Hey! This thing is still a Work in Progress. Files, instructions, and other stuff might change!

Bluetooth Mini Track Loader

by Backmann Jan 4, 2018
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Do you have a pinout of the board wire locations numbers? I am trying to use a Bluno (Nano with Bluetooth built into it)

Hi Dennis
If you scroll down in the Thing Details section you will find a complete schematic with numbers and wireing.
Else you will also find all the pin assignments in the top og the Arduino code. Here it's very easy to change if you want to use other pins. Just remember to use pwm pins for the servos.

Thank you for sharing, and congratulations.
Should we install special books for the arduino?

Hi Vincent
I honestly don't remember. You might need the servo lib but i think it's a standard Arduino lib.

Hi Tyler
Yes I know :-D it's a great idea Zedpi has come up with.
You just need to remember to print the files named LegoTrack instead of BigTrack.

Comments deleted.

Just a question how do you get power from all the stuff into just two ports do you solder all the cables onto two ports I think i am missing something can somebody point it out for me

Hi Yussuf
Yes all the + and - go to the on/off switch soldered together on each pin.
If you look at the pictures in the post printing section you see on the pictures that a lot of wires are going up to the switch.

Wow thanks for the lightning-fast reply

what to use flex filament on belts?

Is this works with arduino nano + ipad ?

Hi Sojus.
I'm sure it will run on a Nano. But I think it won't fit inside the shell. The space is extremely tight.
When it comes to the ipad I don't know. I only have Android devices and I can't find a link to the app for Apple store. If you in some way can run android apps on your ipad it might work.

What code did you use for the bluetooth?

Hi Lance
The Android app can be found here.
It's not an app I have created. It is an app I used for a remote controlled car I had.

Thank you for the quick reply Backmann but what I meant to ask was what did you do to connect the Bluetooth module to your phone to control the Arduino pro mini.

Yes okay I see.
If I remember correctly. I went into my Bluetooth menu on the phone and scanned for new devices. Here my Bluetooth module showed up as linvor. Then I paired with the module.
I don't remember if this was troublesome or required a password.
Then I opened the RC app and pushed the gear button. Then selected Connect to car. And then I select linvor. And that's it.
I attach some photos from the RC app where I have painted some arrows on.
I hope this will help you. Otherwise let me know and I will try to make a short movie where I make the connection with a new Bluetooth module. I have something like 10 of them in my desk drawer :-)

I got it to work! Thank you!

Where is the code? I can't find it

Under Thing Files there is a file called Bluetooth_Track_Loader_v001.ino this is the code.

The Servo Horn from SG90 war to big for the arm hole.

Comments deleted.

the 1x On/Off switch https://goo.gl/78AyvA listed in the parts list is different then the one showing on the schematic plan, or am I wrong?

Hi Steven
It's the On/Off switch that I used.
It's a single switch with two breakers inside. That's what I have tried to illustrate in the schematics.
You need to break off the plastic shell of the switch to be able to fit it into the body parts of the Loader.

what kind of resistors are connected to led and buzzer? cannot find info about them here?

Hi Steven
I use 220Ω 1/4 watt resistors.

Weich flexible Filament you User? How you modify the servo for endless spinning?

Hi scr1tch
I have used a no name China TPU flex. It's not optimal and have started delaminating between the layers.
I have bought some original NinjaFlex to try making some new belts but not made yet.
In the "Post-Printing" section you will find a video descriping how to modify the servos for endless spinning

is there anyway to get the 3d model files for this guy? i would like to tweek the charging port and power switch to accommodate an on-board charger and also add some neo pixel lights. the 3d models would make my life easier and i would post the updates as a remix after testing

Hi Alex
Sounds like an interesting mod.
I have uploaded the SolidWorks 2016 files in the Thing files section.

Hi Backmann.
Thanks for sharing your project. I have a problem in calibration of the servos.
Even I change the left servo parameter, it doens't stop moving.
Do you know why?
I'm using arduino Nano.

Hi Fabio.
Are you making changes in this section of the code?
int Left_zero = 89; // Edit here if Left belt is turning in stopped (don't go below 80)
int Right_zero = 85; // Edit here if Right belt is turning in stopped (don't go below 80)
int Bucket_zero = 5; // Edit here to raise Bucket from lowest position (don't go below 0)

Is the speed changing when you change the Left_zero parameter?
Are you using the PWM pins on the Nano for the servos?


Hi Soren.
Yes, I'm using PWM pins, 9 and 10; I changed to pins 5 and 6 and now only servo's Bucket is working. I changed the buzzers and light pins. The others don't working. The battery could be a problem because ! changed to Nano?

Hi Fabio
Sorry for the waiting time.
Maybe its because you need a value below 80.
You can do that but you will have to correct everywhere where it says -80 to match the number you requer.
I think it will be ok just to change to -70 and then you can play with the values between 80 and 70.

I don't know about the battery. I have personally considered to use a small 1s lipo to 5v stepup module. Then it would be a more stable powersupply and that might keep the servos more stable even when the battery discharges?
I have had a look on this one because its extremly small. https://goo.gl/Sqj7j8 But it's unfortunately sold out right now.
This one might also do the trick https://goo.gl/6w5TF8 it's just a little bigger.


try using this voltage regulator with a low voltage cutoff this will protect the battery from over discharge and give a constant stable 5v that all the electronics require to work properly.

the same company has really nice and cheap continuous micro servos so no modding a servo needed

Hi guys,

I am new here and just love the work what Backmann did. I printed all the files but is there any assembly drawing, video or any tip please. Thanks! Waterloo.

