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I built a framework for robot wheels a while back using OpenSCAD and used it to create a few different wheel styles. I recently decided to combine them all into one massively configurable wheel model, and add a number of new features as well. The result is an OpenSCAD file with 46 parameters that provides a limitless set of combinations and wheel designs. I call it One Wheel To Rule Them All.
It includes twelve tread patterns (all configurable in often surprising ways), eight core spoke patterns (also highly customizable), configurable support for o-rings, bands, and even optical encoder timing slots (directional and non-directional), and a lot more. Plus, I’m still adding features as I think of them.
First, here are a few images of the types of the various basic elements, as well as a few variations that show the flexibility of the designs. For example, as shown in these images, the Spiral style can be used to create a variety of interesting designs that you might not think of when you think “spiral.” After the images you’ll find full details on the parameters.
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- Highly Configurable Parametric Robot Wheel – Biohazard variation
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- Highly Configurable Parametric Robot Wheel – Tread Styles
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- Highly Configurable Parametric Robot Wheel – Spoke Styles
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- Highly Configurable Parametric Robot Wheel – Spiral variation
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- Highly Configurable Parametric Robot Wheel – Spiral variation
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- Highly Configurable Parametric Robot Wheel – Spiral variation
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- Highly Configurable Parametric Robot Wheel – Spiral variation
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- Highly Configurable Parametric Robot Wheel – Hub and Rim Styles
It’s important to note that you can configure this wheel to such an extend that it may not be printable at home with extruded plastic printers. In these cases, services such as Shapeways could come in handy.
The source file is available at http://www.thingiverse.com/thing:21486, or on github at http://github.com/alexfranke/Highly-Configurable-Wheel.
Tire Parameters
Often wheels are built around the tires. In this section, specify the properties of the tires you’re using, and this will define the diameter of the wheel. If you’re using o-rings, the tireCSDiameter should be the cross-section diameter of the o-ring, or if you’re using some other flat tire material (such as rubber bands), jsut specify the its thickness. If you’re not using any tire at all, set the tireCSDiameter to zero.
- wheelWidth: The width (or thickness) of the the wheel
- tireCSDiameter: Cross-sectional diameter (CS) — How thick is the tire rubber?
- tireID: Internal diameter (ID) — How wide is the inside opening?
- tireStretch: Circumferential stretch percentage (usually 1 + 0-5%) — How much to you want to stretch it to get it on?
Rim properties
The rim sits at at the outside of the spokes and supports the tires or added treads. Installed tires (such as o-rings, rubber bands, etc) are set into grooves carved out of therim, while trads are added onto it. Keep this in mind when you’re using tires — as an example, the rim height should not be smaller than the radius of o-ring tires.
The rim also supports rotary encoder timing holes for wheel feedback. Use the padding parameters to adjust the location of those holes. See the compiler output for helpful information about the distance indicated by each timing hole. Directional timing holes will produce a second set of holes that are 90 degrees out of phase with the first. This allows you to stack sensors at the same location over the wheel instead of trying to position them along the circumference. Directional timing holes essentially double the resolution. You can also double resolution by looking for both rising and falling edges.
- rimHeight: The height of the rim portion of the wheel
- timingHoles: The number of timing holes to carve into the rim
- timingHoleInPad: The inside padding for the timing holes
- timingHoleMidPad: The middle padding if direction timing holes is selected
- timingHoleOutPad: The outside padding for the timing holes
- directional: A directional encoder renders two sets of slots, 90 deg out of phase
Tread Parameters
In this section, specify the properties of the tire tread you want to render. If you’re using a wheel (e.g. o-ring, rubber bands, etc), then use either the “o-rings” or “slots” settings, which will cut a groove (or grooves) in the wheel rim to fit the tires. The othertreat styles will render a tread pattern protruding out from the tire surface by the amount you specify in third part of “knobSize”.
