One of my goals for the 3D Printer was fast and cheap production of gears. Buying plastic gears can be expensive and they often require modifications. This can waste a ton of time. In addition, they might not be the exact number of teeth required for a project. I decided to test the 3D printer and determine what settings and orientations were best for high quality parts.
I started off by printing some 64 pitch gears. I was curious to see if the printer was capable of making these parts. The results were pleasantly surprising! All of these close up shots were taken with my phone. I hacked together a macro lens using a thumb sized magnifier. I taped the lens over my camera and got a 10x zoom! The only down side is there is a fair amount of distortion over the images. However, it reveals details that the camera or my own eyes couldn't see alone.
This is one of my first test prints of a 64 pitch gear. There is some surface roughness that can be seen on the gear, but all of the teeth seem to have a reasonable profile. This gear was printed in the coarsest layer height (0.1mm per layer). The layers don't seem to create "steps" in the teeth.The surface roughness is still pretty good even though the layers are visible
This is a picture that just looked cool. I have no idea what happened with the focus of the camera but it added some neat effects. This gear was printed on the highest layer resolution (0.025mm per layer). Here the layers can't be seen. It just looks slightly opaque.
Here is a side by side comparison between the course and fine layer resolutions (0.1mm and 0.025mm per layer respectively). Both gears seem to have reasonable tooth profiles. It is hard to tell whether there is warpage in the teeth as the lens created considerable distortion in the picture. The lens also created a very shallow depth of field so only portions of the gear are in focus at once.
I also worked on larger gears. The majority of these gears are 32 pitch - 40 tooth gears. I wanted to see how different orientations of the gears in the printer would cause different amounts of warpage on the overall shape. I also wanted to see how various levels of post curing reduced wear on the gears. I also printed a set of 20 pitch - 25 tooth gears. All of the gears meshed fine, however some warpage in the gears led to noticeable wobble on the shafts. I found increasing the resolution and adding more supports during the printing helped to mostly eliminate these issues. I'll have some projects coming soon that will be built off of these gears. There is also a cluster gear in this photo that contains a timing belt pulley in addition to a 32 pitch gear. This part couldn't be made through traditional machining techniques, so I'm very excited to see what unique structures I can design and build with the 3D printer.
I've always wanted to build a Hexapod. They look pretty cool with all of the legs moving in sync. They can also be used as a desktop toy, unlike my RC car, which is basically an outside only toy. The biggest problem with hexapods is they are really expensive. A proper hexapod requires three degrees of freedom for each leg. This ensures that the leg doesn't need to slide on the ground. The three degrees of freedom per leg and six legs require a hexapod to have at least 18 servos. The servo cost adds up fast and had previously discouraged me from building a hexapod. Recently I came across micro sized servos (HXT900 9g servos). These servos cost about three dollars each. Even with 18 servos that still isn't too expensive compared to typical on brand servos that cost about 20 dollars each.
I wanted to build the hexapod around my new 3D printer. The first thing I decided to do was integrate the servo splines into the legs themselves. After a number of test prints I was able to confirm it is possible to create micro size servo splines with my 3D printer (Form1+). I also wanted to keep the design minimalistic and avoid over complicated joints and leg segments.
I bought three servos before I committed to building the hexapod. I printed and assembled one leg to ensure the servos would be strong enough to drive the leg. I also wanted to test the tolerances on the servo splines with multiple servos. This image shows the leg prototype, The only change I made to the leg design was an increase in the depth of my logo.
This was the first "production" run for my 3D printer. I had to make six copies of each leg part as well as the body section. Aside from one print failure (on the main body servo mount plate) everything printed perfectly. I literally couldn't make these parts through machining given the orientations of the splines and the shapes of the parts.
This is the body piece ( the one that printed correctly) as it came off of the printer. There was an update to the printer software that dramatically reduced the material wasted in the support structure for the parts.
Here is the part before support material removal. The supports are removed with wire cutters and then the remaining bumps on the part surface are removed with a file.
The final part looks pretty clean. All of the dimensions seem to be within tolerance for the hexapod. There is some warpage in the part that occurred after the post curing, but it shouldn't prevent the part from being usable.
Each servo requires two 2-56 screws to be threaded into the frame. My hand got pretty tired trying to screw all of the servos into the mounting plate. Each servo fit nicely into the plate.
I decided to try fitting all of the pivots into the lower central support plate. It was fun getting to see the hexapod come together.
This was the first time the hexapod was fully assembled. I knew the wiring would be an issue, but I didn't realize how messy the hexapod would look without proper wire management.
