3dof Motion Simulator
James Talbot
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Founded in 2006, SimXperience (a Villers Enterprises Limited Company) is a premier full motion racing simulator and related peripheral manufacturer with expertise in electronics, engineering, manufacturing, software development, vehicle dynamics and vehicle simulation. Our products are utilized worldwide in driver training facilities, homes, simulation centers and race driver development programs.
I've already mentioned it in the "force feedback joystick" thread. Me and a friend are currently building a motion flight simulator.
It is equipped with 3 servo motors I have left over from building my CNC machine. They have 1hp to 1kW and each drive a ball spindle with 20mm diameter and 10mm pitch. So we have 3 degrees of freedom (roll, pitch and lift).
The motors are powered with 230VAC drivers controlled by a P1 each.
We are currently doing experiments with an ARM based motion controller. I don't doubt that it would be powerful enough to do all the calculations but the documentation is rather poor. So I fear it would be faster to develop a controller based on the P2 from scratch than it would be to find out how the ARM controller works and how it has to be configured. We were able to get one of the motors moving a bit up and down but we haven't managed to perform a proper homing procedure.
So plan B is to use my already existing CNC controller board and modify it a bit for the project. I'll eliminate the stepper motor driver daughter boards and simply output the step/dir signals directly to the servo drivers.
The plan is to use the ethernet jack to connect it to the PC running the simulator software and to communicate using UDP. There is already a motion cueing software available for the PC that calculates the movement of the servos from the simulated trajectory of the plane. So all I have to do is to limit the acceleration, velotity and position range of all axes to protect the rig (and the pilot) from damage.
You'll laugh to death but...it took me minutes of pondering on the fume extractor purpose in this project (why the hell one needs a fume extractor thing where there is no petrol powered engine nowhere to be seen) until I realised it is not a part of the project at all . My mind still surprises me after all these years we spent together.
VR googles generate motion sickness because the visual impression (horizon banking) is different from what your sense of balance tells you (standing straight on the floor). This is like watching a movie inside a car that is driving over a bumpy road but the other way around. If both senses match then you don't get sick. Well... of course only as long as you fly calm and respectful. If you overcontrol the plane or fly acrobatic patterns it's your fault.
BTW, we have installed pneumatic cylinders in the center to counterbalance the weight. Fully loaded with pilot and co-pilot the weight is above 300kg and so the static force of 1kN per motor would be near the continous current limit and probably overheat them quite soon.
It's the whole purpose of a simulator that the simulated motion doesn't fully equal the real motion. Otherwise it wouldn't work with limited space. Only the direction of the forces generated have to match. For example you can generate a feeling of acceleration by tilting the seat backwards. This causes the gravity force vector to not go straight down but instead it has a component going to the back of the seat. See explanation here. Moving with a constant velocity cannot be distinguished from not moving at all without a visual reference.
Err, no need to argue or "split hairs". But the limitation is the (main) purpose, in my point of view. It allows to practise flying with limited cost, space and risk while still being as realistic as possible. If you have the money, access to an airport and dare to risk your life you don't need a simulator.
Ok, back on topic. The software for the P2 board should be quite simple. As I said, the PC software does all the motion cueing calculations and sends UDP packets to the PC containing a position value for each servo axis. All the P2 has to do is to check the ranges of theese positions and their derivatives so the axes don't hit a mechanical stop and the velocity and acceleration don't exceed their limits. It then generates step and direction signals for the servos from the velocity (delta position) values. A state machine handles startup and shutdown or emergency stop conditions.
On startup all servos slowly move downward until a homing switch is triggered. After this they move to their neutral center position. When connecting to the PC the position is "blended" from the fixed center position to the current target position of the simulation software to avoid any sudden jumps or jolts. For shutdown the procedure is reversed. The position is blended to the neutral position, then the rig moves to the parking position all the way down.
