New 6dof Stewart platform for a school project

Thanks, I PMed him.

Hi everyone, I'll still be working on the 6dof soft, answering question, sending source code, as long as I have an internet connection, don't worry! but I won't make new big developpement as fast as I did previously. I'm very enthousiast to see people using the 6dof software and I feel we are not too far from a full scale model!

Hi Robin,
Hi everyone,

Robin, you've done a great and very interesting project !!! Many thanks for sharing it with us.

Now that your 6dof master is practically ready to use, I wonder if someone is still interested in the calculations regarding the inverse kinematics of this type of moving platform....

By the way, I'm interested, so I tried to solve the equation from where you left a few posts ago and I would be glad if you could tell me if this is also your approach or if I'm partially or totally wrong.

Then

recapping, you wrote this:

given the points :

|PFTx|
|PFTy|=PFT
|PFTz|

(points of the moving platform translated and rotated)

and

|PLx|
|PLy|=PL
|PLz|

(point of the kneecaps wich contain the unkown servo)

where:

PLx=PBx + L1*cos(Servo)*cos(beta)
PLy=PBy + L1*cos(Servo)*sin(beta)
PLz=PBz + L1*sin(Servo)

The equation

||PFTPL|| = L2

says that: distance between the two points PFT[i] and PL[i] is equal to L2 (length of the rod):

So, I solved in this way:

(PLx[i] - PFTx[i])^2 + (PLy[i] - PFTy[i])^2 + (PLz[i] - PFTz[i])^2 = L2^2 ->

(PBx[i]+L1*cos(Servo[i])*cos(beta[i]) - PFTx[i])^2 + (PBy[i] + L1*cos(Servo[i])*sin(beta[i]) - PFTy[i])^2
+ (PBz[i] + L1*sin(Servo[i]) - PFTz[i]) = L2^2 ->
…..
…..
After some algebraic manipulations we may write the equation in this form:

A[cos(servo[i])]^2 + B[(cos(servo[i])] + C[sin(servo[i])] + D = 0

Where
A,B,C,D are real numbers coming from the manipulations,
servo[i] is the unknown,

Defining:

X=cos(servo[i])
Y=sin(servo[i])

We have a system of 2 equation :

/
| Y=-A/C*X^2 - B/C*X -D/C
<
| X^2 + Y^2 = 1
\

wich represents the intersection between a parabola and a circumference.

Solving the system by substitution

x^2+(-A/C*X^2-B/C*X-D/C)^2=1

Yields a 4th order polynomial :

a*X^4+b*x^3+c*x^2+d*x+e=0

a,b,c,d,e are numers coming from the calculations,
X1,X2,X3,X4 are the roots of the polynomial.

Finally we have 4 pairs as solutions for the system:

(Xi,Yi) for i=1,2,3,4

Now I presume that not all 4 pairs can be valid solutions, since X=cos(servo[i]) and Y=sin(servo[i])
we pick out values of Xi and Yi within the range [-1,1] and finally we extract the angular position servo[i].

Well, I stop here....

...comments, corrections are welcome , of course.

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Hi Dirk Dark, nice avatar pic!

The beginning is very correct but I think you missed one or two simplifications. When you develop the equation there are a lot of simplifications which happen.
If you think of the problem in geometrical terms you realise there are 2 solutions: the servo angle and its opposite.
So what I got after simplifying is something like this:

A*cos(Servo) + B*sin(Servo) = L2^2 - C ; a little simplier

then use cos(x)= (1-t^2)/(1+t^2) ;t = tan(x)
sin(x)= (2t)/(1+t^2)

and you'll get a second order polynome easy to solve. Then just choose the right solution between the two.

Remember for your simplifications: sin(x)^2 + cos(x)^2 = 1.

I can give you the solution if you want, but I think it's more valuable to find it yourself. Nevertheless if you ask I'll give you no pb.

Good luck with your work :hi:

Robin

Hi Robin,

Your 6DOF platform is quite amazing. I am impressed. I am currently testing a 2 DOF platform drive system based on Jim Cairns system. It works well with FSX. That said I am intrigued enough by your 6 DOF platform to want to look at the setup more closely by actually building it.

Although I have poured over your posting here, I do have a couple of questions that I hope that you can answer :-

Is the User interface and Motion control software written by yourselves available as source code for me to use as the basis for my own design?

If it is, could I have a copy please?

Also, do the servos have to be digital as the hitec HS-6965 is, or can they be ordinary servos?

My intention is to build a 6 DOF platform using a mixture of analogie components as well as servo motors. The main issue is that servo motors that are big enough to power the motion dierctly are horrendously expensive. So the idea I have is to use a smaller servo motor that can turn a power steering box input shaft. I have tested this setup using a rangerover powered steering box, which has a lever rather than a rack. a simple wiper motor can turn the input shaft, and a 1/2 HP electric motor can turn the powered steering pump which in turn drives the steering box. The lifting force is quite something, 6 of these should lift more than enough weight to allow a cockpit and two people.

