sentra Posted July 21, 2013 Share Posted July 21, 2013 man i just removed the old stuff and installed a tiney servo directly to the needle, it was about 1 minute of work. 1 Quote Link to comment Share on other sites More sharing options...
mikey Posted July 21, 2013 Author Share Posted July 21, 2013 Servo would be great except you lose you odometer and also I have nothing to attach the other end of the servo to. Quote Link to comment Share on other sites More sharing options...
sentra Posted July 21, 2013 Share Posted July 21, 2013 see your point on odometer, to counter the other one those micro servos are easier than a stepper, as far as you can just usually wire it directly to micros output gnd & powersupply edit - did you mean nothing to connect to as in digital dash? Quote Link to comment Share on other sites More sharing options...
mikey Posted July 21, 2013 Author Share Posted July 21, 2013 Yeah, there's no speed sensor anywhere currently, so no signal to convert unfortunately. I've got this BLDC motor almost working. It's talking to the ESC and I have a button which effectively goes from full throttle to zero throttle. Problem is when I go full throttle it cuts-out after about half a second. I think it has something to do with the modulating signal changing slightly and the ESC cuts-out. I'll keep playing. http://s1230.photobucket.com/user/mmcl055/media/VID_20130721_174146.mp4.html Quote Link to comment Share on other sites More sharing options...
Simon Posted July 21, 2013 Share Posted July 21, 2013 Are you powering the motor from a separate source? Make it so the button only goes to half throttle and see what happens. Quote Link to comment Share on other sites More sharing options...
mikey Posted July 21, 2013 Author Share Posted July 21, 2013 Less throttle was the answer, I was giving it a duty of 50% which is waaaay over 100% throttle, dropped it down and now working. Just tryiing to get some consistant slow speeds now. Quote Link to comment Share on other sites More sharing options...
mikey Posted July 21, 2013 Author Share Posted July 21, 2013 This is a video of it running at the slowest speed the controller will run at: There's a couple of problems, that speed is far to fast, but also depending on how much load I put on the motor the speed jumps around quiet a bit. During that vid I'm changing how much weight I put on the motor which has a big effect on speed. Time will tell if this will be an issue or not. I need to organise a proper connection between the motor and speedo and see how it goes. Quote Link to comment Share on other sites More sharing options...
Simon Posted July 21, 2013 Share Posted July 21, 2013 Hmm, you might have to use 3 mosfets and drive it straight from the PIC. Quote Link to comment Share on other sites More sharing options...
mikey Posted July 21, 2013 Author Share Posted July 21, 2013 Hmm, you might have to use 3 mosfets and drive it straight from the PIC. To achieve slow enough speeds? I can drive the motor with the motor driver chip I was using for the stepper I had before. If I dont wanna run full speed though I have to PWM each coil as I go. Probably not a major problem. There's even open source ESC code for PIC's I can use. But, would running a lower KV motor be enough to slow things down without all the bother? One issue with the ESC is I _think_ they detect speed by reading the unused coil while they charge the other two. So that explains why it's susceptible to load but doesn't end out skipping steps. This is all just a theory / what I've pieced together today by reading / I know fuck all about these motors. Quote Link to comment Share on other sites More sharing options...
mikey Posted July 21, 2013 Author Share Posted July 21, 2013 Hey Ned, what make/model is that ESC? There's no marking on it. Some dont go below 30% duty, I wonder if this is one of them. Quote Link to comment Share on other sites More sharing options...
Simon Posted July 21, 2013 Share Posted July 21, 2013 But, would running a lower KV motor be enough to slow things down without all the bother? That would probably work but It wouldn't be enough. You would still have the same problem. There's even open source ESC code for PIC's I can use. I'd use that. This way you can get real slow speeds. It would probably be more accurate too. Quote Link to comment Share on other sites More sharing options...
mikey Posted July 21, 2013 Author Share Posted July 21, 2013 That would probably work but It wouldn't be enough. You would still have the same problem. The same problem being non-constant speed when under load? Quote Link to comment Share on other sites More sharing options...
Simon Posted July 21, 2013 Share Posted July 21, 2013 Nah, not being able to get low RPM with the ESC. It might start turning at 1000rpm rather than 1800 etc. Quote Link to comment Share on other sites More sharing options...
Ned Posted July 21, 2013 Share Posted July 21, 2013 Just lower the voltage to 7v or something and that will drop the speed by a bit as well, and a low kV motor too. You would need 6 FETs, not 3 BTW as you need 3 half bridges. I would be happy to modify some AVR code to run on the ESCs and try that. Seems like the easiest way to go maybe? Quote Link to comment Share on other sites More sharing options...
mikey Posted July 21, 2013 Author Share Posted July 21, 2013 The ESC does some sensing of the supply voltage and beeps warnings when it's too low. Not sure where that cut off is but it wont run as low as 5v. I don't have a proper adjustable power supply unfortunately. The motor control chip I have has all the H-bridges I need, but I'm just not sure if PWM modulating the motor in open loop will work and it sounds like a truck load of work.... Modifying the AVR code would be great. But I'm just a little unsure if it'll work... If we slow down the motor too much I'm guessing it wont induce enough current in the unpowered coil to sense the correct timing and work in closed loop. Open loop seems to make more sense to me than closed loop anyhow, as we want to run at a set speed so we dont care about the optimal timing. However to avoid overstepping I have to PWM the coils as well as adjust the timing I switch them on and off. And at this point my brain hurts.... Quote Link to comment Share on other sites More sharing options...
Simon Posted July 21, 2013 Share Posted July 21, 2013 You should be able to get away with not PWMing the motor and just switch each coil on and off in the right sequence? That will work fine in open loop providing the motor is big enough to keep up. Quote Link to comment Share on other sites More sharing options...
mikey Posted July 21, 2013 Author Share Posted July 21, 2013 You should be able to get away with not PWMing the motor and just switch each coil on and off in the right sequence? That will work fine in open loop providing the motor is big enough to keep up. Yeah, maybe, it's worth a shot. I'll try and give it a go tomorrow. Quote Link to comment Share on other sites More sharing options...
mikey Posted July 21, 2013 Author Share Posted July 21, 2013 It must be possible to get ESC's that work with precise speeds, otherwise RC helicopters would be shit. Edit: Yeah, looks like a lot of ESC's allow you program them in constant speed mode. Which is probably what I need to do. Ned, any idea what model ESC this is? Or of that open source ESC code supports constant speed mode? Quote Link to comment Share on other sites More sharing options...
Ned Posted July 21, 2013 Share Posted July 21, 2013 Have no idea. Just some cheaply non branded thing. You can control those motors to go as slow as you want. Google/youtube bldc gimbal controller or something and people use those motors as stepper motors (actually, they rewind them if they want to keep them energised at a set position, but you get the point) Quote Link to comment Share on other sites More sharing options...
Simon Posted July 21, 2013 Share Posted July 21, 2013 Maybe ESC from a radio control car rather than a plane, if they even have BLDE car motors? Maybe RC plane stuff doesn't work for low speed because a plane just doesn't need to. What use is a little propeller turning at 10-100 rpm? lol Quote Link to comment Share on other sites More sharing options...
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