Imagine the tire is mounted on a robot and facing straight at you. The “knobSize” parameter defines the size and shape of knobs in an [x,y,z] format, where x goes across the rim, y goes up and down along the perimeter of the wheel, and z protrudes out from the wheel toward you.
The “staggerOffset” parameter allows you to stagger knobs across the tire by an amount you specify. Set this to zero if you want all the knobs lined up along the perimeter and aligned with the edges of the rim.
“numberOfKnobs” specifies how many knobs there are across the tire, and “lineThickness” specifies how thick the lines are from “drawn” tire styles, such as “x”, “cross”, and “zigX”. You can use these pameters together in creative ways — for example to extend a single tread profile across the width of the tire, or to create a contiguous zig-zag.
Finally, “radialTreadSets” defines how many sets of treads are rendered around the wheel. Each set contains two rows in order to create the staggered effect.
Tread styles are:
- none: No tread is rendered
- cross: Each knob is the shape of a plus sign with the specified lineThickness
- o-rings: Grooves are cut into the rim to accept o-ring tires
- squares: Each knob is a rectangle, whose size is specified by knobSize
- spheres: Each knob is a smooth bump, whose size is specified by knobSize
- cylindersX: Each knob is a cylindrical shape running across the wheel, whose size is specified by knobSize
- cylindersY: Each knob is a cylindrical shape running along the perimiter of the wheel, whose size is specified by knobSize
- cylindersZ: Each knob is a cylindrical shape protruding from the surface of the wheel, whose size is specified by knobSize
- spikes: Each knob is a cone or spike protruding from the surface of the wheel, whose size is specified by knobSize
- slots: Grooves are cut into the rim to accept flat tires, defined by numberOfKnobs (number of grooves), the first and third numbers in knobSize to define the width of the slots and the depth, and spaceBetweenTires for the distance between the tires and also from the outside edges to the first slots.
- x: Each knob is in the shape of an “x” protruding from the surface of the wheel, whose size is specified by knobSize
- zigX: Each knob is in the shape of a zig-zag protruding from the surface of the wheel, whose size is specified by knobSize
- v: Each knob is in the shape of a “v” protruding from the surface of the wheel, whose size is specified by knobSize
- treadStyle: none, cross, o-rings, squares, spheres, cylindersX, cylindersY, cylindersZ, spikes, slots, x, zigX, v
- knobSize: The size of each knob [across wheel, along the perimeter, prodruding]
- radialTreadSets: How many sets of treads to render around the wheel (2 rows per set).
- numberOfKnobs: The number of knobs to render per row.
- staggerOffset: A distance to offset the staggered rows.
- lineThickness: The line thickness for “drawn” styles, such as “x” and “zigX”
- maxTires: For o-rings, the maximum number of tires per wheel
- spaceBetweenTires: For o-rings, the space between each tire, if there are more than one
Spoke-related Parameters
This section is used to define the spoke style of the wheel. Some of the properties are only applicable to certain wheel types, and these properties can be used together in creative ways to create a wide range of tire designs.
The “proportion” property affects how some spokes are rendered. The first number is the proportion of the design from the center of the wheel to the inside of the rim, and the second number is the proportion of the width inside of the wheel. For example, to create spokes that are roughly in the shape of a “U”, you can use a “circle” style, and set the proportion to [1.5, 1.0], for cirle spokes that are 150% as long as the distance from the center to the inside of the rim, 100% as wide.
Use spokeInset to specify the inner and outer inset of the spoke area from the inner and outer faces of the wheel. You can use a negative number to make the spoke area stick out further than than the rim. The hub position will be based on the inner surface resulting from this inset.
The spoke styles are:
- biohazard: A biohazard logo-inspired design. Set numberOfSpokes to 3 to mimic the logo.
- circle: Spokes in a circlar or oval form, defined by spokeWidth and proportion.
- circlefit: The maximum number of circles that will fit between the center and the rim, with a set of smaller outer circles specified by outerHoleDiameter.