I'm currently implementing the state machine. The step/dir signal generation is already working. Next thing is the UDP protocol implementation. This should be quite easy as UDP doesn't need any procedures for connection establishment or termination. There are no acknowledges so lost packets are not repeated. This makes everything extremely simple and is ideal for real time data transmitted in small units. Repeated packets would be outdated, anyway.
Yesterday we had the first successful flight with the real sim software (XPlane). This is with the ARM based motion controller. It works but I'm not really satisfied. (The main reason for most improvements...) Although the controller claims to have 2ms update rate for acceleration and velocity control and 550kHz max stepping frequency the motion is awfully jerky and noisy. I'm curious what my step/dir-diagnosis would show if I'd connect it but I'm not sure if it's worth the time. I think instead of analysing what's wrong it should be better to do it right, or in other words with a propeller.
Its 3-DOF motion simulator, with 737- replica throttle unit, replica 737 Yoke system along with combat pedals 4-5 larges LCD screens, powerful computers running everything, I have replaced the overhead panel with a large LCD touch screen.
Some of you may know me from the Canadian airports I released, but now I just want to share a motion simulator project I just completed. I recently became interested adding some motion to VR, but I quickly learned that commercially available rigs are very expensive, so entry cost is too high, and there is no motion compensation solution that works well with WMR OpenXR (Reverb G2), rendering some solutions unsuitable. So that was disappointing. Then I learned that people are building those rigs themselves. I read about that and I was hooked. Research followed, parts were ordered, and soon I started building.
When I finished the initial tuning and tried it in VR on my HP Reverb G2 for the first time, I was speechless. The result surpassed my expectation. Similar to switching to VR, this is another moment of
3DOF is more difficult and more expensive to build. Otherwise the more degrees of freedom - the better. 6DOF is best, but 6 powerful motors or actuators will cost thousands. I honestly feel there's more than enough motion to feel realistic. I was planning to add yaw motor, but I'm not sure I want to do that anymore, I think this is so great I'll leave it as is.
I wish there was a company that sells home-use 2/3DOF motion platform rigs like these that are super modular for incredible immersion and ease of use, at a low enough price point for it to gain popularity in the wider flight simming community. Until then, I believe going the DIY route is the best way.
Since this video I've replaced the old Saitek yoke with a DIY Boeing-style pendular yoke (a huge difference, feels amazing!) that also converts to a joystick, and a Boeing-style 3d-printed 8-axis throttle quadrant - now I got speed brake, 2 throttle levers with TO/GA and A/T disconnect buttons, and 2 full axes of reverser levers, prop and fuel levers (for GA aircraft) and a flap lever. Few switches too.
I'm now building a left-side HOTAS throttle that converts to heli collective control, and will build a switch/gear/button box to extend my VR control box. When all done, I will make a new post and video of the whole rig.
With four actuators, one in each corner of the rig, our 3-DOF motion system heaves, rolls, and pitches. The system is triggered by input from the simulator, tilting the rig in the corresponding direction. The system reacts to rumble-strips and curbs by moving up and down. It leans to the side in corners. Forwards when braking. The rig get lower in the rear and higher in the front to simulate acceleration.
Heave is motion up and down. With four actuators the SIMRIG motion system lifts your entire rig. Feel the curbs and the imperfections in the track. Notice carefully crafted details in the asphalt never before experienced.
Pitch is rotation forwards and backwards. The SIMRIG motion system tilts your rig backwards during acceleration and forwards while braking. Feel the braking force instead of relying solely on the position of your feet.
SIMRIG Control Center is included with all our motion system products. It is responsible for managing the motion system while extracting telemetry data from your favorite simulator and converting it into motion.
The SIMRIG motion systems mount to almost any aluminium extrusion rig. Off the shelf solutions are available for the common sizes 40x40, 80x40, 100x40, 120x40, and 160x40 mm. Others are available on request. See documentation for more details. Don't hesitate to contact us if you have questions regarding your rig.
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