The inspriation for this work is credited to Foehnsturm. We are going slightly different ways with it, but the principle is the same (and his!). The purpose of this system is to allow dual head printing
with different materials without worrying about nozzles clashing with the print, or oozing anywhere (oozing will be contained within the tool storage area). Print with support everywhere. Support on main grip unit to be removed before fitting (the support on which is part of the design for printing it).
See pics of the robot for the quality of prints I am getting from this setup. Printed at 0.1, 65mm/s, no infill, fan full.
Note that I had a few issues with the e3d clogging. I added a few drops of light machine oil to the head break/heatsink and had no issues since. Might be worth trying this if you too run into issues.
Second head is height adjustable, but will need to be mirrored in cura (X way) so that it suits the opposite side of the machine (or you can choose to mirror the small head, depending on what side you want it). Similarly, the tool mount can simply be mirrored for other side (the one which corresponds to the head, e.g height adjustable).

Here is the gcode I use, simply doing a look up and replace in text edit. I look up 'T1' and replace with:

;EXTRUDER 1 DROP, EXTRUDER 2 COLLECT

T1

G0 F12000 X100.000 Y180.000

G0 F3000 Y192.5 ; This Y coordinate is where the head needs to be to be inline with the wedge

G0 F12000 X50 ; Start of wedge in x direction

G0 F3000 X4.7 ; Where the head terminates, finishing the movement to shear the print module away

G0 F9000 Y100.000 ; magnets sheared, pulling head away

G0 F12000 X180 ; To other side of machine

G0 F3000 X199.7 ; location for adj module in x direction to pick it up

G0 F12000 Y180

G0 F3000 Y184.3 ; location to engage the head

G0 F3000 X150 ; then slide it out

G0 F12000 X120 ; safe area

G0 F12000 Y100 ; back to print

;END

You may need to adjust the coordinates to fine tune to your ultimaker. Just use the ulticontroller and axis adjust to see where the coordinates are for you, and replace accordingly above. Same goes for the piece of gcode to drop off module 1, and collect module 2. Look up 'T0' and replace with;

;EXTRUDER 2 DROP, EXTRUDER 1 COLLECT

T0

G0 F12000 X100.000 Y180.000

G0 F3000 Y184.3

G0 F9000 X150

G0 F3000 X199.7

G0 F9000 Y100

G0 F12000 X50 Y180

G0 F3000 X4.7

G0 F3000 Y192.5

G0 F3000 X50

G0 F9000 X80

G0 F12000 Y100

;END

Check out  all of the photos to see where parts fit. The final pieces to finish everything off have now been uploaded. Note that the fan wire for the main grip unit is supported by 3mm filament. There is now a piece to glue on top of the module for the filament to be pushed in to.
I've added a photo of the very first dual print. Its printed at 0.15 with no infill, no wipe shield and prime tower, and no ooze shield. Its a little rough, mainly due to printing too hot. Also excuse the missing hand, the support structure came loose from the bed. I'll try another print and upload the results using the wipe shield.
Comments and ideas for improvements welcome.