- diamond: Spokes in the shape of a diamond (rhombus), defined by spokeWidth and proportion.
- fill: Fills in the spoke area with a solid cylinder.
- line: Straight line spokes, like you would see on a typical wagon wheel.
- none: Leaves the spoke area empty and does not make for a very useful wheel.
- rectangle: Spokes in the shape of a rectangle, defined by spokeWidth and proportion.
- spiral: Spokes in the shape of a semicircle, defined by curvature, reverse, spokeWidth.
- spokeStyle: none, biohazard, circle, circlefit, diamond, line, rectangle, spiral, fill
- spokeInset: The [inner,outer] inset of the spoke area from the surface
- numberOfSpokes: Number of “spokes.” Set this to three if you’re doing the biohazard design
- spokeWidth: This is how wide each spoke is.
- proportion: proportion to rim, proportion of width
- curvature: For “spiral”, this is how curvey the spokes are. >0, but
- reverse: For “spiral”, setting this to “true” reverses the direction of the spirals
- outerHoleDiameter: For “circlefit”, the diameter of the outer holes, or zero for non
- concavity: Concavity distance of spoke area for [inside, outside] of wheel
Hub Parameters
These properties define the hub — or how the wheel connects to the motor. The default values for the captive nut are precise for a M3 nut and will make the nut a very tight (if not impossible) fit. I prefer this because it allows you to “melt” the nut into place with a soldering iron. However, if you don’t have a solder iron or prefer a looser fit, then just adjust the nut diameter and thickness. (M3 hardware is, by default, set to 3mm screw diameter, 5.4mm nut diameter, and 2.3mm nut thickness.) Similarly, the holes for the motor shaft and grub screw are also precise. This allows the holes to be drilled out for a more precise fit. Again, you can adjust these to suit your needs.
The hubZOffset can be used to “sink” the hub into the wheel, and it defaults to half the wheel thickness. For example, when the hubHeight is 10 and the hubZOffset is -2, then the hub will protrude 8mm from the wheel, but the shaft hole will be 10mm deep. The set screw will still be positioned in the middle of the exposed vertical height, and the fillet/chamfer will also be rendered in the correct position. This property is also useful if you want to poke a hole entirely through the wheel. (e.g. If the wheel is 6mm thick, set the hub height to 16 and the hubZOffset to -6, and you’ll get a hub that protrudes 10mm from the wheel surface with a hole that extends all the way through the wheel.)
To mount a servo motor, set includeHub to false, set shaftDiameter so that the hole will accommodate the servo horn screw and any bit that protrudes from the top of the servo horn. Then set the servoHoleDiameter to the size of your mounting hardware, and set servoHoleDistance1 and servoHoleDistance2 to the total distance between mounting holes on your servo (not the distance from the center). These sets of mounting holes will be rendered at 90 degree angles from one another. If you only want one set of holes, set one of the values to zero. Adjust the angle of all the holes to avoid openings in your wheel design if necessary using servoArmRotation.
Use innerCircleDiameter to specify a solid inner circle to use as a base for the hub. This can be useful if you need a a solid surface for servo mounting hardware or for the base hub fillet/chamfer.
Use outerNutTrap to create a nut or bolt head trap on the outside (bottom) of the hub area. Used in conjunction with shaftDiameter and false for includeHub, this will create a wheel that can drive a bolt much like the large gear on Wade’s Extruder. (This feature is inspired by that design.)
Use servoNutTrap to create nut traps for bolts used to mount the wheel onto servo arms. This feature was suggested by AUGuru.
- includeHub: Set to false to remove the hub and only include the shaft diameter hole.
- hubDiameter: The diameter of the hub portion of the wheel
- hubHeight: The total height of the hub
- hubZOffset: The Z position of the hub, negative numbers from the surface of the wheel
- shaftDiameter: The diameter of the motor shaft
- innerCircleDiameter: The diameter of the solid inner circle under the hub, or zero for none.
