DIY Linear Actuator design

oops

OK since english is not my native language it's sometimes difficult to understand the content... and humor is a lot harder to identify

Better late than Never @My.stAr and all information appreciated , ya gotta love this forum . someone will always step up to the plate as our American cousins would say, Thanks for that insight it helped to answer something about platform design, I decided to split the Plans into 2 section one for Linear Actuator and the other for my Take on the actual Platform build , will try to get these posted later when I'm home Cheers

i thought that you already finished building your platform
This forum is really great! Learned a lot already, and i'm sure that i will get more knowlegde during the next months

These projects are never finished more like a state of constant development LOL:- I have attached the last lot of update to my CAD drawings ( Use at leasuire but alter to suit your needs ) For any one the want to look them the Linear Actuator and the Platform I Built are now on 2 separate docs

OK guys another autodrive session really chucking the beast around setting cranked up Bid PID settings and the biggest problem at the moment seems to be the issue I have where the simulation drops out to hold ( park Position ) every now and then.

Trying to figure out if it Pcars Glitch ( but no one else seems to see it :-(
Is it AMC controller related ( tried various setting still here )

Is It BFF motion controller software (Ians helping out where he can but this seems new ) :-(

this is my in your face problem as the mechanics of the sim and speed seem fine ...
open to suggestions even thinking about redoing the controller layout as an option )

not all doom and gloom as i'm encouraged by the fact that the actuators and 2 X 32's sabertooths are all holding up well .. think i'll do another Current data log run with the new settings on the sabertooths to see what the system says .. had the amp meter indicate overload for blip on the 400 amp range so need to see if that's true

will get try this sorted and keep you guys in the loop , its gonna turn out to be something silly I just know it

Cheers Crew

I red the whole thread and found it quite interesting. Great job! It's... inspiring

It's a nice try but unless I missed something I disagree with your analysis.

To answer the original question... indeed, to increase the roll/pitch motions the upper platform has to be smaller than the base. Having the upper platform larger than the bottom one damp the roll and pitch motions.

To make it simple to understand, take the center of the platform as reference, expand one actuator at full stroke and you get a platform tilt. Reduce the lever arm (platform center/actuator fixing point) by attaching the actuator closer to the center and do the same, the tilt is bigger.

It works the same in all direction so ideally the upper triangle should be smaller. Difficult to achieve with the seat in the middle and due to the height of your actuators, but you can improve a bit if I'm right ☺

When I say "one actuator" it's to simplify, you have to imagine it on the X or Y axis (and vertical ideally). In your case it's a combination of actuators and you compare the effective stroke on X axis for example.

Actuator needs to be tilt toward the seat so you'll need shorter actuators (motor mounted on the side) or a larger base.

If your rig is homing, sounds like it may be a BFF configuration issue. Can you post your BFF settings? What is your 'Crash Gs' set to?

And still the answer is no.

The question was if it is different with the SAME values. Top 850 mm and bottom 700 mm. OR top 700 and bottom 850.
Why should it make a difference?

Just imagine you are sitting in the 700 mm top platform. The earth is under the 850mm bottom platform. You have the possibility to roll and pitch the upper platform with lets say 20°.
And now imagine that you, in the upper platform, are the center if the earth and due to your enormous weight your top is now not moving, instead you are moving the whole world with the bottom platform.
Would this change the possible angle of 20°?
Of course not!! everything is the same. The lengths of the actuators, the fixing points ... You meausure the angle between the top and the bottom platform. And it doesn't matter which one is on top and which one on the floor. Except the fact that the Motors will see a diffent load.

The other point is when you have one given value for the bottom platform and can change the upper one. But that is, what i said: you'll change the possible roll and pitch movement.

