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This is sort of off-topic, but I reckon you guys if anyone might be able to help me.. Just now I was rambling about the possibility of an electrostatic 'engine', similar to that of a combustion engine. It would have a charged plate at the top, and another plate underneath (the piston, if you will) , connected to a crankshaft. An extrusion on the crankshaft would serve as a switch which would connect the piston plate to ground at the bottom of its cycle. Now, the top plate is connected to a high voltage generator of some sort. You then spin the crankshaft, which moves the piston plate up and down. When the piston plate reaches the top, it connects with the top plate, and electrons flow into it, thus charging it. Like charges will repel, pushing the piston plate downwards. When it reaches the bottom, it is grounded and therefore free to move upwards again. Voila, you have created the worlds most inefficient motor. I'm not suggesting this would be practical or even possible to make, given the no doubt miniscule forces involved, but is the theory sound or not?
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Jan 16, 2008 16:58
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I'm thinking of buying some thyristors from ebay, and I'm having a bit of trouble understanding the datasheets.. What is the difference between Vdrm and Vrrm? (the given values are 400v Vdrm and 600v Vrrm) Link to datasheet: http://www198.pair.com/kuncow/ftoc.pdf - the ones I'm considering are P270CH04
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Jan 19, 2008 11:22
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I've got a small heap of IRF 3415 mosfets lying around (150V 43A abs max) These are N-channel, and I'd like some P-channel with similar capabilities for building H-bridges and the like. Any suggestions? I've had a hard time finding anything similar. (I don't necessarily need a particular transistor, just places/ways to find them) Also thought I'd mention that a while ago I snatched some MONSTER thyristors from ebay. One of them about 6500 volt, the other 8000v. Both with peak surge currents in the 60kA range. Paid about 20bux for each. For the time being they live in a cardboard box in my living room. They're probably plotting to kill me.
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Jul 23, 2008 11:01
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Delta-Wye posted:Poking around on mouser, the FQA36P15 is a 150V/36A P-Channel MOSFET. I found it by simply going to their MOSFET page and choosing p-channel and high voltage and current requirements, and reading through the 30 or so it returned. Thanks! I found them on ebay for $2.13 a pop. Think I'll just have to give them a try. The same seller has some insane transistors though. 1200V 54A? I had no idea you could do something like that in a TO247 package. Astrolite fucked around with this message at 00:09 on Jul 26, 2008 |
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Jul 26, 2008 00:04
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Can I get some advice on my H-bridge? I want to build a dual H-bridge motor controller for my RC crawler. The H-bridges would be controlled by some kind of atmel chip, perhaps an ATTiny. The bridge will be running at a pwm frequency of say 3000hz. For the sake of safety I have tried to make it impossible to short circuit the bridge by having a bridge off pin (V4) and a pwm control pin (V3). The battery voltage is 8.4v (V1) and the mosfets IRF3415 because I have a bunch of them. These are n-channel, so a voltage doubler chip is used to make the V2 voltage which is needed to run the gates of the top mosfets. I have tried to make this as simple as possible, but although this design appears to work in simulation it makes very inefficient use of V2. The doubler chip can only supply 80mA, and I am burning it all away by sinking the mosfet gates to ground. R1 and R3 can't be increased because the mosfets have a rather high gate charge (200nC). 
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Apr 1, 2009 17:34
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BattleMaster posted:Why not just use a dual H-bridge IC? Haven't really found any of these (or single ones for that matter) that put out the currents/voltages I'd like to use. The crawler doesn't need very much (8.4V 6A per motor) but I kinda wanted to have a scalable design for future projects such as CNC servos. Poopernickel posted:dedicated gate drive chips (I recommend these) Sounds interesting. I'll have a look around. As for the bootstraps you mentioned, that's something I didn't even consider, need to absorb some more knowledge I guess..
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Apr 1, 2009 18:40
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BattleMaster posted:Oh, when you said "RC crawler" I was envisioning something much, much smaller. What are you using to power that thing, a car battery?! Haha, while 6A is admittedly the peak current draw this thing still drains batteries like nothing else. It's got a 2cell (~8V) 9400mAh lipo pack in it. By the way, I've got another rc car with a mamba max brushless system, which apparently can draw upwards of 80 amps peak. There's some zesty mosfets in that one for sure.
