Printing issue: detail falls down!

Hello, we are a team printing the Poppy robot (https://www.poppy-project.org/) with Wanhao Duplicator 4 using PLA.
We have a trouble when printing tall parts such as forearms:

• in the first 5-6 centimetres, everything goes well.
• Later, extruder starts to damage printed surface touching it
• Then extruder move the detail and it falls down

Attachment 4171

Attachment 4172

We tried to change parameters of the printer: feedrate, temperature of extruder and layer height, but it did not help.
On this screenshot there are parameters of one case:

Attachment 4173

Did you have the same problem and if yes, how did you solve it? We assume that the problem is in fault that accumulates with time. Can you advise something?

In two words, active cooling. I don't have your printer, but I'm sure there is something on thingiverse to add a fan for active cooling of your PLA while printing...

Quite to be surprise, I would expect the 15mm/s feed rate would work without fan at 200C. But yea like above, a fan blowing directly on the print layer.

I would also do a temperature check, what you see is not necessarily what you get. You should get a reference thermocouple, another temperature sensor such as laser, or anything else that can give you reliable values.

I dont remember what vid it was on. Maybe Barnacles Nerdgasm. Yet he mentioned that anything tall and PLA should have rafting enabled. Rafting increases the surface tension when some one is printing tall objects. I hoe this helps and would like to hear how you did with this information.

Maybe this applies to any tall object? At that height, it would not take much to knock the print off.