Here is my programming testing setup. I was at my house for the winter break and no longer had access to my 3D printer. I had CNC access but I didn't particularly want to get covered in chips as I usually do when machining. I used a raspberry pi model a+ as the controller. This raspberry pi is the smallest one currently available. I wanted to run the hexpod with linux and python because it makes the programming easier. The hexpod currently connects to a computer over wifi which was really easy to do and should be a convenient way to control the hexapod. The two blue boards are PWM driver boards from adafruit. Each board can drive up to 16 servos ( I needed to drive 18 so I had to get the second board). The boards are controlled with an I2C interface. This means I need a minimal number of pins from the raspberry pi to control all of the servos. It helps to keep the wiring from being a mess.
Here is an early motion test. I programmed the legs to look like they were walking. I still needed to calibrate each servo and complete the actual leg motion program. This shows the hexapod moving its legs near the peak servo speed.
This was the first PCB I milled on a proper milling machine. I've always had access to a dedicated PCB mill, so coming up with my own milling procedure was fun. I drew the circuit board in SolidWorks so it would be easy to generate the G-Code for the CNC. A proper circuit CAD program like eagle probably would have been a better choice.
The PCB I milled was for the hexapod's power supply. This supply is capable of driving up to 20A at 5.5V. I wanted to drive the hexapod with a 7V battery, but the servos and raspberry pi wanted 5V. Each servo doesn't draw very much current, however the combination of all 18 which could all be running at full torque at one time would overwhelm most power supplies. I decided to go with the 20A supply to ensure there would never be a sever voltage drop that could shut down the raspberry pi.
Here is the final hexapod assembly. I ended up milling three plates from polycarbonate to create the electronics mount. The electronics are all held in with zip ties. I would have used screws, but I didn't want to make the standoffs required to mount the electronics with screws.
Unfortunately during testing I managed to break three servos. Shipping the hexapod back from break caused another four servos to die. All of the servos broke at the same internal gear. I haven't been able to finalize testing my leg motion code without a fully functioning set of legs . I chose not to use an existing set of code for the legs because I was excited to create my own algorithm from scratch. I need to rethink my servo choice and look into getting slightly more robust servos. Currently I am looking at using metal gear servos that are around five dollars each. I'm sure the hexapod will be up and running quickly once the new servos are integrated into the design.
My transmission design for the Mini Combat Robot uses large servo gears. Unfortunately the output from these gears is a spline shaft. I had to come up with a way to easily adapt to the spline without making a sketchy connection with the servo horns that are meant for those servo gears. My first technique for making a servo spline can be done with a milling machine. It's a fairly straight forward and doesn't require special tools.
I put a "blank" shaft into a collet block. The collet block isn't required, however holding a round part vertically in a vise can be difficult to align. It also has a good chance of slipping which could break tools and ruin the part. The first thing I did was drill a set of starter holes. I used a small carbide ball end mill because it was the only tool that could make a mark smaller than the drill bit I wanted to use. Each hole corresponds to one of the teeth in the spline. I designed the holes so the outer edge would meet up with the tip of each spline tooth.
Once I made all of the starter dents, I proceeded to use the final size drill bit. Each hole was very close, but none of the holes intersected. If the holes intersect the drill bit will likely drift and break. The final step was to mill out the center. Milling out the center creates the inner part of the spline. It is important to design the geometry such that the leftover wall between the drilled holes fits between the spline teeth. I simply plunged and endmill down to the desired depth and let it swirl around to the correct diameter. This opened all of the holes drilled to the center.
This is the final shaft. The part fit snugly on the spline and didn't seem to damage the spline even under loading conditions. I used this part on the Mini Combat Robot until a design iteration forced me to a 3D printed design (I no longer had access to a mill). Any mill with CNC or even a digital readout can produce splined holes.
This is a 3D Printed replacement for the metal adapter. I needed a different pulley, but I couldn't use the metal spline shaft for the upgraded design. I decided to 3D print an adapter instead. I used the same geometry as the metal spline and simply printed a new adapter. It also slipped right on and worked first try.
Here is the 3D printed servo adapter as well as a splined shaft that copied the original servo spline. I doubt an FDM type 3D printer could produce the details required for this spline to work, so I'm glad I went with the SLA type 3D printer (Form1+). Making giant servo splines led me to test miniature servo splines.
The first part to my process to make a servo spline is getting a picture of the spline itself. I use this picture and one reference dimension (the outside diameter of the spline) to trace the spline profile. This seems to be pretty reliable and is able to get details that my calipers can't measure.
