7 Aug 2006 tbenedict   » (Master)

Still waiting on the props (perhaps today!) and my copy of Dennis Clark's OOPic book. But I did get a chance to do some more work on the ROV and on my Mark III.

I ran the motors while hooked up to a digital power supply and RTD for measuring temperature. Driving at 3.0V it drew 0.38A no-load and ran at 34C (base temp 25C). Stalled at 3.0V it peaked out the power supply, drawing 2.18V at 2.2V. Basically the power supply clamped and wouldn't let it go dead-short.

At 6.0V it drew 0.52A and heated up to 46C pretty quickly. My guess is closer to 50C, but I didn't leave the motor running past five minutes. Since stalling at 3V peaked out the limits on the supply, I didn't try stalling at 6V.

With the motor submerged in water, 3.0V drew 1.8A with no measurable increase in temperature (it's heat-sinked to the water, so I expected this.) A 6.0V it drew 2.2A in the water.

What I take this to mean: Motors draw current like nuts when wet. So I can't put this ROV under microprocessor control very easily. For the money I'd spend on a beefy enough H-bridge to handle the current, I could just as well build dry enclosures for the motors and run off the 1A H-bridges I've got on both my micros. I have yet to try these motors with props in the water, but the requirements are only going to go up, not down.

Running at 3V still produced plenty of torque. So long as the props don't totally stall the motors, I'm going to under-drive them and see if I can prolong the motors' lives a little longer.

On the Mark III OOPic, I scaveneged more stuff and made more diagnostic tools. I had some micro switches removed from some mice that I soldered directly to some headers to plug into the Mark III Sensor Board. The jacks are arranged just like the Handyboard digital I/O jacks (which also match the ones on the Miniboard and the 6.270 board). I have a Miniboard, so this is handy. These went in the toolbox with the diagnostic LEDs I wired up to headers. Makes troubleshooting a breeze.

I'm sending out the announcement today for our club's second meeting. This lights the fire under my butt to get this ROV finished. I'd like to demonstrate it at this club meeting and see who's interested in building one. I also need to build out a mini sumo ring so if anyone else brings their sumo bot we can throw them in and let them go at it.


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