737-800 6dof Stewart Motion Platform Project...

[sagrada737]

Hello Folks,

As I mentioned in a previous post, I am in the process of "considering" building up a Motion Platform for my full-scale 737-800 Sim.  I have been in a prelinminary testing phase working with the motion software and motion hardware to better understand the viability of this kind of complex project as it might apply to my 737 Sim.

I am now in the testing phase of interfacing and controlling a 1/8th scale model of the motion platform using mini-servos to actuate the linkage 6 degrees of freedom (6dof) as output by FSX via the motion software/controller systems.  Thus far, it seems to function well and has demonstrated to be quite stable and reliable.  Stability and reliability are criteria of significance for a full scale motion platform moving a 2,000 lb mass back and forth for 6dof.

Another purpose for building up the 1/8th scale model of the motion platform is to gauge how a full-scale platform with Sim on top will function within the confines of my Sim Room - keeping mind that the display needs to actively ride along with the Sim.  Based on initial testing with the model, it looks like my Sim Room will allow for a full-scale version of this kind of motion platform.  I still need to confirm this by building a simple 1/8th scale model of my Sim and place it on top of the platform model to see it move about within the confines of my Sim Room.  Having adequate safety clearance is important.  Drawing calculations are one thing, but I have found it valuable to work with active models in the initial concept/design phases for projects like this.  A big project indeed 

One of the most interesting considerations has to do with calculating the required torque for each of the six segments on the Stewart Platform.  This is quite a complex consideration that involves specs for movement and acceleration for each of the Cues on the 6dof platform, which are pitch, roll, yaw, sway, surge, and heave.  All this makes for a lot going on to accomplish this movement, and a big factor for controller/motor/gearbox requirements.  There are also issues of CG tolerance and moment of inertia issues relating to dynamically moving a heavy mass at relatively high frequencies one direction to another.  Anyway, such considerations are not new, and can be resolved for a specific requirements.  In my case, I have decided to use a Variable Frequency Drive (VFD) to control a 220VAC 3-Phase motor through a high-reduction Gearbox that will yield 8600 in.lbs of torque at the Output Shaft at 11 RPM.  This combination of control electronics and motor/gearbox will serve to actuate a 4" Lever that in turn will move a Push Rod connected to the Upper Platform in the classical Stewart Platform configuration.

Another very important consideration has to do with the amount of movement/acceleration needed for creating a "motion effect" (Vestibular Sensitivity) as seated within my 737 Sim flying under FSX.  Fortunately, I have concluded thus far that movement/acceleration provided by the VFD/motor/gearbox will allow for the "sense of movement" I am looking for in such a motion platform for my Sim.  Another positive conclusion has to do with the ability through the 6dof motion software to "tweak" the motion Cue parameters to accomplish a "custom" motion result.  This is extremely important as resultant movement in all these 6dof cues can produce some extreme motion if not setup correctly for the desire flight model - 737 in my case.  For example, I can reduce ground/taxi movements so these cues do not vibrate the Sim to death - a serious consideration with our level of Sim hobby gear.

A concept I am working on is to compensate for the reduced Sim motion platform movements for all ground operations.   I plan to off-load these vibration inducements to a sub-platform that is part of, but isolated from the main motion platform, which uses a transducer to induce proper vibrations to give the "sense" of ground activity, eg taxi bumps, touch-down, etc.  This should help preserve the Sim hardware from most of the damaging vibrations that the motion platform is capable of inducing into all hardware attached to the upper motion platform.

The most serious consideration is one of safety for using and operating such a full-scale motion platform.  Sam knows full well how careful one needs to be working on and operating such hardware under computer control.  Hence, in all this testing, safety is constantly on my mind, with careful attention to "crush zones" and stability that is reliable in all areas of motion platform systems.

Anyway, I continue to move forward with the idea of having a full motion platform for my 737-800 Sim.  But before I start building the proverbial "boat in the basement", I will need to build up and test a full-scale segment of the Motion Platform under load to confirm torque/acceleration/response capability as interfaced real-time to FSX.  At some point, I will decide to either shelve the project, or make a major investment and build up the real deal. 

The video link below shows some preliminary testing of the 6dof possibilities with the servo model.  Perhaps you will find this initial test interesting, and can visualize what it might be like sitting in a full-scale 737 Sim on top of such a platform.  My wife says I should invest in "barf bags" 

Mike

The video shows active testing under FSX, with Sim-Avionics using BFF 6dof motion software, AMC1280USB motion controller acting on the mini-servo scale model flying in a Holding Pattern, and an Approach into KSFO.

https://www.youtube.com/watch?v=mIfY82Dcyf0&feature=youtu.be

[Sam Llorca]

Very impressive Mike, can't wait to see the final result, just be careful with it I had my share of scare with motion platforms, after my final tweaks on finding the correct CG it perform much better now. Cheers.

[sagrada737]

Thanks for the comments Sam.  I have to admit, that upon seeing your beautiful full-motion Sim, I was inspired to try and explore some possibilities for my own 737 Sim. 

You are quite right about safety issues with this kind of full-scale motion platform.  Minimizing "crush zones" is paramount and safety procedures are critical to ensure that no one gets hurt.  Also, as you pointed out before, having a "Master Kill Switch" in the cockpit is important, along with the ability to egress the cockpit if something goes wrong with the computer control.

As you mentioned, CG considerations are very important, and understanding the "CG Limits" of the motion platform is key to smooth operation and keeping the high power controls from exceeding temperature limits.

Take care,
Mike