What is IR Comp and Why Should I Care?
The best analogy for IR Compensation is the Cruise Control on your car. When you want to keep your car speed at a specific MPH you set your cruise control. When you come to a hill your car needs more power to climb the hill so your Cruise Control gives it the right amount of gas to keep the speed constant while climbing the hill.
Most potters wheels have the same feature but it has a much less sexy name, IR Compensation. the “I” refers to current and the “R” refers to armature resistance. The adjustment is hidden in your wheels control box on the controller’s circuit board along with settings for speed control and torque. Manufacturers don’t like you messing with these settings because they are generally “tuned” to the size of your motor, pulley, belt… you get the picture.
So, to use the analogy: your wheel is the car, IR Comp. is the cruise control, Amperage is the fuel, the force you put on your wheel while throwing (especially centering) is the hill and the foot pedal is… well the foot pedal and the motor is the motor. Now I personally do not like using Cruise Control in a hilly area. That is primarily be-cause I have mostly owned small engine vehicles where I have to slam the gas pedal to the floor to get up hills and when I let cruise control try and do this it gets a little jolty (not sure if jolty is a word but I think you all know what I mean).
The bigger the engine (motor) and the smaller the hill (pressure on the wheel head), the less dramatic the joltyness (can I trademark that word?). A few more things come into play like the sophistication of the controller and the degree of IR Comp employed, but let’s get back to that later.
So, if I am driving an old VW Bug that needs a tune up and you are in a brand new 12 Cylinder engine Jaguar and we hit the same hill, I am going to slam my pedal to the floor boards while you barely have to move your foot. In other words, the adjustment is subtle because it is not putting much strain on your huge motor. This is probably why they never put cruise control on VW bugs. It would probably pop the seat right off the rails.
Okay, so what does this have to do with throwing pots? For most people, not much. For people throwing very large pots and for people throwing very thin, wide bowls at low speeds, it can be the difference between success and failure. Imagine you are dropping the walls on a 3 ft. diameter, razor thin, platter and the wheel gets a little unexpected jolt when the IR Comp kicks in.
Let’s face it, your foot pressure could be less smooth then the IR Comp so what is the solution? Buy the Jaguar with the 12 cylinder engine and never set your cruise control. In Skutt terms, get the wheel with the biggest motor you can afford and don’t worry about IR Comp because we never turn it on.
The founder of Thomas Stuart wheels, now Skutt Wheels, was a big pot potter. When he designed the wheels he specifically chose a motor that was strong enough to maintain a consistent wheel head speed, while the wheel was turning slowly, subjected to the resistance created by the weight of a lot of clay and without having to incorporate IR Comp.
So let’s get back to controllers. If you are not going to use IR Comp you are going to occasionally have to put your foot down on the gas to maintain wheel head speed. When you do this you want the power to be delivered as smoothly as possible. Think of the SSX Controller upgrade like replacing your carburetor with an electronically controlled fuel injector.
The SSX controller has more sophisticated and robust components. One of the most important of these components is it’s large capacitor. A capacitor stores energy much like a battery. Having this stored energy allows you to feather in the power when you needed it more precisely and therefor results in a smoother transition at low speeds.
For 99% of the potters out there, our 1/3 HP motor with the standard controller is perfectly satisfactory for their needs. Unless you are working with a wheel every day, making challenging pieces, you probably will not even notice the difference of any of these factors we just discussed. So, save your money for clay and just concentrate on whether you want a built-in splash pan or a removable splash pan. We will talk about that in future Blog Posts.