- setScrewCount: The number of set screws/nuts to render, spaced evenly around the shaft
- setScrewDiameter: The diameter of the set screw. 3 is the default for an M3 screw.
- setScrewNutDiameter: The “diameter” of the captive nut, from flat to flat (the “in-diameter”)
- setScrewNutThickness: The thickness of the captive nut
- baseFilletRadius: The radius of the fillet (rounded part) between the hub and wheel.
- topFilletRadius: The radius of the fillet (rounded part) at the top of the hub.
- chamferOnly: Set to true to use chamfers (straight 45-degree angles) instead of fillets.
- servoHoleDiameter: The diameter of servo arm hounting holes, or zero if no holes
- servoHoleDistance1: Distance across servo horn from hole to hole (0 to ignore)
- servoHoleDistance2: Distance across servo horn from hole to hole, rotated 90 degrees (0 to ignore)
- servoArmRotation: The total rotation of all servo holes
- servoNutTrap: Size [indiameter, depth] of servo arm captive nut, or 0 (any) for none.
- outerNutTrap: Size [indiameter, depth] of a captive nut, or 0 (any) for none.
Quality Parameters
- $fn: Default quality for most circle parts.
Here’s a 3D printed T10 lamp shade that I designed and printed last night. A few weeks ago while searching for LEDs, I noticed an ebay listing for very inexpensive 12V automotive lamps that combine nine bright white LEDs. I believe these are sometimes called “wedge lights,” and are used as turn signals or interior lights.
Because reprap printers typically operate with 12V power supplies, I figured this would be a perfect way to light up the print bed. When the lamps arrived last night, I got out the calipers, worked up a design, and printed it out. I had a little difficulty removing the support material, but I’m pleased with the results.
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- 3D printed T10 LED lamp shade
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- 3D printed T10 LED lamp shade
Here it is on Thingiverse: http://www.thingiverse.com/thing:20809
The ebay listing for the LEDs (which were $1.50 for two) was titled “2 pcs WHITE Xenon SMD 9 LED HID 194 168 T10 Car Light.” It was designed exclusively with OpenSCAD.
T10 LED Lamp Shade by Alex Franke (codecreations) is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
OpenSCAD apparently doesn’t have an easy way to make an arc or wedge, or any way to do a partial rotate_extrude. This presented a problem when I started to design my Parametric Encoder Wheel, because in order for it to look nice, it would need to have lots of extruded arcs or partial rotate extrudes in order to make the holes.
Creating an Arc with OpenSCAD
Here’s how I solved the problem. Currently this will render slots up to 180 degrees around, but extending it should be pretty easy. If you’re doing a lot of these in your model, be sure to use render(), or badness will occur.
/*
* Excerpt from...
*
* Parametric Encoder Wheel
*
* by Alex Franke (codecreations), March 2012
* http://www.theFrankes.com
*
* Licenced under Creative Commons Attribution - Non-Commercial - Share Alike 3.0
*/
module arc( height, depth, radius, degrees ) {
// This dies a horible death if it's not rendered here
// -- sucks up all memory and spins out of control
render() {
difference() {
// Outer ring
rotate_extrude($fn = 100)
translate([radius - height, 0, 0])
square([height,depth]);
// Cut half off
translate([0,-(radius+1),-.5])
cube ([radius+1,(radius+1)*2,depth+1]);
// Cover the other half as necessary
rotate([0,0,180-degrees])
translate([0,-(radius+1),-.5])
cube ([radius+1,(radius+1)*2,depth+1]);
}
}
}
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
I received several filament samples from New Image Plastics in Ohio, ranging in length from about 1-4 feet. Here are the measurements I took from various points on each strand. I measured all the way around the filament and recorded the minimum and maximum values:
Orange 1.75mm ABS (Sample 1): 1.70-1.73, 1.70-1.73, 1.67-1.70, 1.71-1.74
Orange 1.75mm ABS (Sample 2): 1.71-1.74, 1.71-1.74, 1.71-1.73, 1.70-1.73
Orange 1.75mm ABS (Sample 3): 1.67-1.70, 1.69-1.73, 1.67-1.69
Orange 1.75mm ABS (Sample 4): 1.68-1.70, 1.66-1.68, 1.67-1.70
White 1.75mm PLA: 1.69-1.71, 1.68-1.73, 1.68-1.73, 1.68-1.73, 1.68-1.72
Clear 3mm ABS*: 2.87-2.91, 2.90-2.95, 2.90-2.94, 2.88-2.93, 2.86-2.95
* They noted that the clear plastic “is to sample only we do not have clear resin to sell” [sic].
