Hi,
I remember having read that somebody asked what is the advantage of the CEM arrangement against the conventional arrangement of en equatorial mount.
Let me try to explain it as far as I do see it. It has all to do with the levers involved in how they carry the load or better said how the load is distributed onto the ball/tapered bearings.
Look at the image of a CEM mount at the end of the message.
The main load is held by the DEC assembly sitting inbetween the 2 bearings (see green arrows) and so both bearings in this scenario are carrying the same load and no angular torsion is applied on the bearing eg. the load is running radially and no axial force acts on the bearings. That is the main purpose of ball bearings if they are no special axial ball bearings. For axial loads normally tapered bearings are used as for example does ASA in their mounts.
Now let us add the same weight onto the counterweight shaft situated at the right side outside the right ball/taper bearing. Now the left ball/taper bearing will get an axial deflection of the inner ball/taper ring according to the ratio of the lever size of the CW to the lever size of the right bearing to the left bearing. In this case it seems to be 3:1 for a CEM. This means that a load of 30 kg counterweights will act with 10kg force on the left bearing and act with a bit of deflection.
Now imagine a normal equatorial mount as we all know them before the CEM arrangement was introduced.
The DEC assembly which carries the equipment is situated in front of the right bearing and the CW shaft too. So the rotating point of the forces is the right bearing. Now on a standard equatorial mount we take the sum of the equipment plus the amount of counterweights let us take 30kg of equipment and 30kg of counterweights this makes up a weight of 60kg and this load will apply a force taking the same lever ratio of 3:1 at the left bearing will have a load of 20kg which in this case is a load 100% more on the left bearing then compared to a CEM.
For example on a Losmandy G11 (I own two of those) the lever ratio is even worse and equals to 1:1 (just measured it and see image of my G11) and in my case I have 35kg of equipment and 30 kg counterweights on it and that means that on the right RA needle bearing (Losmandy uses needle bearings) with 1.25" shaft diameter I am loading the bearing with 65kg which turns out to be 650% higher load then on a CEM mount. Now even worse there is an accessory which is sold for the G11 to space the DEC axis away from the RA axis which makes the lever force even worse maybe up to 1:2 loading the right needle bearing with the double of the whole weight on it. That is the reason why I extended the DEC axis assembly to get more angle before I need to do a meridian flip. (you can see my DEC extension on the second mount in the background)
That is how I see this enchilada of normal vs CEM mount. The ZEQ25 or CEM25 is even better as both loads do act radially on the bearing and no additional torsion is applied except the torsion equivalent to your latitude.
I hope I did not forget something 
Thanks for reading
Image of the CEM120 was taken out of the un-boxing video of johndcrisp and so credits to johndcrisp for this image which is part of his un-boxing video. Copyright belongs to johndcrisp and never was meant to be usurped by me 
Edited by Real14, 17 February 2018 - 09:54 PM.
