Bring down toaster handle using Servo

Hello Friends,


I am in the process of completing the project which is responsible for bringing down the toaster handle at 7AM in morning. My list of items include:
Servo 030N
PicAxe 28x1
LCD/RTC

I have placed a string around the toaster handle and servo horn / star - the problem is the toaster handle is not coming down fully.

Question is:
Do I need a 360 degree servo? Or Gear motor to do the job?
Any ideas on how to build a mechanical push mechanism?

Simple code I have thus far:

main:
serout 7,N2400,(1)
pause 10
serout 7,N2400,(0)
pause 490
goto startservo
goto main

startservo:
for b0 = 1 to 50
servo 0, 75
pause 500
servo 0, 150
pause 500
servo 0, 255
next b0

Why is the toaster handle not going down fully?

Is it due to:
limited travel of the servo motor or
servo has insufficient torque ?

If the former, would a longer horn/arm on the servo providing greater travel suffice?
If the later, would a higher rated servo suffice.

Thanks for quick reply. My guess it is both. I can try bigger horn and see if it helps; but I found that I need to provide some tension / stretch around the string with each servo rotation.

Any other ideas?? Below are my servo stats:

* Bearings: Bushing
* Gears: Nylon
* 60° speed: .23 sec @ 4.8v
* 60° speed: .18 sec @ 6.0v
* Torque: 47.00 oz*in (3.38 kg*cm) @ 4.8v
* Torque: 56.00 oz*in (4.03 kg*cm) @ 6.0v
* Measurements: 1.56 x1.14x1.40 inches (39.6 x 29.0 x 35.6mm)
* Mass: 1.45 ounces (41.1g)

Hi

You need to consider the distance the toaster handle has to travel and how far the servo horn can travel (end stop to end stop).

So all you need to do is extend the servo horn arm to sufficient length to travel the required distance. The servo will have to be moved further from the toaster handle as the length of the servo arm is increased.

I'll leave the comments to someone else re the dangers of leaving a toaster unattended if your mechanical arm prevents the toaster from releasing the toast when done.

Hope this helps

Well, we now have all the required numbers relating to the servo.
What we need next are the numbers relating to the toaster.
We need to know how far the handle has to move and how hard it needs to be pulled. With both sets of numbers a design (or lack of) is then possible to determine.

So, measure the handle travel with a ruler. (at the point your string is attached).
Measure the force required. Attach a weight to the string that is just heavy enough to pull down the handle. (F=ma).
Then do the sums.

Does a 60° rotation at your selected horn length offer enough movement?
Is ~0.04Nm/[horn length] enough force? (from your measurements).

A couple of quick and easy tests plus some simple sums will answer your questions.

You'd probably get the best results using a 'sail winch servo'. These are very strong servos that rotate multiple times - typically around 3.5 turns. They also have a drum for spooling the string onto - ideal for this application.

A

Looks like a simple geometry problem to solve the horn length.

Can we find how far the servo horn can travel based on these commands -
servo 0, 75
servo 0, 225

You can also consider allowing sufficient distance in the servo horn length to achieve arm tip over travel and then include a stiff spring to take up the tension as the toaster latches in but the servo arm moves slightly further.

Then (as already mentioned) once the toaster is latched, don’t forget after a few seconds to return the servo arm to the “Off” position so that the toaster mechanism is free to release when the tost is done.
Otherwise there could be more toasted than a slice of bread

Why not - put bread in toaster = press down handle but leave switched off. use Picaxe to turn it on in the morning - That way you avoid the difficult mechanical interface and replace with a more simple electrical interface.

Depends how your toaster works. This would work with ours.

Friends thanks for many suggestions - as you can see I am being tested lot of different levels nows - physics, computer, electrical.
I have only few days left (2) to finish up the project!

Changing SErvo, or mechical interface is lot of work at this point.

If I change the bread toaster to Over toaster with turn-on knob - will it be simple? Can I make it work with what I have?

Please help........... I got thus far thanks to cool PicAxe PCB, MC, . Pull me through by making something turn and project a success!!!!!

First thing is don't panic - and be careful of taking what you have and, in an attempt to make it better, actually make it worse. You'll likely get more credit for a project which pulls the lever only part way than a pile of bits that you claim would work if only you had not run out of time.

With the deadline looming-up fast it may be better to go to Plan B; concocting excuses and explanations as to how what isn't perfect very nearly is, needs just a minor change but time or money ran out. If people can perceive it as "it works" it's just as if it does work, it is a success.

