Author Topic: robotic winch help?  (Read 1950 times)

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Offline algar32Topic starter

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robotic winch help?
« on: September 30, 2011, 05:23:51 PM »
I am trying to make a winch that can pull about 1 to 3 pounds about 6 feet of vertical distance as quickly as possible. I have found a winch for a servo and a servo that I was thinking about using.
I have no idea whether the servo can pull 1 to 3 pounds. Do you think it can pull one to three pounds? Nor do I know long it will take it to pull the 1 to 3 pounds 6 feet.  How quickly do you think it can pull 1 to 3 pounds? How long will it take it to pull it about 6 feet? Can the winch I selected even hold 6 feet of rope?

Please help. Thanks.

 winch http://www.vexrobotics.com/276-1546.html
servo http://www.dealextreme.com/p/hitec-hs-7985mg-high-torque-digital-servo-with-gears-and-parts-12-4kg-torque-20102

Offline Soeren

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Re: robotic winch help?
« Reply #1 on: September 30, 2011, 10:36:37 PM »
Hi,

I am trying to make a winch that can pull about 1 to 3 pounds about 6 feet of vertical distance as quickly as possible. I have found a winch for a servo and a servo that I was thinking about using.
I have no idea whether the servo can pull 1 to 3 pounds. Do you think it can pull one to three pounds?

If the specs are as stated, the servo can pull up to 3lb with an 18cm pulley mounted in place of the servo horn. This will be the fastest way of doing it.


Nor do I know long it will take it to pull the 1 to 3 pounds 6 feet.  How quickly do you think it can pull 1 to 3 pounds? How long will it take it to pull it about 6 feet?

A shade more than 2.5 seconds (again if specs are for real).


Can the winch I selected even hold 6 feet of rope?

There's no reason to buy the winch kit at all, just make or buy a pulley that can be mounted on the servo.
How much "rope" a given pulley can hold depends on the diameter of said "rope", but for 3lb, a heavy polyester sewing thread will do. If spun thread makes the load spin too much, get some braided thread instead. For max strength vs diameter, us either carbon fiber thread or an aramide like Kevlar.


You are aware that you'll have to disassemble the servo and modify it to make it continuously rotating, as well as to provide a servo signal for running it?


You sure chose some expensive parts. Vex parts are expensive which doesn't surprise, but close to $80 for a servo from a Chinese site is ridiculous, especially when you factor in their usually very overrated specs and their up to several month delivery times and it's probbly a clone rather than a genuine Hitec part.

This servo is around twice the strength, which means you could double the diameter of the pulley and get down to around 1.25s for the 6' lift - and it's $11 cheaper.
This one will need to be modified as well.

Any particular reason not to use a gearhead motor (which will be stronger/faster) rather than a servo?


A better way to solve whatever it is you're trying to do, is to specify what you need (In empirical terms rather than approximations and subjective values), i.e. max 3lb (if that's the max) in n.nn seconds.
When the numbers are in place, you pick the servo (or whatever you need) that does this for the least amount of money.

Since you don't reveal the purpose, your options for powering it, or whatever's gonna drive it, I cannot say if this is the best solution.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline algar32Topic starter

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Re: robotic winch help?
« Reply #2 on: October 01, 2011, 06:02:17 AM »
I am trying to pull a small skateboard/ mini longboard.  thanks for your help. 

Yah I thought i was going to have to continuous mod the servo, but wasnt sure. Thanks for that.

Offline algar32Topic starter

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Re: robotic winch help?
« Reply #3 on: October 01, 2011, 11:14:39 AM »
I plan on using the servo you suggested. But no winch? You say a pulley would be bettter. But I want to be able to lock in place once it is up 6 ft in the air. And then be able to unlock it and just have it drop to the ground via gravity. What would be the best way to do this?

Thanks for your help.

