Team MedBots

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EpicentrE
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Re: Team MedBots

Post by EpicentrE »

Anything around the 100w range is typical for ants, I think. Weight tends to be somewhere between 20 and 30g. I normally try to stick below 1500kv for spinners, but as you're going to be gearing it down a lot you probably want it to be as high as possible.
Scott Fyfe-Jamieson, Captain of Epic Robotics. Champion of AWS38/41/42.
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AntRoboteer
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Re: Team MedBots

Post by AntRoboteer »

Phileep 2 was awesome! Definitely one of my favourites!
Rapidrory
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Re: Team MedBots

Post by Rapidrory »

Yeah, that is the motor in Bad Idea; Great amounts of power, terrible terrible mounts (they get very thin just as they go under the can). Bad Idea gets away with it as it has separate external bearings and support both sides of the blade, but that's not a trivial task.
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Max
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Re: Team MedBots

Post by Max »

Hmm do you have any pictures of the underside/ from the side of the motor? I wonder how hard it would be to rebuild the base to provide better mounting points.
Max
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Re: Team MedBots

Post by Max »

What size mosfet would people recommend to drive one of the high power any weight gear motors with PWM? And what current capacity diode would I need to protect the MOSFET from induced emf flowing the wrong way (which will also act as an electronic break)?
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Shakey
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Re: Team MedBots

Post by Shakey »

Motors like the pololu HP stall at around 1.6A on 2 cell (2.4A on 3 cell) so really anything just over that should be fine.
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Max
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Re: Team MedBots

Post by Max »

I thought when using PWM you need a mosfet rated substantially higher than the stall current of the motor as when driving not at 100% duty cycle the midget can see much more current (for shorter times) than the motor is seeing? ie if say the motor was drawing 1a but is running at 50% duty cycle the FET will see 2a half the time and 0a the other half?
Or have I got that wrong?
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Shakey
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Re: Team MedBots

Post by Shakey »

You may be thinking of when a motor is reversed which can see extremely high peak currents over the stall of a motor (as the voltage is the battery voltage + the generated back emf of the motor). A motor that draws 1A at 100% with draw 1a at 50% but only half the time making the average current 500mA. There is tiny variation in this by nature of capacitance/inductance of the motor but it's basically not a concern particularly at these levels.

The real thing to make sure is that you can switch the FET on and off fast enough. While it is on fully it has a very low resistance, if it isn't on fully it will have enough resistance that it will heat up quite a bit. Though normally in an antweight just driving the FET off of a microcontroller (PIC/Atmel etc.) is fast enough. It's only really beetle/feather/heavy esc's that need to worry about this.
Nuts And Bots - For all your components and ready built antweights!

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Rapidrory
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Re: Team MedBots

Post by Rapidrory »

Or just don't worry about any of that and just use a suitably rated motor driver chip :L
Rory Mangles - Team Nuts

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NanoTwo Motor Controllers: https://nutsandbots.co.uk/product/nanotwodualesc
Max
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Re: Team MedBots

Post by Max »

Ok cool. So something like this should work fine:
http://pages.ebay.com/link/?nav=item.vi ... 1712256525

Not sure what the 4th pin is for, I guess it's just connected to the drain.
Then a fly back diode like this:
http://pages.ebay.com/link/?nav=item.vi ... 0964398644

To protect the mosfet from back emf
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