once moving. Which means that if the vehicle is on a grade steep enough to start rolling on it's own, it will then continue to accelerate once moving and some sort of braking system is needed to control speed downhill. This is why most of my four wheel wagons have working handbrakes, as although my track is flat, others aren't.
The other thing to remember is that the rolling resistance of rolling stock is higher on curved track than it is on straight track. It was higher on a 1200mm curve by a factor of about two when I did some testing a while back, so I developed a wheelset where one wheel in a wheelset is free to rotate on the axle. Wagons fitted with these wheelsets now have the same rolling resistance on curved track as they do on straight track.
If you have a hobby shop locally that specialises in r/c cars and buggies, they usually have a range of suitable size miniature ball bearings. I looked at making some ball bearing wheelsets a while back to minimise rolling resistance on curves and was going to use 3x8x3mm shielded bearings, but eventually used plain bearings.
A 1:60 grade may not be steep enough to do what you want, as ball bearings aren't friction free, especially when grease lubricated as most are. Adding them between wheel and axle will certainly minimise the effect of curves though.
To minimise rolling resistance you will also need to have metal wheelsets (if you aren't already using them) with squeaky clean and smooth wheel treads and rail.
The only way to know for sure will be to experiment and test each change you make until it works, or you find the optimum gradient. Personally I'd do it in the workshop with a length of track on a board, so you can control all the variables.
Regards,
Graeme
ps. What direction do your prevailing winds come from? Wind resistance from that sail may well override any improvements you can make to rolling resistance........
You may well be correct.
However I will experiment!
I won't worry about the sail - that is removable and not needed when under gravity.
I have metal wheels on it at the moment. I have painted the treads. I wonder if that has an impact?
I will report back if I get anywhere.
Trevor
Re: Gravity running on the RVOM
Posted: Wed Oct 07, 2020 10:52 am
by GTB
Trevor Thompson wrote: ↑Tue Oct 06, 2020 8:52 pm
However I will experiment!
I won't worry about the sail - that is removable and not needed when under gravity.
I have metal wheels on it at the moment. I have painted the treads. I wonder if that has an impact?
I will report back if I get anywhere.
Sounds like a plan. Experiment beats theory and pontification every time........
Painted wheel treads are effectively plastic wheels, so won't help and will get dirty quickly. I clean wheel treads after painting the wheels with paint thinner and a pipe cleaner. If the paint is very stubborn, a fibreglass pen leaves a nice shiny surface.
I think gravity working can be made to work, but it may take a steeper gradient than 1:60 to be reliable. The horseshoe curve between levels won't help, but making the wheels rotate separately on the axle will minimise the effect of curves.
Regards,
Graeme
Re: Gravity running on the RVOM
Posted: Wed Oct 07, 2020 7:04 pm
by Peter Butler
Somewhere I have seen a 16mm scale, motorised 'gravity' train, which is not in the spirit of the idea I know, but works!
Re: Gravity running on the RVOM
Posted: Wed Oct 07, 2020 7:34 pm
by Trevor Thompson
Peter Butler wrote: ↑Wed Oct 07, 2020 7:04 pm
Somewhere I have seen a 16mm scale, motorised 'gravity' train, which is not in the spirit of the idea I know, but works!
Yes Peter I have seen them as well. As you say it isn't in the spirit of the thing - and I cant help but try to do it the hard way!
Trevor
Re: Gravity running on the RVOM
Posted: Mon Nov 02, 2020 9:42 pm
by Trevor Thompson
I have been experimenting - and have made some progress.
I ordered ball bearings, 3mm ID, 6mm OD and made experimental plastic wheels on the 3D printer.
I have tapered the treads (which I don't usually bother to do particularly if I am making the them in the lathe) and reduced the flanges to 0.5mm deep. I was thinking that they might self steer around curves and avoid the flanges making contact with the rail (and causing friction) - yet to see if that has any impact. I have also made a new chassis which incorporates compensation to make sure each wheel maintains contact with the rail.
IMG_1008.jpg (370.43 KiB) Viewed 7765 times
The photo shows the new chassis with its experimental wheels. You can see the ball bearing. It is unshielded ( less friction without shields?) and there are two of them in each wheel, about 1mm apart. I cleaned the bearings to get rid of the preserving oil in them (which was causing friction) and lightly lubricated them.
The bare chassis with a weight added (300 grams) rolled freely on a gradient of 1 in 167. The original boat (with the same weight added) on its painted steel wheels and brass chassis required a slope of 1 in 64 to get it to roll.
So whatever transpires with the wheel experiment it looks like I have a viable boat to gravity run in the spring!
Trevor
Re: Gravity running on the RVOM
Posted: Mon Nov 02, 2020 11:19 pm
by metalmuncher
Trevor Thompson wrote: ↑Mon Nov 02, 2020 9:42 pm
I was thinking that they might self steer around curves and avoid the flanges making contact with the rail (and causing friction) - yet to see if that has any impact.
