I have never tried working with a servo before but I have read some and watched several videos.
I understand how small hobby servos work ... it makes complete sense for something only rotating 180 deg.
But I have a project where I need the servo to rotate several revolutions ... basically a follower system.
I would have a hand wheel that ... with an encoder .. that can for the sake of arguments rotate 3 or 6 revolutions (user selectable ).
I now need a servo that would rotate 3 turns.
So I have either a 1:1 or a 1:2 ratio.
What I don't understand ...on a hobby servo, you have at one end say 20% pulse width .. and at the other end say 80%.
If you rotate several revolutions, then how could this work?
Or would it work completely differently ... more like a step motor ... just move the servo so many pulses (reading an encoder) ????
Or maybe you literally build a servo using the Arduino as the controller. Feed the motor based on a separate feedback (encoder) that will only go around once (gear it 3:1 on the servo shaft) ????
I know it can be done ... have seen it done twice with industrial equipment.
Is there a good tutorial out there I can read or watch that might explain how to do this ?
I hope I explained what I want to do ...
I can think of two examples ...
on a milling machine .. you turn a small hand wheel and the table moves. The hand wheel is calibrated with the servo (and lead screw) so that one turn is equal to .100"
a wheelchair van I saw .... a small hand wheel was located on a stand with an encoder on it. There was a servo motor hooked to the steering wheel shaft. When you turned the small wheel, the servo moved at a 2:1 ration. 6 turns on the hand wheel turned the steering wheel 3 revolutions. Just as an FYI, the owner only had one complaint .. . every time he wanted to drive, he had to turn the wheel all the way left till it hit a stop ..... then all the way right ... then put the hand wheel the point he wanted to call center (he had a spinner on it) and hit a button to say it was center. He did this every time he go into the van.
Anyway, there are two examples of how this could be used.
Thanks so much .... Mike
What do you want to rotate? How much torque (twisting force) does it take? How fast do you want it to rotate?
Look for sail winch servos. Controlled like hobby servos but geared to rotate for up to 4-6 full circles.
Also, look to 3 phase AC servos that can spin and spin and spin and have several flavors; such as servos that can drive radar or keep a CWIS on track to its target.
What do you think keeps this level and aimed on all 3 planes:
You mentioned CNC so also consider a STEPPER motor as these tend to be the most common motor used in CNC machines. Often controlled by an encoder wheel of some description.
Steppers come in two varieties being either open loop with no feedback.
Closed loop with feedback so you can ensure absolute positioning.
Additional information here stepper vs servo
Another facet of servo vs. stepper is what is the minimum increment of rotation you need. A stepper can give you perhaps 0.01 degree or 0.001 degree movement on a consistent basis. An industrial servo and controller can give you repeatability movement of 0.00001 or less movement. And then there is the question of speed of movement from one position to the next. Servo can run much faster.
Sorry, thought I had responded but I don't see my post ...hmmmm.. maybe I should learn to use the from before I and arduino
Thanks so very much for the information!!!!!!!!!
Now I have a lot more homework to do.
I am a machinist by trade (served my apprenticeship in the 80's) and also build industrial control panels (many with PLS's and HMI touch panels ... just never used servos or step motors).
I have at least three projects to look at in the near future ...
First, I have an old CNC full size milling machine in storage. I got it cheap as the controller was dead and obsolete (no parts). I know it has servos on it). I need to think about a controller for it.
Second, I have a couple of old lathes. Problem, inch thread cutting only. I want a follower system ... as the chuck turns, a servo (or step motor) turns the lead screw a certain amount. This would make it possible to cut any thread imaginable ... metric, inch or ???
Third, do need to think about a wheelchair van (well I would like to try a golf cart or something first). I need to get a small remotely mounted wheel to turn the steering shaft ... and similarly a lever to move the gas, brakes and gear selector. This is a large and long term project.
Just FYI ... I just finished an elevator. It would have cost $40 K to purchase one. Used the mast off an old forklift ... total project cost $2K
Thanks so much .... Mike
Steppers for the machines and servos for the cart.
I say this from having a CNC machine building background (hence the nickname)
There are a LOT of retrofit kits out there for specific machines where the correct motors are or can be included. so knowing the machine makes and models would allow us to help with that aspect.
There are also a lot where just the control system / hmi itself is available, allowing you to use that as an upgrade path.
For the already CNC machine you would want to look at the many many kits available to you.
If the lathe is NON CNC then a kit WITH the motors would give you a simple method.
You could start with the HMI
The steppers with integral feedback
Certainly pick ONE project at a time so as not to become too confused.
Additional retrofits 01
Additional retrofits 02
Or google the make of your machine and add retrofit to the end of the search eg bridgeport retrofit.
Thanks so very much for all the information !!!
Way back in the 80’s when I served my apprentiship, all the machines I used were manual.
The last job I had was with Westinghouse Nuclear … a lot of CNC machines even in the repair shop.
I now have a couple manual Bridgeport mills, a few manual lathes, … everything is older and thus imperial. I only have one “baby” lathe (an old 6 x 18 Atlas … really more of a toy) that will cut metric threads. It is amazing how many times I have had to use it rather than say my 12 x 48 Cincinnati.
The CNC I picked up was a Fryer MB-14
The electronics had been updated a few times till they could not get spares … then I bought it for scrap price.
Still seems in great shape.
The shop probably won’t be finished till spring … so everything is in storage till them.
I plan on using the winter to “play” with arduinos and catch up on a few smaller projects I can do in the basement.
Thanks so very much !!!
BTW there are some nice cheap cheap VFD's out there that will combine with the CNC rigs to give you full range spindle speeds.
On lathes and mills that means you can face using auto CSS.
I was actually looking at the VFD / coverters.
All my machines are 3 phase but I have single phase power.
I had a bit of everything in the old shop ... rotary converters and VFD's (de-rated and with the phase loss disabled).
When the price was high, I even used one large VFD into a panel and shared it between machines.
The VFD's have become so cheap, I am thinking of putting them on every machine.
I am 58 and this will be my "retirement" shop ... well don't think I will ever get to retire. My wife was paralyzed from the shoulders down in a diving accident when she was 12. We have been together for 12 years now. I just got finished building an accessible house (took me 7 years as I did a lot of the work myself and still worked at the same time out of the unfinished part of the house). I work out of the house so I can take care of her and earn a living. We live in a rural area (well all of VT is rural .. 42,000 our largest city). I have farmers all around me and they are always breaking something. I have been come a repair shop. Without a "real" shop (all the equipment is in a tractor trailer beside the house here), I have been doing just small jobs and on site work. I can't wait to get the new shop up.
Thanks again so very much for all the information !!!!!!!