To drive 6 of these steering boxes, I will need a hydraulic accumulator, and a larger pump and electrtic motor (all relatively cheap commercial vehicle type stuff)

I will be opening a new thread shortly covering all of this.

Many thanks for your replies in advance. Keep up the good work.

Is it just me or is the file damaged. When I d/l it, it comes up as a .pdf and when I try to open it, it just says that the file has been damaged? It clearly states that its a .zip file in the preview though not sure why my computer is recognising it as a .pdf.

The zip works for me.

However, try this repacked archive in 7z format:
6DOF.7z

regards

Thanks, got it.

Hi Robin,

Not sure if you still check this thread, but I just want to say thanks so much for writing that great 6DoF program!
I've been tasked with creating a 6DoF motion platform for my summer job to simulate a range of different motions (ocean waves, a person walking etc) to test energy harvesting devices- possibly these will be used in mobile phones or other devices in the coming years.
I have barely any experience programming, and finding that great software you wrote freely available is a massive help to me!

I'll be actuating the platform with 6 HS-7950th digital servos- i need really high torque since the platform has to move through +/-50mm at 5-10Hz with a 10kg load. This takes a lot of force and very fast servos. The servos will be driven by PC via a pololu micro maestro controller.

A question for you or anyone else here- is there a way to interface your program with the pololu controller to control the movement of the servos? And does the program only work for input from a game via xSim, or is there some way of inputting some basic motions for it to follow (like a vertical sine wave, horizontal sine wave, etc) because all it will need to do is go through a series of motions to test energy harvesting devices efficiency to several different motions in all 6 DoF.

Hi guys
Where find I some formula or how to calculate force power of complete 6 dof system?
For exaple: What can be load capacity of one actuator, for 100kg weight on upper place?
Direction of actuators is +- 30 degrees.

Been a while since i built my 6dof servo model using Robins excellent sofware, as i recal there was a manual test screen that allowed you to move any servo and so tst the software without x-sim ( but dont quote me on that )

Hi wannabeaflyer, you're exactly right, I've already been playing around with Robin's software and it is most excellent! To say it saved my a$$ in this project would be an understatement, considering my non-programming background :thbup:, especially in working out the dimensions of the platform i need to get the specified range of motion.

What I'm after is a way to input some simple motion sequences into the program rather than an x-sim input from a game... This shouldn't be too difficult and it could be done roughly manually with Robin's software anyway... I guess I'll just have to play around with the code and look at how it receives it's inputs from x-sim.

I'm guessing that it'd just be a matter of finding which variable controls the height of the platform, and changing it to a sine wave with the appropriate frequency and amplitude, and doing the same for heave etc.

Hello, i was impressed when i see this mini motion 6dof, i studie on a fakulty of computer ingeniring in Slovenija, 5 semester.
I muss alsow make some project by robotics, and i decided to build the same 6dof console, i will please you if you have some plane for mini console, and source code for pololu servo controler, this where a big big help to me, i will use this components:

i will simulate motions trought x-sim2

http://www.robotshop.ca/lynxmotion-ball-link-set-4-40.html
http://www.robotshop.ca/Hot/lynxmotion-threaded-rod-4-40.html
http://www.robotshop.ca/Hot/pololu-micro-serial-servo-controller.html
http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=270662265235&ssPageName=STRK:MEWAX:IT

Many many thantks to all

Hello,
Happy new year...
I managed to link x-sim and the 6dof software..
The 3d simulation move perfectly...
My problem is how to move the servo...
i'm using the sd84 board..but i don't know which channel i need to connect the servo...
please guide me on this...
thank you...

Thanks for nice share, BTW where can i down the Robin's 6DOF sample ?

Hello everyone,

I am a student of Information Technology in a University of Brazil and escvolhi as a project of completing the course, build a prototype of a 6 DOF Stewart platform for use with flight simulators and can represent the movements made by the plane on the screen physically.

However, I do not know where to start and would help to persons who already have expertise.

Researched many sites and forums but got no success.
Could anyone tell me what are the first steps and where should I start?

What parts should I get? What do I need?
What language should I use (C + +, C #, C, etc.)
What steps to build a physical prototype of the platform?
Among other questions ...

Please can contact me through my email (lucianolsc@gmail.com)

Now, thank you attention.

Sincerely,

Luciano Cavalcante

I really need your help!!!

hi, My name is jonny from the UK. this is my first post here.

i have been working on a Steward platform project and i have been forwarded to this site for extra help.
i have been looking at some of the work here that you guys have done. very cool.

My question is can the 6DOF.7z downloadable file be used with the SSC-32 serial servo controller?
With Atmel ATMEGA168-20PU
http://www.lynxmotion.com/p-395-ssc-32- ... oller.aspx

Hi all, take a look at my big 6dof platform and help me with the program for her!!!
my platform we-need-some-programmer-for-6dof-platform-t3465.html