When I wired up my Reprap and started printing, I noticed that all my prints were mirrored along the Y axis — I’d set it up with the end stop at the front and configured it so that the print bed moved forward when I clicked Y- in pronterface (printrun), and not back. (When the table moves back, the print head essentially moves forward along it.)
The end stops were already in place and I didn’t want to move them, but no combination of INVERT_Y_DIR and Y_HOME_DIR in Configuration.h would work. I even tried changing Y_ENDSTOP_INVERT, knowing full well that it wouldn’t help either.
So how do you flip an axis without moving the end stop or the home position? The answer is to change both INVERT_Y_DIR and Y_HOME_DIR in Configuration.h, and also swap the values for Y_MAX_PIN and Y_MIN_PIN in pins.h for the specific motherboard you’re using.
A couple of people have noticed this, so I thought I’d write it up. There’s nothing wrong — it’s just something to be aware of if you’re soldering up a Sanguinololu 1.3a PCB.
If you look closely at the circuit board where the FTDI chip goes, you’ll notice a tiny solder bridge between pins 25 and 26 (below the “L” in “FT232RL”). I noticed it when I first inspected the board, and I looked at the original gerber files to make sure it was part of the design. It is, in fact, part of the original design (see photo below), so there’s no need to try to remove it. (To confuse the issue, the instructions even say to look for things like this.)
If you did remove it, that’s okay, too — those pins (which both go to ground) are still connected inside of the outline of the chip.
One other thing to note is that the pin headers along the top of the board sit a little further in than those along the other sides. This is also exactly as it is in the original gerber files, but it means that the PCB might prevent some right-angle headers (like those in the Mouser project kit) from plugging all the way in unless the male headers are soldered a little high. (See the second photo.) This is probably more of an aesthetic issue than a functional one, but if you want to make sure they plug in completely, you can use one of the female connectors to space it properly when you solder it on.
Yeah, free. If you’re starting a 3D printer project (such as RepRap) at your public K-12 school in the United States for the benefit of the students, then we’ll give you a free Sanguinololu v1.3a PCB to help you out (while supplies last). They typically sell for about $12-14. We won’t even charge you for shipping.
What is a 3D printer? Check out the video at the bottom of the page for an introduction.
Not a school but want one anyway? I’m selling some of them to raise funds for a printer for a local school. Just select “None – Buy one” for affiliation below, and I’ll send you the details. They’re $11, shipping included within the USA.
Sanguinololu 1.3a PCB
We don’t see any reason why kids shouldn’t have access 3D printing technology in their problem solving toolkit, and soldering up the electronics is all part of the fun. A club with only six kids raising $50 each could be well on its way to building and operating a 3D printer for its school, and while the electrionics can typically amount to 1/3 or more of the final build price, hopefully a free PCB will help ease the pain a bit.
Are you interested? Submit the form below for instructions on how to get your free Sanguinololu 1.3a PCB.
What is a 3D Printer?
Here’s an introduction to the technology:
The shipping “estimator” at Mouser.com is a little vague, so I thought I’d post the results of a recent order. In general, you’re not going to know the shipping cost or the weight of your order until after it’s shipped.
