I’ve been doing some thinking about the idea of a very large Maslow, which has been mentioned a time or two on the forums. I’m not planning on building one at this time, but every time I look at the end wall of the 8x6 / 9x15 wind tunnel at work, I imagine what it would be like to use a Maslow on a canvas that size.
First, I think for a really large Maslow, the best option is to mount the motors to the sled with the “unused” chain hanging. That way the motors aren’t supporting all the weight of the chain. I suspect it would take a really large area to need a thicker chain.
What other modifications would be needed for a large Maslow?
First, I think for a really large Maslow, the best option is to mount the
motors to the sled with the “unused” chain hanging. That way the motors aren’t
supporting all the weight of the chain. I suspect it would take a really
large area to need a thicker chain.
this doesn’t actually help, it doesn’t matter if the unused chain is below the
sled or on the other side of the motors in the top corners. Unless the unused
chain is resting on some other support (in which case you have to worry about it
getting tangled), the motor has to support the full weight of the chain.
The value of being able to use triangular kinematics FAR outweigh any advantage
of having the motors on the sled.
What other modifications would be needed for a large Maslow?
really only software changes defining the workspace size.
As the chain gets very long, you may need to add some compensation for the sag
of the chain in the software. We may very well end up doing this anyway, but the
longer the chain the more it would matter.
The final area to be concerned about is the fact that your work area is
completely vertical, that means there’s very little force to drive your bit down
into the workpiece. If you are just painting/drawing, this isn’t a problem, but
if you are cutting, this will mean that you need to move very slowly for plunge
cuts. It may mean you need to slow down your normal x/y feedrate, but you will
have the most trouble drilling down into the material.
The trouble is that it’s impossible to keep the chains straight, the question is
how much droop you can survive. As the chains get longer and the tension is
reduced, you will have more droop
Think about the sled being at a bottom corner of the work area. One chain is
close to vertical (80 degrees in a stock maslow), at this point, this chain is
supporting almost all of the weight of the sled (something like 98% of it), the
remainder of the weight is acting on the second chain.
As you can see, adding more weight is rather inefficient at keeping the chains
tight.
This is why I was saying that the software would probably need to be modified to
account for chain droop. Instead of trying to eliminate it, allow for it.
how about using gt belts instead of chains? (reducing droop by getting chain weight out of the equation)
though the gt belts could have stretch? but stretch might be more easy to measure and calculate.
i suck at math, droop and stretch could be much alike…
In both cases (droop and stretch) you need to estimate the force being applied
and the length.
These numbers then get plugged in to a formula and you adjust the chain length
according to the error.
There will still be errors, because the exact amount of strech and the exact
force on the chain is going to be impossible to know exactly, but we can get
pretty close and that will eliminate a lot of the error.
@dlang, you’re right, the weight of the chain doesn’t decrease significantly by moving the motors. I’m conflating two thoughts i had. The real purpose of moving the motors to the sled would be to make a more portable Maslow. You also raise a good point about the gravity issue with vertical surfaces, like buildings. Perhaps a vacuum system to provide some grip force?
@dlang, you’re right, the weight of the chain doesn’t decrease significantly
by moving the motors. I’m conflating two thoughts i had. The real purpose of
moving the motors to the sled would be to make a more portable Maslow.
there is one person working on this. I’ve got mixed fealings. I think the
difficulty in anchoring the chains solidly enough (and knowing the precise
distance between them) is bad enough to go the telescoping tube approach. It’s
not quite as small as ‘everything on the sled’, but it’s still so much better
than hauling a full maslow around that I think it could work.
You also raise a good point about the gravity issue with vertical surfaces,
like buildings. Perhaps a vacuum system to provide some grip force?
try it before you complicate things, it may not be a big problem. But it’s
something to check on.
Let me share a few random brainwaves on this ‘all on the sled’ idea
Placing the motors on the sled.
The advantages:
all electronics in one compact area.
Short leads
Replace a bit of he brick weight
less ‘antenna’ effect the induction of the motor wires sends EM noise, that can be picked up by the sensor wires and give false readings
The disadvantages.
an always moving USB cable. (his is more sensitive to failure then a powercable)
Wifi or BT could be an option, but again the magnetic fields could cause problems, but wifi and BT also introduce configuration mess, Arduino, Windows, Apple, Linux, Android, This could just create more quesions then we can answer.
A powerful machine is a machine that just works when it needs to work, and only fails by human error.
In other words: keep it as simple and low tech as possible.
The Advantages and disadvantages seem to cancel each other out. That’s cool, this keeps things open for experimentation and will keep the evolution alive, and unfortunately that doesn’t give us any clear answers.
So now I have yet another virtual Maslow floating around in my brain…
Not, if the worksheet lays flat on the floor instead of standing upright.
Let’s leave that idea in cold storage for now. Just that it is out there for someone who likes a challenge like this.
Does that really make a difference? It just can replace the weight of the bricks
apropos Bucky: Would Circular kinematics also be an option nest to Quadrature and Triangular
as in shoulder and elbow joints
Not, if the worksheet lays flat on the floor instead of standing upright.
Let’s leave that idea in cold storage for now. Just that it is out there for someone who likes a challenge like this.
if the worksheet lays flat on the floor, then you have to have a completely
different mechansim (as you don’t have gravity to pull the chains tight) and so
are talking about a very different machine.
Does that really make a difference? It just can replace the weight of the bricks
it’s not a matter of weight.
in the standard maslow kinematics, the points where the chains attach to the
sled are fixed, this means that the sled tilts as it moves around the work area.
This leads to hard math and many machine dimensions that need to be very
precisely measured. The result is accuracy problems.
in triangular kinematics, point at which the chain attaches to the sled moves so
that the chain always makes a straight line pointing at the bit. This is looking
like a huge improvement in terms of accuracy
apropos Bucky: Would Circular kinematics also be an option nest to Quadrature and Triangular
as in shoulder and elbow joints
There is a term for an arm with a pivot at the base and a pivot partway down the
arm, I don’t remember it.
if the worksheet lays flat on the floor, then you have to have a completely
different mechansim (as you don’t have gravity to pull the chains tight) and so
are talking about a very different machine.
[/quote]
true… lets leave that for what it is for now.
[/quote]
I hope my ‘out of the box’ brainwaves are not a distraction. I share them in the hope that they trigger someone else’s brain to ctreate something ore usefull for the Maslow project. Hopefully something brutally simple and effective.
Think Buckminster Fuller (Bucky) making the largest strongest possible object wile using the least amount of material. (What we now call durable and sustainable)
Bucky used circles domes and tensegrity. To me this has many parallels to the Maslow approach i
Tetrahedron being the most sturdy and stable structure made me think of Maslow style kinematics suspended in Tetrahedral space (4 chains from the corners to the effector without depending on gravity)
Anyways my mind is wandering off hehe…
A plain and simple LARGE Maslow, no-nonsense, strong, reliable, stable and affordable.
There is nothing wrong with the current Maslow design, so I really hope i’m not driving thoughts away from that. (can’t say this too often)
@vertex: Your mind wanderings are welcome, especially in the large/small Maslow threads, which are all about tossing about crazy ideas. Who knows, one of them might not be so crazy.