Without a solid axle connecting left and right wheels you don't get a good steering effect due to a tapered tread, there are lots of demo videos/explanations of how coupled conical train wheels steer, this one shows how wheels with individual bearings doesn't work, although obviously a four wheeled wagon won't just fall off the track like the axle does in the video:
I have seen in the Hudson catalogues they made axles with both wheels loose on the axle, so not all real prototypes used solid axles to make use of the steering effect. They advertise those wheels as better for tight curves, I presume because they are so tight the conical wheels don't have enough effect and the flanges will contact anyway.
I wonder if it's better to spread the load across four bearings per axle like you have, or have fewer bearings with one bearing each side of a solid axle...
Re: Gravity running on the RVOM
Posted: Tue Nov 03, 2020 12:43 pm
by Trevor Thompson
Interesting video.
Lots of quarry wagons had wheels which were loose on the axles. Not just able to rotate independently but able to change gauge. Of course they used double flanges.
Anyway back to the point, maybe I am waisting my time with tapered treads - but it doesn't matter because I can alter the profile and reprint the wheels. On the other hand it might still minimise flange contact. I may have to increase the flange depth as well.
The main thing is that I have the potential for it to roll under gravity.
I look forward to having to organise radio controlled brakes!
I look forward to having to organise radio controlled brakes!
Trevor
Could you use RC to operate the sail? It might even go uphill on a windy day!
Re: Gravity running on the RVOM
Posted: Thu May 05, 2022 1:30 pm
by Trevor Thompson
A bit of an update on gravity running.
Sparked really by a running session with Simon earlier in the week. He took one of my trains up the line and discovered that when he uncoupled the locomotive to run around the train the train took off down the line on its own.
So what have I done?
There are two types of wheel bearing arrangements.
Firstly early wagons (and the slate workmen's train "coaches") had inside bearings. It is straightforward to add ball races to them:
IMG_2198.JPG (1.62 MiB) Viewed 4500 times
You can see an early wagon (a Dandy wagon which I suspect should have had inside bearings) and in front of it a printed bearing housing, which has a through hole for the axle of 4mm diameter opened out to 8mm diameter for 3mm at each end. There is also a packet of ball races in the photo, 3mm bore, 8mm outside diameter. The 3mm diameter axles are threaded through the housing after pressing the races into the bearing block - and then the bearing is bonded into place.
More complicated to achieve (but the end result is very satisfying) is to do the same with outside bearing wagons and coaches. In this case I found some very small bearings - 1mm internal diameter, 3mm outside diameter and 1mm wide.
The axles were turned down to 2mm diameter for 5.5mm and then to 0.95mm diameter for 1.1mm, at each end. Clearly this requires a lathe, and is easier to achieve with a digital readout system.The axles ready to use:
IMG_2195.JPG (2.06 MiB) Viewed 4500 times
They are sitting on a wagon body which was modified to accept a geardtrain and motor! I don't think I will actually need to use it on my own railway!
and with wheels and bearings added:
IMG_2196.JPG (1.3 MiB) Viewed 4500 times
The biggest issue in assembling these is that I have dropped bearings on the floor and I cant find where they have ended up.
Finally this wagon has descended on its own from further up the line - and its going quite quickly here:
IMG_2197.JPG (3.07 MiB) Viewed 4500 times
I have yet to get the Spooners Boat to perform this well - but I am sure it can be done.
Trevor
Re: Gravity running on the RVOM
Posted: Fri May 13, 2022 5:44 pm
by Old Man Aaron
Absolute inspiration as always, Trevor.
Certainly making progress, I've no doubt you'll have the boat running away soon. Have you had any derailing issues on gravity movements?
Never thought they'd make bearings that small! A fitting offering to the Small Parts Abyss that is the floor.
Re: Gravity running on the RVOM
Posted: Tue May 17, 2022 8:20 am
by SimonWood
Trevor Thompson wrote: ↑Thu May 05, 2022 1:30 pm
Sparked really by a running session with Simon earlier in the week. He took one of my trains up the line and discovered that when he uncoupled the locomotive to run around the train the train took off down the line on its own.
Chocks away! I can confirm that the bearings make a world of difference and introduce a new problem with runaway trains! An immediate solution - magnetic chocks, specifically one of Trevor's magnetic couplings, stuck to his steel track...
Of course since then, ruminating on the problem, I've realised this is the perfect opportunity for working r/c brakes...
Re: Gravity running on the RVOM
Posted: Sat May 21, 2022 10:00 am
by Trevor Thompson
Yes - I have thought about RC controlled brakes!
Might have to look further into that.
And of course I have designed a printed magnetic chock!
And I still cant see where those dropped bearings ended up.
Trevor
Re: Gravity running on the RVOM
Posted: Wed May 25, 2022 7:55 pm
by SimonWood
Trevor Thompson wrote: ↑Sat May 21, 2022 10:00 am
Yes - I have thought about RC controlled brakes!
Actually I'm not surprised by that
Might have to look further into that.
Excellent!
Re: Gravity running on the RVOM
Posted: Sun May 29, 2022 5:33 pm
by Andrew
Fans of Spooner's boat might enjoy seeing it race three real boats, five mins in to this video:
If you start a few minutes before that there's some 16mm FR models to enjoy too...
