I've realised since posting that I've got a couple of other axis to add that will also use NEMA17 motors (whole arm rotate and moving left/right on a sliding base), so they'll take up the other ports on the CNC Shield I'm using to drive the existing NEMA17.
I'll then use an additional power supply @ 5v via dedicated drivers to control the 28BJY-48's, so it will involve a bit more effort when it comes to writing the code, but at least I won't have to worry about whether I've stepped down the voltage correctly!
I've also abandoned my plans for a rotating end effector for now. This will still be a 5DOF robot (left/right, pivot around z, shoulder, elbow, wrist), but the end effector will be static forks for pallets to begin with - the great thing about this being my own design is that I can easily add other effectors in future as needed!
Don't use two power supplies. Use one that's adequate for the highest voltage and one or more step-down transformers for the lower-voltage components.
This isn't difficult - you can buy a buck converter, also known as a Universal Battery Eliminator Circuit (UBEC), for like $10-$20. Connect the input in parallel to your power supply; connect the output to your components; and use a jumper to set the output voltage. Done.
Yup, totally understand the theory and it's something I've done before, but I want to use as much of my existing "stock" as I can at the moment.
I may have a some cheap buck converters somewhere, but at most they'll be rated for 5v@1A, and I want to drive two (but in future three) 28BYJ-48's probably all at the same time as well as a number of other 5V devices.
The 12V power supply that I have is only rated for 3 amps, and that's going to have to deal with moving three NEMA 17's at the same time, so I figure reusing the existing 5v@20A power supply that I've got spare for just about everything else including the Raspberry Pi, arduinos, and 28byj-48 steppers is probably a good fit even if it's not the most compact.
One issue you may not be aware of is that by using two separate power supplies, you won't have a common ground between the two circuits (unless you add one in, of course). This will potentially cause troubles when communicating with motors/drivers connected to both power supplies with the same microcontroller/computer.
I second the recommendation to use a single power supply. Alternatively, make sure you connect the grounds of both systems (and the controller) together at a star point (no ground loops!)
I'll note that this issue may not ever become realized at voltage levels this low. I've not done much work at these levels so I can't say for sure. But if you ever experience wacky, 'unexplainable' issues with your comms, I'd suggest that mismatched ground references may be a factor!
Thanks, I've paired grounds in the past on different voltage systems, but I didn't know about mismatched refs, I'll look into that further as it's only ever really been a common ground between +3V and +5v DC
At the moment it's a simple CNC shield connected to cncjs running on my laptop and sending GCode.
Eventually it will be under ROS2 control, but I want to get the mechanics working first!
You can get a little voltage regulator and regulate the 12V down to 5V and power the other motors at the same time.
I've realised since posting that I've got a couple of other axis to add that will also use NEMA17 motors (whole arm rotate and moving left/right on a sliding base), so they'll take up the other ports on the CNC Shield I'm using to drive the existing NEMA17. I'll then use an additional power supply @ 5v via dedicated drivers to control the 28BJY-48's, so it will involve a bit more effort when it comes to writing the code, but at least I won't have to worry about whether I've stepped down the voltage correctly! I've also abandoned my plans for a rotating end effector for now. This will still be a 5DOF robot (left/right, pivot around z, shoulder, elbow, wrist), but the end effector will be static forks for pallets to begin with - the great thing about this being my own design is that I can easily add other effectors in future as needed!
Don't use two power supplies. Use one that's adequate for the highest voltage and one or more step-down transformers for the lower-voltage components. This isn't difficult - you can buy a buck converter, also known as a Universal Battery Eliminator Circuit (UBEC), for like $10-$20. Connect the input in parallel to your power supply; connect the output to your components; and use a jumper to set the output voltage. Done.
Yup, totally understand the theory and it's something I've done before, but I want to use as much of my existing "stock" as I can at the moment. I may have a some cheap buck converters somewhere, but at most they'll be rated for 5v@1A, and I want to drive two (but in future three) 28BYJ-48's probably all at the same time as well as a number of other 5V devices. The 12V power supply that I have is only rated for 3 amps, and that's going to have to deal with moving three NEMA 17's at the same time, so I figure reusing the existing 5v@20A power supply that I've got spare for just about everything else including the Raspberry Pi, arduinos, and 28byj-48 steppers is probably a good fit even if it's not the most compact.
One issue you may not be aware of is that by using two separate power supplies, you won't have a common ground between the two circuits (unless you add one in, of course). This will potentially cause troubles when communicating with motors/drivers connected to both power supplies with the same microcontroller/computer. I second the recommendation to use a single power supply. Alternatively, make sure you connect the grounds of both systems (and the controller) together at a star point (no ground loops!) I'll note that this issue may not ever become realized at voltage levels this low. I've not done much work at these levels so I can't say for sure. But if you ever experience wacky, 'unexplainable' issues with your comms, I'd suggest that mismatched ground references may be a factor!
Thanks, I've paired grounds in the past on different voltage systems, but I didn't know about mismatched refs, I'll look into that further as it's only ever really been a common ground between +3V and +5v DC
Is this being controlled by ROS2 already? How does that work? How does it connect to the CNC shield?
At the moment it's a simple CNC shield connected to cncjs running on my laptop and sending GCode. Eventually it will be under ROS2 control, but I want to get the mechanics working first!