• Adding Speed Control with a BLE App

    shane.snipe • 12/28/2019 at 17:13 • 0 comments

    On one hand, this log is kludging together snippets of example code to control my speedster. On the other hand, this may also be my first noteworthy hack with it comes to how the motor is controlled. Enough spoilers, this is how I did it. 

    I have been working with Thunkable off and on for mobile phone apps. I had Thunkable classic working with BLE a couple of years ago but Thunkable X or cross platform did not support BLE until earlier this year. Now it is working and it is fast and it seems very robust.  Check it out at thunkable.com.  Here is the tutorial on BLE. https://www.youtube.com/watch?v=sNpCTsVifo4

    The link to my project in thunkable is here. I will continue to work on this but hopefully it continues to be functional!  https://x.thunkable.com/copy/8fb9477a0c64124cb1102b88990c27ed

    Obviously, there is some Arduino code that needs to interface with this app. This was my biggest concern when I watched the video but the example code written by Neil Kolban worked flawlessly once I got the UUIDs correct.  Here is the code. It is a standard library example.   https://github.com/nkolban/ESP32_BLE_Arduino/blob/master/examples/BLE_write/BLE_write.ino

    So if you came across this hoping to figure out how to hook your ESP BLE to your phone the resources above were sufficient for me to get it going. The rest of this log is about my struggles and triumphs in bending the motors to my will.

    First you set up your interface and drop in  you buttons, labels and sliders. You also need the invisible component the BLE. I know I am not winning any design awards with this one but it works!

    The slider is meant for speed control and the left and right buttons are for turning.

    Here are the blocks I used and an explanation of my understanding of them.  First you need to check if your targeted device is available so you use the scan function and print a list of available devices. 

    I have only used this with the live test function on thunkable so far and occasionally I will have to dump it and restart it to make sure I can see the ESP32. However, I have always been able to connect. The scan takes 20-30 seconds.

    Next once you see your device pop up on the label, press the connect button and you get an immediate connection. There have been some discussions that the first scanning step can be skipped if you know your device is available. I have yet to try it. Here is the block for connection.

    Now the Arduino code has some standard communication in it.  It sends out Hello world until something has been sent to it and then it starts to echo what it receives. So to make sure I can hear from the Arduino I added a receive block. 

    So far I have not changed the UUID from the example code but there is link where you can get a new UUID. 

    I also included the error code if this is not working. So if I see Hello World or the value I am sending on my phone screen, I know my phone is communicating with the ESP32.

    The next blocks are for sending data to the to ESP32 to control the movement.

    The motors have a high and a low speed and an enable. The low speed still goes like 20 mph so it was not suitable for indoor use.  I tried to pulse the enable at various PWM frequencies. However, Goldilocks was no where to be found. Either I pulsed to long and it shot across the room or it was I too short and it never really got going. So I was stuck! I considered just making it an outside bot and focusing on turning it but it is December in Chicago and it is too cold outside to run my bot. 

    So here is my first real hack for this project. I remember the training I got when i was selling this motor  15 years ago. The motor has a look up table for the initial acceleration. Once it is up to significant speed, the speed is set by the frequency from the crystal. So there seemed to be a chance to replace the crystal with an external signal.  Now this...

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  • Anatomy of the board

    shane.snipe • 12/01/2019 at 18:54 • 1 comment

    I have always wanted to use the box of motors I had left over from the lead free transition to  make some robots. The motors were the DD6450 motors and they 30W 24 V motors that spun at 2850 RPM. I had found some rubber rings that fit well over the motors and turned the outer rotors into wheels.  The on board drivers made this motor pretty easy to drive with an Arduino but I wanted to be able to control it with my cellphone so we had a bit of 3.3V output from the ESP32 to 5V input problem. Here is the basic pinout:

    So 24V runs directly from the battery so that is not an issue.  Pins 1,2 and 8 work with 3.3V inputs. Pin 3 keeps the circuit running while not powering the motor. Maybe it is good for fast starts but I have not been using it. 

    The pin that has been a thorn in my side is Pin 9 CW/CCW.  For some reason the 3.3V pin can not drive it. It actually does not run when attached to a ESP32. So to get around this sticky problem, I added a L293D motor driver. I use the 3.3V to switch the 12 or 16V coming in. I then drop it through a 5V regulator to drive the motor pin. 

    I wanted to make this controller as compact as possible, both to make it easy to mount and to save the cost of making the pcb. I used the MH-ET ESP32 shown below. 

    On the top side  board I mounted the motor controllers, linear regulators and output pins. The ESP and the logic to drive the motors do not take much power so I did not attach the heat sinks to the back plane. 

    Full disclosure, this is a mechanical engineer making one of his first boards. It is functional but I can imagine I broke a hundred laws of elegant circuit design in making this happen. If anyone wants to school me in the comments, I am all ears. I probably would start with the power and ground inputs right next to the mounting holes in the bottom left corner above. I guess I am using nylon mounting screws!

    Here is the top of the board.  This is actually a big step for me. Being a MechE I generally do not believe in capacitors but I put to see if it helps out at all. On other projects with this motor I have had some intermittent operation where touching the circuit made it work. It could have been a bad solder joint but after hearing of the story from Jeri Ellsworth on how the China fab team removed the capacitors and made her C-One project not work. She put her hand on it, changed the capacitance and figured out that she did not make a dud of an ASIC. In the abundance of caution, I added capacitors to this board. Lots of them!

    Outside of this board, the robot will only need a terminal strip to attach the 12V-16V. I am leaning towards 4 x 18650s just because I do not have a battery holder for 3. I want to get the BMS going but the first round will charge outside of the robot.

    So from the top, the pinout is:

    5) CW/CCW  -- Pin 9 on the motor. This is boosted to 16V through the driver and then dropped to 5V.  Pin 34 for the left motor and Pin 32 for the right motor direction.

    4)  Speed -- Next pin down is pin 8 on the motor, and 35 for the left motor and 27 for the right motor. There is a high and a low speed and low will probably be good for most driving.

    3) Ground --  Pin 5 on the motor. Pin 4 will go to the ground on the power strip. 

    2) 5V -- This is Pin 2 on the motor. I believe this is what powers the electronics. My hope is that if this is off, the 24V wired directly from the batteries will not be drawing any current.

    1)  Start Stop -  This should work as an enable, disable.  It is pin 33 for the left motor and pin 25 for the right motor.  Pulsing it may provide some crude PWM and make it somewhat possible to run this robot indoors. 

    For completion here is the Kicad board 

    I am not sure if anyone can find similar motors but if they are available, here is the board. ...

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