Novak GT7 programmable performance
Mess you’ve just been defrosted from cryo-sleep, you’re no doubt familiar with Novak’s Cyclone Series of electronic speed controls (ESCs). The Cyclone (and most recently, the Cyclone C2/TC2) has been our Readers’ Choice favorite ESC since it was released in 1997. In addition to a very small footprint, the Cyclone was notable for its small size and groundbreaking programmability. By jacking it into your PC or Novak’s hand-held Pit Wizard, you could customize it with your settings for Drive Frequency, Minimum Drive, Drag Brake and a host of other performance parameters.
Similar programmability is featured in Novak’s newest pro-racing ESC, the GT7, but now you don’t need an external programming device; you just need your index finger and the setup button. The GT7 is 30 percent smaller than the Cyclone, and clever hardware designs include a factory-installed power capacitor, a removable receiver harness and an integrated switch mount.
Installed power capacitor. Unlike the solder-on or plug-in capacitors of the Cyclone series, the GTTs power cap is hard-wired into the case at the factory (removing it will void the warranty). A thoughtfully designed bracket makes it easy to tape the capacitor anywhere, or you can slide the bracket into a slot on the side of the GTTs case.
Variable Throttle Step (VTS) technology. Think of throttle “steps” in this way: if an ESC had just one step, it would work like an on/off switch-no throttle or full throttle and nothing in between. Two steps would give you more control-no throttle, 11 throttle and full throttle. Ten steps would allow more precise control; 100 steps would be even finer, and so on.
Novak’s VTS system varies the number of steps (up to 1,300!) according to the frequency of the program you select. Lower– frequency programs have more steps, so you won’t have to sacrifice fine throttle control for low-frequency punch. With a high-frequency program, the GT7 uses fewer steps; this prevents the throttle from feeling “mushy” while it preserves the extra-smooth control of a higherfrequency setting.
Adjustable Drive Frequency, Brake Frequency, Minimum Drive, Minimum Brake and Drag Brake. The GT7 is factory-programmed with seven throttle programs (see the “Novak Factory Throttle Settings” chart for the particulars). With the exception of the Minimum Brake setting, the values for programs 1 to 6 can’t be changed, but program 7’s values for Drive Frequency, Brake Frequency, Minimum Drive, Minimum Brake and Drag Brake can be customized. (See the “Program 7 Throttle Options” chart for the available values and the “Glossary of Terms” for an explanation of those terms.)
The Minimum Brake value of all the GT7’s programs can be set to your liking. The Cyclone Series allowed very fine programming of a greater variety of performance parameters, but the GT7 limits adjustability to those that most affect “feel,” and there are five values to choose from for each parameter. Those racers who didn’t exploit the programmability of the Cyclone (guilty as charged) will be much more tempted to give customizing a try, thanks to the GT7’s simplified programming system.
Constant Force Braking and Drag Braking options. In addition to the value choices of Brake Frequency and Minimum Brake, the GT7 lets you select Novak’s Constant Force Braking or Drag Brake setup (if you aren’t familiar with drag braking, see the “Glossary of Terms”). Introduced with the Cyclone C2/TC2, Constant Force Braking was designed to provide linear braking at all speeds by sensing the motor’s rpm. Since electric cars use the motor’s electromagnetic field for braking, the motor’s rpm affects the braking force available: the lower the rpm, the less effective the brakes. To counteract this phenomenon and to provide consistent brake “feel,” the GT7’s Constant Force Braking circuitry adjusts the brake signal relative to trigger position and motor rpm.
One-Touch Set-Up and onboard programming. Novak was the first to introduce pushbutton setup, and now all but the most basic ESCs use pushbutton setup. In addition to the usual setup function, the GT7’s One Touch button is used to select programs and to dial in the program 7 profile. You don’t have to plug the GT7 into a PC or Pit Wizard; all adjustments are made right at the ESC.
Direct-solder wiring tabs. The Cyclone Series’ solder posts worked well, but the GT7’s solder tabs are much easier to use. The circuit board exits at the rear of its case, and the power wires pass through holes in the board. This design makes it easy to heat the wires from underneath the board for easy removal and replacement.
Slide-mount on/off switch. The Cyclone C2/TC2’s integrated on/off button was cool, but depending on the location of the ESC, the button wasn’t always easily accessible. The GT7 returns to a conventional, sliding on/off switch, which can be placed anywhere you like (within the reach of its harness, of course). But the best place for the switch is the GT7’s case; like the power-capacitor bracket, the switch can be docked into a slot in the case for a secure, tape– free mounting.
Removable input harness. This welcome feature was new with the Cyclone C2/TC2, and it returns with the GT7. The input harness (three wires and a connector for the receiver) can be unplugged for easy bundling or replacement. The included harness is 10 inches long, and Novak offers a 4.5-inch harness as an option.
Transmitter Check mode. The GT7 will program and operate normally with as little as 90us (microseconds) of forward and brake trigger throw, but Novak recommends 500us of forward throw and 90us of brake throw. The Transmitter Check mode makes it easy to set these values on any radio that has adjustable endpoints. After you’ve selected this mode, the GT7’s LED will indicate when the suggested values are reached as you operate the transmitter trigger and set the endpoints.