Here is a screen shot from the CAD I used for the servo spline. I get the spline dimensions by tracing the profile that comes from the drawing. It is surprisingly fast to CAD this way. The camera image reveals a lot of details that my measuring instruments won't capture.
Here is a servo spline made for a micro size servo (9g servo). The printer was able to handle the small details required to make the spline.
The gear fit perfectly onto the servo first try. I attempted to strip the spline, however I only managed to cut myself with the 3D printed gear teeth. I was unable to get the spline to skip on the servo.
For future projects using large servos I will attempt to make more metal shafts and splines. I find them more durable than the 3D printed parts. I also know the servo gears will strip before the metal spline slips. The 3D printed splines for smaller servos are too awesome. I'm still amazed the printer can handle details like that. The cool part is these splines can be put into any 3D printed part. It doesn't matter whether the part is round, square, or even a hexapod leg!
I decided to use my new 3D printer to solve any engineering problems with the mini combat robot. The first problem was making the motor controllers fit in the space I left for them.
Here is the motor controller mount as it came from the 3D printer. The part wasted a lot of material in the supports. I designed the part to fit the motor controllers perfectly into the robot frame. This part might be machinable, but I would avoid making this part if I didn't have a 3D printer.
The new motor controller mount allows me to fit the wires in to the available space. It may look messy, but I'm just happy I could make the motor controllers fit into the frame. I knew the motor controllers would fit into the frame, but I didn't account for the wires or connectors. These left the space a bit too cramped to properly mount any of the components. The new 3D printed mount allows me to securely mount the controllers without risking damage during combat matches.
The robot looks pretty slick. I was able to replace the old 3D printed parts either with properly machined components or parts printed with my new 3D printer.
This underside view of the robot shows how the motor controller fits into the robot. I still need to replace the top and bottom plates with real armor instead of thin acryllic.
I didn''t quite mange to finish the robot before losing machine shop access. I've been able to replace most of the poorly 3D printed parts with either higher quality plastic components or metal components, however there is still a fair amount left to finish the robot. The biggest thing the robot needs is a spinner.
I got invited to a Halloween party about two hours before the party started. The party had a mandatory costume policy. Being an engineer and a new owner of a 3D printer I figured I HAD to 3D print my costume. The first thing that came to mind when thinking of 3D printing and Halloween costumes was an arc reactor. I've seen a bunch made on the internet and even a few for various Halloweens in the past. I remember that I had a box of LEDs. Unfortunately, I discovered that I only had two blue LEDs. Luckily I also had eight red LEDs... so the obvious costume became evil IronMan. I spent about 30 minutes drawing up the part in SolidWorks and then sent it to the printer. The print time was a little under two hours (it's cool to be slightly late to parties). While the part was printing I had to make the wiring.
I pushed each of the LEDs through a 1:1 drawing of the frame. I soldered all of the LEDs together with some solid wire to give some structure to the electronics. I also used two bent spiral wires for the + and - connections to the battery. I tore away the paper to release the electronics for the final assembly. I didn't use any current limiting resistors or a proper current driver because the battery voltage was lower than the rated voltage for the LEDs. I also figured that the small coin cell battery wouldn't be able to supply enough current to fry six LEDs in parallel.
Here's a top side view of the arc reactor. Each of the LEDs stuck out from the frame to ensure maximum brightness. It also saved some material and print time.
This is the back side of the arc reactor. I have paper shoved between the battery and the contact to prevent the LEDs from turning on. I didn't have a switch so the back has to be unscrewed to connect and disconnect the battery.
This is the arc reactor shining through my shirt. The camera doesn't do a very good job showing how bright the LEDs looked shining through my shirt. I used lots of tape to hold it in place.
Surprisingly the arc reactor stayed lit up all night. I didn't even have to break out the spare battery and hex key that I kept in my pocket. The design wasn't too great, but im pretty proud of it considering it went from concept to finished product in a little over two hours!
After thinking it over for a few months I decided the usual FDM type 3D printer I was building (the kind that squirts out plastic like a hot glue gun) wasn't going to meet my needs. I just moved and no longer have access to mills, lathes, or other metal working equipment aside from my trusty file and hand drill. I decided a 3D printer was the only way to continue my projects without making a mess in my apartment. After looking around at the different available 3D printers I came across the Formlabs Form1+ printer. This printer uses SLA technology. SLA printers use a photosensitive resin that solidifies when exposed to a light source. The resin in this printer cures with a UV laser.
