I found a Chinese "DC Dual Axis Pan Tilt Solar Tracking and Monitoring Robot, Heavy Load High Torque All Metal X Axis Y Axis Worm Gear Motor".
The details are given below but I am having difficulty understanding them (assume no knowledge on my part).
The description says that the motors are "ultra low speed". I asked what speed and was told 1RPM and that for 96 revs of the motor the worm would make 1 rev.
The motor voltage is listed as 5V-12V-24V and its power as 30W.
Firstly can a DC motor really run at 1RPM or is there perhaps other gearing between the motor and the worm gear?
Doesn't the speed of a DC motor depend on the supply voltage, so should there not be different RPMs quoted for the three given supply voltages?
What current would the motor draw and would this not also depend on the supply voltage e.g. would the motor draw 6A with a 5V supply and 2.5A with a 12V supply?
If I was using a 12V supply how could I vary the motor speed using an Arduino?
If I ran the motor for 14 minutes (96/4=14) could I accurately conclude that the worm had rotated by 90 degrees?
TIA
Description:
The fuselage is made of all-metal, and the bracket is made of ultra-thick aluminum alloy, with excellent stability! Ultra-low-speed worm gear motor, all-metal gear, torque 35KG, with self-locking, to achieve all-round dual-axis tracking, two horizontal limit switches, and two vertical limit switches to prevent winding wires.
Specification:
Motor name: worm gear motor
Motor voltage: 5V-12V-24V
Motor power: 30W
Horizontal rotation angle: 340°
Pan Tilt base size: 86MM
Pan Tilt Height: 420MM
Pan Tilt Mounting Panel: 40x100MM
Worm: 240MM
Horizontal load bearing: 60KG
Vertical rotation angle: 120°
Vertical load: 25KG
Bracket material: aluminum alloy + 3MM steel plate
Gearbox material: all metal gears
Product weight: 1.02KG
worm gear ratio: about 1:96
1 yes/probably
2 usually, yes; I'd suspect 3 different motor models
3 first guess, W/V = I, so...
4 PWM
5 see above. It also will depend on your definition of "accurately". Within a degree? a minute? a second?
Taking onboard the responses I would like to clarify my questions and correct my arithmetic
There is a DC Motor and a worm gearbox. It seems clear that the gearbox has a 1:96 ratio. However I am being told that the Motor has a speed of 1 RPM, that seems very slow, do you really get DC motors as slow as that? Is it possible, perhaps probable, that there is a lot of gearing contained within the "motor" module?
There is no option to select different motors so I assume they are saying the motor can have a supply voltage between 5 - 24V. So the speed would vary with the supply voltage?
The spec says the motor is 30W, but is it true to say the current will be 6A with a 5V supply and 2.5A with a 12V supply because if the speed varies with the supply voltage won't the wattage and hence the current also change? Since only a single figure is being given for power perhaps 30W is the maximum power?
It sounds like I could use PWM to vary the speed, is there an example of how this would be done with a 12V supply if the motor is using say 2.5A ?
If the motor output shaft really does turn at 1RPM and I run the motor for 24 minutes (96/4=24) will the gearbox output shaft turn by 90Degrees +/- 0.03 degrees? Is the accuracy unrealistic and if so what might be reasonable to expect?
the motor output shaft will make 24 complete rotations.
5V-12V-24V
These are definitely selectable options, regardless of what the ad suggests. The motors will have different winding resistances for each of the voltage options, but motor power (30W) will be the same.
It seems clear that the gearbox has a 1:96 ratio
Unlikely, for a 1 RPM gearmotor. The shafts of naked, brushed DC motors typically rotate at several thousand RPM when powered at the rated voltage.
The documentation on that web page is totally inadequate. But the gizmo might work for your application.
The pan/tilt must come with the option of three motors, 5V, 12V or 24V. Each will run at 30W so the respective currents will be 6A, 2.5A and 1.25A
So that leaves me with the problem of speed. The sun appears to move across the sky at 360/24hours (15degrees/hour) which is the equivalent of 0.25RPM. So I need a panning mechanism that can pan at that speed. Alternatively I might use it stop/start incrementing it by say 1/4 of a solar diameter at a time or 0.125 degrees.
The mechanism shown is cheap enough to be interesting, but expensive enough that I don't want to buy it unless I can be sure that it will do the job.
It looks to me as if the pan and tilt tables are connected directly onto the gearbox output shafts.
I was thinking that those shafts would make be running at 1/96 RPM so in 24 minutes they would make a 1/4 turn or 90degrees. You seem to be suggesting that the gearbox output shafts would make 24 complete turns.
The device is clearly intended to track the sun, probably with a small solar panel mounted. Does anybody have any thoughts how the tracking speed is supposed to be achieved?
Use PWM to control the motor speed, over a large range.
Also, you can raise or lower the voltage of the motor power supply (basically the same process). The voltage rating for a brushed DC motor is nominal maximum (not absolute maximum), so if the specification is 1 RPM at 5V, it will be 1.2 RPM at 6V and 0.4 RPM at 2V. Most 5V motors will run on voltages as low as 1V.
You seem to be suggesting that the gearbox output shafts would make 24 complete turns.
Not a "suggestion", a straightforward, grade school level, mathematical fact. If the gearbox output shaft turns at 1 RPM (rotations per minute), and you run it for 24 minutes, the gearbox output shaft make 24 rotations.
What key questions should I ask the supplier?
Ask the supplier questions for which you want the answer. I would ask:
What are the actual pan and tilt rates, in degrees per second (or minute) at a given motor voltage.
