In March 2003, Phase III-X of the Ultimate Rustler project at UltimateTraxxas.com was rapidly drawing to a close. After a number of component swaps between my many vehicles, I was left short one ESC and decided to buy one for the Rustler that would be efficient enough to squeeze the most power out of a stock motor, flexible enough to be used in future projects with modified motors, and yet cheap enough to leave me with gas money to get to & from the local racetrack. I have had nothing but good fortune with DuraTrax speed controls in the past, and at $74.99, the Intellispeed 8T Pro looked to be a real powerhouse at a bargain price.
The Intellispeed 8T Pro is an unimposing unit. At 1.73" x 1.22" x 0.71", it's almost identical in size to a Novak Cyclone, but its outward apperance is fairly cheap due to its light blue molded case, single raised setup button and basic four-color sticker. If you can get past first impressions, though, you'll be in for a number of surprises.
The package includes capacitors, thick 12-guage wires and heat shrink, plus optional heatsinks and a much appreciated Schottky diode (this small component is soldered to your motor to aid smooth and cool running and minimize the effects of radio noise). The ESC's input/output tabs are firmly mounted and protrude well above the the case for easy wire installation. People used to sport-level speed controls will expect battery & motor wires to be pre-installed, soldered directly into the circuit board. The IntelliSpeed 8T Pro's pro-style setup allows the user to install whatever length and style of wire he/she wishes, and replace it to change to different applications. Also, the 8T Pro uses 3-wire external circuitry, where one wire each is routed to the negative terminals of the motor and battery, and a single common positive wire is shared. This allows the shortest, neatest, lowest possible resistance external circuits to be formed by the user.
One truly striking feature of this ESC is its use of a 6.0V BEC, in contrast to the standard 4.8-5.0V system used in most less-than-top-of-the-line speed controls. This gives a 25% speed and torque boost to your steering servo, instantly, for free. Ever see a servo spec sheet that says something like "0.18/0.15sec?" With a 4.8V BEC, you get 0.18sec speed. With the 8T Pro, you get 0.15sec speed. A+.
It's also worthy of note that the 8T Pro includes an extra small output wire for powering ultra-fast FET servos such as those made by KO Propo in the UK. These servos use full 7.2V power for maximum speed and torque. FET Servos aren't widely used in the US as yet, but it's impressive that DuraTrax accommodates them on such an inexpensive unit.
Once you've installed the 8T Pro, the real fun begins. The moment you begin the setup process, you gain immense respect for the Big Blue Button (I'll call it the BBB). Most ESC's require that you use a funky little tool to activate a 1.5mm or so setup button. The Intellispeed 8T Pro, on the other hand, can be programmed with a push of your big toe, thanks to the raised, easy-to-feel, gentle-touch BBB. One press of the BBB and a few transmitter throttle lever movements is all it takes to do basic setup. The default settings give you a 20 amp current limiter, normal brake action and a 3.9kHz drive frequency. You can then either choose from four additional profiles or go into fully manual setup. Here are the manual setup options:
- Turbo: Off, 0sec, 0.24sec, 0.54sec, 1.0sec, 1.5sec, 2.0sec, 2.5sec, 3.0sec. In practice, once you engage full throttle, this setting determines the delay before current limiting is turned off.
- Current limiting: 10-100A, in 10A increments.
- Brake minimum: 0% to 100%, in 10% increments. This determines the minimum amount of brake that will be applied when you barely tap the Tx throttle lever in reverse.
- Brake maximum: 0% to 100%, in 10% increments. Determines the maximum amount of brake that will be applied when you move the Tx throttle level into the full brake/reverse position.
- Quick start: "On-Road," "Off-Road," 0.04sec, 0.1sec, 0.16sec, 0.2sec, 0.3sec, 0.5sec, 0.70sec, 1.0sec. A numerical setting here will disable the current limiter for the selected period of time only when starting from a dead stop. The "On-Road" setting will disable the current limiter from a dead stop until you return to neutral throttle or hit the brakes for the first time. This system can be re-armed remotely from the transmitter. The "Off-Road" setting disables quick start, leaving current limiting on at all times.
- Drive frequency: 0.244kHz, 0.976kHz, 1.95kHz, 3.9kHz, 7.8kHz, 15.6kHz.
All of this functionality is accessed through the use of the one BBB and an ingenious menu-style system whereby you "scroll" through options using your throttle lever as an up/down arrow. At any given moment, you're shown where you are in the menu and/or what setting you've selected by a simple light code displayed by two LED's. This level of built-in programmability is unbeatable in the 8T Pro's price range.
As of this writing, I've used this ESC in my Ultimate Rustler for about an hour of total runtime. As I'm running a stock motor and adjust forward traction via my slipper clutch, I turned off the current limiter and ran at 3.9kHz with no Turbo or Quick Start and full brake range. The ESC performed exactly as I wanted it to. The power came on strong and the brakes were smooth. Even after 15 minutes of continuous running with no heatsinks, the unit had no noticeable warmth beyond ambient temperature.
Now, a few general words about stated motor limits on ESC's. "No limit" ESC's have extremely heavy-duty components rated for ridiculous current draw and thermal resilience. However, when you pick up a unit that is rated down to a certain number of turns, you enter a wild and unpredictable grey area -- it's a recommendation and limit of liability, not a definitive statement. When an ESC says "15T" on it, for example, this means that you will void the warranty (if any) and likely damage the unit if you use a motor that is 14T or below. However, there's nothing to say that you can't overload it with a 15T or even 16T motor. Depending upon your gearing, the voltage of your cells, the timing on your motor, the number of winds and the strength of the magnets, you may exceed the ESC's component ratings without surpassing the motor "limit."
Sure, this can be considered deceptive advertising, but it's a fact of life. The Intellispeed 8T Pro says on the box "Motor Turns Limit: no fewer than 8 turns." I'm sure you could overload it with a hot, recent-model 9x1 overgeared in a stock (heavy) Rustler, so a bit of sense & sensibility is called for. The real-world motor turn limit depends upon your exact application & setup, including even the amount of airflow you get over the ESC.
Here's a quick comparison of some key figures versus ESC market leader Novak's similarly-priced Fusion and more expensive, top-of-the-line GT7:
|Novak Fusion||Duratrax 8T Pro||Novak GT7|
|Weight:||1.87 oz.||1.45 oz.||0.93 oz.
(no heat sinks)
|On-Resistance:||0.0013 ohms||0.0005 ohms||0.00058 ohms|
|Max current:||240A||4700A (?)||640A|
|BEC:||5V, 0.5A||6V, 3A||6V, 3A|
|Drive frequencies:||1.0 kHz, 7.8kHz||0.244kHz-
The Intellispeed holds its own on paper, though the current rating is questionable (possibly accurate under laboratory conditions with artificially chilled, constant-temperature drive transistors).
DuraTrax has had some missteps in product quality in the past, leading some hobbyists to ignore many new products they market. In the search for a high-quality, inexpensive speed control, though, I would recommend that even the most heavily-prejudiced anti-DuraTrax fanatic take a serious look at the 8T Pro and other products in the Intellispeed line.