billbedford wrote:The bolster is fixed in place with two torsion pins. This gives it plenty pitch and a little roll freedom.
But the side frame ends are solidly linked, so no twist freedom to handle even small bumps on one side of the track only? I can tell you from lots (really lots) of experience, with many similar plastic designs over here, that none of them stay on the track with P:87 wheels. My Bachmann MK1 ones didn't either, until I added equalization to handle it. Even ones with open ends like below didn't have enough twist flexing freedom.
and ones designed to be even more flexible:
Symmetrical pitch is really only needed for vertical curves. But regardless, the really simple way to provide bogie pitch on plastic trucks is to have a slight crosswise ridge on top of the bolster. That way there is no stiff resistance to pitch movement. If you want a little roll freedom as well, make it a tad crescent shaped vertically. On this RTR, the ridge is on the king pin, but of course they have the option of molding their own floor.
Either way, with roll freedom, you have to make sure (or adjust) the coach body c of g is perfectly central sideways. Otherwise the coach will have a permanent static sideways tilt.