karu
Posts: 1
Joined: Fri Dec 07, 2018 10:42 pm

HELP - Stewart Platform

Fri Dec 07, 2018 10:52 pm

I am building a Stewart platform for a school project and I need some help choosing the battery and the motor controller appropriate for my actuators. The speed that the platform will run does not matter to me, and the load that each actuator will drive is 50 lb.

I am using the following linear actuators:
https://www.servocity.com/hda8-2

Please let me know your thoughts. Although I am fairly comfortable with Python, I am a complete beginner in raspberry pi and circuits. :D

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Joel_Mckay
Posts: 227
Joined: Mon Nov 12, 2012 10:22 pm
Contact: Website

Re: HELP - Stewart Platform

Sat Dec 08, 2018 11:34 am

a linuxCNC Hexapod uses 6-axis odd kinematics models, and the pi3B+ can barely handle our Cartesian setup.
The RT kernel we use is here:
https://sourceforge.net/projects/microm ... spberry-pi

However, I suspect you may find a Pi's limited resources difficult to use for this type of robotics problem.

Languages like Python/Matlab/Java/NET are not appropriate around low latency scheduling systems.
These platforms usually use Assembly/C/C++, RT kernels, and or special motion controllers ( Verilog ).

A platform moving around a 50lb end effector could seriously injure someone.
Maybe start with a miniature version people physically could overpower, as you are guaranteed to make mistakes learning how these complex platforms work.

Take care,
J

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OutoftheBOTS
Posts: 702
Joined: Tue Aug 01, 2017 10:06 am

Re: HELP - Stewart Platform

Sat Dec 08, 2018 12:03 pm

Here is a great video made by servo city the seller you listed and it explains all the different options https://www.youtube.com/watch?v=L5tx64G1ilQ

U have linked the middle type of actuator where it has feed back wires but not the circuits that create the control loop based upon the feed back. It you buy the last option where the circuits to create a servo actuator (feed back control loop) r already built in will make your project much easier see https://www.servocity.com/servos/linear-servos

Then basically then you can control it with any servo board and a power supply. I usually use something like this https://www.aliexpress.com/item/16-Chan ... ee1b91386b that can control 16 servos and use jumper wires to connect the I2C communication between the board and the RPi but if you like to be flash and neat you can use something like this https://www.adafruit.com/product/2327 that uses the same chip to create the signals to control the servos.

You will need a power supply that can supply enough amps to power all the servo actuators. I would suggest a very small car battery will do the job fine.

Idahowalker
Posts: 433
Joined: Wed Jan 03, 2018 5:43 pm

Re: HELP - Stewart Platform

Sat Dec 08, 2018 7:29 pm

I have made a XY stabilized platform with a LIDAR scanner sitting on top of the platform.

I found the RPi is great at processing data but trying to get the RPi to process data and maintain a level platform plus other stuff... Eh, better to let something like an Arduino MEGA or DUE do the heavy lifting. If the DUE (32 bit, 80Mhz, preferred) or MEGA(16Mhz) are physically, too big look into an ESP32 (32 bit, 2.4Ghz) or a STM32 bluepill( 32 bit, 72Mhz)

I run a MPU6050 connected to the RPi on a separate core, multiprocessing. The collected MPU data is turned into Arduino servo writeMicroseconds data to keep the XY platform level. A LIDAR sits atop the platform, gets triggered, by the RPi, to fire, sends the info back to the RPi which turns the data into an 'image.'

The RPi is good for some things.
Without knowing why you are deleting my postings, I will not know how...

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