Switch set up

[MartinHughes]

Hi there,
My son is making a 9v drop tower as a project, like those things in the funfair that go up, drop when it hits the top and then starts again. So he has the motor and shaft and bucket set up. Turn on motor bucket moves up the shaft on a cog and rail system, hits a switch which turns off the power drops to the bottom onto an elastic buffer platform, and hits another switch which turns on the power again and repeats. what switch can he use both at the bottom and the top?

The bucket should sit on the bottom switch I guess. When the power is switched on the bottom switch stays "on" when the bucket reaches the top and activates that switch, the power turns off and the bucket free falls onto an elastic band platform buffer and hits the bottom switch which turns the power on again. I was reasonable at electronics about 30 years ago but am at dinosaur level now.. Any help would be appreciated.

 

[Delta Prime]

Welcome to Maker Pro.
You like movies.

 

[MartinHughes]

Thanks. still no wiser on the switch though?

 

[kellys_eye]

Put a magnet on the bucket and use 'reed switches' as the contacts.

A Complete Guide to Reed Switches

This expert guide focuses on reed switches, explaining in detail what reed switches are, their applications, how they work, and so much more.

uk.rs-online.com

 

[Delta Prime]

Thanks. still no wiser on the switch though?

One on top one on the bottom.

. I was reasonable at electronics about 30 years ago but am at dinosaur level now.. Any help would be appreciated

No problemo. But please do not hesitate to ask.
The International Electrotechnical Commission (IEC) and the National Electrical Manufacturers Association (NEMA) have slightly different symbols.

Limit Switch Explained | Working Principles - RealPars

Limit switches explained: In this article, we're going to introduce you to a device called a Limit Switch.

www.realpars.com

 

[Bluejets]

Reed switches would work as "signal" device but would not carry motor current.
Micro switch ok if non critical as far as absolute position top or bottom is concerned, which should be no worries.
Would need to shop "China" for cheaper price though.
One through everyday electrical outlet would be 5 to 10 bucks each whereas through Ebay etc. from China "5 for $5.00"

https://www.ebay.com.au/itm/256075943224

As a side note, you mention 9v, hope that's not smoke alarm type battery as it won't last 5 minutes.
Better use a battery case and five or six AA cells, last heaps longer.

 

[Harald Kapp]

There are 2 types of switches:

1. latching switches. Example: the light switches in your home. When you operate such a switch, it stays in that position until you reverse it.
2. momentary switches, also often called pushbuttons. Example: the buttons on your TV remote control. The switch is active only as long as you press it.

Why do I mention this?
In your son's application neither of the two types can be used alone without some additional technology:

1. latching switches:
   If you were to use these, the bucket will operate the switch when the bucket reaches the end position, but what then? Assume the bucket moved upward and reaches the top. It then operates the top switch and reverses direction (let us for the moment ignore how this exactly is done). Now the bucket moves down, reaches the bottom and operates another switch which tells it to move up again. But the switch on top is still in the "go down" setting.
2. momentary switches/pushbutton (for the sake of clarity I'l use this term):
   Same scenario: bucket moves up, reaches the pushbutton. Pushbutton is activated, bucket starts to move down. But once the bucket leaves the top, it also stops pushing on the pushbutton. The pushbutton is released, the bucket no longer receives the "go down" instruction.
   Same on the bottom.

Ways out of this dilemma:

• Use pushbuttons to activate latching relays which in turn control motor direction.
  The modern version of this would use a microcontroller (e.g. Arduino) to perform the necessayr steps like registering the pushbuttons' state and controlling the motor.
  This is imho out of the scope of your son's project.
• Think out of the box and go the old fashioned mechanical way:
  Use a single double throw double pole switch to reverse the motor direction. This video shows an example. Instead of the rocker switch used in the video, use a lever switch (example).
  - Drill a hole into the end of the lever.
  - Feed a strong thread through the hole.
  - Make a loop from this thread between the top and bottom of the tower such that the loop is attached to the bucket.
  - Make two knots in the loop such that one knot operates the switch when the bucket reaches the top position, the other knot operates the switch when the bucket reaches the down position.

I'll try to visualize my idea:


- bucket moves up
- knot for top moves clockwise-> when bucket is on top, knot for top operates the lever switch by moving the lever down.
- motor reverses direction, bucket moves down
- knot for bottom moves counterclockwise -> when bucket is at bottom, knot for bottom operates the lever switch by moving the lever up.
- motor reverses direction, bucket moves up


This is the most simple setup I can envision without using additional electronic circuitry.

 

[Delta Prime]

If you use your imagination all you need is one switch.
A microswitch has 2 limit switches operating together and sharing a common terminal. One limit switch is normally open and the other is normally closed.

To be technically correct, the switch configuration is Single Pole Double Throw, or commonly referred to as SPDT.

The dashed line indicates that both switches are mechanically connected and will operate at the same time

Think of the basket as the light bulbs you would have to run the length of the arm almost to the very top of the drop Tower then. You have the basket tip of lever to latch that arm and have it free fall until it reaches the bottom unlatching it,the process starts over again. Only one switch but additional mechanics involved. I doubt you would hear any clicking.

 

[Harald Kapp]

@Delta Prime : Afaik you haven't understood the problem. There is only 1 motor which needs to be reverse to drive the bucket up and down. A SPDT switch is insufficient. A DPST switch is required.

Or, if you insist on using a SPDT switch, you need 2 batteries to be able to reverse polarity. Se this schematic:

 

[Delta Prime]

Afaik

Have never come across that could you elaborate please sir.

 

[Harald Kapp]

As Far As I Know

 

[Delta Prime]

So he has the motor and shaft and bucket set up. Turn on motor bucket moves up the shaft on a cog and rail system, hits a switch which turns off the power drops to the bottom onto an elastic buffer platform, and hits another switch which turns on the power again and repeats.

I thought he just wanted to turn the power on and off to the motor at the appropriate time. It was only a suggestion.

 

[Delta Prime]

@Delta Prime : Afaik you haven't understood the problem. There is only 1 motor which needs to be reverse to drive the bucket up and down. A SPDT switch is insufficient. A DPST switch is required

I am on the fence on that one!

 

[AnalogKid]

What limits or determines the speed of the descent? Does the platform drop at the same rate it climbs? You say that power is removed from the system when the platform reaches the top. Does that mean that gravity works against the motor inertia to bring down the platform?

Whatever the answers, you need a latch. This can be a relay, an IC, two transistors - lotsa ways to do a latch, and we need more information about your system. Power supply voltage and motor current to start.

The lower switch applies power to the system, but that power must be maintained after the platform has come off of the switch. That means that power is latched on. Similarly, power is turned off when the platform hits the top switch, and stays latched off until the platform reaches the bottom switch. One latch does all of that, called a set-reset flipflop. If the descent really is powered only by gravity, then you do not need to reverse the polarity of the motor power.

ak

 

[Delta Prime]

If you want to drop tower this is an idea only. And it can even be said you don't need a flip flop for a drop tower it's a flip & wait. For the gondola to drop and or bucket.

 

[Bluejets]

This will work..............2 c/o relays, 2 pushbuttons, 2 limit (micro) switches.

 

[Delta Prime]

This is why I like the scientific approach.