Mapping 6 Motor Drive?

After several months of stalling/tripping/dropping issues on our 4 motor HS drive., our team is adding a six motor HS chain drive. We use a power expander. We plan on using motor ports 4,5,6,7 for the drive. We are using Y connectors on ports 4 and 7. On each Y one motor controller will run straight and the other will run indirect through the power expander. The other ports (5,6) will have one straight wired motor controller. Ports 4 and 6 will be used for the Left drive. Ports 7 and 5 will be used for the Right drive.

A 2 motor RD4B lift (2,9) is on the power expander. A single motor mogo lift is on Port 3. A single motor cone spinner is on Port 8. 2 motor 4 bar cone lift is on Port 1,10.

Our thoughts are formerly we have always used Ports 2,3,8,9 for drive; new ports 4,5,6,7 will help rule out internal–semi-fried, fried ports- cortex issue(though we think there is none because we did a visual, nasal inspection). (Also adding all new motors and motor controllers) Also now each motor on each side of the drive will be on a separate 4 amp breaker (e.g. for the Left drive 4 straight Y on 1-5; 4 indirect Y on power expander and 6 straight on 6-10).

We are also updating firmware, reflashing cortex, joystick and rewriting code.

Thoughts, proposals for other modifications?

You have a power expander, that’s a third 4 amp breaker. The best way to do a 6 motor drive from a power distribution stand-point is 2 motors in 1-5, 2 motors in 6-10, and 2 on the PE. That way you should have 50% more amps available to your drive then only using the cortex ports

Is there not a concern that the difference in the level of the batteries will lead to inconsistencies when driving? Especially during control, when you may not have sensor based corrective software?

@MayorMonty With all 3 on one battery and bank (using a Y connector to join 2), you could be running up to 75% of the amp limit which puts you on the threshhold of tripping if you use anything on the other three ports.

I’ll add my two cents. I like to map everything out in excel to get an idea of what goes where. I’ve done one below for you of what I think would be best.

Some tips:

  1. I would try to separate your drive instead our four motors all on the PE, throw some of that onto your cortex breakers.

  2. Your DR4B should almost never be split across two breakers. Think about it, if one breaker trips, you are now trying to drive the whole thing on the other breaker, which if attempted, will quickly cause the other one to fail. A DR4B can’t operate with half its motors, so no point in splitting it up. Also, if it dies, you don’t want to tie up your entire robot while it resets, you want to still be able to do other things (ex. drive.)

  3. Cluster your drive together with things that don’t run that often. Your drive is likely pushing those PTCs the most, so pair it with low-load things. In your case, the MoGo lift and cone spinner. The MoGo lift draw a bunch, but only for a very short period of time, not sustained.

  4. Finally, much like with the DR4B, don’t mix up left and right drive in an attempt to ensure that the robot can always drive straight. If you blow for example both rear of your drive motors (2 of 6) and attempt to keep driving on it, you’ll soon kill the rest. I prefer to place the entire right drive on one PTC and the entire left on another. When using a PE however, be sure to keep battery voltages similar and run a drivestraight() function.

@ethan_matlack Thanks for those thoughts. Though we have only two motors on any one breaker(note the Y cable is getting one straight wired and the other indirect through PE), your suggestion of three on one battery and three on another is interesting. The key there would be not letting either battery drop too far below the other as you note. The vexing thing about this process is no solution is linear. The upside is more than likely asking each battery to deliver 50% of the drive power will be more consistent than asking one for 66% and the other for 33%. Currently with the 4 motor direct drive, we are getting 100% from one battery and I am wondering whether the issue there might not be too much current draw by but a brown out on the battery’s ability to deliver as we do notice rapid draw down at times.

Btw for ITZ, we are not too worried about the DR4B tripping anything. It would be different for Skyrise but if two motors with unlimited elastic assist cannot lift one 8 oz cone we have bigger issues.