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Old 2006.09.02, 04:48 PM   #7
LBRC
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Join Date: Mar 2004
Location: Northwest
Posts: 550
The only “glitching” caused by a 2x2 or even 2x3 FET stack is when it’s installed improperly, i.e. overheating or static damage, which happens quit a bit, since most people don’t use static protection and less than ideal soldering equipment, sort of like doing surgery on a kitchen table with a carving knife, with enough skill and luck the patient can survive but it’s a traumatic experience.

As for capacitors, especially with a modified motor, because of the amount of current involved you might as well try throwing cotton balls at the car to help the motor along and supposedly reliving current deprivation/spikes from the steering in this case. Look up the definition of Farad then calculate the amount of current actually being applied, or if your not up to the electronics and math just take your cap, charge it, and connect it by itself to a motor lead and see if you get any movement at all, then repeat the process with progressively smaller motors to see how small the motor has to be and how big the capacitor has to be to get even a micro second of help.

On the practical side the first thing I would do is try the car in another location, if location makes a difference it’s a TX/RX problem, if location and range does not make a difference, then why not first put a stock motor in with a freshly charged set of known good batteries to see if current delivery makes a difference. Remember a motor draws the current the mosfet H-bridge amplifier does not force that current into the motor. If you experience more “glitching” with a modified motor compared to a stock then the two most likely culprits would be either your batteries, or quite possibly the FETs where damaged by the handling and installation procedures used when stacking them. A hot motor with low current delivery batteries can indeed deprive the steering of power for example that’s the Iwaver’s main nearly insurmountable problem because of the week inefficient steering motor driver, the problem however is rarely an issue with a Kyosho Mini-Z. For example even with a 2x3 stack of 4562’s running a T1 in a very heavy Tagu 1/25 conversion chassis on a 1/14 scale carpet track using cheap Powerizer batteries and a 9 toot pinion I have no “glitchy” steering issues.

One problem with some of the reasoning mentioned in your other FET thread so far is that a working efficient FET stack does not draw more current from the battery, a small but important distinction is that a stacks less resistance generates less heat allowing the motor to receive power (voltage/current) that was previously being used by the inefficient single mosfet. In other words, the current drain from the battery stays the same with the same motor, the only difference is that more efficient mosfets allow more of that power to actually reach the motor instead of generating heat in the mosfet which is what destroys the mosfet when a motor draws too much power.

Most common cause of steering glitches in a Mini-Z:
  • Low TX power; can be either batteries or poor antenna (TX or car) connection.
  • Loose or unsecured servo encoder/potentiometer (pot), can also be caused by the pot being pinched too tight too. Either way it causes the same problem the variable resistance does not correctly indicate/match the servo position.
  • Signal interference/dead spots. For example this summer I have my home track setup in a 20’ x15’ screen tent and the close proximity of the insulated (ungrounded) metal poles caused a dead spot in the far right corner which was especially noticeable with a low power Epoch TX or a KT-5 with weak batteries. By grounding the tent poles I was able to significantly reduce the problem.
  • Low battery power, which actually starves the receiver circuitry causing the glitch not the steering driver itself.
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