Maximum Practical Amount Of High Strength (393) Motors

I know the allowed amount is 10, but I would like to know if someone has tested what the maximum amount of high strength motors with a power expander before the robot would become unstable or crash.

In our robot we I just posted about we were able to run 8 393’s at about the same time using no power expander and nothing happened at all. I’m thinking it will be VERY hard to trip the breaks.

Have you tried 4 motors, or 8, stalled at the same time? That seems like it would trip the breakers.

we ran our intakes, lift and drive at the same time, totaling up the 8 393’s. It could have been 10 if 393’s fit in small spaces. But we ran perfectly fine, there’s nothing to be worried about.

We have 10 393’s on our bot, and it works perfect! We haven’t tripped a breaker yet!

Despite what has been said below, you need to be careful on how you are running the motors and the power distribution. We have discussed this topic before in threads such as this

https://vexforum.com/t/how-many-393s-do-you-tentatively-plan-to-use/21418/1

Even with only four 393 motors stalled you will be using more current than the PTCs in the cortex and power expander can support for more that a few seconds.

Take a look at this thread and the others it references, it explains where the “sweet spot” for running motors is.

Also bear in mind that the surface that the robot is driving on has an effect on the required motor power. Every year we hear stories from teams that had robots that would drive ok during practice but tripped the PTCs during a match. Every surface will present different friction to the wheels, drive you robot on the competition tiles and calculate the speed the drive motors are running. Then based on the graph in the thread I referenced you can calculate the motor current and estimate if you are likely to trip either the motor or cortex PTC.

I understand that you should still be careful. However our findings have been similar to banditofernando’s. One of 8701’s robot uses all 393s running mostly simultaneously on one battery. It has never stalled, nor tripped any breakers.

I would still be careful pushing the limits like that. Like jpearman has already stated, practice is much different than competition. I know that 4886A does quite a bit of stress testing, but unless you actually put up the fully wired up robot against some other fully wired up robots in various game situations, you can never be sure that you won’t trip breakers.

e.g. if you were fighting against another robot for position while raising the arm to goal height and your arm happens to catch on their robot or another field element, you could easily find yourself stalling 8 or all of your motors.

Today i pushed an frc robot. My robot is wired so 3 393s are on each breaker and the motors are all on the speed setting. The only thing i blew were people minds.

Persionally, I am only going to be running 6 -> 8 393’s (lack of parts), but if I had the chance I would go with all 393’s.

I have seen plenty of robots running off 10 393’s, and as long as you are careful (I.E. don’t go round trying to push a super heavy, geared up wallbot like 2W) I think you will be fine with 10 393’s.

lol :smiley: that’s just made my day.

~George

Our team has been running with ten 2-wire 393 motors on our robot since the beginning of the season, and we have never had any problems. The 393 motors simply work much better than the 269 motors overall. You should never be pushing your motors so much so that if they encounter a bit of resistance in competition, they will trip the breakers. So, if you are pushing them to a more reasonable amount, they will be the better choice to use on your robot.

~Jordan

I fully agree with you :wink:

We have had no power losses, tripped breakers, or stalls.

Could it be an older cortex that can’t fully support all 10 393’s? We have the newest.

For the same high load, two 393s will draw less power than one 393.
Time to recalibrate your intuition, or learn engineering.

I am with you here. Although it is wise to use the 393’s due to the power and efficiency… it does put your robot more at risk to easily tripping PTC’s in a stall condition. Like SweetMochi says, there will be situations around the trough where lifts and robots are competing to score or descore in robot to robot combat which will draw the big currents. You must either back down or probably stall some motors in an equally matched event. Backing down may not be an option if you are going to lose the match to a big stack trough score.

Although you can never be sure that you won’t trip breakers with only driver skill you do have an option in software: Smart PTC Current Limiter . This insures that you will never (or almost never) trip breakers no matter what motor set you use or driver skill.
(Actually, I was hoping that teams using 10 393’s would be experiencing some trouble so they would be motivated to try the software…Guess I’ll just have to wait until the need arises:)