Hi guys,
I have a question related to making a robot arm.
If I use pan/tilt brackets. The servo will be very weak if I make a 30-40 cm arm
I was looking at this guy. He is using gears to get more power for the arm
My project is light years from this. But are there readymade components to buy? Like geared pan/tilt brackets or something?
/Johan
Hi CrossRoads,
Thanks for your response.
Not quite what is was looking for. Something that will easily work as shoulder and elbow joints and a bit more price efficient:-)
/Johan
What kind of stuff can you make? There are plenty of bearings belts sprockets and gears available, but its
the mounting for them that is usually the tricky part to design and make.
What kind of loads do you want to handle? To what precision? At what speeds? Those are the
first things to get a grip on, because that determines what's a plausible approach.
There are other places to look. HobbyKing, even Sparkfun is selling robot parts now. There are dedicated robot shops too.
Hi guys,
True, I was not very specific. I want to get an idea of what is available then base the design on that. But I would say low precision, slow speeds and a couple of kg load.
I have done some digging around and have really found anything good. I must say I am a bit surprised.
As you point out there is always the options to design and build something.
Maybe even regular pan/tilt brackets would work if I do a light weight design and use some strong servos
/Johan
A couple kg is going to be tough. I don't think hobby servos will be able to lift a couple kg without significant modification to the servo mechanism.
You might want to check out gyrojeremy's robot arm. He posted a couple links to videos here. It looks like he was able to reduce the weight on the arm a bit by using rods to transfer motion from the servos to the joints. I thought he did a good job.
As you can see from gyrojeremy's thread, powering a lot of servos can be a challenge.
I'm personally not a fan of servo controllers (not that they've been suggested). I give some of my reasons for my aversion to external servo controllers in this reply.
I thought that inmoov article was very interesting. I like the technique of moving the pot from the servo to the joint. Though I'd much rather see some sort of encoder used at the joints. Pots wear out. I have to regularly replace servos on my hexapods. I think the main point of failure is the servos' pots. I'm using pretty inexpensive servos so the pots might not be very high quality but the experience has got me looking for a way to replace the pots if I can.
and a couple of kg load.
You might make your motors using windshield wiper motors. Check youtube.
Those would draw some hefty current I imagine, by the amount of snow they can push off a windshield.
And here i was hoping for easy 
I will check out the windshield wiper engine ide. Thanks guys!
/Johan
Moving a few kg takes either high current or big reduction ratio gears and a longer time.
You have to start putting some numbers down for a start, get a rough idea of torque speed
and power.
And here i was hoping for easy
If it was easy, you would see lots of similar arms others would have already built.
This sort of thing seems to be the best eBay can do for reasonable torque gearmotor, 0.86Nm isn't
half bad really, and only 50mA at 24V (allegedly).
http://www.ebay.co.uk/itm/24V-DC-Gear-Motor-Variable-High-Torque-Gear-Box-Electric-Reduction-Motor-30-RPM-/272104639114?hash=item3f5ab34a8a:g:nS4AAOSwNphWZ65a
isn't there anyway to just use stepper motors and say some l298n drivers I think that's the driver and nema 17 stepper motors would be plenty of power and you can get the motor and the drivers form ebay for inexpensive thats what I was going to ask about using as I am building a bot arm and head and torso and was looking at how to use this setup with a arduino sorry not trying to hijack your tread just looking for the same thing
NEMA17 steppers have a pull-out torque of upto about 0.5Nm, and thus a usable torque a lot less than that
(pull-out torque is not the same as running torque). Not enough to wave a few kg about at any distance.
For a robot arm you may well need microsteps (1.8 degrees is a lot when waving an arm about), then the L298
wouldn't do, you'd need a microstepping chopper driver.
But then you'd get away without an encoder or position sensing pot...
As I say start with the figures, calculate the required torque and power and then pick a motor, unless you
are happy to shorten the arm when you find it doesn't work, or downgrade your load capability.
There are continuous rotation servos, though I have not worked with them, and also it's my understanding that others can be modded to be continuously rotating. If the requirements are for weight and not for speed, what about a pulley reduction system? This seems to me like a simple, able to be made with household materials solution. If you need more inspiration, I'd look into the types of rigging sailing ships would use to turn, operate the sails, etc. Also, you'd need some low-stretch cord preferably.
You mean toothed belt and sprocket? Difficult to get more than 5:1 reduction ratio, typically
you want 50:1 to 200:1 reduction for this sort of thing.