@wannabeaflyer2 thank you for the drawings
@Sleeperstyle
one more point: I think you agree, that it's no difference in the angle with a 850/700 mm or a 700/850 mm build, don't you?
And now it comes to your point: making the upper platform smaller. this increases the possible roll and pitch, but just to a certain point. Then it will reduce the possible tilt of the top. And when you found the best angle for the most roll/pitch you just turn around your whole rig. You still have the same possible tilt. But now you are able to make your new top platform smaller. this again will increase your possible pitch and roll.
You can do this, until all actuators are parallel and as near as possible to the center. So with the smallest platform radii possible. this would be the optimum for the maximum tilt. So, if you cannot make your top radius smaller, because there is an annoying seat in the middle, and you want to have more roll/pitch, you can also make your bottom platform smaller
But there are 4 more DoF to consider

@wannabeaflyer2 & SilentChill : where did you get your botom UV joint ?, I'm having a hard time finding something right :/

EDIT :

This for example ?, in dia = 8 (should be able to tap a M10 into it)
Out dia = 16mm should be enought ?

https://fr.aliexpress.com/item/5pcs..._6&btsid=067c0263-775b-4bc7-8ce0-31a0ef6062b0

Hi Seatime The Crash G's is set to default 5 at the moment and only really rtips when I actually crash ( That would eb with me driving LOL ) as I'm using the autopilot mode the car is on the track the whole time , and it just sometime see this dam Phantom hold signal ?????

;
; Configuration file for BFF Motion Driver v3 - 6 DOF, for visually enclosed hexapod type platforms only
;
; This parameter MUST be left at 000
VALim2=000
; Driver Revision = 3 for 6DOF driver
Drvr_Rev=3
; COM port and Baud rate for cue output
; Output is 8 bit, no parity, stop bits 1, flow control off
; Output Mode is either BIN, HEX2 or NONE for the 6 DOF driver
Port=COM3
Baud=250000
Mode=BIN2TH
; Number of data sets to run before sending motion data to output
Nsets=100
;Platform Type, =4 for Stewart hexapod platform
Rig_Type=4
;Hexapod nominal real dimensions (need be approximate only)
;
;Pitch circle radius of upper actuator end connections - mm
Rad_u=680.0
;Pitch circle radius of lower actuator end connections - mm
Rad_b=642.0
;Vertical height of upper connections above lower connections when actuators are at mid stroke position - mm
H_mid=1000.0
;Angle subtended by the lower end connections of an actuator pair - degrees
Ang_Sub=102.0
;Actuator working stroke - mm (actual stroke that matches the working electrical feedback range)
Act_Stroke=350
;Crank arm radius in mm, if there is no crank set =0 (ie for linear actuators). Must be greater than 0.5 x Act_Stroke
Crank_Radius=0
;Height of pitch and roll center above upper actuator pitch circle - mm
Rot_Height=60
; The actuator working stroke length in 0-255 position feedback scale
FALim1=200
; The midpositions of the actuators in 0-255 position feedback range
PitchStart=127
; The %tage of actuator stroke length of the start/hold position
VALim1=20

;The proportion of full movement to actually use for each DOF - in %tage of full range
; The %tage of range the Pitch cue can use
FALim2=45
; The %tage of range the Roll cue can use
LALim1=45
; The %tage of range the Heave cue can use
LALim2=25
; The %tage of range the Surge cue can use
SU_prop=30
; The %tage of range the Sway cue can use
SW_prop=20
; The %tage of range the Yaw cue can use
Yaw_prop=40

