I bought three 17hs19-2004s1 stepper motors cheap and are now planning on making a camera slider with pan and tilt. I am looking to having it battery powered, even if it is only able to operate an hour or little more.
I have A4988 drivers with heatsinks that I was planning to use for the steppers, but now I realize the amperage might be a problem? I could of course lower amps and loose some torque.
Again, the use case is pulling low resistance slider, as well as pan and tilt a camera (low friction and force required obviously also in focus for these two parts)
Anyways any suggestions for a safe battery solution to such a project, or is it unrealistic? (I am beginning to suspect motors optimised for this specifc usecase might be an idea... oh well)
The provided details for the steppers:
Weight: 1.5kg Step Angle: 1.8 degree Number of Connectors: 4 Case length: 48mm Shaft length: 24mm D Cutting Length: 15mm Shaft diameter: 5mm Frame Size: 42mm x 42mm Rated Current/Phase: 2.0A Phase resistance: 1.4 ohms Voltage: 2.8v Cable length: 1 m with plug Induction: 3.0mH+/-20% (1KHz) Holding Torque: 59Ncm Motor type: bipolar stepper motor.
An A4988 will not be able to provide the 2 amps needed by those motors. It's practical max is about 1.4 amps, maybe a little more as you have heat sinks. The slightly more powerful DRV8825 will also not be adequate. If you need the torque available from the full 2 amp current then IMHO you should get drivers that are capable of supplying at least 3 amps so you have a bit of headroom.
Having said that you may find that you get enough torque with the current limit on the A4988 set at 1.5 amps.
Assuming the motors are given the full 2 amps then their power consumption will be 2A x 2.8v = 5.6 watts. At 1.4 amps they would draw about 4 watts. Stepper motors draw the full current even when stationary so are not really suitable for battery power. The three motors together would draw about 17 watts and if they were powered by a 12v battery the current draw from the battery would be at least 17 / 12 = 1.4amps - say 2 amps to allow for inefficiencies. To operate for an hour that would require a 4 amp-hour battery (because battery capacity is usually wildly overstated). Note that these are very rough figures (and my maths may be wrong) so it would be wise to allow for the possibility that you need a battery twice that size.
You are absolutely right about the A4988s. Your suggestion might be the best approach: start out with them, see what level of torque is needed, and then if necessary, buy more powerful drivers. Do you have a suggestion for 3 amps?
It is indeed ill fitted for battery, but would still like to try the option.
So it sounds as if something like a regular LiPo 11.1v 5000mah might do the trick? Or perhaps a sort of 4s2p configuration of e.g. 18650 batteries. But then I’m pretty quickly over my own skills – Ideally it would be a solution that could be charged without removing it from the device, and if a standardized form of charger could be used = superb, albeit requiring some more components for the battery. Again, solutions are most welcome.
As you say the actual draw (and quality of battery) comes into play. Again, the exact amp-hours will have to be determined after tests
Sorry, no. I think the drivers with TB66xx chips may be the most economical
So it sounds as if something like a regular LiPo 11.1v 5000mah might do the trick?
That sounds like it would be worth trying. If you want high speeds from the motors an even higher voltage would be better (within the limits of the driver's specification).
A standard LiPo with a proper balance charger will be by far the safest. LiPos have a nasty habit of going on fire if mistreated.
Robin2:
I think the drivers with TB66xx chips may be the most economical
A man of my mind, economical is a nice word.
Robin2:
...an even higher voltage would be better (within the limits of the driver's specification).
Ah, maybe 14.4v then.
Robin2:
A standard LiPo with a proper balance charger will be by far the safest. LiPos have a nasty habit of going on fire if mistreated.
Great point, I will look into whether a relatively simple compact charger is available, not really into the big clunky things we used to charge LiPos for hexacopter and the like.
So, this is a bit embarrassing, but I have confused myself when looking at a power supply for the project (until the battery solution) I would need a power supply rated to supply at least 12v, and minimum 6A right (as 3 steppers times 2A)
So annoying the amount of product with missing specifications…
Spaziba:
So, this is a bit embarrassing, but I have confused myself when looking at a power supply for the project (until the battery solution) I would need a power supply rated to supply at least 12v, and minimum 6A right (as 3 steppers times 2A)
No. You need a power supply that can comfortably supply the watts needed by the motors. As I mentioned earlier that is about 17 watts and (as I also mentioned earlier) 17 watts requires about 1.4 amps (say 2 amps, to be safe) from a 12v power supply.
Robin2:
No. You need a power supply that can comfortably supply the watts needed by the motors. As I mentioned earlier that is about 17 watts and (as I also mentioned earlier) 17 watts requires about 1.4 amps (say 2 amps, to be safe) from a 12v power supply.
Excelent, thank you very much for all your help Robin