Offline Soeren

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Re: robotic winch help?
« Reply #4 on: October 01, 2011, 11:46:00 AM »
Hi,

I plan on using the servo you suggested. But no winch? You say a pulley would be bettter.
The pulley plus servo is in itself a winch (if made for it ;D)


But I want to be able to lock in place once it is up 6 ft in the air. And then be able to unlock it and just have it drop to the ground via gravity. What would be the best way to do this?
OK, skateboard going up out of the way, locked in place and later dumped to the ground?
Sounds dangerous to misplaced toes ;)

I'd use a regular DC motor for a project like this, as it will have much more power in the same "packet size" and will be easier to control with fairly simple electronics.

With a metal worm drive, you can get the gearing in one go and it is self locking, so when the motor stops, the skateboard is locked in place. Reverse motor direction to lower it.
A limit switch to stop it at the right height can either be mechanical or using a slotted optocoupler.


How do you plan on controlling the up/down (start/stop) motion?
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline algar32Topic starter

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Re: robotic winch help?
« Reply #5 on: October 01, 2011, 12:25:52 PM »
Well my plan is to have a back pack with a pulley and the motor attached. It will have about 5 to 6 feet of rope with the longboard attached on the other end. When I am done skating I will simply press a button and the board will be pulled onto my back. The board will have a dropforward (dropbackward i guess)  so that the rope is a weigh from your feet when skating and so that when it is being pulled up it doesnt hit the back of your leg much. I understand that this defeats any chance of ever doing tricks... but I dont do tricks I use my board to commute. Once I am done commuting I get tired of carrying it around and I thought it would like to be able to suck it right onto my back. Once it is locked in place I would like to be able to unlock it so that I can just pull it off and start skating without much resistance from the pulley.

As far as how I am going to make it work. Like I said I would like to have a button or switch on the front strap of my backpack so that I can just pull it up. I would imagine I could program it to pull until there is no more rope to pull or I could just press the button until it is all the way up on my back. I have yet to figure out what would be the best way to do this.

The DC motor sounds good... but I dont even no where to start on picking one out... I want it to be fast and if it could maybe 5 pounds that would be great.

Sorry for the rambling ^^^

I am trying to explain this as best I can :)

Offline algar32Topic starter

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Re: robotic winch help?
« Reply #6 on: October 02, 2011, 06:28:20 PM »
Do you think I could find a DC motor that meets these requirements in the dump or scrap it from something else? If not what price range am i looking at and what specs would it need?

Thanks.

Offline Soeren

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Re: robotic winch help?
« Reply #7 on: October 11, 2011, 07:03:08 PM »
Hi,

Sorry for the delayed answer - I kinda forgot about it as I tried to figure exactly how dangerous I thought it sounded :)

And my conclusion is that I think you have to find another way to hurt yourself ;) as this sounds too downright stupid (no offense meant), as so many things can go wrong with a "rope" connecting you to the board and I really would hate to see you get a Darwin award :)

The idea of hauling it up on your back fast sounds like it could result in a lot of *ouch* as well and my best advice is to make a simple sling out of webbing with some Velcro or snaps to quickly close one loop around the board, with a larger loop to carry either diagonally over one shoulder, or if you like, in a sort of backpack harness.

Stop, kick the board up into your hand and wrap the webbing around it with the free hand - not as high tech, but probably as speedy and a whole lot safer ;D
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline algar32Topic starter

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Re: robotic winch help?
« Reply #8 on: August 12, 2012, 06:32:45 PM »
No offence taken. I've had stupider ideas I assure you :). I fall off my board all the time, so if I had a few spills playing around with this setup I wouldn't mind.  I only cruise around campus, so falling there would be difficult (even for me) to get hurt. The idea isn't so much practical, but it's something I've wanted to do just to see it in action :). If you guys have any other suggestions for what motor you would suggest please post them :).

Also, this is a really late reply. I just lost this tab a while ago and a buddy and I were skating today and I remembered it.

 


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