Updates on the RepRap build

Last week I received 5 NEMA 17 stepper motors for my Prusa Mendel RepRap. They are pretty small and I’m a bit worried that they will be to weak for some parts of the printer (mainly the extruder) but I have to wait and see.

I also ordered a complete RAMPS kit and 1 kg of plastic filament from 3D Gadgets. The shipment from china with FedEx was super fast but since I work office-hours it seems impossible for FedEx to deliver it to me.

I hope I’ll find a solution to get my package and will post some pictures on both RAMPS and the steppers when it arrives.

I also discovered that I could run the whole RepRap on 24 V using RAMPS or that I could divide it so the steppers and extruder run on 12 V using the 5 A fuse on the board and the heatbed running on 24 V using the 11 A fuse allowing me to push 264 W of power into the heatbed. Should be enough.

To buy before first print:

  • Extruder
  • Power supply
  • Endstops
  • Piece of glass to use as print surface.

Prusa Mendel printbed

I put together a heated printbed for my Reprap using three parallel 10 Ω 100 W power resistors. The resistors are screwed onto a 220 mm x 200 mm x 5 mm aluminum sheet. This will make the whole printbed a 3.3 Ω 300 W heating element.

Printbed power resistors
Three 100 W power resistors connected in parallel will act as a heating element.

On top of the sheet I will place a 220 mm x 220 mm sheet of glass to use as a print surface.

Top of printbed plate
Top of printbed plate

When printing the printbed should be between 60° C and 110° C depending on which plastic is used.

Since the main voltage used on the reprap is 12 V, maximum power that can be achieved is

[latex]
\frac{U^2}{R} = \frac{12^2}{3.3} = 44 W
[/latex]

My guess is that it will take at least two eternities before it gets hot enough, but for a start I’ll use the printbed temperature logic built into the RAMPS controller card.

Later on I think I’ll build my own temperature controller with either a step-up or a separate power source with a higher voltage to get more power out of the printbed.

Not much happening right now

It’s been a while since I had any updates here. I’ve had a lot to do and, no energy to work on any of the projects here for a while. I think that the first project I’ll resume when the summer is over is my Prusa Mendel RepRap.

RepRap Prusa Mendel
Current build status of the printer

Whit this done I could start making parts for really cool multicopters.

Quadrocopter revisited

I started talking about multirotors with a colleague a couple of days ago and I suddenly got the motivation back to finish my quadrocopter that I started to build over a year ago. I wanted to build my own quadrocopter controller based on my kalman filter for angle estimation. But I never really got the control parameters tuned good enough for stable flight.

I don’t think I’ve posted any pictures on the quadrocopter in my previous posts so I’ll post some here.

Assembled quadrocopter before painting
Assembled quadrocopter before painting
Earplugs used to isolate controller board from vibrations
Earplugs used to isolate controller board from vibrations

and some videos to show how far I got with the controller tuning.


The first thing I did when starting to work on the controller again was to rewrite the controller part of the code from scratch. This time I think I’ll implement two different control modes, one that I call stable and one that I call acrobatic. Actually I’m more interested in the stable mode since I want to use the quad as a camera platform but it’ll be nice to have an acrobatic mode as well. This is two rough sketches on how I plan to implement them.

Stable quadrocopter controller
Stable quadrocopter controller
Acrobatic quadrocopter controller
Acrobatic quadrocopter controller

In the stable controller the angle of the platform is controlled by the radio, while the acrobatic takes the angular rate as an input. If you tilt the stable platform 15° and then release the controller it will return to horizontal level while the acrobatic will continue to lean 15° until you pull the lever in the opposite direction and tilt the platform back.

As I wrote in my post about the Kalman filter it is actually two identical filters for pitch and roll working completely individually. This works great for angles up to somewhere around 45° but the filter will go crazy if you start doing loops  and rolls. That’s why the Kalman filter is removed in the acrobatic mode leaving a controller that works directly on the gyro signals.

Right now the code is ready and parameters for the new PID controllers needs to be found. Last time I did this I built a rig but I left that at my parents house a while ago.

Quadrocopter test rig
Quadrocopter test rig, the quad rotates freely around one axis.

I dare not to test the new parameters without having the quadrocopter securely fastened to something heavy. On full throttle the motors produce around 1,2-1,4 kW of power which can do some real damage. I realized that the hard way…

My hand before the doctor stitched it together .
A 3cm long cut in my hand (actually 4 or 5 cuts from the rotating propeller) before the doctor stitched it together.  It was all the way through the skin, I was lucky that no tendons were harmed.