; Pitch Cue Calculation Settings
; Scaling factor to be applied to raw forward accelerations
; When aircraft is on ground
FaScaleg=1.00
;When aircraft is in air
FaScalea=1.00
; Time constant for low frequency isolation filter for forward acceleration tilt cue
; When aircraft is on ground - secs/rad
TCfg=1.38
; When in air
TCfa=1.38
; Cap level for acceleration magnitude that will be processed for cue in m/s^2
FaCap=2.42
; Time constant for low pass filter to washout pitch accel part of cue in sec/rad
TCpa=1.49
; Proportion of pitch angle to be added for pitch rate contribution.
RateP=0.05
; Time constant for high pass filter to washout pitch rate part of cue in sec/rad
TCpr=0.86
; +/- Pitch angle cue demand that will give full scale rotation of rig in radians
FAMax=0.250
;Reverse output sense, =0 No, =1 Yes
Pitch_Rev=1
; Roll Cue Calculation Settings
; Scaling factor to be applied to raw lateral accelerations
; When aircraft is on ground
LaScaleg=1.0
;When aircraft is in air
LaScalea=1.0
; Time constant for low frequency isolation filter for lateral acceleration tilt cue
; When aircraft is on ground - secs/rad
TCllg=1.72
; When in air
TClla=1.72
; Cap level for acceleration magnitude that will be processed for cue in m/s^2
LaCap=3.384
; Time constant for low pass filter to washout roll accel part of cue in sec/rad95
TCla=0.95
; Proportion of roll angle to be added for roll rate contribution.
RateF=0.24
; Time constant for high pass filter to washout roll rate part of cue in sec/rad
TCl=0.95
; +/- Roll angle demand that will give full scale rotation of rig in radians
LAMax=0.352
;Reverse output sense, =0 No, =1 Yes
Roll_Rev=1
; Heave Cue Calculation Settings
; Scaling factor to be applied to raw vertical accelerations before any calcs are done
; When aircraft is on ground
VaScaleg=1.0
;When aircraft is in air
VaScalea=1.0
; Time constant for initial low pass (smoothing) filter of vertical acceleration
; in sec/rad
TCva=0.22
; Exponential factor to be applied to accel values above 1.0m/s^2 to exaggerate response.
VaPw=1.0
; Cap level for acceleration magnitude that will be processed for cue in m/s^2
VaSat=3.865
; Time constant for high pass filter to washout heave cue in sec/rad
TCvp=0.00
; Scaling factor to be applied to recorded light-turbulence heave accel in air
Turb_Scalea=0.0
; Scaling factor to be applied to generated heave accel for runway rumble
Turb_Scaleg=0.0
; Time constant for final low pass (smoothing) filter of heave cue in sec/rad
TCvf=0.14
; +/- Heave demand that will give full scale heave of rig (in accel units - m/s^2)
; set this to the same value as VaSat
VAMax=3.865
;Reverse output sense, =0 No, =1 Yes
Heave_Rev=0

; Surge Cue Calculation Settings
; Time constant for high frequency isolation filter for forward accel for surge cue
; When aircraft is on ground - secs/rad
TCSUg=1.38
; When in air
TCSUa=1.38
; Cap level for acceleration magnitude that will be processed for cue in m/s^2
SUaCap=11.75
; Time constant for low pass filter to smooth surge cue in sec/rad
; In air ops...
TCSU1a=0.05
; On ground ops...
TCSU1g=0.05
; +/- Surge accel demand that will give full scale movement of rig in m/s^2
SUaMax=11.075
;Reverse output sense, =0 No, =1 Yes
Surge_Rev=1
; Sway Cue Calculation Settings
; Time constant for high frequency isolation filter for lateral accel for sway cue
; When aircraft is on ground - secs/rad
TCSWg=1.72
; When in air
TCSWa=1.72
; Cap level for acceleration magnitude that will be processed for cue in m/s^2
SWaCap=17.324
; Time constant for low pass filter to smooth sway cue in sec/rad
; In air ops...
TCSW1a=0.10
; On ground ops...
TCSW1g=0.10
; +/- Sway accel demand that will give full scale movement of rig in m/s^2
SWaMax=17.324
;Reverse output sense, =0 No, =1 Yes
Sway_Rev=1

