The circuit works fine to power the lamp. When I get the brake, I'll make sure there is a diode across the terminals of the electromagnet.What voltage do you get over the lamp (assuming a 'scope measure here)?
Anything I have missed here to have this circuit drive the brake?A generous heat sink!
What voltage do you get over the lamp (assuming a 'scope measure here)?
You'd be better off with the MOSFET you mentioned and the two BjT's for a driver.
I don't have an oscilloscope,Oh, I thought this was a "school" project :)
but my voltmeter shows 0 Volts across the lamp terminals when the Arduino output pin is at 0 Volts. My voltmeter shows 10.28 Volts when the Arduino output pin is at 5 Volts. (My voltmeter also shows my power supply putting out 11.47 Volts instead of 12 Volts.)That sounds about right and that's 1.2V (6W at 5A) of lost power.
That makes sense. I'll replace the Darlington transistor with a MOSFET. If not too much trouble, having a schematic would be nice, just so I don't misunderstand anything.I'll draw you one... In between the flick that's on the boob tube in about 12 minutes.
i would go for a relay, that is driven by tip120 you are using, so you would not fry anything, [...]Interesting!
Oh, I thought this was a "school" project :)
For the Schottky diode, will a 1N5817 work?1N5817 is a 20V device, so I wouldn't. 1N5818 is 30V and I'd go for at least the 40V handling of the 1N5819. There's probably not any real price difference and just a single breakdown due to a too weak diode might cost you way more, in terms of labor and a new diode..
I'm not too worried about the speed of the gate, since the PWM frequency of the Arduino pin is only 500 Hertz.It's not the frequency of the signal I'm worried about, it's the rise and fall times of same.
Actually, all this is for an electric car project. With some other family members, I am building a new type of electric car. It's more to try out some concepts than to build a car to actually drive on the roads.The more (tried&tested) electric cars on the road the better, so every project that bears that way is good - now that the flying cars never arrived ;D
Your help on a variety of topics for this project over the past year or two has been very valuable. The only thing that is still a problem is steering. Everything else is close to being ready.Great, remember me if you build something like the Tesla Roadster (http://www.teslamotors.com/roadster/specs) or the Koenigsegg Quant (http://www.gizmag.com/koenigsegg-quant-512-bhp-four-seater-solar-all-electric-car/11167/picture/70903/) :D
What's the steering issue(s)?
I haven't found a good way to steer the wheels. The plan is to steer each wheel individually by sending it an 8-bit number (0 to 255). We need an electromechanical device to turn the wheel.Unless it's for being able to turn the wheels 90° for a smooth parking, I wouldn't touch it. There's a well proven steering geometry that's hard to beat - if weight has a say in it, carbon fiber rods may be the ticket.
At first I thought of using a linear actuator. But they are too slow and weak.They come in lots of different speeds and strength, ut wouldn't be my first candidate either.
Someone suggested (it may have been you) to use the existing steering gearbox, and just replace the steering wheel with an electric motor. We would then get another steering gearbox for the wheel on the other side.I really think you can get in a lot of trouble by steering each side separately - what if one wheel stics? I'd prefer they followed along, rather than taking different routes in that situation - less emergency handling to know/learn.
You thought a windshield wiper motor might work as the electric motor. So I've been trying that out, and have tried to write a PID program to control the motor. But I'm not sure the motor has enough torque.With a conventional Ackermann geometry, it should have as much (or little) torque as a skinny 16 year old girl ;D
Another problem has been the mechanical linkage between the motor and gearbox. Finally, it's hard to find a place to put a potentiometer to give feedback on the steering angle.Potentiometer *aargh* How short do you want it to last? ;D
None of those are huge problems. But there are a lot of problems, all of which need to be solved. So the steering still needs a lot of work. We may even have to come up with a whole new idea on how to do it.I may be repeating myself, but if you stick to the good old steering arms to yank with the connecting rod, you only have one motor to worry about and a gearhead with a rack and pinion should take care of the interface.
Otherwise, the car is coming along nicely. It's no Tesla Roadster, or Koenigsegg Quant. (Those are really nice cars.) But our car is a whole new architecture for an electric car that may lead to much better cars in the future, as well as change the carmaking industry.I'll drink to that ;D (As long as it doesn't come out looking like a Skoda :D)
But the whole point of our car is to do things a little differently.Ah OK, I think we're on the same page now (at least I'm getting there inch by inch ;))
By being able to change the steering geometry on the fly, we can get better performance at no added cost.I see.
we want to have all four wheels steered, braked and driven independently. We will then have a true four-wheel drive car, with each wheel being an interchangeable module.I've had similar thoughts for 'bot wheels, but with the motors built into each. Something like an outrunner BLDC with a tyre, perhaps with a "layer" of gearing in between, but my present lack of an easy accessible mech space makes it hard to build motors :(
But as you point out, that will be hard to do. So I am trying to figure out whether to abandon the ideal solution and take a more practical approach. Your comments help.Hey, don't let me scare you off trying new and exciting roads!!
And I want an absolute reference rather than a relative one. That's why the rotary encoders and Hall sensors I found did not seem like they would work well. Ideally, I would like to put the position sensor right on the steering knuckle and get a resolution of half a degree.You can get absolute Hall encoders - somewhat expensive compared to other ways, but not prohibitively so (around $30..50 a chip and sold in 3..5 piece sample packs IIRC a little steep).
This car has been an interesting project, and as I said, your help on some of these questions has been very good to have. Thank you.You're very welcome!
Here's a schemmy...
(http://That.Homepage.dk/Img/MOSFET_Driver.png)
Consider C1 only for experiments and with a higher value R5, to deliver enough charge voltage to the gate for a swift turn on, while keeping the average current lower.
[...] I'm not sure what type of MOSFET would work here. Back then I was thinking of using an STP40NF10L. Would that work?Yes that would work fine - and so will any that can handle the current, so if you have some already, or cannot get the STP40NF10L, go for the one with the lowest RDS-ON