I need a printer than can make parts with fine details, high accuracy, and decent strength. Although I'd love a printer that could make metal parts, however I'm a few orders of magnitude away from being able to afford one. I decided to settle with a printer that makes plastic parts. The FDM printers (like the one I am/was building) are nice because they have become very popular. The popularity has driven down the material costs which makes the printers very affordable. There is also a large number of users who have lots of great tips and tricks for getting high quality parts. Unfortunately the nozzle design in an FDM pritner limits the minimum features size. The fusion of layers through heat also tends to leave voids which causes very different properties depending on a part's orientation in the printer. This can make "engineering" grade parts difficult to make.
The SLA printers have only recently become available to hobbyists, so there is not a very large number of users. The material is somewhat proprietary, so it costs 3-5 times more than an FDM printer for a given volume of material. The quality from the SLA printers can't be beat by the FDM printers. The laser curing technique is able to make much finer details in the parts. I expect to be printing gears that are 32 and maybe even 64 pitch. The parts are also solid, so the material properties are going to be the same regardless of the part orientation. There should also be fewer voids in the parts, which will make "engineering" grade parts easier to produce.
Here's the printer in all its glory. I personally find the printer aesthetically pleasing. It also fits well on my bookshelf.
Here's the setup for my first prints. These parts are shock spring mount replacements for my rc car. The original ones no longer fit properly due to my machined replacement parts not being the exact same geometry as the original components.
The printer readout is pretty cool. It tells me the remaining print time and the number of completed layers. The remaining time is exact and can help me schedule my time around the printer so I can be as productive as possible.
This printer is upside down compared to FDM printers. The table rises out of the resin to grow the parts. It's a pretty neat concept and seems to work well.
Here are the final parts after removing the excess resin with isopropyl alcohol. They came out perfectly first try. I'm sure more complicated parts or parts with tighter tolerances will require some test parts, but parts like these take nearly zero effort to make.
Overall I'm pretty happy with the printer. I have more project ideas than ever now that I can make parts without labor. I'll be running test parts for things like gears and press-fits. For now I'm not going to finish the 3D printer I started making. The FDM printers can't make the parts I want to make. It is a good XYZ CNC platform, so I should be able to use it for another project some time in the future.
I've wanted a real RC car (not one of those tiny indoor only RC cars) since I was a little kid. Now that I'm a big kid I can just go out and get one. In this case I mail ordered a relatively cheap 4WD 1:10 scale buggy. The frame came as a kit. I had to pick out the motor, motor controller, radio, and batteries. I already had the radio from the mini combat robot, which cut the cost of the car. The reason I decided to buy a RC car instead of building one was that I didn't want to build something and then decide it was boring. I figured a cheap RC car would require repairs and could have an opportunity for many custom parts.
Here's a sweet action shot of the car before parts started breaking. I put a "somewhat" larger motor and battery in the car than suggested. The car's peak speed is over 40mph! (timed by driving on a football field) It probably has more power than I can control... I flipped it and hit things a full speed many times as well as taking jumps that brought the car around head height in the air. Needless to say the cheap plastic parts started breaking real fast.
Here's the machining of a new shock absorber mount. The original part didn't break, but it bent ~45 degrees. I decided a metal version would be a good first upgrade for the car.
Here is the aluminum part next to the original (which I bent back). I removed some of the extra "adjustment" holes that were in the original part. I also remade the pockets to make the part considerably stronger. I don't expect this part to break before any of the other parts on the car.
After a few more jumps I busted the front A-arms. I didn't have a spare axle so I was forced to bend this one straight again. Thankfully the axle was made from cheap steel and I have decent pliers.
Here is the A-arm that broke. The plastic split at the axle. This part is not a simple 2D part like the shock mount.
I started the part from flat aluminum plate. I forgot how slow it is to mill with a 1/8" endmill...
I wanted to save material so I did a REALLY good job orienting the stock on the mill table.
Here's a before and after picture of the side machining. The parts required a total of 3 sides of machining each.
My trusty mini-vise did a great job holding the parts. I also tried a set of carbide drill bits. They seemed to drill much better than my sketchy old drill bit set.
The new A-arms look pretty nice on the car. The shock spring mounts rub the aluminum a bit. I'll need to make some replacements to prevent any possible damage to the shocks.
Here's the whole car with its cover attached. The rear wheels are pretty worn down. Those will have to be replaced soon as well.
Here's the car without the cover attached. The electronics are fairly compact. I've been very impressed with the motor and motor controller combination. Neither has melted yet!
Overall I'm glad I bought an RC car instead of making one from scratch. I really wouldn't be able to beat the price I paid for the frame. When a part breaks I can have fun making a replacement. Eventually the whole car will be custom!
