Now can anyone expand upon Phil's work and suggest a way to make a REVERSIBLE hi-amp controller?.
Extra credit: Two options, one fed from and R/C Rx and the second controlled by a 5K pot. Steve Tyng A hint: use a board from an el-cheapo servo to supply the pulses to feed into an H-Bridge using the same FET's On Aug 11, 1:23 pm, Steve Tyng <[email protected]> wrote: > Yep, not much to it it is there? The only thing I'd do different is > use four wires of the same length to trigger the FET gates (instead of > the current bus arrangement). This would sync timing between the FETS > a little better. > > Steve Tyng > > On Aug 10, 3:35 pm, "Phil Downs" <[email protected]> wrote: > > > Hi all, > > > I had a bit of spare time on my hands, so I started looking at a speed > > controller for my ‘Pile of bits’ > > > I have done some reading up and now know how these work, looking at the > > price (and features I don’t want) I decided to have a little play about. > > > As my motors cant be reversed by swapping the supply lines round, and are > > case grounded anyway, all I need is the speed controller bit. > > > I found a cheap 9-24v dc PWM controller board, assembled and tested for > > about £5, so I got a few to play with. > > > I got a couple of packs of automotive mosfet’s off ebay and sat down to see > > what I could come up with. > > > The ‘As Purchased’ board:- > > > PMC Board.JPG > > > After some playing and testing, I removed the original POT (a cheap and not > > very good one) and replaced it with a bigger (still 5K) one with a proper > > spindle. I didn’t put this on the board but put a 2’ lead on it to simulate > > it being at the other end of my tank. > > > The meter now shows the controller working much more accurately. > > > The next thing to do was to add additional mosfet’s to the gate feed, ‘I > > wonder how many it can drive?’ was the question. > > > After adding a jumper point on the gate side of the on-board mosfet, I > > connected it to the new chip, and it worked perfectly. After adding another > > and making sure that both new chips were operating independently and > > identically, I kept on going, eventually I got to 5 additional mosfets plus > > the on-board one, all working fine. > > > After a bit of a tidy and fixing the whole lot to a bit of scrap wood I > > ended up with this:- > > > PROTO1.JPG PROTO1A.JPG > > > Now the original board was rated at 3a (the chip can handle 12a, the PCB 6a, > > so sold as 3a), each of the new IRF2804 Mosfets is rated at 75a at 10v (62a > > at 12v) so with suitable heat sink (I’m planning to use the motor mount, > > that’ll save wiring the –ve as the tab is the –ve drain) this simple > > collection of bits should be capable of running a motor of 250a at 12v > > (3Kw!) now my new motors shouldn’t even reach half this maximum load. > > > All I have to do is gear the throttle servo to the new POT shaft, and I have > > a speed controller for under £10. > > > What have I missed, it seems too easy? > > > I can get away with only using two additional chips, but I always > > over-engineer everything I do, if things are only running at 30-50% of > > maximum, it’ll last longer (in my mind at least). > > > Just in case you’re wondering, to reverse my motors I have to change the > > terminal the +ve line is attached to, a chunky relay and a battle switch for > > each motor will do the trick. > > > Any comments? > > > Phil. > > > image003.jpg > > 31KViewDownload > > > image005.jpg > > 28KViewDownload > > > image007.jpg > > 23KViewDownload > > -- 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
