First Electrical Project.. Help?! - Just an idea at the moment

Right, so im interested in electronics and im not a dim-wit so hopefully this will end well, rather than with my hair on end and steam coming from my ears! I have a background in PHP so i have a logical mind, its just applying it to the real world which IMHO is considerably harder than programming as the laws of physics dont matter there!

Here's the plan... To make a robotic hand that responds to my grip. I know it sounds complex as a first project but hear me out... A push button switch (PBS) on each finger tip, or possibly underside of each finger. Essentially this is mounted on a glove that also contains a battery pack of one or two 1.5v batteries. The robotic hand is like the mythbusters one, some bike chain threaded with elastic to make it curl up/grip when resting, and motors which pull on strings like tendons that then make the fingers go straight. Its not perfectly set in stone yet but thats the idea.

So, on the glove the switch on say, the index finger, will complete a circuit which sends electricity from the battery pack over a longish (1m or 2m) wire to the motor on the robotic hand which pulls the index finger string, hence making the finger stretch out and ungrip....

i might reverse this (have the elastic make the finger stretch out and motor grip) but, thats not the issue... The problem is i cant have my motors spinning at 5000rpm!!!!!! I need about 60-100rpm really. Ive found a device on an electronics site (maplins, big retailer here in the UK) that promises to do just that, it can take 1.5-3v input and tone a motor down to just 60RPM, perfectimo!! However, i was wondering how this works and if its possible to make one myself?

I dont suppose it is as simple as a variable resistor only letting through a fraction of the power to the motor, as i expect this would just make the motor spin very lowly but very weakly, which isnt ideal! i need a reasonable amount of torque, nothing amazing but it needs to be able to counteract an elastic band basically. I also need all this to be as small as possible. I dont really have need for a PCB, its just two wires per finger on each of the robotic hand and glove, so really only about 20 wires, two batteries, 5 motors and 5 switches. simples... Its just this RPM issue really, once i can overcome that then i think i can do this... I only thought of it today tho, so its very rough but it has scope....

If i can in the future make an accelerometer bracelet i can make it swivel on a base with the help of a simple arduino board, maybe even have a spooky twitch effect when the glove isnt being used I think a full scale arm is a long way off but in theory it just needs a switch to be activated when i stretch my arm (perhaps activated by a string run along my elbow that pulls a switch when i extend) and another switch to be activated when i contract my arm and a few motors... But anyway, can anyone help?!

 

 

 

Comment/Reply (w/o sign-up)

So this is what you're trying to do? Explain more is I understood wrong.
[attachment=1809:roboarm.png]
You could also use hydraulic. In fact, I recommend hydraulic pumps and stuff over the motor movement thingy you've chosen. Instead I would use the motor for the fingers, hydraulic for wrists and other major movements.
You could make yourself a kind of a switch which reverses the poles and then you've got motion to the opposite direction. If you want movement and power only in one direction, then use springs to "open the arm". But the motor will be screaming if you have strong springs, so make sure they are just enough to open the hand.
Describe more.

Comment/Reply (w/o sign-up)

good idea you have there. There have been many orthopedic doctors that have been working on this subject for years now. AKA Bionics. I have a friend that has a arm like that, Works from a charge sent from her brain to the stub in her shoulder. She is still in the learning stages with this, but can move the fingers a little.

 

 

 

Comment/Reply (w/o sign-up)

As for the rpm problem, here's the solution. You can also use wheels with teeth and then use chains with them. But make sure the teeth are the same size in both wheels!
[attachment=1810:roboarmthingy.png]
With this solution you'll also get more force, so moving the whole arm and going against springs should not be a problem (unless your arm is gonna weight a LOT).
Have fun!
As for triggering movement, you can't do this mechanically without just using buttons and mechanical switches. If you want to wear some kind of glove and by moving that, the arm would move, you gotta enter the programming section. I think those things are made using visual basic...

Comment/Reply (w/o sign-up)

for now i only want the fingers to move! If nobody saw the mythbusters episode youtube: mythbusters ninja robotic hand

That should show you a nice hand mad of bike chains, shoe laces and elastic, heres a little circuit diagram ive mocked up for one circuit for one finger. In the real deal i would have the wire from the battery split into 5 on both sides to provide power to all 5 motors, i think with 2 1.5v batteries i should be ok... but we will see, anyhoo:

[attachment=1812:robot.jpg]

so basically the cell provides power through the circuit (i think the switch should be on the positive side, but meh, it'd work!) which is broken by the switch. My current idea is either a PBS on the inside of my finger knuckle that is depressed when i make a fist, or two strips of metal on the top side of my finger that make contact when my finger is straight (for that option id reverse it so the motor pulls the finger straight, the spring pulls the finger into a fist) Anyway.... The little diagram in the top right shows the motor and string system. This is for the "Motor makes it straight, spring pulls it into a fist" option.. so by default the finger is clenched into a fist (imagine all 5 digits, fingers and thumb) by the spring/elastic. Then, wearing my glove i extend my fingers which makes the metal contacts engage (imagine two lollipop sticks glued to the top side of your finger, one on the first section and the second after the knuckle, so that when bent they are apart, but when the finger is straight the second stick is lowered onto the first, making a contact) so the motor spins, pulling the string tight and the robot finger straightens.

I realized that this only gives me on/off controls, so the glove wont actually follow the motion of my fingers, but using my fingers i can control how far/if the fingers are extended or not (by activating the switch for a split second allowing the motor to pull the finger half stretched etc..) but anyway.... the problem i have is that at 3000rpm the motor will burn out, the string will snap or at the very best it will be far too fast to be realistic, so i need to gear it down. i could like baniboy said use gears/belts but i need 5 of these motors/gearboxes mounted on the back of a hand sized prop (but i guess i culd make a gigantic hand....) so size is an issue. i actually dont have a soldering iron or anything at the moment, i lost my cheapo one ages ago! so its still an idea at the moment.... A rapidly complex one at that!

So will a variable resistor slow the motor down or will it just make it incredibly weak?

Comment/Reply (w/o sign-up)