; Yaw Cue Calculation Settings
; Scaling factor to be applied to raw yaw accelerations before any calcs are done
; When aircraft is on ground
YaScaleg=1.0
;When aircraft is in air
YaScalea=1.0
; Time constant for initial low pass (smoothing) filter of yaw acceleration
; in sec/rad
TCYa=0.1
; Exponential factor to be applied to accel values above 1.0rad/s^2 to exaggerate response.
YaPw=1.0
; Cap level for acceleration magnitude that will be processed for cue in rad/s^2
YaSat=5.0
; Time constant for high pass filter to washout yaw cue in sec/rad
TCyp=2.0
; Time constant for final low pass (smoothing) filter of yaw cue in sec/rad
TCyf=0.2
; +/- Yaw demand that will give full scale yaw of rig (in accel units - rad/s^2)
; set this to the same value as YaSat
YAMax=5.0
;Reverse output sense, =0 No, =1 Yes
Yaw_Rev=1
;Runway heave effects
;Slow acceleration sine wave amplitude at takeoff speed m/s^2
RW_Amp_3=0.0
;Slow sine wave frequency at takeoff speed - in cycles per second (Hz)
RW_CPS_3=0.75
;Fast acceleration sine wave max amplitude m/s^2, set a very small value to effectively disable if platform does not have good high freq response
RW_Amp_1=1.0
;Wheel Diameter for Fast Wave Frequency - m, set at unrealistically large dia to simulate centerline bumps
RW_Dia=0.5
;Reference take-off speed for calcs - knots
RW_Tos=100.0

;Trace Output, =0 no output, =1 raw accels & final cues, =2 heave cue calc outputs, =3 pitch cue calc outputs, =4 roll cue calc outputs
;Use for setup purposes only - do not leave on - the processing will eventually grind to a halt as it tries to store all the data.
itrace=0
;Flag to indicate whether Booleans are needed, =0 No, =1 Yes, setting to 0 will reduce the processing load slightly (non LAN operation only)
Use_Bool=0
;For Remote version, Receiving Port on this machine, defaults to 48001 (for MSFS or X-Plane LAN comms)
PortS=48001
;IP Address of this machine on the LAN
;IPAddress=192.168.1.68
IPAddress=127.0.0.1
;Use Joystick input? =0 No, =joystick number for Yes eg =1 =2 =3 etc
Use_Joy=0
;Motion Drive data loop sleep time in ms
MD_Delay=10
;Process priority
Priority=Normal
;Kill, Prefix, Drive and Hold hot keys
Key_Kill=Tab
Key_Prefix=\
Key_Drive=d
Key_Hold=h
; Joystick number for driver remote control buttons, =0 to disable, otherwise set to joystick number on system
Joy_But=2
; Kill, Drive and Hold joystick buttons, set any =0 to disable it (these are active only if Joy_But is non-zero)
But_Kill=2
But_Drive=8
But_Hold=7
;By actuator or by DOF scope output, =0 by dof, =1 by actuator
Scope_Mode=0
;Go to drive mode as soon as the motion driver initialises =1 yes, =0 no, setting =1 will also disable the checks made for X-Plane running on the
;motion driver PC (ie the driver will start and go straight to drive even if X-Plane is not running)
Drive_on_Start=0
;Trigger acceleration level in G's for crash detect (active in come racing card sim versions).
;If vehicle acceleration above this value is detected the motion software assumes a crash has
;occurred and will send the motion driver to Hold to protect the platform.
Crash_Gs=5.0

End of File

mate thanks for any assist on this its driving me barmy

This is the Uj joint I used in my project would have gone bigger But price got steeper

http://www.ebay.co.uk/itm/12mm-Dia-...691524?hash=item541b80fec4:g:WiYAAOSw65FXvaMa

ok thanks

I think I'm going to follow you on this one !

How did you fixed it to the actuator / floor ?

EDIT: I may be able to do a 12mm shaft from a M14 rod ! My father have a lathe

I agree with what you say, if you take exactly the same geometry upside down you have the same limitations. But if you move the actuators upper end toward Z axis the situation improves. Let's try to move forward

The question was: "Does a Smaller Top platform in relation to the Bottom mean the operating platform angles are greater or less ie. 700 circle Radius on top platform with say 850 on base give greater angles of operation than say 850 on top with 700 on bottom .."

