Need to know ASAP
Need to know ASAP
I don’t think a spec has been published for the VEXplorer. It is designed to run at 9V, and Ricky Torrance already told you that the 9.6V battery is above it’s design spec on this thread.
As for the lower end, I’ve used a standard 7.2V NiCd with my VEXplorer and that works well. It should be safe to experiment to determine the lower bound, since under-voltage is unlikely to cause damage.
So, anecdotally, I’d say the range is at least 7.2V - 9.0V. It is probably safe to assume the same 6-9V range as the VEX Microcontroller. From poking around inside the VEXplorer receiver, it does not appear to have as much power protection as the VEX micro, so I believe it is more likely to be damaged by running it at too high of a voltage.
Are you talking about the transmitter (Tx) or the receiver/controller (Rx)? The former takes a 9V battery, but the latter takes six AA cells, which range from ~1.2 to ~1.5 V each, depending on the type, giving a ~7.2 to ~ 9V for the six-cell battery (to use the term in its technical sense, rather than the colloquial).
Two thoughts for your consideration:
Although excess voltage does cause some failures (breakdown of insulation, for example) directly, that usually takes a voltage at least several times the design working voltage. It is excess current that causes most common failures induced by excessive power. (This is why fuses and circuit breakers (which sense current, not voltage) protect in most cases.) The connection is through Ohm’s Law, which tells us that, for a resistive object, current increases linearly with voltage. That said, there are some devices (including some motors) that will, under a given mechanical load, draw more current at lower voltage. Therefore, at too low a voltage, there may be too high a current in a motor driver circuit.
Purely speculatively (I haven’t opened my Vexplorer Rx/CTLR and don’t have a microcontroller to open.), it may be that there’s less “power protection” in the Vexplorer unit because it isn’t as sensitive to overvoltage or overcurrent.
PS: Ricky Torrance just replied
that the Vexplorer controller will operate at as little as ~3 V, but noted that the motors would be rather weak at that voltage.
I was referring to the receiver/controller.
Yep - in general, over-voltage causes breakdown and over-current causes heat failure. In semiconductors, particularly digital ones, the breakdown voltage is often very near the operating voltage range. The processor in the VEXplorer receiver/controller has an operating voltage range of 2.3V-5.5V and an absolute maximum rating of 6.0V.
In the VEXplorer receiver/controller it appears to be powered via a voltage regulator. I wasn’t able to get a part number off the regulator, so I don’t know its specs. However, this tracks with Ricky’s answer in another thread that the processor will continue to operate down to around 3V: 2.3V for the CPU + a small fraction of a volt for the LDO regulator + some margin for voltage fluctuation.
Possibly, but I think it is more of a cost issue. The VEX microcontroller sells for $150 by itself, whereas the VEXplorer controller is only $40 for the transmitter, receiver/controller, and battery pack.
The microcontroller has a 4A PTC over-current protection device on the battery input, and a voltage regulator with thermal/over-current protection for the digital I/O port power rails. Also, all the signal lines are protected with current-limiting resistors and (what appear to be) clamping diodes. I don’t think any short could cause damage to the unit, and I don’t think it would be easy to electrically damage the unit using only VEX accessories.
The VEXplorer receiver/controller has a voltage regulator for the CPU, but all the other components are powered directly from the battery line. I suspect you could cause heat damage to the unit by shorting the AUX output port. The motor ports appear to be driven by pretty standard 6-transistor H-bridges (4 drive transistors, and a pair of bias transistors for the positive rail switches). I don’t know what the specs are on these transistors, but they are in standard SOT-23 cases and don’t have any heat-sinking.
Despite the best efforts of 60 teenagers over three years, our collection of a dozen VEX controllers hasn’t had a failure (yet). Thanks for the detailed description, Dean.