Step one. Bought the van.
Hello Everybody, First post. I camp a lot in tents but after spending three days straight in a tent in the rain at Dolly Sods I swore I'd make a change. Here it is. Bought it Wednesday. Dro...
Forum Discussion
Kitchen Cabinet, Post #26
With the protective box done it's time to finish up the electronics for the dump valve. First thing is to do something about the motor speed. Since it's interfacing with a plastic valve handle I want to slow it down. I'm afraid it might snap off the handle at full speed. I'd read about something called Pulse Width Modulation (PWM) which allows you to control the speed of a DC motor by turning the power on and off very rapidly. The amount of time the motor is turned on versus turn off is the duty cycle. The lower the duty cycle, the slower the motor.
Printed the instructions off the internet and breadboarded the circuit using a 555 timer chip to drive it.
Got it working but the circuit was of a general nature so had to do some configuring for this specific application. While doing this I started thinking. Since the motor is only making a quarter turn at a time the PWM circuit was probably overkill. Maybe I could slow it down with some resistors instead. They are dead simple to use.
Unhook all the fancy electronics and hook the motor straight up to 12 volts of battery power and start testing some resistors.
Long story short. A 1 ohm resistor reduced the speed but also the torque so much it wouldn't turn the valve. Two .1 resistors in series worked best.
Now how to control the stopping of the motor when the valve has reached it's full turn. The cradle can only turn 90 degrees before it bangs up against the frame stopping it's movement. To preserve the motor and it's gearing I want it to stop it before it hits the frame. With that aim in mind I had welded on two nuts to the outside edges of the cradle. One on each side.
Screw a bolt into the nut then add a limit switch to the side of the frame. As the cradle is closing (or opening) the valve, depending on the side, the head of the bolt approaches the button on the limit switch.
At the point where the valve is completely closed (or opened) but just before the cradle makes contact with the frame the bolt head pushes on the button breaking the motor circuit.
Using the bolt as the contact point allows me to adjust it back and forth by rotating it. For as crude looking as it is there is some real fine control. When I have it just right use a lock washer and nut to hold the bolt in position.
The previous pictures where of the closing limit switch. This is the opening limit switch.
The switches themselves came from the sofa-bed construction. Both of these switches where damaged when the little metal lever either got badly bent or the plastic tabs it pivoted on were broken. I held onto them and they work just fine in this application.
I had to grind off the remains of the two plastic tabs on the top of the switches.
How to wire it up? Stare at it for a while then get a pen and paper and sketch up a circuit. Use a diode on each limit switch to by-pass that switch if the cradle is rotating away from it.
Wire it up and give it a try. I'm proud to say that it worked right the first time. Not often so lucky.
Youtube video of the motorized valve in operation.
In the video I'm under the table powering the motor from two 6 volt batteries sitting on the floor. It's not hooked up to a switch so I'm just swapping the two motor leads from plus to minus and back again to get the valve to open and close. Don't know why the video is such poor quality. Must of hit the wrong setting on the camera.
Install the motorized valve into the freshly painted box.
You can see the side holes where the box will bolt to the tank brace. The base plate gets screwed into place only after the box is bolted to the brace.
Take both end plates off and apply generous amounts of Silicone II to all seams then screw back together. Smear silicone wherever I think it might help keep out moisture.
One job left. I forgot to see how many amps the motor pulled as it was turning the valve. I'll need to know this so I can use the correctly valued fuse for the motor circuit. Problem is that it happens so fast I had trouble getting a good reading. Had to call for some help.
As I worked the clamps on the batteries Bob would keep a close eye on the voltmeter then call back the reading after each run.
Her highest reading was 6.47 amps.
continued -
With the protective box done it's time to finish up the electronics for the dump valve. First thing is to do something about the motor speed. Since it's interfacing with a plastic valve handle I want to slow it down. I'm afraid it might snap off the handle at full speed. I'd read about something called Pulse Width Modulation (PWM) which allows you to control the speed of a DC motor by turning the power on and off very rapidly. The amount of time the motor is turned on versus turn off is the duty cycle. The lower the duty cycle, the slower the motor.
Printed the instructions off the internet and breadboarded the circuit using a 555 timer chip to drive it.
Got it working but the circuit was of a general nature so had to do some configuring for this specific application. While doing this I started thinking. Since the motor is only making a quarter turn at a time the PWM circuit was probably overkill. Maybe I could slow it down with some resistors instead. They are dead simple to use.
Unhook all the fancy electronics and hook the motor straight up to 12 volts of battery power and start testing some resistors.
Long story short. A 1 ohm resistor reduced the speed but also the torque so much it wouldn't turn the valve. Two .1 resistors in series worked best.
Now how to control the stopping of the motor when the valve has reached it's full turn. The cradle can only turn 90 degrees before it bangs up against the frame stopping it's movement. To preserve the motor and it's gearing I want it to stop it before it hits the frame. With that aim in mind I had welded on two nuts to the outside edges of the cradle. One on each side.
Screw a bolt into the nut then add a limit switch to the side of the frame. As the cradle is closing (or opening) the valve, depending on the side, the head of the bolt approaches the button on the limit switch.
At the point where the valve is completely closed (or opened) but just before the cradle makes contact with the frame the bolt head pushes on the button breaking the motor circuit.
Using the bolt as the contact point allows me to adjust it back and forth by rotating it. For as crude looking as it is there is some real fine control. When I have it just right use a lock washer and nut to hold the bolt in position.
The previous pictures where of the closing limit switch. This is the opening limit switch.
The switches themselves came from the sofa-bed construction. Both of these switches where damaged when the little metal lever either got badly bent or the plastic tabs it pivoted on were broken. I held onto them and they work just fine in this application.
I had to grind off the remains of the two plastic tabs on the top of the switches.
How to wire it up? Stare at it for a while then get a pen and paper and sketch up a circuit. Use a diode on each limit switch to by-pass that switch if the cradle is rotating away from it.
Wire it up and give it a try. I'm proud to say that it worked right the first time. Not often so lucky.
Youtube video of the motorized valve in operation.
In the video I'm under the table powering the motor from two 6 volt batteries sitting on the floor. It's not hooked up to a switch so I'm just swapping the two motor leads from plus to minus and back again to get the valve to open and close. Don't know why the video is such poor quality. Must of hit the wrong setting on the camera.
Install the motorized valve into the freshly painted box.
You can see the side holes where the box will bolt to the tank brace. The base plate gets screwed into place only after the box is bolted to the brace.
Take both end plates off and apply generous amounts of Silicone II to all seams then screw back together. Smear silicone wherever I think it might help keep out moisture.
One job left. I forgot to see how many amps the motor pulled as it was turning the valve. I'll need to know this so I can use the correctly valued fuse for the motor circuit. Problem is that it happens so fast I had trouble getting a good reading. Had to call for some help.
As I worked the clamps on the batteries Bob would keep a close eye on the voltmeter then call back the reading after each run.
Her highest reading was 6.47 amps.
continued -
