What are Degrees of Freedom DOF in Sim Racing Motion Platforms?
2 DOF. 3 DOF. 6 DOF. What does it mean for Motion Platforms in Sim Racing, Flight Sims and other Simulation Games? Let's find out!
DOF stands for Degrees of Freedom, which is physics lingo for defining how something moves in relation to a fixed set of parameters (consider x and y-axis on a graph, except in 3-dimensions). In other words, it classifies how something moves.
But we're not physics graduates, we just want to how it is used with Motion Platforms in Sim Racing and other simulation games!
In total, there are 6 degrees of freedom, and as we said above, each of these essentially represents a different type of movement:
...we could try and explain each of these with words and diagrams, but we think it's probably easier to get some videos that show each of these in action in motorsport, so we can all understand what they mean. Let's go!
1) Elevation/Heave (moving vertically up or down)
Whenever you drive along an uneven surface, your tyres will will move up and down as they move over the undulating surface. This vertical displacement is the elevation/heave. Applied to sim racing, whenever you hit a compression or peak/jump a crest, or drive over bumps/undulations in the road, your motion platform will rapidly rise/drop to simulate this behaviour - same as when you drive along a bumpy road in a sport cars, you are bounced all over the place. Having Elevation/Heave in your setup ultimately makes the experience much more realistic; you feel like you are actually driving over a realistic, uneven surface, like you do in a car.
2) Strafing (moving horizontally left or right)
Strafing is movement on the horizontal axis (left or right, or 'laterally'). Whenever you turn a corner, inertia means you are pushed into the side of your seat, and in the context of a motion platform, you'll get strafing to replicate this inertia when you turn a corner. Expect to experience strafing in conjunction with Surging (our next DOF), because strafing on its own isn't common in sim racing (that is, you normally move forward/backward AND left/right, not purely just left/right). We've all seen (and perhaps given) passenger rides where the passenger is thrown from side-to-side in the corners - this is akin to what you will get from strafing.
A scenario where you could get pure strafing is if you were stationary (in pit lane for example) and you got T-boned (someone crashes directly into your side) - or, something like this:
3) Surging (moving forwards or backwards)
It doesn't get much easier than surging: forwards and backwards movement. Acceleration pushes you back into your seat, and braking/deceleration has the effect of 'pushing you' out of your seat, hence seatbelts and harnesses are required to rein you in!
In the below video (paying particular attention to their helmets) you see how these folks in the drag car are launched back into their seats when accelerating, and immediately 'pushed out' of the seat when the acceleration stops.
4) Yawing (oversteer)
Yawing is more commonly associated with flight simulation, where one uses yaw and/or roll to change horizontal direction. In sim racing, yaw is where the rear axle slides, simulating traction loss at the rear, which consequently changes the direction of motion of the car (i.e. oversteer). Interestingly, learning how to incorporate sufficient yaw (i.e. a small amount of oversteer/slip angle) into your driving is how you maximise your lap time, requiring a refined driving method that controls the balance of weight throughout the car.
As we see in the great video below, showing (a lot of) oversteer, the rear of these cars slides out, and this in turn changes the direction of the nose of the car.
5) Pitching (tilting forwards or backwards)
Pitching is also a nice easy one, and the best reference for this is to watch any racing cars when they brake heavily at the end of a long straight - you'll see the nose of the car dip down and the rear of the car lift up, as the weight of the car is transferred over the front axle. Likewise, when you see the car accelerate, the nose lifts up and the rear squats down, as the weight transfers over the rear axle. You do not see single seater cars pitching much, due to their low amount of suspension travel.
Here is a video of Stadium Super Trucks, which perfectly demonstrates pitch: as they brake at the end of the straight, watch the rear bumper abruptly lift as the the whole body pitches forward under braking; likewise under acceleration, you see the bonnet lift as the whole body pitches backwards:
6) Rolling (pivoting on one side)
Rolling involves the car pivoting on one side. Consider the amount of body roll in a car; a softly-setup car will have a lot of body roll in the corners, whereas a sports car will be more 'flat'. If you drive on banked oval courses, then you won't be sitting horizontal, you will be sat parallel to the banked surface and the car will be at a roll angle. In the context of a motion platform, it will tilt from side to side to simulate roll.
As seen the video from Top Gear © these two old saloons illustrate perfectly body roll in the corners:
..and for completeness, here is an example of 'excessive rolling'
So there we are - all 6 Degrees of Freedom explained and illustrated in action in motorsport.
Clearly, as Sim Racing becomes ever more popular, customers want best equipment which provides them the most realistic and authentic experience possible, closest to real life. The more information you have about the behaviour of your car, typically which you feel through the wheel, pedals and your seat, you understand more clearly how the car is behaving, and are able to know the limits clearly and drive faster - so, the more information you have, the faster you can go. A motion platform provides you with a new level of information and feeling, as you feel if the car is understeering or oversteering, you feel if the wheels are spinning and you're not getting the power down efficiently, you feel if a wheel is close to locking. It's this information which you feel in real life, and which is often missing in sim racing, that makes the biggest difference. Motion platforms are a dynamic platform which feels far more like real life than any static sim rig. If you want the closest possible setup to real life, you need a motion platform. The costs are of course, a lot higher than a static sim rig.
There are 2 ways of getting a motion platform setup - you can either purchase motion actuators to add to your existing rig that will add the motion to your existing sim rig, or a full bespoke motion platform with the motion actuators installed to the frame from the factory.
Upshift is proud to supply products from Qubic System, an industry-leading range of motion simulation products.
The Qubic System QS-220-PL motion actuator set provides industry-leading performance for your sim rig. The QS-220-PL comprises 2x motion actuators in the set plus control module, and multiple sets of these can be combined to obtain higher DOF. The most common setup is to order 2 sets of QS-220-PL (totalling 4 actuators) which will transform your rig into a 3DOF motion platform.
If you are seeking the Ultimate Motion Simulator, then we have your answer: the Qubic System QS-S25 6DOF Motion Simulator.
The QS-S25 is the pinnacle of motion platform technology, providing full 6DOF motion and unbeatable realism. If you want a simulator that feels like reality, then you need the Qubic System QS-S25.