The block diagram above outline the control system for the Spider Robot. The prototype was a mock up to test the basics of the concept and to proceed I want to make some changes:
- We need a proper CPU and I see no reason not to add in a Raspberry PI to execute AI logic. The servos and sensors are easily controlled by one of our BasicPI Hat’s, which leave us to design a PSU. I like the current 11.1V LIPO at 1.5AH. It should give several hours of operation.
- We need to add sensors. A few ultrasonic transceivers will enable us to check distance to surrounding objects, a MPU9255 adds Magnetometer, Accelerometer and Gyroscope, a couple of microphones adds hearing etc. Raspberry PI have digital camera option with possibilities for optical detection options. The rest is easily added to the IO processor.
- We need to work on the mechanics around the legs. I need a stronger servo on the inner arm and a better wiring solution to the legs. The problems detected was partly the servo breaking after continuous usage, plastic parts not taking the beating and wires worn out.
My first plan was to use a Raspberry PI Zero, but using a Raspberry PI 3 makes a lot more sense in this case. This adds the Wifi option directly.
This robot prototype uses a simple wooden box as body and 6 pan&tilt camera holders with a total of 12 servos to move around. The picture is a prototype to test the concept. I initially used a 5.2Ah LIPO but the total weight on the servos was getting a bit much, so I dropped down to a 1,2Ah LIPO.
The second issue was that I needed a 5V PSU for the Servos and testing with a 5A PSU I realized that peak load was above 10A. I used 4 x 50 cent DC-DC adaptors in parallel to get sufficient juice. This makes the PSU part quite big. I have been considering something smarter for PSU, but the 50 cent breakout boards are hard to compete with in cost (and weight).
The control system on this prototype is an Arduino Uno with a Servo Shield. It works ok for testing, but it add up to some size (and weight).
My main concern is however the mechanics around the Servo’s. These small 9g/12g Servos are not made for continuous usage and they tend to break down during testing.
Looking at my Rx breakout board I realize I need to add a LED for status. I don’t like wasting pins, but not having a Status led will be a pain.
This is the current revision 1.0 of the Rx breakout board. I am trying to find a decent way to display schematics, but the EDA I use is a bit limited in that respect. I am not going to mention what I use because I intend to change that to an open source EDA soon.
This SWD Adapter was created to avoid the need for 2.54 pitch connectors on the boards and to have a standard way of supporting a debug environment with the mini version of ST-Link v2.
The form factor above is made narrow to allow it to be connected to a Hat that is in the middle of a mounted stack. The square version below is the same with a different form factor. These are PCB’s with two connectors that can be soldiered for hand, so they are designed to be dead cheap in volume and will be adapted to various boards.
I have used this for a while myself and it makes development on these boards a lot easier. The standard uses 10 pins, but keep in mind that only 4 of those (SWCLK, GND,SWDIO and RESET) are required. 5V/3.3V is just added for convenience. The serial port is nice, but might need to be dropped on some boards.
This is mostly for my own usage. I have a strong preference for wiring and testing on bread boards before I order PCB’s. Sometimes it saves you 2-3 extra rounds to be able to do simple concept testing. I have plenty of breakout boards with STM32, but I fancied my own with my own SWD connector etc. For now I am using the first GPIO Hat’s for Zero more on breadboards they are not designed for than on the Zero. It only have components on one side using a two layer PCB, so this is designed to be cheap.
This breakout will work for STM32F103Rx, STM32F105Rx, STM32F107Rx and STM32F405Rx. It might work for others as well, but I have not checked yet.
It’s only 20 by 50 mm and my most painful PCB so far. It will run a BLDC motor with up to 2-3A in peaks, 1,5A in average. As mentioned before this was a draft. I am letting this rest a bit because I was not fully satisfied with the outcome.
What is special with this one is that it supports 3 current sensors, 3 Back EMF sensors, 3 Hall sensors etc. What I am not happy with is the 1,5A limit on the DRV8313. As I routed this I felt more and more that DRV8313 ended up as a bottleneck in the middle of the PCB and was not helping on the size either because my design add so much ouside the driver chip itself.
I am considering several options – one is to use SO8 size gate drivers and FET’s. This will require 6 SO8 chips, but I believe they will improve routing and the current I can get out of this solution. The small motor above will only require 0,5A, but it would be nice to have a CAN-X controlled ESC capable for larger motors. I believe we should be able to get 5-10A out.
A second option is to use DRV8301. This has the advantage that DRV8301 contain a separate Buck converter for the MCU with 1,5A available. I do however fear that this will be difficult without increasing the size of the controller.
Again – work in progress. I will be back on this and other motor controllers later.
I have drafted a few Hat’s so I am adding an overview just to move content into the new blog.
Zero GPIO was my first Hat. This is the new, revised version that I have not ordered yet. I am waiting to verify SPI interface before I order new Hat’s. For the Zero I actually also need to get a Zero as I don’t have one yet. Out of Stock they still are after 6 months.
I also added a full size version of the GPIO Hat with a proto-typing area.
Another Hat in both Zero and full size version is the Servo Hat’s with 16 and 32 servo connectors. The Zero version uses the STM32F103CB which is 48 pins. The 16 x version will soon be used in a Robot project with 12 servo’s.
The Hat I am doing software on is the 5 port communication Hat. I need to verify SPI interface with RPI on this. I am using a Raspberry PI 2 for now. Progress on this work can be read through other posts.
The Zero Com Hat (above) has not been mentioned before. This 3D model is illustrative, but it show a Zero Hat with a RS485, a CAN and a 2.4Ghz NRF24L01+ port. One version of this also uses normal Wifi. The drawback with this hat is the mounting of the NRF24L01+ breakout board. I need to find a way to mount it properly as it will not handle vibration well if mounted as illustrated on this model. This model also still uses the 2.0 pitch connectors that I decided to remove so it is “work in progress”.
I am changing to WorldPress as basis for the blog system since it offers far more options than the old system. The old blog will still be available until content is replaced. This will also allow us to add more content than just the blog as we move forward.