I've been struggling and making slow progress with my rewiring of the DC motors in my B9. I decided to replace all my Pololu H-Bridges with a Sabertooth / Kangaroo combo. The Pololu H-Bridges were very good and did the job but I thought the Sabertooth / Kangaroo combo would make for a simpler setup with easier coding and better performance. well, that's all still to be seen. The coding is easier once you get to understand the serial commands and being able to use the servo controls and scripts in EZ Builder is awesome. However the setup really wasn't that much simpler. I'm still having some issues with error codes at startup that stops any signal input. I'm working with Dimension Engineering to resolve this. I think it may be the potentiometer I'm using. Also I needed to add a battery for some place for the Sabertooth to dump the regenerative power, diodes to keep from back feeding the power supply from the regenerative power and I still need some way to shut off the new boards.
This brings me to my question; How are those of you using the Sabertooth turning off your controller? The battery keeps the board energized and you cant disconnect it because if done the Sabertooth has no place to dump the regenerative power. If the motor is moved by hand the Sabertooth can damage itself if it cant put the regenerative power back into the battery. I can think of a few ways and all will need a switch of some kind and a blocking diode. Something like this:
I'm powering the boards from a 24vdc switching power supply with a 24vdc battery paralleled between it and the boards for the regenerative power to be dumped into.
Different ways to switch I can think of are:
1). A manual switch with a diode across it. This wont work as I don't want to mess with a different off switch for my DC current and my B9 is powered from wall AC current through converters.
2). A low side TIP122 switching circuit operated from EZB and startup scripts from EZ Builder. The Sabertooth is self powered from the 24v power input that supply's the motor voltage. If done like this I'd need to totally isolate all neutral and common grounds going to the Sabertooth / Kangaroo boards and open them at the TIP122 switch. If I try to switch the neutral at just the Sabertooth power input point I still have a neutral feed on the other side through the Kangaroo X2 Where the EZB signal input is attached.
3). A high side switching circuit. I could build one and just switch the hot lead feeding the power input of the Sabertooth and this would turn off both boards. I'd need to use Power MOSFET as the TIP122 may not handle the amperage max I'd be pulling. The TIP122 is only rated for 5 amps and I may pull more then that at times. The Power MOSFET would be able to handle that load. I'm still trying to understand this high side switching circuit. I'm not really sure if I will only need one MOSFET in the circuit or if I need a pre-driver to drive the MOSFET. I've seen drawing of it donn both ways:
Still not sure which is the proper circuit to use and if I use the pre driver one what values to use. I still need more research to find out. Any recommendations? I'd love to find a High side switch that EZB could control. I did find one at SparkFun but it controlled 4 lines, was a shield type board and cost $60.
4). I could switch the high side with a relay triggered with a Low Side Tip122 switching. This seems redundant and I don't like the long term problems that may arise using a relay. Manly that the contacts on a relay may pit and fail and the relay would be energized all the while the robot is powered up.
EDIT: Here's the final circuit that works nicely. I've placed diodes in circuit to both let the Sabertooth dump regenerative power back into the battery and also to keep the Sabertooth from back feeding the power supply. Without these diodes the Sabertooth and power supply would stay powered up from the battery after the robot was turned off. Also if the Sabertooth stayed powered after system shutdown the Kangaroo X2 would return errors and not run when the robot was started up again. Seems that if I shutdown near a limit switch and let the Sabertooth/Kangaroo slowly drain the power out of the battery till it was dead these errors would happen. It was very frustrating. Now when the EZB disconnects from EZ Builder this switching circuit will open and shut down the Sabertooth/Kangaroo and the diodes will act as described above. Here's my circiut:
I used the resisters listed. With the following Power MOSFET driver and Transistor pre-driver I'm good up to 55v and 19 amps:
Q1 MOSFET driver: IRF9Z34NPBF
Q2 Transistor pre-drive: 2N3904
Sub the Motor in the drawing for the Sabertooth.
Anyway, sorry for the long post. I'd welcome any thoughts or ideas.