Rate Gyro Driver

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Rate Gyro Driver

Postby Sorceress Sarah » Fri Mar 05, 2010 11:07 pm

I have an application for which I need to build a driver. I have several Honeywell GG440A18 rate gyros that I would like to include in a robotics project. These gyros consist of a 24vac split-phase spin motor and a LVDT transformer for signal pickoff. The motor requires 24vac @400 Hz lead and lag (90 degrees), while the signal pickoff is driven with an 800 Hz sine wave at 9vrms. I have a test rig with 3 gyros configured for pitch, roll and yaw, and I have been successful driving the spin motors with a pair of 7-watt audio amplifiers driving the lag coil from both ends with a non-polarized electrolytic providing the phase lead. My trust HP 204D oscillator was able to drive all 3 pickoffs simultaneously, and I see three good signals with proper amplitude and phase shift on the pickoffs. The output is 1 mV per degree per second angular velocity with the phase shift indicating direction of rotation. Total current draw on the entire test rig was 350mA using a Leader LPS 152 power supply.

So here's the question: Can I use the PowerPSoC to drive the spin motors? the ability to spin each one up and monitor it's health on a single chip is a big bonus, but I am not sure how to drive the AC motors with the MOSFETs. Some guidance would be much appreciated. I have read the previous posts on using triacs, but they seem to be more for large voltage industrial motors and not directly applicable to this situation.

What I would like to do is to drive each gyro with one CY8CLED03D01 with one MOSFET providing the drive for the lead coil, another driving the lag coil and the third MOSFET driving the pickoff. THIS file:

http://shieldedpair.net/BAE5413/Lab%207 ... n_Idea.pdf

describes well how to read the pickoff.

I'd like to drive the MOSFETs with a PWM, varying duty cycle sinusoidally to drive the motor leads and the pickoff. . . So the questions become:

1. Am I an idiot? (or is this a workable plan?) If I'm an idiot, we end here, otherwise we continue to question 2. . .
2. Do I need any "glue circuitry" to drive the coils, or can I go straight off the pins of the chip?
3. Is there a benefit to using the "PRISM" driver over the PWM?

Finally, I would like to take each digitized pickoff and packetize it over I2C to a USB-capable part for interface with a PC.
Sorceress Sarah
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Re: Rate Gyro Driver

Postby yzr » Wed Mar 17, 2010 12:46 pm

The power controllers available on the PowerPSoC are really not well suited for driving motors. The FET drivers are low sided meaning that even if external FETs are an option, we cannot create any half or full bridges.

This said, several designs have been created where a PowerPSoC is controlling a motor (brushed-DC). In these designs, the only available feature is a current catch and motor ON-OFF. These designs do not have ability for speed or direction control.

If only a simple FET control is required, a regular PSoC with external FETs may be more desirable.

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