The Physics of Operating Wheels and Creative Implications.

Operators use mass, weight and inertia for creative purposes every day on set. A heavy dolly. A big crane. A lightweight handheld camera. Operators seek to control inertia as well. A steadicam is a tool that isolates the inertia of the camera from the steps of the operator. A gimbal is a machine that slows/controls rotational inertia using algorithms. Throughout cinema history fluid camera movement has required making it heavier, having better finesse, using springs, dampeners, isolators, track. As the computing age has intersected cinema, motors and algorithms have joined the ranks in stabilized heads and gimbals.

Whereas most of these efforts with a focus on manipulating the inertia of the camera, the Inertia Wheels focus on the operator. They manipulate the inertia of the hand wheel and even the hand itself. And much like other inertia-manipulating tools of before, the Inertia Wheels also have limitations and its abilities exists on a continuum.

All tools that seek to manipulate inertia have limits.

This is because inertia is actually limitless. It is said that a penny dropped from a tall building can kill someone. This adage reflects an important truth, that weight, speed, and mass are also tied to time. Move 2 ounces 30 feet in 0.3 second, that’s a tennis ball serve. Move 0.5 ounces the same distance in 0.01 second, that’s a bullet.

Tennis rackets and bulletproof vests are both tools designed to stop the inertia of those objects. Each meant for a specific purpose, with their own limits. The Inertia Wheels are designed to stop the inertia of your hand.

Understand the difference between a tennis ball and a bullet. You understand the limits of the Inertia Motors.

The Inertia Wheels’s physics system was designed to elevate operating in the most common operating conditions and work well in all operating scenarios. This means most of the time on set, the motor physics are there to empower and assist the operator creatively and technically. And when pushed to the limits, the motors can be reduced such that they are out of the way.

The main way these limitations manifest is in, what we call, a motor slip. The motor slip occurs when the motor applying the physics is unable to apply enough force necessary to counter the operator and maintain the illusion of a heavier wheel. In this instance, the motor is pulling too much amperage and as a precaution disengages. The most obvious scenario for this is a whip pan.

The simple solution is to simply turn down the motor’s mass setting or give the wheels more voltage (up to 35 volts). The more advanced solution is to understand what’s happening and add back in a little finesse.

Let’s take a deep dive.

An object in motion wants to stay in motion.

Imagine a large cement block on super smooth wheels with big handles. Your goal is to try to move the block. As you approach the block, you give it a gentle push to first see how heavy it is. It doesn’t move. It’s feels heavy.

It feels heavy? But your brain doesn’t have a scale. How can it tell? In your hand, you have nerves. These nerves can tell how firmly an object is pushing back into you. It instantly, without you even noticing translates that force into a mental model of the object.

You lean your body in and push firmly with your hands. As you start to move it, you feel the weight of the box pushing back into your hands.

This force/feeling in your hands is the inertia of the block. In physics terms, it is equal and opposite to the force you are applying to the box. An object at rest, wants to stay at rest.

Now the block is up to speed and moving on its own. It’s very heavy and the wheels are very smooth. Once it is moving, it keeps going. Your goal is now to stop the block from moving. So you grab the handles and pull. As you try to bring it to a stop, you feel the block pulling on your hands. You even feel it in your feet as you are forced to try to keep your footing.

This force is also inertia. An object in motion wants to stay in motion.

Imagine an empty cardboard box in the same scenario. As you push on it, you feel a smaller amount of weight/force pushing back on you. As you try to stop it, it’s easier and requires less force.

This is all because of mass. Mass is particles of atomic stuff. An object with a lot of mass, like a cement block, takes a lot of force to move or to bring to a stop. More atomic stuff. An object that’s light, like an empty cardboard box, takes less force to move or to bring to stop. Less atomic stuff.

An Inertia Wheel in motion wants to stay in motion.

The actual physical wheels on the Inertia Wheels are made of aluminum. Atomically, there’s a good bit of atomic stuff in aluminum, but not as much as heavier more expensive/fragile materials like brass or stainless steel.

To make the Inertia Wheels feel like they have more atomic stuff, the Inertia Motors do a relatively simple task. They try to maintain the wheel’s current speed.

Going back to the cement block, what does it do? If it’s stationary, it tries to be stationary. If it’s moving, it tries to keep moving. The cement block also tries to maintain its current speed.

This simple idea is at the core of the physics engine in the wheels.

The weight is in your hands.

The atomic mass in your hands is also relevant.

Take your imagination back to the cement block scenario.

The block is moving at speed. You grab the handles. But instead of putting your body weight to try to stop the block, you just grab the handle and hold.

What happens to your hand? Well the block moves it. Easily.

This is because your hand’s mass/inertia quickly joins the mass/inertia of the entire block and is pulled right along with it.

This means that not only do the Inertia Motors have to move the mass of the wheel. They must also move the mass of your hand/forearm. This is what you expect, so this is what the Inertia Wheels must do. This is relevant to understand, so that you can understand the motor doesn’t just have to move the wheel, it must also move you.