My recent order totaled $189.12 and had 33 line items, including all kids of components (resistors, capacitors, ICs, connectors, crystals, buttons, crimp terminals, etc), in quantities ranging from 2 to 250, primarily for assembling four Sanguinololu circuit boards (with some exceptions, plus some other stuff).
Selecting residential delivery via USPS to North Carolina, USA, the Mouser shipping estimator listed $6.95 for 1 pound and $9.60 for 2 pounds. I guess that the order wouldn’t weigh any more than 2 pounds. The actual invoiced shipping cost turned out to be $7.74.
Although the order was prepared the previous night, I didn’t remember to actually place it until just after 4:00 EST on January 25, 2012 — so I had just missed the same-day shipping cut-off time. The order shipped on January 26, and the credit charge (for the exact invoice amount) was posted on January 27.
The delivery tracking updates were as follows:
- Out for Delivery, January 28, 2012, 9:55 am, CHAPEL HILL, NC 27514
- Sorting Complete, January 28, 2012, 9:45 am, CHAPEL HILL, NC 27514
- Arrival at Post Office, January 28, 2012, 5:08 am, CHAPEL HILL, NC 27514
- Electronic Shipping Info Received, January 27, 2012
- Depart USPS Sort Facility, January 27, 2012, FORT WORTH, TX 76161
- Processed at USPS Origin Sort Facility, January 26, 2012, 8:18 pm, FORT WORTH, TX 76161
- Accepted at USPS Origin Sort Facility, January 26, 2012, 7:03 pm, MANSFIELD, TX 76063
One final note: Recently I’ve noticed that there are a number of different ways people pronounce Mouser. Recently I’ve heard Mouse-er (rhymes with house-er), Moze-ure (rhymes with rose-ure), and Mau-zer (rhymes with cows-er). So how do you pronounce Mouser? It’s pronounced Mau-zer (rhymes with cows-er), but I still like to think of it as Mouse-er.
I’ve set out to build a Prusa Mendel for $300. So far I think I’m doing pretty well. The top part is what I’ve already picked up, and the bottom part is what I have yet to purchase — that’s where I still have some flexibility in cost. The first column is the percentage of total cost for that part. Shipping charges for a group of items from the same supplier are listed with the first item in that group. [Note: This chart has been updated many times as I build, and as because I'm already up and running with my reprap 3D printer, there's no longer anything left to purchase.]
Where I discovered mistakes, I’ve corrected them. For example, I actually ordered nylock #6 nuts instead of regular ones. In cases like these, I’ve just corrected the prices and pretended like I never incurred the cost of the wrong product.
There’s one important point I’d like to make out here: I was patient, I waited for good deals (and occasionally got exceptional ones), and I arranged some group buys for bulk discounts. Often if you agree to purchase larger quantities of a product, you can secure a discounted rate, and so that’s what I did where I could. You might not find all of the same deals I did, but you may get pretty close if you are patient and work with your suppliers.
I’ve added a table below that breaks out the electronics order, including what I had on hand, what I bought from ebay, and what I didn’t actually need. (Welcome Hack A Day readers!)
Finally, be sure to scroll to the right in the spreadsheet views for important notes or shortcuts on most line items.
Electronics
It’s not easy to find concrete examples of shipping costs for McMaster-Carr online, and they don’t tell you what an order is going to cost to ship until after it’s already shipped — and that can be a little scary especially if you’re ordering odd sized parts, even if they only charge their shipping cost. So here’s a real example of shipping costs for a small order with some long parts to NC, USA. The order was placed online and shipped the same day from their Atlanta, GA, USA location.
For a reprap build, I ordered these items, which include three 3-foot steel rods, 200 nuts, 292 washers, and 200 machine screws. Shipping was only $6.52 for everything. That’s not bad at all…
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