Animating a Run Cycle

Setting key positions for the feet and hips

It is easier to animate in layers, so this example has the upper half of the body in a separate layer so we can first concentrate on the lower half. As all energy/movement initiates from the hips, it is a good idea to start blocking out your hips first.

We are going to create what is called a run on 6. In traditional animation the frame rate is 12fps. So a run on 6 has each step taking 6 frames, thus two steps a second. For PAL or film that is roughly double. So for a 3D run we will start with a step that takes 14 frames.

- First change your keys to flat/clamped before you start setting any keys
- Pose your lower half such that the leading foot almost touches the ground.
- Cleanly plant your extremes, just by positioning the pelvis first. (don’t worry about the feet positions as yet. You can draw a CV curve to assist you with the trajectory of the pelvis. As a rule of thumb the height of the curve should not be much greater than half the height of your character’s head.
- I have used the Ghosting function of Maya so that you can see all the different extremes in one image. To show ghosting, select the geometry you wish to ghost and then select Animate > Ghost Selected (and use custom keyframes in the options)

- Now with your position right you can swap the middle foot pose around.

- At this stage we will only work in the side viewport, so be careful to only move your feet and pelvis only along the plane of your viewport (YZ plane for my setup).

- Now the next step is to block in the up position of the pelvis

- Now to finish off the pelvis placement we will add in the contact extreme and the pass extreme. NB: Don’t move the feet, just the pelvis, no matter how ugly it may look.

Now with your extremes blocked out for the pelvis we can position the feet for each extreme.

Note that for the pass and contact extremes the planted foot should remain planted for pushing off and landing respectively. The image below shows the trajectory you should aim for with the passing foot in a run cycle. It lifts up higher on the first half of the arc and lowers on the second half when the heel rotates forward ready to receive weight.

Now adding the left foot trajectory as well we have.

Now we can line up our feet with our foot trajectories.

Here is the stepped animation so far.

Pelvis Roll
Now that our timing and poses pass as some kind of animation we can start to refine the behaviour of the hips. As we are animating in layers, it makes things easier if we create another character set for the pelvis rotation.

- In the pass position the hips rotate upwards to accomodate the passing leg. But in order to balance, the centre of the pelvis also has to be translated (in this case to the right) in order to maintain balance over the centre of gravity.
Select the pelvis controller (make sure you are using Gimbal Rotation) and move to the down positions (frame 0,14,28) and rotate the hips up for the passing leg.

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- When one leg is extended forward the hips also rotate forward.

With the roll now added on the hips we get the following animation (the keys have been changed to linear).

Now we need to work on the weight of the legs. The above animation looks really floaty and lunar. For the specified timing the character needs to demonstrate greater effort in lifting his weight to have such timing.

First lets visit the graph editor and work on our tangents. Things to check for are tangent overshoots, and to add in discontinuous tangents when the feet hit the ground and when they take off.

Now we can make the running steps seem heavier by repositioning the keys. Currently our keys are evenly spaced.

By delaying the pass and the contact extremes by a few frames we can add greater weight to this run.

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The Spine

Now that we have a halfway acceptable animation going, we can work our way up the body. The spine essentially counters the movement of the hips. So for the first key on the Pelvis (the down extreme) we twist the spine to counter for the up/down rotation. Always be aware of the line of balance.

Then at the up extreme we need to counter the forward rotation of the hips

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Countering the pelvis rotation for the up and down extremes gives the following

The Head

As can be seen the in animation above, the head is getting thrown around a lot (very happy-go-lucky). For a concerted run, the head should be facing forward and be somewhat focused on a target (unless, for example, the character is being chased by an assailant).

Another subtle detail that can be added with the head is the small secondary motion of the head after the up extreme.

The Arms

The arms carry a lot of the personality of the run. The essential arm movement for a run will have the widest swing on the up extreme, and the smallest at the down extreme.

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Loosening up the arms

As the arms are receiving the energy from the pelvis they act a bit like tails and we need to show a small amount of delayed energy transfer up the arms. The easiest way to do this is to stagger the FK keys of the arms using the dope sheet editor.

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Which give us the following animation, which is an acceptable run cycle.

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Note on scaling keys

When you have finished your run cycle and weighted it accordingly it is not advisable to scale your keys as your keys spacing reflects the weighting of the character running and scaling would result in an unnatural looking transfer of weight.