I plan to visit my parents in a couple of weeks, I’ll post an update once i fetched the test rig.

Propeller driven Lego car.

Lego Technic is perfect for creating quick prototypes of pretty much anything, combine this with RC stuff and you can create really fun stuff. One simple example is the robot i describe in this post:
Sunday afternoon robot

My old Lego is usually stuffed away in a box in the basement, but when we have kids visiting we usually bring it up to the apartment. I suspect I’m the one enjoying it most and this time I built a RC lego car

Lego Propcar 1
From the side
Lego Propcar 2
The motor and propeller us used as a pusher
Lego Propcar 3
The battery, ESC and receiver is secured with a rubber band
Lego Propcar 4
I use a HXT900 servo to steer

After a few testruns I added a propeller protection bar to minimize the risk of running into something with the propeller.

Lego Propcar 5
Propeller protection

Runs great, I’ll probably update this post with a video when I’ve recorded one.

Battery bag for my E-Bike

Last weekend we borrowed a sewing machine to make new curtains for the apartment. When I was sewing the curtains I realized that It wouldn’t be very difficult to make a custom battery bag for my e-bike. I would like a bag that I could mount in the frame triangle and have room for 4 Turnigy 6S 5Ah batteries. Doing some measurements, calculations and drawing I came up with this design

Battery bag drawing
An outline of the battery bag, the red triangle is the frame, the blue rectangles are batteries and the gray rectangle is the controller mounted on the frame.

I went to the fabric store and found a black nylon fabric that had a PVC layer on one side. This should be fairly water resistant and I plan to spray it with some textile waterproofing spray as well. I was recommended to use a thread for furniture which is much stronger than ordinary thread as well. A couple of hours thinking, cutting, and sewing later:

Battery bag
I use some Depron in the bottom, and some foam in the two corners to protect the batteries and fill out the bag.
Zipper
The zipper has a bit of fabric folding over it for water protection
Hole for cable
The hole for the cable is also waterproof since the side of the bag overlaps ~10 cm where the cable comes out.
Cable
I'm using the cable I made for the E-Puch. This cable is for two turnigy batteries in series and two in paralell with a 60A fuse. The LEGO part is just for size reference.
Packed
Everything fits nicely inside the bag

The bag fits perfect on the bike!

Battery bag on bike
Battery bag on bike
Battery bag in frame
Battery bag in frame

Pleas write a comment if you think I should make some kind of drawing and description on how to make a bag like this.

Have somebody seen my magic smoke?

A little while since the last post, this is maybe old information if you have read my posts on Endless Sphere or the Swedish Electronics Forum. We played around for the whole weekend with the moped until the motor got enough. My guess is that several hard accelerations during a short period of time heated the stator enough for the insulation to melt.

The black insides of a BLDC motor
The black insides of a BLDC motor

Not pretty! I’m afraid I’ll have to torment my hands with another rewind. A member on SEF is good enough to donate a large roll of 1,5 x 2,5 mm flat copper wire to me which I will use for the rewind. I have three different actions to prevent this from happening again.

  • Increase the gear ratio. Less torque on the motor means less current.
  • Increase kv, one less turn of copper wire will increase kv to match the higher gear ration and reduce the resistance. It will also leave more room for air to flow through the motor
  • Forced cooling, I’ll put a fan in one end of the motor to force more air through.

I’ve also ordered a spare motor from china. The 80-100 is very hard to get nowdays, but I found a 80-85 motor with the same mounting profile and axle. But i’ll keep a close watch on the stock of the 80-100 motor.

First testrun of the E-Puch

Today I’ve made the first test-run of the E-Puch. As I’ve written about before it is an old ICE moped that I’ve removed the engine and replaced with an electric BLDC outrunner.

Today, me and my brother threw everything together for a quick testrun just to see that everything works, and try out the performance.

E-Puch ready for testrun
E-Puch ready for testrun

I will soon write a post about the motor controller which I ordered from a guy named Lyen on the Endless Sphere forum. It is currently set to limit battery current around 40 A, but I think I could increase the current limit by 50% without any modifications. Which would give 50% more torque.

Controller temporarily mounted to the frame
Controller temporarily mounted to the frame

The motor is mounted on two 5 mm aluminum sheets that are bolted in the original motor holes in the frame.

Motor and motor mount
Motor and motor mount, I think I'll remove the axle on this side.