Time. The invisible x factor.

So far in our discussions of the cement block, we’ve focused on imagining changing the blocks speed slowly. But in practice, with the Inertia Wheels, if you change the wheels speed slowly, you will never experience a motor slip. This is because over long time intervals, the motors can easily apply the necessary physics.

Motor slips occur when you change the wheels speed rapidly, ie over a short period of time. Usually less than a quarter of a second.

This gets back to the bullet/tennis ball examples. Imagine both aimed at a cement wall. Both will seemingly hit the wall in an instant too fast to see. Yet the result is vastly different. To understand the result, let’s slow down time at the moment of impact. We’re specifically interested in how long it takes the bullet/tennis ball to impact the wall, start to finish. The moment it first touches to the moment either the wall has broken or the object has been brought to a stop.

A bullet weighs less and is smaller but traveling faster. When it impacts, its speed gives it tremendous force. All of that force is applied instantly and rapidly. Almost in a single instant, the cement wall breaks.

A tennis ball weighs more, but is squishy and larger. The size spreads the force out across a larger surface area. The squishy design spreads out the force across across time. Because the ball is not incredibly rigid, as the first part of the ball contacts the wall, other parts of the ball continue to move and deform. They will dissipate their energy into the cement wall over a period of microseconds. Even though it looks bounces off instantly, the squishiness of the ball means that it happens rather gently.

Play both back at full speed and both impacts happen in the blink of an eye.

In one scenario, something happened too rapidly and something broke. In another, it seemingly happened seemingly just as quickly and nothing broke. Motor slips can occur in exactly the same way.

Common causes of motor slips.

As we’ve discussed the cement block example, we’ve talked about how mass responds to force in a couple of ways. First, it pushes back and resists change. The more mass, the more it pushes back. It also pulls you. The more mass, the more it pulls.

We also talked about the tennis ball and how squishiness allows energy to dissipate across time. With the bullet, we’ve talked about how its rigidity and speed causes energy to transfer fast enough to break structures. And by comparing the tennis ball and the bullet, we’ve seen how mass, rigidity and speed can have different results even though both can play out too fast for us to see.

Now let’s apply what we’ve imaged to the Inertia Wheels.

It must push back

The Inertia Wheels have less mass than they appear to. The rest is a fabrication. When using higher mass settings, the whole system must apply more power to simulate the effects of higher mass. Just like the cardboard vs cement. Real mass has inherent energy and potential for limitless energy. Fabricated mass converts electricity to force. It has a limited maximum energy. As you push on the wheel, it pushes back on you. This requires energy. The higher the mass setting, the more force it will push back with. There’s a limit.

If you exceed that limit, motor slip.

Too Rigid = Too fast

Just like the tennis ball, our fingertips are squishy, our muscles are elastic. You have the power in your finger tips to grab the wheel with such force that your bones create a rigid connection with the wheel, like the bullet. Remember, the motors must also move your hands. When the grip on the handle is rigid, the motors will have a rigid connection with the mass in you. Without any squishiness or elasticity, it must move your mass instantly, with no delay. This instantaneous requirement means the motors cannot spread the required force across time.

Extrapolating an example: with a lighter grip the motor may have 0.05 second to apply the force. With a tighter grip maybe it only has 0.01 seconds. Both are too fast for us to see. But the tighter grip happens 5x faster and requires 5x as much energy/second.

If you go too fast, and again, exceed the limit of how much energy can be applied, motor slip.

Your brain knows what to do

Imagine you are trying to loosen a jar that your friend cannot open. You grab the jar, give it a quick twist, it doesn’t budge. What do you do? You adjust your grip, hand, forearm, back, maybe even stance and try again. All of that happens instinctively. You consciousness is just thinking I need the jar to open, your body does the rest.

Our entire body has an incredible ability to understand an object and adjust itself to manipulate that object when we want and how we want.

When operating Inertia Wheels, you brain perceives the wheel as heavy. Your brain can move the wheels in a million different ways. If your creative will dictates that the wheel needs to changes directions now the direction of the wheel will change now. Your grip will tighten, your forearm will adjust for more leverage, maybe even your shoulder blade will move forward. And like real physics, the Inertia Wheels will try to counter all of that with an equal and opposite reaction.

It won’t work, motor slip.

One simple solution: inform your expectations.

Hopefully by now you have a mental image of how the Inertia Wheels and your brain are working together in a complex, yet intuitive way. Motor slips happen because of a complex set of factors. Time, mass, energy, mental expectations.

But usually it’s simply because our brain truly believes the Inertia Motors. As you touch the wheels, your brain analyzes them, and builds a mental image of the wheels. The mental image is mostly correct. If you move the wheel a certain way, it will respond in a predictable way: the way all objects with real physics respond.

The illusion just breaks at the extremes.

Accounting for this is actually quite simple: inform your brain’s expectations. Do this by trying to cause motor slips. Your brain will actually build another mental image, a mental image of failure points. And when operating, it will avoid them.

Yep, it’s that simple.

(And also… turn down your mass).