Postby tlfong01 » 2019-Mar-14 Thu 8:40 pm

jamesh wrote: 

2019-Mar-14 Thu 5:37 pm
tlfong01 wrote: 

2019-Mar-14 Thu 1:31 pm
tlfong01 wrote: 

2019-Mar-14 Thu 12:30 pm

4tronix Robots References

Amazon 4tronix Picon Zero v1.3 Intelligent Robotics Controller Board for Raspberry Pi
https://www.amazon.co.uk/4tronix-Intell … B01E8MXQWY

robotics controller board for Raspberry Pi
Fully supported with extensive Python library
drive Servos, NeoPixels, LEDs, Motors and many other output devices
use Analog or Digital inputs, or even directly access temperatures with a DS18B20
Multiple power options for the output devices and motors

4tronix Robots summary notes

TT130 plastic geared DC3~6V motor
N20 metal geared motor
28BYJ-48 stepping motor ULN2003 boards

Motor/Servo Driver
L293DD H-Bridge motor driver
DRV8833 DC/stepping motor driver
ULN2003 stepping motor driver
PCA9685 16-channel PWM servo driver


WS2812 Neopixel LED

Raspberry Robotics Robotics for beginners with the Raspberry Pi – Richard Keenes 2019mar10

Can you please avoid spamming the forums with loads of links, and also reduce the amount of colour in your posts, its disconcerting and makes your posts difficult to read. Must also take ages to write for no benefit.

Thank you for you advice.

So I will avoid spamming links and colouring posts. My apologies for any disconcerting caused.
I am an electronics and smart home hobbyist.


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Postby jackbarks234 » 2019-Jun-19 Wed 4:48 pm

Gavinmc42 wrote: 

2019-Feb-25 Mon 10:59 am

I get magnets from here, trying to figure out if a high ratio magnetic worm drive gear box could be made

Those TT motors are the best value for hobby bots, good to learn on.
And once those cheap motors wear out you can replace them with lower current, higher voltage 12V ones.
Because they are cheap speed can be dependent on brush wear.
Try driving in a straight line.

Replacement RS-130 size motors are low cost, even here only $1.

Is it important where you buy the magnet? Supermagnetman doesnt ship to my country, but https://magnetpartner.com/ does. I guess its pretty much the same thing? Or?

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Postby Gavinmc42 » 2019-Jun-20 Thu 9:09 am

Is it important where you buy the magnet?

Not really important, I think most are made in China anyway.
I get from Supermagnetman because he has a very wide range and I get 100’s at a time.
There are wholesalers that might restock his stuff, industrial suppliers not online retailers.

Those 5mm coloured spheres look interesting, I don’t have any of those ;)

I’m dancing on Rainbows.
Raspberries are not Apples or Oranges
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Postby OutoftheBOTS » 2019-Jun-20 Thu 1:44 pm

I seem to be coming to this discussion very late.

How to answer the age old question that has dogged robot builders since the beginning of time “How to make my robot drive straight“. I have lost count at how many hours I have spend chasing this unicorn :)

There is a few options.

Stepper motors as they turn very very precise and is why they are used in CNC machines.

Servo type motors that have a feed back loop on the position of the motor (usually a quadrature encoder). Basically it is a fast loop that reads the position of the encoders then if they are incorrect for what you want then it adjust the PWM power to the motor then repeats. This is not easy to do on a RPi because RPi isn’t real time. It is much easier to use a MCU that has a hardware encoder counter like the STM32 MCU family.

Using a feed back loop for another sensor for positioning like the MPU family of IMUs but this requires some pretty fancy coding to do sensor fusion to remain accurate

The stepper motor option will be the simplest one to implement. Just buy a stepper motor with enough torque and a Driver that can handle the need current. I suggest using micro stepping not for accuracy but rather for smoothness of motor rotation. You can see an example of both servo motors and stepper motor in action on the 5x5x5 rubik’s cube solving robot I build. Servo motors open and close the grippers but all the rotation is done by steppers https://www.youtube.com/watch?v=sD4bG8hPYLQ

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Postby Gavinmc42 » 2019-Jun-21 Fri 9:49 am

I once had to drive two electric linear rams at the same speed for a solar panel tilt mechanism.
I used one of those small DSP micros from Microchip which had two encoder inputs.
All I did was keep the counts within +/-5 or 10 of each other, slow one down when it gets ahead etc.
Probably the simplest DSP coding I have ever done and it still works fine 10 years later.

Steppers are ok but can loose sync that’s why most CNC machines have Zero position detectors.
DC motors with encoders are also ok.

3Phase Brushless outrunner motors with gyro/accel feedback are the newest solution.
How good these are is shown in all those camera gimbals on drones.

Could you use gyro/accel/compass with DC motors?

Well Drones are now using Arm Cortex M3/4s for stability controls, Pi’s will need this too.
Could a Pi Zero be used instead of M3/4?
Probably, with latency issues?
Could the QPUs be used for the Quaterion coding?

One guy has done a drone with a Pi, so a two motor ground bot should be much easier.

I’m dancing on Rainbows.
Raspberries are not Apples or Oranges

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