Now that front alignments and ackerman is covered...I would like to cover one more important topic that not many people pay attention to...Steering Lever Ratio.
WHAT IS LEVER RATIO?
When you turn a wrench, shorter wrench will require more strength than a longer wrench.
This is part of the "simple machine" you learn in 5th grade science
.
But there is more to it.
You've seen adjustable servo horns where you can adjust the length of the servo horn.
To achieve the same amount of steering stroke, you have many options to choose to achieve that with the lever ratio, or simply the radius of the servo horn and the angle. Depending on the radius from the servo center to the steering link, you are able to dictate how much servo stroke to use relative to your steering stroke.
WHY IS STEERING LEVER RATIO IMPORTANT?
In the diagram above, both arcs will generate the same 'length' of arc to move the steering from full lock to full lock. However, the 'angle' of the movement in the servo horn is different.
For example, a shorter servo horn achieves a certain length of arc at 60 degrees, a longer servo horn can achieve the same length of arc by only moving 40 degrees.
It seems to be more 'efficient', however, you must not forget that this translates to how much the front tires stroke with the movement of servo, which is controlled by your steering.
So, is it easier to control the steering with a longer servo horn or a shorter servo horn?
This is up to you and your feel...unless you have 'magic' hands, the 'accuracy' of the steering control can be achieved by using 'more' servo stroke. You can achieve 'quicker' steering using a longer servo horn, but any twitch in your hands, will transfer to your front tires. The steering lever ratio will dictate the balance of accuracy versus speed.
SO HOW DO I SET IT UP?
With adjusting the servo horn length, you will need to adjust the EPA on the radio. If the servo stroke and the steering stroke matches perfectly, the EPA will be 100. If you are using a longer servo horn, your EPA will become lower, a shorter servo horn, EPA will become higher. In other words, if your default EPA setting is below 100, you can shorten the servo horn to increase the EPA, or visa versa.
HOW DOES STEERING LEVER RATIO RELATE TO GYRO?
Now that you know the servo horn is not just a 'thing' you got with your kit to slap on your servo...
The balance of accuracy versus speed, also applies to the gyro setting in RWD RC drifting.
The servo horn below is adjusted to achieve EPA 100 both left and right, which means the full stroke of the servo matches the full stroke of steering. This is my current setup.
This is the servo horn at maximum length, with EPA around 85-90 to get full stroke. The steering will become quicker.
This one is at the shortest point, with EPA around 125 to get full stroke. The steering will become slower.
This is same with how gyro input affects the self steering, or counter steering in RWD RC drifting.
The shorter the servo horn, the higher the EPA, makes the gyro work smoother.
The slower the mechanical setting is, the gyro will become slower, but beyond a certain point, may be too slow and cause spinouts.
The longer servo horn, the lower the EPA, makes the gyro work quicker.
The quicker the mechanical setting is, the gyro will become quicker, but beyond a certain point, will make it twitchy and cause wobbles.
I recommend to try to set the steering EPA 100 to match the full steering stroke as a default, and adjust from there based on your feel. Needless to say, EPA left and right MUST be identical.
Even at the same gain, by tuning the steering lever ratio, the overall drive feel will change. The amount of countersteer will also change.
If your chassis is twitchy and wobbles, and cannot increase your gain, or if you want more 'smoothness' in how the gyro and your steering input works, try working with the steering lever ratio.
Here is a great tutorial on adjusting the servo horn and EPA setting, and how smooth the gyro becomes.
Happy drifting!
March 31, 2018 / Charlotte NC
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