Friday, January 2, 2015

Replikeo Prusa i3 Rework Build - Part 2: Assembly

Part 2 will describe the process of building my Replikeo Prusa i3 Rework. Having already taken inventory in part 1, I will continue following the wiki instructions with Y-axis assembly. Below are the pictures from the build.

Y axis assembly

Y axis assembly with carriage

X and Y axis assemblies

X, Y, and Z axis assemblies

Z Steppers added

Attach uprights to base and add X,Y steppers

I don't remember having any serious problems with this portion of the build. I was able to put what you see above together in a few hours. Some screws were too long as I had seen documented elsewhere. I just put some extra washers underneath them. On the z-axis threaded rods, the nuts did not fit snuggly into their housings, so I added a drop of hot glue to each. Other than that, I pretty much followed the instructions. Next was the extruder assembly.

The extruder assembly required a little teasing. It is worth noting that this is the only printed part that is included in the kit. As such, some trimming of support material was required. I was not overly impressed by the print quality. I plan to print a replacement at some point and expect mine to come out much better. The biggest problem was that the hole for the j-head was not round. Luckily the j-head is almost exactly the same diameter as the drum sander attachment on a dremel tool. A bit of sanding and it was good to go. Below are some pictures.

Assembly before stepper

J-head hole enlarged
Hot glue added to keep bearing in place

Fully assembled extruder before stepper

At this point the only things left to do were add the heated bed and wire everything up. Wiring will be in part 3, but I will put the heated bed pictures here. I debated for a while how to best attach the thermistor. Eventually I ended up using silicone sealant and some kapton tape I had. The wide kapton was not included in the kit, but many smaller pieces of the stuff included in the kit could be used if that is all you have. In the end, the silicone did nothing. I would just leave that off.
Thermistor included in the kit. Wires are presoldered and heatshrinked

Thermistor taped to heatbed

Printer ready to be wired
Its worth noting that I used springs to support the heated bed instead of washers like in the wiki instructions. I think it's fairly obvious how to do this; the springs are included in the kit.

At this point the only wiki page left is Electronics and Wiring. Part 3 will address wiring and initial software setup.

-Matthew




Thursday, January 1, 2015

Replikeo Prusa i3 Rework Build - Part 1: Unboxing

About a month ago I decided to build a 3D printer. This only left me with the task of deciding what kind of printer to build. While I had dealt with the Makerbot we have at school, I did not want to shell out that kind of money for a prebuilt, so I decided to go the RepRap route. After consulting with a friend that has a RepRap and searching around online, I came up with a few options to decide between.

Eventually those options narrowed to two. I would either build an OB1.4 printer. Or I would buy a full Prusa i3 rework kit. With Christmas break fast approaching and not wanting to forget a screw and have to wait until next semester I decided to go with the full kit from Replikeo. At the time I couldn't find too many reviews on it, so I decided now that I have it up and running I would post a few things about how it went. I would encourage others that buy the printer to do the same.


Long Story - Short 

I would recommend this kit to anyone with a little electronics and mechanical knowledge (the basic knowledge needed to build any RepRap). I got it up and running in about 4 days. Maybe 25ish hours. While I have some improvements planned, it had everything I needed to get it going. I really like the injection molded parts. The electronics look genuine. I am glad I purchased the kit instead of sourcing my own.

Long Story - Long

I ordered the "iron" 1.75mm Replikeo kit for $350. Shipping from wherever to my house in Southern Tennessee (USA) was $90. Addtionally I ordered $23 of Hatchbox PLA filament from Amazon and a Full Graphic Smart Controller from Ebay for $25. Everything came for less than $500. 

Shipping took exactly how long they said it would. 3-5 days via DHL. I think I got mine in 5 days including a weekend. Mine was not beaten up like another post I saw. I was irritated that there was no parts list but HERE is the wiki page. Now here are some unboxing pictures.
All my purchases together. Replikeo box is one the right.
Removed from the cardboard
Top removed exposing the frame
Steppers and Power Supply
ABS filament, electronics (in cardboard box), and rods protected below.
Threaded rods and smooth rods protected in packaging

I thought this was interesting. Apparently this kit was made just for me (that is my name).
Hardware and Electronics removed.
Electronics in anti-static packaging
All small parts laid out.

After getting it unboxed I took inventory of all the parts. While I did not bother to count all the small screws I estimated that I had enough of each. All the electronics were included. The one thing I would recommend is getting a longer USB A-> B Cable. The one included is tiny and inconvenient. I had one sitting around from my Arduino projects. The Arduino appears to be a "real" Arduino (or else a pretty good clone).

The injection molded parts are really nice. I don't see any of them breaking anytime soon, and it makes assembly very easy. While I would probably have used higher gauge wire on some components I am more or less pleased with it. The heated bed works well and the carbon fiber build plate is working well so far.

That is all I have for the unboxing section. Look for the next part (HERE) soon when I post pictures of the build.

-Matthew

Saturday, December 27, 2014

Linearizing the Sharp IR Ranger (2YOA21) with an Arduino

Today I will be linearizing a Sharp IR Ranger. More specifically, I will be using the Sharp 2YOA21 F 04.


First, a quick word on why we would want to do this. The Sharp ir rangers are a very effective means of measuring distance. While ultrasonic sensors (for more about those see the Sensors label) can be fooled by textures and echos, ir sensors are more susceptible to interference from outside light sources and changes in material reflectivity. Therefore,  if a cheap measurement system is required in a varying environment (eg, a mobile robot) a combination of ultrasonic rangers and ir rangers can be quite effective.

If you have found this page, you probably already know this, but I will state it anyway. Sharp ir sensors have an analog output. However, the analog value does not have a linear relationship to distance. In this exercise we will find the function that does relate the two and use that to take an analog value and convert it to a distance.

Wiring

As stated above, the sensor has an analog output. Connect the red lead to +5V, black lead to GND, and yellow lead to A0.

Aquire Data


I used a simple sketch that took the average of 5 values and printed it to the screen. I then manually copied it into an excel spreadsheet along with the measured distance value. 


Fit Data

Once you have acquired the data, plot it. Some points will most likely fall outside of the trend. Exclude those points and fit the rest. My fit was Value = 1893.9*Distance^-0.92. 



Use Equation

Solving the equation I got above for Distance gets me this, Distance = (1893.9*Value) ^-1.087.

This is something we can plug into Arduino code. At this point it is only right to note that the method I am using will involve floating point math. There are methods that avoid that. If processing power is at a premium, you might want to check those out.

The important piece of code looks like this:


  float Distance = pow((sensorValue / 1893.9), -1.087); 

If you want the whole thing, you can download my code HERE.

That's all I have. I hope it was useful.

-Matthew