I have board that needs to rotate 360 degrees and bounce back with acceleration and deceleration.
See attached (step.jpg and S3-timewarp).
The Board weights about 3 pounds and is 4'x3' and is pretty well balanced.
On the bench with no load the application works great, but it can't handle the torque needed.
Motor is a Nema17 with 59Ncm (84oz.in) rated 2a per coil running at half step with 8825 set to 1.4a for 2 coils. It gets feed 20v power.
Its missing steps big time.
Before I go out and buy a bigger stepper motor, power supply and driver I am wondering if mechanically I am going about this wrong. I do need it stop and rotate somewhat precisely. In other words, it can't really miss steps or it will eventually get misaligned.
Here are my thoughts:
Smaller steps with slower speed ( will try that tomorrow but don't have much faith)
different motor (not stepper). Like a dc with gearing. But I need to know position so I can rotate when it gets back to the top so I think I still need to stick Stepper Motor. If push came to shove I go just go with a timed rotation and not worry about having to rotate back when it reaches the top.
adding a GT2 Timing Drive Pulley 40Teeth Tooth with a belt and perhaps get better leverage.
Ideas?
Second question:
I have another project that requires rotating a lightweight but large tower (10') that spins slowly on a 3' turntable.
(see attached s3-airstairs)
It doesn't need any accuracy. Just spins at a slow RPM occasionally moving faster then slowing down.
This looks like a good DC geared solution but I have no experience with that (just starting my research).
Does someone have links to a good suppliers along with what is needed to drive a non-stepper geared dc motor.
Finally
What is less expensive all things considered, DC geared motors and driver or Stepper & driver?
Again just starting my research but I could easily be comparing apples to oranges since I don't have any side by side experience.
I can't figure from the pictures how your machine is intended to work. It looks like you are trying to tilt a disc about its diameter rather than trying to rotate it like a wheel. Maybe you can draw a diagram and post a photo of it.
If you don't need speed than reduction gearing will give a reduction in the torque load on the motor. But I have no idea how to figure out what is actually needed.
Maybe getting a more powerful stepper driver so you could use the full 2 amps that the motor is capable of would be sufficient. Or maybe you need that plus a reduction gear. Or maybe the reduction gear will be sufficient with the driver you are presently using.
For a large object the MoI (moment of inertia) will dominate, so that's something to calculate, at least
roughly. MoI goes up with mass and with the square of dimension (off-axis distance), so it grows fast
for large items.
Torque = MoI x angular acceleration
(units being Nm, kgm^2, rad/s/s)
I don't know MoI. I have three different applications so I purchased a mix of motors.
I dropped the steps down to 16 and it helped, but still need more torque.
Talked to Pololu about geared DC and while it would be about half the cost, it's brushed and I loose design flexibility.
Geared Steppers can be used anywhere since nothing I need currently is high rpm.
So I bought
1 x Gear Ratio 4:1 Planetary Gearbox Nema 23 Geared Stepper Motor
23HS22-2804S-PG4 (US218) = $ 58.50
.424 degree for a little higher speed (compared to std 1.8deg)
1 x Bipolar Stepper Motor Driver Max 4A Current 40VDC Input 16 Subdivision
ST-6600 (US051) = $ 21.00
1 x Gear Ratio 14:1 Planetary Gearbox High Torque Nema 17 Stepper
17HS19-1684S-PG14 (US213) = $ 33.00
.131 degree
With the 3x difference in step degrees between the two I can get a feel of RPM.
My application is a little different. I run LED light scenes with FastLED. It can take a lot time if you have a long led string and it affects the motor speed. I had to make some minor code changes to call the LED .show function only when there is a change in LED scenes (40ms regardless of mcu processor).