Hi Ottawa
The best I can offer you at the moment is the descriptions in the Post printing section in the Thing Details tap.
Here you will find a schematic of the electronics and some photos of how to fit everything inside the Track loader.
You can also find a video of how to modify the servos for the two belts.
If you run into problems just ask your questions here and I will do my best to answer as quick as possible.
Best regards,

is the pro mini the 5v version or the 3.3v? is there a problem with the unregulated battery voltage straight to the raw pin?

It's the 5v version.
Only problem with the unregulated voltage is that when the voltage gets low the servos gets a little out of sync. Meaning the track loader starts to turn slightly when driving straight and when standing still it rotates very very slowly around itself ; -)

i would use a 5v regulator because unstable voltages can damage the sensitive electronics we are working with.
try using this voltage regulator with a low voltage cutoff this will protect the battery from over discharge and give a constant stable 5v that all the electronics require to work properly.

the same company has really nice and cheap continuous micro servos so no modding a servo needed

thanks for the answer, i just uploaded the code and it works great! really well made :-)

That battery (The 180mAh one) is not shippable to US anymore.. can I use a 220mAh 3.7V 1S 50C instead?

Acording to banggood the 220mAh battery is only 3mm longer than the 180mAh.
If this is true it will most likely fit but it will be an extremly tight fit.
I have added a picture with measurments. The 220mAh battery will be 0,5mm behind the servo for the arms.
I think its worth a try.
The battery I have taken the measurments from is this one from Banggood: https://goo.gl/eN2QxB

Is the track correct? I printed it and gets super loose.
I had no issue with any of the other parts, just missing he track to make this
guy move. :)


Oh Shit.
I just realised that I have actually made the wheels after the Zedpi size and not the Lijingwei size.
That is why you have very loose belts.
I will change the file names so that no one gets confused.
Sorry for that.
I think if you print Zedpi's SmallPulley the small track will fit perfectly.

Hi Nandox7
It is the correct belts. My belts are also a bit loose. I used 3 drops of hot glue in the drive wheels to create some forced pull effect on the belt notches. It's not ideal but it does the job.
One question. Have you printed my wheels og the wheels from Zedpi's version?
If you have printed Zedpi's version you also need to print his belts because the wheels are smaller.
Best regards,

Hi Søren

Thanks for the reply.
I've printed your wheels (easy to check as all have the postfix _SB).
I see he trick with the hot glue is that they would barely get any grip, what I tried in the mean time was to print the track from Zedpi
and it fit better. A tad too tight but I'll use another more flexible filament to allow it to stretch a bit more.
See here the difference in size: Yours is the one outside.: https://photos.app.goo.gl/R6jC3wpmL4IGS8Tl2

One last question, did you resized your version by a given ratio? Asking to see if it could be easy to just resize the Zedpi's fork and snowplow tools. :)


PS: Really cool idea to have this work with Bluetooth. No need to carry my RC radio to the office. ;)

Hi Nando

Yes exactly. It's much easier just to bring the track loader and we always carry our phone everywhere. ;-P

I'm told by Chardels that if you print the wheels and belts from Zedpi's design it will fit on this version as well. That could be a solution. I haven't tried it myself.
I don't know the scale ratio because I used the versions from lijingwei. Who has uploaded .stp files of all the parts. So it was easy for me to import it into Solid Works and edit the shell parts.
Chardels have made it with the forks. I will PM him and ask how he did. Maybe he is willing to share the files with us.

I'm working on a small charger device for it right now. I have all the parts printed and the electronics in place. I just need to make a instruction and then it will go on thingiverse.

Cool stuff! Thanks for the reply.
I'll check the wheels and belt size from Zedpi's. I may still need to make a small change to them as even yours
don't fit as good as it should on the servos that I have. I'm using old HXT90 servos that are stlightly differnt to the SG90.
The case is the same but the arms differ a bit in side.

Hope to have this done by the weekend to start looking into the firmware. :)
Plan to implement a few things in there, will share later in case anyone is interested.

Hello again, if I use the wheels from Zedpi's design, will your version of the loader (with hollow inside and bluetooth control) be compatible with the lego track?

Hi Chardels
Honestly I have no idea. I haven't tried it. But i dont think it will fit.
If you test it please let me know if it works.

I did test this, and it works. If you print the wheels from Zedpi's design the positions of the holes on the frame are still the same and the lego track fits perfectly. I have everything printed and everything wired up and working I just cannot get it all to fit inside the frame. Driving me crazy.

I will take a picture of how I have put everything inside the frame and upload it shortly. Maybe that will help you.
Please share pictures of your built when it's assembled I would love to see it with the lego tracks.

Thanks, yea that would help alot. I will for sure share pictures when I get it assembled.

Hi Chardels
I have added a bunch of pictures and some description in the Post printing section. I hope this will help.
I'm trying to make a assembly video but I'm having some troubles with getting a proper lighting and camera angle.
I'm absolutely no expert in video making ;-)

Hey Backmann, I love this project and want to build it myself, but I don't understand how one thing works. How are you having more than 180 degrees of turning from your SG90 Servo Motors? (for the left and right tracks)

Hey Chardels
I have added a description/video in the Post-Printing section.
I hope this will be helpful to you and everybody else.
Best Regards,

Thank you it is helpful. I was thinking thats what you did but I just wanted to be sure.

Dear Friend,
Is it possible to get the APP for bluetooth connection?
Do you have a sketch for the Hardware wiring?

Best regards from Austria

Dear Marcin
I have updated the description with a link to the Android App.
I´m still working on the Arduino code and the wiring schematic.
I hope to get it done in the next couple of days.
Best Regards,

Can you give me the code, i want to try with Arduino NANO

Dear asessinerx10
I will upload the code in here as soon as I'm done with it.
I'm sure the sketch will work on a Arduino Nano but I don't think it will fit inside the track loader.
Best Regards,

The Arduino code is now uploaded.