IMHO it's not only a matter of radius, the actuators location/orientation matters as well. In the current geometry actuators are arranged more or less tangential to the circle meaning they are pushing outward Z axis whereas they should be more "radially arranged" and push inward to maximize the motions. By aligning the upper and lower platform (rotate 60° of one or the other) you would decrease the actuator upper connexion point/Z axis distance and improve the motions. But the seat will end up higher, or the base larger.

i see we agree
but for the pitch roll movement it would be even better to minimize also the bottom radius. If you have the minimum top platform radius and you cannot go smaller, you can still decrease the radius of the bottom platform to increas roll/ptich, but only until both radii are identical, else roll/pitch will go down again.

you cannot maximize all motion together. so you have to consider the other DoF too. If you align the actuators radial with a angle phi=0° you will maximize roll pitch, yes, but you'll lose the ability to rotate the platform, so won't have any yaw. The actuators are tangentialy, with the same radii on bottom and top platform, because you have all motion there.

I don't know if get this right^^


What about starting a seperate thread?
I'll add some pics to my description and will add the link here.

edit
here we go:
https://www.xsimulator.net/community/threads/basics-6-dof-stewart-platform.9396/#post-119948

Hi @SeatTime
did the test video of the amc during one of these hold signal glitches and did not see the lcd change state at all , by that I mean when the platform stopped I did not see the lcd flicker it stayed on the " Receiving data " Screen so I don think the issue is AMC related in that respect .
The AMC timeout was put back to 10ms motor speed around 85% PID (P) set at 115 and I =1 D=1 (will double check that )
youtu.be/23AWWWzarZ4

This video shows the problem occurring even with the platform disabled
Im Running P'Cars in Auto driver mode and have BFF visible on the Plasma screen , you see that both programs seem ok then for no reason ( I can see ) the BFF indicate Holding and BFF stops transmitting Data (Motion platform still disabled) I then Press the BFF Assigned Drive button on the steering wheel and then the Motion data is transmitted again so if the Platform was active it would have resumed motion ...you will notice thast several time at the end of the clip it start sending motion but then goes to hold ?????

when you get a chance have a look see for me to see if im missing something really obvious ...the G crash setting is set at the default value of 5 .. Not sure if this is ok for F1 car at Nurembergring Cheers

Not sure why this is Red text ??? Sorry guys

Hi @baykah mine is pinned and bolted to the sim base and Actuator, ideally they should be welded to plate at both ends and then bolted to the actuator and the base or at least secured in such a way that they cant rotate , this will reduce the actuators twisting when under torque load applied during direction changes ,

I will be remounting mine like this once I sort out my little glitch problem .. mine are ok for now but when the bolt slackens you can see the actuator trying to twist .. not a stopper but an improvement

Hi @wannabeaflyer2 - Try these changes in red.

Key_Prefix=\
Key_Drive=d
Key_Hold=h
; Joystick number for driver remote control buttons, =0 to disable, otherwise set to joystick number on system
Joy_But=0
; Kill, Drive and Hold joystick buttons, set any =0 to disable it (these are active only if Joy_But is non-zero)
But_Kill=2
But_Drive=8
But_Hold=7
;By actuator or by DOF scope output, =0 by dof, =1 by actuator
Scope_Mode=0
;Go to drive mode as soon as the motion driver initialises =1 yes, =0 no, setting =1 will also disable the checks made for X-Plane running on the
;motion driver PC (ie the driver will start and go straight to drive even if X-Plane is not running)
Drive_on_Start=1
;Trigger acceleration level in G's for crash detect (active in come racing card sim versions).
;If vehicle acceleration above this value is detected the motion software assumes a crash has
;occurred and will send the motion driver to Hold to protect the platform.
Crash_Gs=18.0

Hi @seatime Ian has sent me a datalogging version off his BFF software just in Case , so i'll try your tips 1st and see how it goes , really appreciate the input good buddy as I really want to move this project along ( meaning Play :-0 )

Will let you all know how it goes later , Cheers and thanks again