What is the best way to control 2 stepper motors and 1 linear actuator?

Thread Starter

ElectEng

Joined Sep 3, 2019
42
I am making a project that will utilize 2 stepper motors and 1 linear actuator. The overall project will consist of 2 steppers rotating a solar panel, zenith and azimuth angles, and a linear actuator to raise the panel and steppers so the panel is roughly 6 + feet high. The overall power will come from a 12V 70 ah solar battery.

What is the best way to control all 3?

I planned to use Arduino Motor Shield Rev3 ( https://store.arduino.cc/usa/arduino-motor-shield-rev3 ) to control the 2 steppers. I do not have the overall details such as voltages or current.

I think some of the linear actuators come with a control board but I do not know much on this subject.
 

BobTPH

Joined Jun 5, 2013
2,047
You do realize that, for the cost of the positioning mechanism, you could add enough solar panels to get more power from a fixed orientation, right?

Bob
 

Thread Starter

ElectEng

Joined Sep 3, 2019
42
You do realize that, for the cost of the positioning mechanism, you could add enough solar panels to get more power from a fixed orientation, right?

Bob
I can't. My project is restricted to a dual-axis solar tracker. I am working alongside 3 other engineers. We have to design the project so each member gets a part.
 

Thread Starter

ElectEng

Joined Sep 3, 2019
42
Is this homework?

Bob
Close. It is a school design project where multiple Engineers must come together to build a project. I am the electrical engineer of the project but will be assisting in multiple areas. The only requirement of the project is to track the Sun using dual axis and store that energy in a battery.
 

ag-123

Joined Apr 28, 2017
40
this thread seem more appropriate if opened in the power electronics sub-forum.
L298 is a bipolar dual h-bridge and if you review the specs the normal (continuous) currents is apparently 2 amps
https://www.st.com/en/motor-drivers/l298.html
the Vce (sat) at 2 amp loads is given as 2v (source) and 1.7v (sink) so the chip alone will dissipate 4 watts when running at the full 2 amps loads. i.e. it will run hot, so a heatsink is probably needed.
the other thing being that given the size of the panel you suggest, it sounds it is going to be pretty heavy
it could probably take rather large torque to even move the panel. so you may need things like some gear boxes having large gear ratios to get sufficient leverage if a rather small motor is used. and if a large motor is used, it may exceed the currents and power the L298 can handle
 

Thread Starter

ElectEng

Joined Sep 3, 2019
42
this thread seem more appropriate if opened in the power electronics sub-forum.
L298 is a bipolar dual h-bridge and if you review the specs the normal (continuous) currents is apparently 2 amps
https://www.st.com/en/motor-drivers/l298.html
the Vce (sat) at 2 amp loads is given as 2v (source) and 1.7v (sink) so the chip alone will dissipate 4 watts when running at the full 2 amps loads. i.e. it will run hot, so a heatsink is probably needed.
the other thing being that given the size of the panel you suggest, it sounds it is going to be pretty heavy
it could probably take rather large torque to even move the panel. so you may need things like some gear boxes having large gear ratios to get sufficient leverage if a rather small motor is used. and if a large motor is used, it may exceed the currents and power the L298 can handle
Sadly we will be using a smaller panel. Roughly 20 W outputting 1.2 A or so. This panel is 16.5" by 19.8". I think the panel weighs 7.5 lbs
 

ag-123

Joined Apr 28, 2017
40
that might be sufficiently small to drive with say a moderate stepper, but it would still depend on the tilting design as assuming it is tilted at the edge and the length to the center of mass is say 19.8" / 2 ~ 9.9", it would still take a motor that has a torque better than 9.9" x 7.5 lbs

it may still be worth exploring with gear motors as the gearbox would provide significant mechanical advantage especially with large gear ratios exceeding say 1:100, it'd just take several gears daisy chained to get that. that would slow down the movements sufficiently as normally ordinary motors normally run pretty fast like in excess of 3000 rpm, dividing that by 100 reduce it to a more manageable 30 rpm, and you may be able to time the motor on and off periods so that it works much like a servo. there are quite a number of vendors selling low cost gear motor on ebay, etc

an issue is that unlike stepper motors, ordinary motors normally don't provide a position feedback and can't hold on to the position. Stepper motors unfortunately consume currents/ power even to just hold on to a position. it may be an issue if you realize that the stepper would be drawing down the battery just holding a particular position as it is on all the time.

alternatively getting a decent servo motor may just solve it, as i think the various servos has that gear motor built in and in addition it provides you with position feedback so tilting and positioning is easy with all that. the servo motor will also need to be powered on all the time if you are holding the position and your positioning algorithm would need to keep it at the position. the only advantage here is the built in gear motor would provide mechanical advantage so that perhaps only a small amount of power is needed

try to have the tilting design such that the panel is supported and tilted at the center of mass, so that it balance itself off pretty much and that only a small power is needed to tilt the panel and maintain the position
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
19,186
Stepper motors can also be switched off when in position and they do posses a certain amount of holding torque.
If a DC motor is used a simple L,S, can be used to position, some Linear actuators come with built in motors and L.S.'s.
Alternatively if a high ratio G.B. is used, over run at switch off may not be a problem.
Also a much lower current motor can be used with DC motor reduction.
Stepper motors require the stated plate voltage and current when operating, DC motors, the current varies with RPM and load, mainly the latter.
Max..
 
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