Custom Kissel design question arm length/angle

I designed what I call a micro Kossel delta. Initially I used a traditional "hanging" hot end whose distance from the nozzle to the arm attachment was about 20mm. It had a volume diameter of about 70mm and z height of about 45mm. It worked great right off the start. Almost no tuning or leveling needed, just some speed and temperature tuning.
I wanted more z height so I put on a Flsun style end effector that pulled the hotend up about 35mm. I have had nothing but nightmares since. Problems with movement, repeatability, over extrusion, under extrusion, lurching, top facing being sparse, you name it.

Is there some Kossel design rule about how long the arms can be for certain center arm angles or something? I am ready to give up and go back to "shorty"!

Is there?

Thanks,
DLC

The printed effectors are only as good as the printer which made it. There can be several issues with it.
Rod-pairs not parallel: The distance between rods at the carrier must be the same as at the effector
The effector triangle has to be equal length: The angle between rods axis' is 60° all around?
Stiffness of the printed part, including the heatsink clamp.

Quote
o_lampe
The printed effectors are only as good as the printer which made it. There can be several issues with it.
Rod-pairs not parallel: The distance between rods at the carrier must be the same as at the effector
The effector triangle has to be equal length: The angle between rods axis' is 60° all around?
Stiffness of the printed part, including the heatsink clamp.

The effector is a commercial one (FLSun), which may or may not mean anything... I checked to make sure the carrier arm spacing was the same as the effector. The printer was running before with home built mini Kossel end effector and worked great. The electrics are fine as is the wiring. The hot end is the same as well. The _only_ change was the end effector.

The big deal I see is that the end effector speeds up and slows down which causes thinning and bunching of filament laid down. If I send a single long G0 command I will see the speed up and slow down during the traverse.

Confused...
DLC

Edited 1 time(s). Last edit at 03/04/2018 12:48PM by dlc60.

Well, I found it. There _IS_ a limit, and a rule of sorts, about the relationship between the length of the rods and the radius of the end effector. I am not sure exactly what it is, but I know that my move to the FLSun end effector was the wrong move. I crafted my own end effector that puts the majority of the hot end above the plane of the rod connections. It keeps the same radius as the default mini-Kossel end effector plate. It moved my max Z from 45mm to 95mm and works great.

Lessons learned:
Not EVERYTHING works. The larger radius FLSun end effector worked fine on a delta with 220mm rods, not so much on a delta with 105mm rods.
Small changes have BIG effects. The mini-Kossel end effector has a 20mm radius, the FLSun is 30mm. The former works, that latter, not so much.

I think I'll put the details of my 300mm tall Micro-Kossel on Thingiverse as soon as I get all the details collected.

Thanks,
DLC