#robotics Logs

Nov 05 2015

07:19 averowsky Im planning to buy new motors and I need to decide between stepper and dc motors
07:19 averowsky dc motors with encoders
07:19 averowsky someone has experience which way is better to go ?
07:56 Snert are you prepared to pay a little less than $200.00 per encoder, plus the cost of the motor?
08:01 averowsky Snert: I seen motors for 15$ and pair of encoders for 8$
08:02 Snert I haven't found anything suitable for my purposes in that price range.
08:03 Snert to each their own.
08:04 averowsky Im talking about pololu micro motors
08:04 averowsky but I heard there are some problems with them so Im not totally conviced to buy it
08:04 Snert yea, one of those gear motors might work for the wrist in my arm.
08:05 Snert if it can have an aencoder fitted to it.
08:05 averowsky There are are encoders for them
08:05 Snert but the other motors in the arm are gonna cost alot more.
08:06 averowsky but I still down know which motors to choose, stepper or dc. There will be a lot of forward and bacward movements, position corrections. Im aware they will not handle for long
08:06 averowsky Snert: What your arm will do mainly ?
08:09 Snert Pick up a beer, hod a camera . point a range finder. Not much at first. Maybe not much ever.
08:09 Snert I cant really think of anything actually useful for it to do.
08:10 averowsky what motors do you use ?
08:10 Snert standing guard, but then nobody is gonna breal into my room, most likely.
08:10 Snert I don't have any motors for the project yet.
08:11 Snert I have several stepper motors and I'll leearn how to work with them.
08:11 averowsky acha.. good luck man
08:11 Snert I'll be working with encoders first mainly.
08:12 Snert it's the hardest and most expensive part of it all.
08:13 Snert absolute position gray code encoders are not cheap.
08:16 averowsky Snert: I was thinking about that https://www.pololu.com/product/2590
08:21 Snert http://blog.pepperl-fuchs.us/blog/bid/209073/7-Questions-to-Ask-When-You-Need-a-Rotary-Encoder
08:22 Snert pololou stuff is okay for experimenting but it's trash.
08:24 averowsky you mean motors either ?
08:25 Snert The absolute encoder will retain your position after power loss and an incremental encoder will not. The incremental encoder usually needs to perform a “homing” sequence after a power loss.
08:25 Snert and my arm will not be doing a homing sequence after a power loss.
08:26 Snert it will not spill the beer it may have in the gripper after a power loss.
08:27 Snert so that alone makes anything pololou out the window - I have not seen absolute encoder motors on pololou.
08:28 averowsky Yep, I think I could live with not absolute encoders
08:28 Snert have fun.
08:30 Snert I go straight for the heroin.
08:40 averowsky for sure I will have fun
08:40 averowsky I do this only to have fun
09:08 rue_house Snert, absolute encoders dont store the position
09:08 rue_house they can always read just what the position is,
09:08 rue_house an example of an absolute encoder is a potentiometer
09:09 Snert yea I know.
09:09 rue_house digital absolute encoders of high resolution are EXPENSIVE
09:09 Snert it's finding a decent one under 200.00
09:09 rue_house WHAT DO YOU CALL DESCENT
09:09 rue_house er
09:10 Snert it's possible but it has to wait is all
09:10 rue_house your making a robot arm?
09:10 rue_house have you heard of resolvers?
09:10 rue_house more complex but a bit cheaper
09:11 rue_house and abolute positioning is only good over 1 rotation
09:12 Snert no, it's like 5 or 7bit gray code.
09:12 rue_house have you heard of resolvers?
09:13 rue_house are you a last-line-only reader?
09:13 Snert yea heard of those.
09:13 rue_house and?
09:14 Snert not finding them within reach - spensive
09:14 Snert http://www.avagotech.com/products/motion-control-encoders/absolute-encoders/single-turn-encoders/aeat-9000-1gsh1
09:14 Snert that is 150.00 on digikey I think.
09:15 Snert they have multiturn too.
09:15 rue_house you realize with 7 bits you get only 128 points per turn?
09:15 rue_house even a resolution of 256 over 90 degrees will suck
09:16 rue_house what do you know about stepper based robots?
09:16 rue_house I assume your arm is stepper based
09:16 Snert nothing yet :)
09:17 Snert the main elbow will be a screwjack.
09:17 Snert that may be the only stepper.
09:18 Snert I found a nema 17 stepper with encoder on ebay for 25.00 - it'll be fun :)
09:19 Snert not sure if it's quadrature or gray prolly quad
09:20 rue_house when you start up a stepper based arm, it goes to a 'home' position
09:20 rue_house thats where all the axies are 0
09:20 Snert mine will be absolute.
09:21 Snert it will not do that.
09:21 rue_house ok, just saying, thats how its done on commercial machines
09:21 rue_house so your using dc servos?
09:22 Snert big deal... 3 or 4 major joints that need expensive encoders.
09:22 rue_house are you going to use dc servos?
09:22 Snert just means I save a little while longer :)
09:22 rue_house are you going to use dc servos?
09:22 Snert prolly not.
09:22 rue_house so, your not using steppers and not using dc servos
09:23 rue_house whats going to move it?
09:23 Snert i can see 1 stepper in the base.
09:23 rue_house hydraulic? pneumatic?
09:23 rue_house ah, its stepper motors then
09:23 Snert maybe 2 total.
09:23 rue_house everything is moved by steppers?
09:23 rue_house ok, whats moving the rest?
09:24 Snert I'm looking it over according to size and stuff.
09:24 Snert there are some fantastic gear motors out there.
09:24 rue_house ok how many axies are there?
09:24 Snert sun and planetary stuff.
09:24 rue_house 7?
09:25 rue_house http://ruemohr.org/~ircjunk/robots/arm8/p1060649.jpg
09:25 rue_house those are 6
09:25 Snert that seems like a safe number.
09:26 rue_house ok, so you have a stepper at the base and a stepper on the elbow
09:26 rue_house that leaves the lower segment, the forearm roll, the wrist pitch, wrist roll and gripper
09:28 rue_house https://www.youtube.com/watch?v=3N7DNfg4p9I
09:28 Snert yep those are quite nice alright - inspiration :)
09:31 rue_house check out images for arm5/6/7/9
09:36 Snert I'm thinking extensible forearm with a linear actuator maybe 4-6 inches. 360 degree wrist.
09:40 Snert about as big as yours but maybe slightly bigger to accomodate whatever motors.
13:04 SpeedEvil http://imgur.com/gallery/dI8xnCj the future of domestic appliances
15:27 rue_house haha that s batter one!
20:44 norias http://robohub.org/blue-belt-technologies-acquired-by-smith-nephew-for-275m/
20:47 rue_house so start a company, market (but you dont have to build) the greatest things ever and sell for millions
20:50 norias uhm what?
21:12 SpeedEvil rue_house: doing too much
21:14 rue_house too much what
21:15 eedEvil fa
21:16 SpeedEvil I was here going to link a relevant xkcd where it was pitching an idea to investors, where the investors diddn't quite notice that the being described pitch diddn't actually involve you at all and was merely describing existing things.
21:17 rue_house :)
21:27 norias hah
21:27 norias fingerCAM
21:27 norias just saw that in a post about CAM software