I think I may have come up with a way to get rid of the spring. It means adding another piece to the arm. I'm not convinced this is a good idea. My test showed it performing well on the lift, but poorly on the drop. This would probably be helped by gravity on the toolhead. I also can't tell how much force can be exerted at either end, though the force in the middle of the range should be decby Annirak - Delta Machines
The problem with the spring is just the range of force required to move it. When the arm is at either extreme, the line is short and the spring is compressed. When the arm is in the middle, the line is long and the spring is extended. Because F=kx, if you want a reasonable force at the extremes, the force in the middle is quite large. Constant force springs are just coiled up leaf springs witby Annirak - Delta Machines
Well, I rigged up a test with meccano. It looks like the spring is going to be a problem. A constant-force spring would solve the problem nicely, though.by Annirak - Delta Machines
I must have been feeling pretty dense last night. I missed an obvious simplification of the math. We left off at: Well, so... Which reduces easily to: Similarly, Looks like I did simplify the math for the upright case after all.by Annirak - Delta Machines
Okay, this is going to be a long post. I should make clear before I go any further that this didn't work out quite how I wanted. I was looking for a simple geometry that would work along the same lines, but it didn't come out how I wanted. It will still work, but the math becomes more complex, not less. That is, unless you turn it the other way up and suspend the arms over the work surface.by Annirak - Delta Machines
I think I may have an optimization for your design, which also gets rid of the arccos. I was thinking about the wheels impinging on the work area and I have an idea which will replace them with a pair of pulleys and a cantilevered beam. I'll try to get it drawn up and posted here later.by Annirak - Delta Machines
I don't see anything obvious. I know it's extra weight, but Johann is moving from a bowden tube to an on-hotend extruder drive for Kossel because of the quality of the print. It's a consideration. I asked him about it; here was his answer. QuoteJohann I think it's much easier to get retraction working perfectly without a long Bowden tube. My goal is awesome print quality without too much hasslby Annirak - Delta Machines
nicholas.seward Wrote: ------------------------------------------------------- > I haven't gone through to check your math but the > geometry that I picked has the ability to greatly > simplify the equations. Your math and mine are equivalent. If you make the same assumptions with mine as with yours, you end up with the same math. I didn't make the a=a and b=b assumptions that you havby Annirak - Delta Machines
nicholas.seward Wrote: ------------------------------------------------------- > Above you guys can see that I will use cheapo hall > effect homing. There will be no need for a full > feedback loop. I like the idea of using the > encoded desk or potentiometer but I am opting for > the simpler design. That makes sense. Failure-resistant sensing methods are definitely better andby Annirak - Delta Machines
ShadowRam Wrote: ------------------------------------------------------- > This will give you absolute encoding to any > resolution you want can afford without the need for encoded > disks or optics. High-res, low noise ADC's are expensive. This is compounded by this design having between 90 and 180 degrees of play. A typical pot gives you between 270 and 360 degrees of rotation. Alsby Annirak - Delta Machines
Hah. Couldn't stop thinking about it so I did the math. You may have some trouble with the speed of the controller, because the coordinate transformation takes some heavy lifting as far as the math goes. You have three input variables: the three angles of the elbow joints, Aa, Ab, Ac. You have three outputs: x,y,z. We need to go the opposite direction. There are ten givens. The three base vby Annirak - Delta Machines
I wonder about the math required for your coordinate transformations. It will not be the simple math that rostock/kossel builds get to use. I'm willing to take a stab at it if you want.by Annirak - Delta Machines
Or use a constant-current diode instead of a resistor. e.g. On Semi NSI50010YT1G Some more info: Constant current diodes are a two-pin device, which is a diode in one direction and a current regulator in the other. They're made by connecting a n-channel jfet with its drain to one terminal, its gate to the other, and a resistor between the gate and the source. They're known under a number oby Annirak - Next Wave Electronics Working Group
nophead Wrote: ------------------------------------------------------- Sample it at whatever speed you like and > reject all the samples that are close to the > supply rail or ground. Wow, nophead, that's a really elegant solution! I like it!by Annirak - Controllers
