TVT - Reducing Wagon Rolling Resistance.
Posted: Thu Jun 20, 2019 3:12 am
This is the result of an investigation I've been working on recently to reduce the rolling resistance of trains, especially long goods trains.
Because wheelsets usually have both wheels firmly fixed to the axle, the rolling resistance and hence the load on the loco, is higher on curves than on straight track. Due to the outer rail on a curve being a little longer than the inner one, one wheel on an axle has to slip a little and the extra friction means it takes more drawbar pull from the loco to keep the train moving on the curve. The smaller the curve radius, the greater the drag. As an example, my bogie wagons have a rolling resistance of 17g on flat straight track and 28g on my sharpest curve of 7'6".
Some manufacturers sell ball bearing wheelsets to counter this effect, but they are expensive. For some reason they also fit ball bearings to both wheels, although only one is needed to give the differential effect.
I make my own rolling stock wheelsets and had been considering fitting a miniature ball bearing to one wheel on each axle, as miniature bearings are easily available and reasonably cheap. Using them takes a bit of precision machining though and I've been looking for a simpler solution.
The photo shows the result of these deliberations. It also shows the result of living near the sea and leaving steel parts lying around unpainted in the workshop.
The difference in rotational speed between the inner and outer wheel on a curve is very small and a ball bearing is overkill. So, instead of fitting a ball bearing in the wheel as originally planned, the wheel seat on one end of the axle was reduced slightly in dia. to provide a plain bearing for that wheel. The free rolling wheel is retained in place on the axle by a little brass collar, which is a press fit and is visible on the r/h wheel set in the photo.
With four of these wheel sets fitted to a bogie wagon, the extra rolling resistance on curves was eliminated. The rolling resistance is now 17g on both straight and curved track, even on the LGB R3 curve I use for checking clearances. Which confirmed my theory that two bearings per axle was not necessary for free running.
Total cost to convert a bogie wagon (4 wheel sets) is 15 cents worth of brass to make the collars, less than 10 minutes lathe time and about 30 minutes disassembling, reassembling and fitting the wheel sets to the wagon.
I know, this is not much use if you don't have a lathe, but it gives some insight into why ball bearing wheelsets are popular in the US. That said, I could buy a lathe and have change left over, for what it would cost me to convert my wagon fleet using commercial wheelsets.......
Regards,
Graeme
Because wheelsets usually have both wheels firmly fixed to the axle, the rolling resistance and hence the load on the loco, is higher on curves than on straight track. Due to the outer rail on a curve being a little longer than the inner one, one wheel on an axle has to slip a little and the extra friction means it takes more drawbar pull from the loco to keep the train moving on the curve. The smaller the curve radius, the greater the drag. As an example, my bogie wagons have a rolling resistance of 17g on flat straight track and 28g on my sharpest curve of 7'6".
Some manufacturers sell ball bearing wheelsets to counter this effect, but they are expensive. For some reason they also fit ball bearings to both wheels, although only one is needed to give the differential effect.
I make my own rolling stock wheelsets and had been considering fitting a miniature ball bearing to one wheel on each axle, as miniature bearings are easily available and reasonably cheap. Using them takes a bit of precision machining though and I've been looking for a simpler solution.
The photo shows the result of these deliberations. It also shows the result of living near the sea and leaving steel parts lying around unpainted in the workshop.
The difference in rotational speed between the inner and outer wheel on a curve is very small and a ball bearing is overkill. So, instead of fitting a ball bearing in the wheel as originally planned, the wheel seat on one end of the axle was reduced slightly in dia. to provide a plain bearing for that wheel. The free rolling wheel is retained in place on the axle by a little brass collar, which is a press fit and is visible on the r/h wheel set in the photo.
With four of these wheel sets fitted to a bogie wagon, the extra rolling resistance on curves was eliminated. The rolling resistance is now 17g on both straight and curved track, even on the LGB R3 curve I use for checking clearances. Which confirmed my theory that two bearings per axle was not necessary for free running.
Total cost to convert a bogie wagon (4 wheel sets) is 15 cents worth of brass to make the collars, less than 10 minutes lathe time and about 30 minutes disassembling, reassembling and fitting the wheel sets to the wagon.
I know, this is not much use if you don't have a lathe, but it gives some insight into why ball bearing wheelsets are popular in the US. That said, I could buy a lathe and have change left over, for what it would cost me to convert my wagon fleet using commercial wheelsets.......
Regards,
Graeme