10 393s

does anyone think 4 393s on a power expander and 6 more in the cortex will work?

Yes, I do, it’s just a case of careful power management.

I feel that it will work. People just have to remember to be careful how much strain they put on their motors. The safest possible amount of 393 Motors you can have on your brain is 6. My team plans to have around 8.

yes, just make sure you “do it right” :wink:

If you are having to limit the power of the motors, or are having to do only one thing at a time (drive/lift), wouldn’t it be faster to just use 6 393’s and 4 269’s anyway…?

This is exactly what my team is thinking

I think all that should be needed is to cut off power to any motors that are stalling. That way, I doubt the cortex/expander circuit breakers would break.

If ‘doing it right’ isn’t working, I can still think of advantages of using 10 393s even if you couldn’t supply full power to all at the same time. Say you put some 269s on your drive so that you can lift your arm and drive at full power at the same time. But what about when you’re only driving? You could increase drive power if you used 393s instead.

Whether this is enough to make you buy 393s to replace 269s you already own I don’t know. I expect most teams will have to keep using 269s for quite a while.

Also, has anyone else found 393s to be generally more reliable than 269s?

If you split what goes on the power expander and direct to the cortex in the right way. It can definitely work. Don’t put all the 393’s doing the most work on the same amp otherwise your going to destroy em.

This is a great application for S/W control of the robots. If you wanted to get really technical you could limit the speed of the various motors based upon how many motors are being run in each electrical path (A/B of Cortex and Power Expander).

Our team developed a rudimentary Motor Stall Detection (and cutout) last year to help avoid thermal issues resulting from an autonomous mode induced stall. This concept could be taken a bit further to provide a ‘realtime’ monitoring of the number of motors on each circuit in use and how hard they are being driven.

This is not a capability I would leave to the end of the build cycle when the robot is being finished, rather I would try to get someone working on the code early in the season if you want to take advantage of more 393 motors but have some control over how hard they are driven.

I’m not sure what our team would think of this function, other than I have a hard time getting them to code initially.

Cheers Kb

my team always prefers 393s to 269s, we usually use 3-wire motors rather than 269s

Absolutely. That reason alone makes me want to use all 393s on a robot.

We had issues with some of the (new) 269s locking up when being backdriven. In a few cases we had to actually disassemble part of the robot to get the motor out, because the axle was jammed so hard we could not slide it out to move the gears out of the way to unscrew the motor…so we like 393s for that reason. We’ve also broken fewer internal teeth and fewer motors themselves of the 393s.

would it be too much of a current draw to use 8 393’s ( 4 on power expander and 4 on cortex)

it has been mathematically discussed on the forums just a few days ago
the search button is your friend :slight_smile:

A 269 can be externally geared to have the same torque as a 393, although it won’t be as fast. We plan to have 6 393s, and 4 geared-down 269s.

I’ve found that some grease in the gears, both the top and bottom of the case, can help with the back driving issues sometimes. Try it out, certainly can’t ruin your motors :smiley:

dont see a problem with it … should work

269’s are not reliable in my experience. As some Texas teams know very well, my team was known for pushing a lot of robots in our gateway competitions, but one of our 269’s on the drivetrain was missing 11 teeth after one of our final competitions! 11!!!

:eek: and i picked you as an alliance partner at nationals!?!?!?

Yes, yes you did.:D:D:D

But we didn’t get disqualified!