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Apr 1, 2009 19:22
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Has anyone here used USART on an atmega16? I'm trying to write an integer to the UDR, but no matter what I do the TxD pin is high constantly (I'm just looking at it with an oscilloscope). I know I'm entering the interrupt that writes to UDR, since I'm writing the same integer to another port, where it shows up just fine. Do I need to have some kind of external load on the pins for USART to work properly? Currently the only thing I have hooked up to the pins is my scope. I'd post my code, but my comp is dead at the moment. Anyway, the USART initialization was copied straight from the atmega datasheet..
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Aug 21, 2009 11:05
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BattleMaster posted:stuff about coilguns Just thought I'd mention that I've been tinkering with a coilgun of my own, using a somewhat nonstandard approach. Essentially, I've been trying to imitate the stuff that is used in modern electric RC cars. In place of SCRs I'm using paralleled mosfets, giving an Rds of 10mohm. The regular steel projectile was substituted by a neodymium magnet. And the capacitors have been replaced by lithium polymer batteries. It may sound like a puny alternative, but even a 5000mAh lipo cell can supply 200 amps relatively continously, and 8 cells in series gives approx. 33.6 volts. Such a gun could fire multiple rounds with essentially no delay, until the coils start melting, that is. The final gun will have 8 stages, but I have already tested a 4-stage prototype, and it's looking pretty good. Optotriggers between the coils are read by an atmega chip, which controls the mosfets. Efficiency is something like 5-10 percent, and it looks like the velocity of the final gun will be about 40m/s with a 20 gram projectile.
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Apr 30, 2011 22:52
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I've got a Rigol DS1052E, and I'm thinking about upgrading. Mainly I'd be looking for a bigger screen (higher res) and 4 channels. Bandwidth isn't important - 50MHz is enough. Are there any good alternatives below 1000bux?
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Aug 30, 2011 15:55
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Slanderer posted:I was gonna get the Rigol scope, if only because two channels is generally enough (esp. since I got a dedicated logic analyzer for looking at big digital interfaces). Was there anything wrong with the Rigol besides the 2-channels, and the screen size? I'm a mechanical engineer, so I don't have in-depth knowledge of oscilloscopes, but the Rigol is in my experience a pretty drat good option for a budget hobbyist. As for other weaknesses, nothing serious really. The cursor interface is a tad kludgy, and takes up a lot of screen space. It's got a fan which is kind of noisy. The refresh rate when looking at low-frequency signals is rather poor, but I don't know how other scopes would compare. Apart from that, I'm very happy with it. I also agree that 2 channels is enough most of the time. It was kinda inconvenient however when debugging my multi-stage coilgun. 4 channels would have been great for monitoring two full stages (optodetector and coil) simultaneously.
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Sep 1, 2011 13:59
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MisterSparkle posted:Essentially there is a bushed DC motor (from a cordless drill), that draws at the above specs. Its to be direction controllable for 200ms pulses, max with 10-15 seconds cool off before firing again. So.. if I'm understanding you correctly there will be a 200ms pulse inevitably followed by a 10-15 second cooldown? In other words - a 2% duty cycle? If that's the case then a single beefy MOSFET with low on-resistance should be sufficient, even without a heatsink. Also, if you don't need instant switching of directions, I'm fairly sure there are relays designed to switch motor directions.. I suppose you could use one of those to switch directions inbetween pulses, and then turn power on/off with the MOSFET. But don't take my word for it - I'm usually satisfied when my stuff doesn't instantly disintegrate. Edit: Apparently it's called a changeover relay Astrolite fucked around with this message at 20:13 on Oct 1, 2011 |
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Oct 1, 2011 20:09
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| # ¿ May 4, 2024 13:50 |
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Anyone thinking of trying out this micro python stuff? http://micropython.org/ It sounds kind of neat, what with running python 3 on a 168mhz microcontroller and not requiring the use of any IDE to write or transfer code..
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Aug 14, 2014 20:21
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