If you want two data points so that you can get a slope, you can always use two sample & holds.by Annirak - Controllers
Noobman, Thank you for your feedback. It made me realise the error I had made about sinusoidal back emf. I will make one more attempt to get my point across. Before I address back-emf, I think I need to talk about how stepper motor drivers actually work. TL;DR: At stall speeds, individual microsteps don't matter anymore; when a microstep is missed, recovery is possible but when a full step isby Annirak - Controllers
I think that you're right that there's an error in my reasoning. Stepper motor back-emf should be sinusoidal, whereas I've assumed it is constant. This will take some more work to analyse properly. In the mean-time, here are the core assumptions: The position of the rotor is proportional to the arctangent of the currents in the two coils. There is no debate about this, this is the physics ofby Annirak - Controllers
Back EMF is a problem in all motors, since it is the limiting factor, it causes torque rolloff as speed increases. Here's a quick back EMF primer: When a wire moves through a magnetic field, or a magnetic field moves past a wire, a voltage is induced, which opposes the direction of motion, according to the right-hand-rule. When this is applied to a motor, what it tells you is that the fasterby Annirak - Controllers
This is a general answer, not so much a specific one. In specific, you should get a board from Traumflug; he's the designer of Gen7 and as such it's best to support him directly where possible. With that disclaimer out of the way, there are two PCB houses I can recommend, but they're not in Europe. They have the best prices for small batches I have ever heard of: For 2 layers up to 10x10cm,by Annirak - Controllers
NoobMan Wrote: ------------------------------------------------------- > Motors specs actually look good, and are the right > type (low coil resistance/inductance types). [ . . . ] > Steppers will > only eat what drivers give them, and for bigger > motors to give more power you need to feed them > more, else its pointless to change them in the > first place. Exactly. Thereby Annirak - Controllers
I agree with Nophead, 17.4 Nm is a huge torque for stepper motors. What are the inductance and resistance of the coils? You may have a problem driving them quickly.by Annirak - Controllers
@xclusive585, the math behind rostock is in the post I referenced above. If you have any questions about it, I'd be happy to explain.by Annirak - Delta Machines
I also ordered one. My wife thinks it would be a great instructional tool for teaching primary school classes.by Annirak - General
I did a rough sketch of how to look at the build area in this post. I suggest you aim for a rounded triangle, with each vertex close to the base of the closest pillar. That way, there are no points in the travel of any arm that are excluded by mechanical constraints. To do this, you need to set up the ratios so that one arm is completely vertical when the other two are completely horizontal.by Annirak - Delta Machines
RAMPS is mostly an adaptor board for the Arduino. It provides drivers for heaters and connection points for stepper motor drivers, temperature sensors, and endstops. It also provides the connection points to feed the main 12V power into the high power devices (motor drivers and heater drivers). The Arduino controls each of these aspects via the hardware on the RAMPS board and the attached stepby Annirak - Controllers
Greg Frost Wrote: ------------------------------------------------------- > Having the belts under tension in one direction > like on a Rostock also means that any backlash due > to belt/pulley mating imperfetions is minimised. That's only true if your acceleration doesn't exceed acceleration due to gravity.by Annirak - Delta Machines
It might, but how much weight is the question. The problem is that the down-force on each carriage changes depending on where the head is, relative to the carriage. As it moves further away from any given carriage, in the X-Y plane, it puts less down-force on the carriage. In addition, benefits of the counterweight have to be *ahem* weighed against the additional inertia added to the systemby Annirak - Delta Machines
crispy1 Wrote: ------------------------------------------------------- > I think that a lot of people here are neglecting > the Prior Art defence. If anything is published > into the public domain before a patent application > is filed, then the patent is void. > > In theory yes, this is how it works. But in > practice, prior art often gets overlooked or just > not foundby Annirak - General
I think that a lot of people here are neglecting the Prior Art defence. If anything is published into the public domain before a patent application is filed, then the patent is void. Thingiverse is our best defence against a broken patent system. For my part, I think that the EFF needs to set up a benevolent patent troll. Here's how it would work: people donate or assign patents to the EFFtrby Annirak - General