Polar Drive and Radio Priority Circuitry. Polar Drive reduces heating at partial throttle and increases regenerative braking. This feature allows you to run the GT7 without a clip-on heat sink, but that’s a moot point because this ESC doesn’t have exposed FET tabs for a heat sink! The Radio Priority Circuitry makes certain the receiver and steering servo have the power they need to keep you in control, even while the pack gives up its last amp.
I installed the GT7 in an Associated T3 equipped with a Sanyo 3000HV battery pack and a 12-turn motor, and I was ready for action after only five seconds of dial-in time on the One-Touch Set-Up button. The GT7 defaults to program i, which is second only to program 7 for smoothness (program i’s frequency is 15000Hz, versus program Ts 23000Hz).
Not surprisingly, the GT7 provided exceptionally fine control, and I was pleased to find it did so with out any of the off-the-line mushiness that can accompany high-frequency operation. The T3 dug in and ripped as hard as I expected it to with 12-turn power, suggesting that Novak’s Variable Throttle Step system must have been doing its thing.
Since the GT7 was able to add punch to a high-frequency program that might have otherwise felt “soft,” I was curious to see whether the ESC could also add smoothness to a low– frequency program. I dialed up program 6, which has a drive frequency of 2000Hz. The 12– turn motor felt like it had even more bottom-end pull when I clamped the trigger, while slow roll– ons showed fine throttle control with just the slightest trigger movement and perfect linear acceleration all the way up to full tilt.
Having tested the extremes of the GTTs frequency spectrum, I quickly made a few passes with each of the “in-between” programs. The ESC responded with a progressively more aggressive throttle feel as I moved from the higher-frequency programs to the lower-frequency settings. It’s well worth a few minutes during practice to take a lap with each program to see which one feels best.
I also tried my hand at customizing program 7. Getting to it is as easy as selecting any of the other six programs, but inputting the values requires careful attention to the instructions and winking LEDs. I would say “Keep the manual in your pit box,” but Novak has gone one better. It has printed the setup, program selection, and program 7 programming instructions on “cheat cards” that you can slip into your transmitter bag’s pocket or stick to your toolbox lid; the cards are adhesive backed.
I didn’t have any specific programming needs for program 7, but I did confirm that all the adjustments Novak promises are indeed available. Average racers will probably never need a custom program 7 (the six factory-set programs will suit any conditions), but if you have the driving skills to exploit this feature, unlocking its potential will require only your index finger.
The stars of the GT7 show are its programmability and neat physical features, but its classic Novak features deserve mention as well. The Radio Priority Circuitry did its usual magic and kept the receiver and steering servo fully powered as the pack flat-lined, and the Polar Drive feature kept the GT7 cool throughout testing. If you’re a sensitive driver, you’ll notice that the Constant Force Braking really does improve lowspeed braking control.
The GT7 is another well-designed Novak ESC, and it’s a significant improvement on the Cyclone Series in its ease of programming and setup convenience. The slide-mounted on/off switch and power capacitors are genius, and the ESC’s six stored programs and customizable seventh program make it easy to find the perfect settings for your needs. My only wish is that the GT7 were less expensive, but I say that about all the procaliber ESCs. Look on the bright side: the GT7 is the same price (give or take a few bucks) as the original Cyclone and the C2/TC2 models, so even if GT7 performance doesn’t come cheap, at least it isn’t getting more expensive!
GLOSSARY OF TERMS
Frequency. To oversimplify, an ESC controls motor speed by cycling the motor on and off many times per second. The number of cycles per second is the frequency In hertz (Hz). It is generally accepted that higher frequencies result in smoother throttle “feel,” and lower frequencies have more “punch.” Frequency is most often discussed in terms of throttle, but an ESC’s brake system also cycles on and off many times each second and has its own frequency. The GT’s drive frequency and brake frequency can be set independently.
Minimum Drive. This is the percentage of full throttle that will be used as the minimum amount of throttle. For example, the Minimum Drive setting for program 1 Is 3 percent; that means the least amount of throttle the GT7 will deliver is 3 percent of full throttle.
Minimum Brake. This is the percentage of full brake that will be used as the minimum amount of brake. The default Minimum Brake setting of all the GT7s programs Is 20 percent; that means the least amount of brake the GT7 will deliver is 20 percent of maximum brake. Minimum brake can be set for 20, 30, 35, 40, 45, 50, or 55 percent. If you don’t select the Constant Force Braking option, the Minimum Brake setting will also be used as the Drag Brake setting.
Deadband. The small amount of trigger travel at neutral that doesn’t actually cause the ESC to activate the throttle or brake is called the deadband. The GTTs deadband is set at 5 percent for all seven programs. That means the Initial 2.5 percent of the trigger’s forward travel and the initial 2.5 percent of Its brake travel Is deadband (for a total of 5 percent).
Drag Brake. Instead of allowing the car to coast freely when the trigger Is at neutral, the Drag Brake setup automatically applies the brake when the throttle Is off. The GT7 uses the Minimum Brake setting that’s programmed by the user as the drag-brake value. So, if you set the Minimum Brake to 20 percent, the GT7 will automatically apply 20 percent of full brake when the trigger is at neutral.
Copyright Air Age Publishing Feb 2003
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