The principle most people defer to when they say not to mount a bunch of crap on the platform is that delta robots are "supposed" to have a lightweight, low-inertia platform. However, principles are only useful inasmuch as they represent what happens in the real world and can be used to accurately predict the likely outcome of some specific given actions and conditions. It's a good idea to keep the low inertia principle in mind. However, to me, principles should be treated like theories (i.e., they have to carry their weight by being proven in the real world.) Not everyone has time to test every principle out to the Nth degree and scientifically validate it, so for the most part we just listen to them and assume they're right until we have some reason to reexamine them. If someone tells you a principle, keep in mind that there's value in skepticism, even if it's just to try something and really know it won't work. In fact, trying something and failing at it provides highly valuable information, so that alone makes it interesting for me. If I spend ten hours on this and come up with nothing, I'm still better off because now I know what will happen and also because it's very likely that I will learn something useful along the way.Eaglezsoar wrote: We've had many threads in the past about placing a direct drive extruder on the effector and I seem to remember that everyone decided that the solutions were too heavy to
work well. In your experience have you seen this working well enough to be a permanent solution? Which would you recommend, the QUBD or the EZStruder? The QUBD
would seem like it would have the lowest profile. The problem would be interfacing the QUBD to the E3D. Most of the ones I have seen on Thingiverse are designed to work
with the QUBD nozzles. Any thoughts from you would be appreciated.
In this case, the question is what effect we can expect if we add a given amount of weight to the effector. Here are the relevant components of the system, and what we care about for each:
- Stepper motors (how much force can they produce, and how much acceleration can they tolerate across their speed range?)
- Drivetrain, consisting of belts, carriages, and delta arms (what is its mass, how much inertia does it add to the system, how much force can it transmit, and how strongly can we accelerate or decelerate an axis before deflection in the belt and delta arms exceeds our desired tolerances?)
- Effector (what is its mass and the mass of everything on it?)
I'm not going to bother getting a QUBD because I already have an EZStruder and that will clamp right onto my E3D if I flip the adaptor piece upside down. The drive motor's center of mass should be as close to the vertical center of the platform as possible to avoid leverage issues. If possible, the stepper will sit slightly above the top of the platform (to keep it from fouling up the arms), the adaptor piece will sit inside the circumference of the platform, and the hot end will hang down underneath. It doesn't weigh as much as the stepper motor, but it might help a little to counterbalance it. (We want the center of mass to be as close to the geometric center of the platform as possible, as mass imparts more moment the further away it is from there, and that hurts our performance envelope.)
Here's a picture of what was printed with a QUBD. He says, "The Mr Shark print below was my best ever PLA print of any of my 3D printers to-date." It looks pretty clean to me! If I can get results like that printing around 50mm/sec on the outside loops, it would be a win. Anything above that is cake. I don't know if you've ever grabbed the platform while it's moving, but those steppers produce a LOT of torque. Like, "I better be careful not to get my fingers pinched by this thing, or they might get broken" levels of force. My initial prediction is that the force they can generate will be adequate to support reasonably high speeds before we run into problems with the arms flexing or the steppers being unable to produce enough torque. The payoff: No hysteresis, leading to cleaner retracts and corners.
. Still some noticeable blobs at 0.15. 0.1 looks pretty awesome. And 0.05 looks pretty good considering it the first ever I've done that low and could deff use some tweaking. (all done at 50m/s & 33% Infill)