Except for the motor and motor sprocket the drivetrain is original.

Original chain with 10 tooth front sprocket and 43 tooth rear sprocket
Original chain with 10 tooth front sprocket and 43 tooth rear sprocket

I use 4 bricks of 6S 5 Ah Turnigy 20C batteries mounted in 12S2P configuration. For now these are in a plastic box on the rear end of the moped.

Temporary battery box
Temporary battery box

And at last a video of my father trying the moped.

Plans for my depron plane

Final CAD model of depron aircraft
Rendering of the aircraft

 

In a comment on the post about my first Depron RC-plane I was asked for the plans. I’m afraid I don’t have the nice 1:1 print on multiple A4 plans that most people are used to, but if someone have a good guide on how I create those kinds of prints I’ll be happy to create one. But for now I can provide the drawing with measurements.

Depron Plane drawing
The drawing of my depron plane (all measures in mm)

And the same drawing as a PDF

I measured up these parts on a piece of cardboard to use as a template. Especially since you need two of all parts except the one in the lower right.

I used the kind of cardboard that you can buy at a painters shop to protect your floor while painting.

RepRap Prusa Mendel

To mount the sensors on the large outrunner as i wrote about in this post I got a couple of 3D printed plastic parts for holding the hall sensors at exactly 17.14°.

Plastic sensor brackets printed on 3D Printer
Plastic sensor brackets printed on 3D Printer

This raised my interest for 3D printing and I started to do some research on which printers that were available. There are several different projects that sell a kit that only needs assembly for example the MakerBot but I decided to go with the RepRap that is a more DIY kind of printer. The main reason of this is that the RepRap seemed to have the highest  buildvolume/price ratio and the community around the RepRap is very large and helpful.

There are several different versions of the RepRap but when I started this build a couple of months ago most people seemed to be building the upgraded Prusa Mendel with LM8UU linear bearings, upgraded z-axis couplings and slight changes in som other plastic parts. The nice thing with a RepRap is that once you’ve built your machine you can print most of the parts needed to build another one. Therefore there are a lot of people around the world selling the plastic parts on for example ebay.

The RepRap can print two different kinds of plastic:

ABS (Acrylonitrile Butadiene Styrene)
Is made from petroleum and has a quite high melting point. This is the kind of plastic which  LEGO blocks are made of. This plastic is softer than PLA and more flexible.

PLA (PolyLactic Acid)
This plastic is made from corn starch and has a lower melting point than ABS and is a little bit harder but more brittle.

I decided to go with parts in ABS, I’m not sure yet if that was a good choice since I’ve heard that it’s more difficult to produce good quality prints with this plastic. I ordered the plastic parts from a dutch guy on eBay and the first parts I got were pretty bat prints all parts were ugly and the x-axis mounts were so warped the were unusable.

Warped x-axis mounts
The x-axis mounts are to warped to insert the x-axis smooth rods in the corresponding holes.

Luckily enough the guy I bought them from were kind enough to send me a new set of parts which were good enough.

Apart from the plastic parts you need what is caled Vitamins, this is all the parts that you cant print on another RepRap. For the Prusa Mendel this is:

  • About 6 m M8 threaded rod
  • About 3 m 8 mm smooth rod
  • A big pile of nuts, screws and washers M3, M4 and M8
  • A couple of 608zz ball bearings and LM8UU linear bearings
  • Printbed
  • 5 Nema 17 stepper motors
  • Electronics (for example RAMPS or Sanguinololu)
  • ~200-300W 12V power supply

The current status of my build is that I’ve acquired and assembled the first five parts in this list, the rest will be bought when I can spare the money.

RepRap Prusa Mendel
Current build status of the printer. The frame is ready, motors, electronics and hotend is missing

The threaded rod, nuts, screws and washers I bought at a local hardware stores (Bauhaus and  Hornbach) and the bearings are from eBay. The smooth rods are from a Swedish webshop called Maskindelen.

To get good quality prints you need a heated printbed and most of the Prusa Mendel DIY kits you can buy includes a heater built on a pcb but since I had a nice sheet of 5 mm aluminum left from the motor mount on the E-Puch, I decided to build my own. The aluminum will be used to spread the heat from three 100 W power resistors mounted underneath the bed. On top of this I will place a 220 x 220 mm piece of glass to print on.

For the rest of the parts I’m pretty sure I’ll buy a Prusa Mendel electronics kit from ReprapWorld togehter with a 12V 348W MeanWell PSU from Sure Electronics on eBay.