cessna platform

[Roland]

Hi Henk,

3-point travel.JPG

Above drawing shows my setup. Each actuator can do 45cm of travel, so the spline on the stabilizing rod should also me able to follow this travel, and accomodate for the +/- 14 degrees pitch and roll angles.

Note that I needed the stabilizing rod as my platform is hanging in the V-belts. If you use more ridgid actuator construction, you may not need it.
Ian's plunger system actually combines the stabilizing feature with weight balance.

Curious what kind of weight balance you are going to use?

[kermit]

Hi Roland,
I will use a springloaded crosscoupling with spline, also the motors and gear unit will use guidence of the potmeters.
According to our electricians the motors will spike/lower the Amps but will be dampend/compesated by some device( don`t know how its called).
The torquearm from the gearbox itself will be fitted with a so called softstart coupling with a special shock absorption system(some type of rubber) .
Also the driveunits itself will have enough torque to overcome the weight difference,and because I will using the potmeters , the programme will know its position.
Further the weight difference will be overcome by the motors just asking more or less amp up to a certain parameter,
after wich the device will step in resulting in a flaw during flight.
Again thats my understanding on what our electricians told me.
greetz

[Roland]

Henk,

Just a note on the importance of weight balance:
A small weight unbalance in my platform already results in big deviations in drive power.

Below video shows some heave tests I did: the scope shows current consumption (top wave) and platform position (bottom wave)
first 3 tests show correctly weight balanced drive: 0.5Hz, 1Hz, 1.3Hz. As speed increases, the required current also increases, but going up and going down requires the same amount of current (1.3Hz results in 30A current peaks = 1kW peak power)
The last test shows what happens when I added 10kg extra weight (by putting a sandbag on my lap) The current unbalance going up / down is nearly 50%. If you have a current limit in your drive, it means that the upward acceleration will be much more limited than the downward acceleration.

http://www.simprojects.nl/images/Platform_power.wmv

Edit: for some reason the movie will not playback on my system after several downloads. If you have the same problem, pls let me know, I'll make it into a you-tube video

[wannabeaflyer]

Excellent Info as always Roland Just to say thanks on behalf of all of us that follow your work...Cheers

[kermit]

Hi Roland,
There is certainly food for thought.
Although there is a difference in the drive approach
Yours is driven by eleasticbands and therefore there is the need of gradual build of force to overcome the enertia
and stretch of the elasticbands, the forces then will collaps as the weight is catapulted in the other direction .
As for mine it will be a so called coldsteel drive were ,
there is nearly no stretch it the drive therefore will be a more constant force/wave in the drive systeem.
Therefore the electric consumption will be more constant factor but thats theoretical physics I think.
Your comments made me think about frequency inverters again.
greetz

[Roland]

Hi Roland,
Yours is driven by eleasticbands and therefore there is the need of gradual build of force to overcome the enertia
and stretch of the elasticbands, the forces then will collaps as the weight is catapulted in the other direction .

Well, not exactly: The coupling from motor to platform is done via V-belts. As far as I know, these have hardly any elasticity. So my drive coupling is actually quite rigid.
The bungee cords are used to create a fixed opposing force for weight-balancing. They are not part of the drive.

[kermit]

Hi,
Maybe I have to watch closer then,
I thought the elasticbands were a part of the drive unit, because they stretch with the movement.
Did you attach them on the platform itself ?
In that case it will only put pullingforce on the platform, or do you have to ajust the pulling force on each side according to the weightbalance ratio.
How do you calculate that force, as you can see this is a learning curve for me
greetz

[Roland]

Henk,

Have a look at the followowing pages:

http://www.simprojects.nl/diy_motion_platform_iii.htm
http://www.simprojects.nl/platform_d...ations_iii.htm

and the other pages on the #III platform, which include some video's.

For the actuator forces, Ian's V2.0 driver has a utility that graphically shows you the velocities, acceleration and required (mechanical) power based on platform weight and (un) balance. You can enter your platform weight distribution and let you play with various parameters. Note that this utility assumes a center post for weight balance, different from mine in which each actuator has a weight balance system.

(The utility can run in demo mode)

[kermit]

Hi Roland,
Please can you tell me if Ian board can drive motors with the following
frequentie-inverter specs 0-10 volt or 4-20 mA or 0-20 mA.
greetz

[Roland]

Henk,

As far as I know, Ian's driver board typically uses I2C to control the MD03 motor controllers. He has also build versions that work via RS232 for driving Sabertooth controllers and RS485 for direct driving a SCN5 actuator. So he does not output DC voltage or current signals. But please double check with Ian.