Hi Andy, Nice job you've done so far. I like your design of the PCB. But I have a few thoughts.
You are saying that your ESC will do 75A continuous because of the Id current on the datasheet of the irf1010ez is 75A continuous at 25°C? This is true when you see it in a very small period of time. If the motors drain 75A continuous via the bridge, one mosfet will dissipate: P=R*I² = 0.0085Ohm *75² = 47,8W !!! 47.8W a mosfet and you have 2 mosfets that are switched so it will be a 100W of energy loss on that small board. In percent this is (at 24V *75A = 1800W): 0.06% No way your mosfets are going to survive that and they will heat up and fries. If you see the the OSMC project. They are using the IRF1405 mosfet with a Id of 169A Continious at 25°C. So if the OSMC use only 1 mosfet per side of the bridge it will give an energy loss of: P = 0.0053Ohm*169A² = 151W. Ther are 2 mosfets on so this wil give 300W a board of heat dissipation. Which is a very high energy loss. Now, if you take 4 mosfet a side, you split the current by 4. (Theoretically an Id of 676A). So if we calculate the new setup it will give this energy loss: 4*( 0.0053Ohm*(169A/4)² = 4 * 9,46w = 37W .. this is 74W a board => 4 times less!! this is only 9,46W a mosfet so with a small fan the board will not heat up. If we see this in percent (at 24V*169A = 4056W ) it will be only 0.018% of loss. A last calculation: if we run this board at 75A it wil give only: 4*(0.0053Ohm*(75/4)² = 7.45W. this is only 15W a board. this iss almost 7 times more efficient then your design. In RC terms: the less power you loss the longer you can run... Your heat-sinks will improve the heat dissipation but 50W per mosfet is a very high number. I don't want to be the smart guy here but I hope I can help you with this information. You can take the rule of 1/4 of the mosfet's Id to run it in normal conditions. I hope this helps... But still a nice Job! Sam D Op dinsdag 28 augustus 2012 03:01:38 UTC+2 schreef Andy Kipp het volgende: > > Hi Folks, > > My name is Andy and I've been on this mailing list for a while now, > but this is my first post. I've started working on a tank (M1 Abrams) > earlier this year, but I've been stalled for the past few months. I > live in Boston and workshop space hard to come by, so I was building > the tank in at my girlfriends parent's house. Sadly, they moved a few > hours away and I was forced to put actual tank building on hold until > I can find a new workshop. > > In the mean time, I've been mucking around with the electrical > subsystem for the tank. My plan is to use an Ardunio microcontroller > as a main controller for the tank (reading Servo signals from the RC > receiver and mixing/driving ESC as well as perhaps advance features > like gun barrel position feedback). I really have little experience > with electrical engineering (I'm a System's Admin by trade), but I > love learning to build things, so I figured why not give it a try. > > Along that line, I decided it would be fun (and educational) to design > a speed controller. My design is based off the OSMC, that Sam posted > so I figured it was a good time to share what I've done. > > A few changes that I've worked on incorporating: > > - 75A continuous current vs 160A continuous (using IRF1010EZ MOSFETS) > - Heatsinks and fans for better thermal management > - Onboard programmable microcontroller to read RC servo signals / > serial commands > - Custom built enclosure (It's got to look nice) > - Lower cost (using less MOSFETs) > > Right now the first prototype PCBs are at the fab house (I use > BatchPCB so it take a few weeks). > > Anyway, I've attached the board layout and schematic. > > Also everything will be open source, and available at: > > https://github.com/kippandrew/TitaniumMC > > Also pictures of my Abrams are online here: > > > http://www.facebook.com/media/set/?set=a.630562156512.2079935.29101609&type=3&l=78fb37825c > > > On Mon, Aug 27, 2012 at 7:29 PM, TyngTech <[email protected] <javascript:>> > wrote: > > These beasts generate a ton of heat. > > > > In every power conversion starting at the batteries all the way to the > > traction force to the ground, there's an energy conversion loss at each > step > > of the process. DC current fights its way through copper to the motor > > controller, current gets turned into PWM current at the controller, PWM > > current goes through more copper to the motors, in the motors current > gets > > converted into mechanical rotation, high speed rotation goes through a > > reduction device then to the drive wheels. At every step there's a loss > of > > energy because no power conversion is perfect. Whatever erg of energy > > doesn't get converted to the next step is dumped as heat into your > paintball > > spewing r/c vehicle of death! Add the fact that most paint their tanks > in > > nice dark colors that loves to suck-in the afternoon sun, our models get > > VERY hot inside and one needs to give cooling a high priority when > designing > > and building their tank. > > > > Steve > > > > > > > > > > > > On Monday, August 27, 2012 3:57:29 PM UTC-4, [email protected] wrote: > >> > >> how are these boards for handling heat (their own and surrounding)? i > have > >> heard in the past these guys tend to play in the heat with their > vehicle's > >> inner temp's rising. I think i heard one planing on cooking eggs on the > >> tank's motors (so i'm guessing the inside of the tank can get pretty > hot on > >> a sunny day) > >> > >> Chris > > > > -- > > You are currently subscribed to the "R/C Tank Combat" group. > > To post a message, send email to [email protected]<javascript:> > > To unsubscribe, send email to [email protected]<javascript:> > > Visit the group at http://groups.google.com/group/rctankcombat > -- You are currently subscribed to the "R/C Tank Combat" group. To post a message, send email to [email protected] To unsubscribe, send email to [email protected] Visit the group at http://groups.google.com/group/rctankcombat