Toaster

Hope your servo can disengage, allowing the toaster handle to lift up on its own when the toast is done. Or there be some burned toast, or worse...

There's something worse than burnt toast??? Maybe burnt oatmeal... I'd go with Post #9 of Rickharris - all the toasters I've seen have a latch which is released by a thermal bimetal strip - no power no release... But then servos are fun and ideally you'd have an arm which comes out of the wall to extend a finger and push the lever down and scare the cat...

Have you thought of fixing a larger disc to the servo? That would give you more movement and more torque but slower speed which should not be a concern.

S2L said:

Have you thought of fixing a larger disc to the servo? That would give you more movement and more torque but slower speed which should not be a concern.

Click to expand...

Suggest you try it S2L!

I think you'll find it will give you the SAME torque (LESS force) and MORE speed with a larger movement.

Do the sums. There's nowt for free in this world!

BeanieBots said:

Suggest you try it S2L!

I think you'll find it will give you the SAME torque (LESS force) and MORE speed with a larger movement.

Do the sums. There's nowt for free in this world!

Click to expand...

Thatll teach me to post first thing in the morning!

baseer said:

I have only few days left (2) to finish up the project!

Click to expand...

on the 15th Baseer only had a few days until the project was due for presentation.
Its now a week since Baseer's last post with no further feedback.

Seems little point on providing Baseer with more commentary at this time unless we are advised that an extension was granted to complete the project.
Latest suggstions are just going around in circles with what was initially suggested.

turn on 20V

Rickharris said:

Why not - put bread in toaster = press down handle but leave switched off. use Picaxe to turn it on in the morning -

Click to expand...

Can you please explain [I think I sound like Pauline Hanson] how to turn on a
240V appliance with a Picaxe ?

SSR

It's simply done with a solid state relay or even mechanical relay - the PICAXE puts out 5 volt signal to activate the relay which then controls the mains to the toast waiting to be burned...

WARNING: MAINS VOLTAGES ARE DANGOUROUS AND ARE NOT AFRAID TO KILL YOU. WHEN MUCKING ABOUT WITH MAINS VOLTAGES TAKE EXTREME CAUTION AND DOUBLE CHECK EVERY CONNECTION MADE. MAKE SURE THE ELECTRICITY IS TURNED OFF AT THE WALL AND THE PLUG IS UNPLUGGED BEFORE FIDDLING. ALSO PUT ALL CONNECTIONS IN A PLASTIC CASING AND MAKESURE THAT PETS AND SMALL CHILDREN CANNOT GET TO THIS CIRCUIT.

Failure to follow these guidelines may result in: http://upload.wikimedia.org/wikipedia/en/2/23/TheBookOfBunnySuicides.jpg or worse (you/pet/child being the bunny).

Seriously though, be carefull

Jamster said:

WARNING: MAINS VOLTAGES ARE DANGOUROUS AND ARE NOT AFRAID TO KILL YOU. PUT ALL CONNECTIONS IN A PLASTIC CASING .

Failure to follow these guidelines may result in: http://upload.wikimedia.org/wikipedia/en/2/23/TheBookOfBunnySuicides.jpg or worse (you/pet/child being the bunny).

Seriously though, be carefull

Click to expand...

I have done the manual running of all new wiring of an old
house , rang electrician and asked could I connect to the switches, lights etc, he said NO (geez those rolls cost a furtune!!)

I have seen video of Arduino turning on a bedside lamp, wondered how to handle mains back then.. I found X10 modules are one method. You can also get RF modules that you swap in to the power board. Its all expensive in relation to my budget.
I have Xbee's , relays, jiffy boxes, picaxe 18M and 28X (lots oif other stuff from Futerlec and Littlebird) I think my hacks would be very safe but frowned upon. Maybe I'll just have coffee, never was big on breakfast

Plastic..

BTW if you use plastic note how flammable it is - I saw a situation where some magnesium chloride de-icer dripped off a tire [from street slush] into a recepticle on the floor with a plastic box and flames came shooting out setting the plastic on fire - it was a ground fault interrupter recepticle too... a safety device which was flammable! I have yet to see toast flaming - I'm just not trying hard enough I guess... just a lot of smoke and noise from the smoke alarm...

most modern toasters use electronic means to engage and disengage the handle
eg an electromagnet and a thermistor and will need mains on for the handle to hold down. however an older toaster i had would latch the handle without power and i could use a timer switch to turn it and a TV on it the morning.

maybe use a pawl ratchet system eg when the motor turns it pulls the handle down but when the handle goes up the ratchet will allow it to go up, similar to a rip cord on a chainsaw except in reverse