[Richard Johnson]

QUOTE (Tonyperks @ 12 Aug 2008, 00:52) <{POST_SNAPBACK}>As it says really, My 2 bachman cl37's judder when going down hill is this something to do with the back emf settings of the decoder, My other loco's cl47, cl20 and 66 dont do this any ideas?.

Other than this very happy set the control speed and they go up and down all day at the same speed no running away at all.

*** Its something often seen with US loco's under heavier loads going downhill, and it is usually more to do with either a split axle gear or end play in the worm shafts. Its not typical of all 37's though - I just chipped and tuned a coal sector 37 and it was about the best Bachmann mech I've seen running wise....

Richard
DCCconcepts

 

[Richard Johnson]

QUOTE (Tonyperks @ 12 Aug 2008, 22:18) <{POST_SNAPBACK}>It may well be play in the worm sets as there is a lot of "shunt" if you push pull the locos slightly .

***You'll need to get some small washers the right size and pack the shafts so there is not so much end play between the shafts and the bearings of the gearboxes... this will fix it. I think Markits may do these.... NorthWest Shortline in the USA certainly do..

Richard

 

[Richard Johnson]

QUOTE (mikebiggles @ 16 Aug 2008, 21:47) <{POST_SNAPBACK}>Hi Tony

Had the same problem with one of my Bachmann 108 DMU's. Turned off the back EMF and it solved the issue with no noticable difference in normal running. I have three of these units but only one of them as this problem the others run fine. So don't really know the reason why i should have to do this.

Hope this helps Mike

***Because when the end bearings have too much slop, the weight of the loco going down hill forces the end of the shaft to move, changing the way the worms relate to the gears, creating a greater pressure, lesser pressure effect on the drivetrain.

This varies the motor load so it varies the back EMF it emits in a more/less/more/less cycle, creating the juddering effect.

Your turning off the back EMF masked the problem but did not actually fix it.

Adding some washers to the end bearing end of the driveshaft (inside the gera tower) at each bogie will actually fix the problem so you can turn back EMF on again.

Regards

Richard Johnson
DCCconcepts

 

[Richard Johnson]

QUOTE (upnick @ 17 Aug 2008, 06:46) <{POST_SNAPBACK}>***Because when the end bearings have too much slop, the weight of the loco going down hill forces the end of the shaft to move, changing the way the worms relate to the gears, creating a greater pressure, lesser pressure effect on the drivetrain.

This varies the motor load so it varies the back EMF it emits in a more/less/more/less cycle, creating the juddering effect.

Richard,

Would this be the case in an upwards incline also

one of the class 37's starts up the incline here with a judder then half way up settles.

***Yes - any time that the load transfers. When going downhill it will shift to the front bearing - uphill to the rear....

Richard