also, back on the lines of 269s, is it too much for a cortex to have 8 269s and a servo in it with a 3000mah 7.2 competition battery, because we are seriously considering buying a power expander because we have 2X 7.2 (3000mah) and 1 X 7.2 (2000 mah) … so we will be contently cycling batteries
It’s not unusual to see teams with only one 7.2v battery, one of team 8888’s roundup robots only had one and it did just fine. However…
Using a power expander obviously helps spread the load.
Having more batteries available at competition helps reduce stress but you should delegate one team member to be the responsible for making sure fresh batteries are always available and they do not get mixed up with discharged ones. When using a power expander, having four batteries available is a good idea at competition, 2 on the robot, 2 on charge.
as previously said, we have 2 (3000mah batteries) and 1 (2000mah battery), we always ensure that the battery we use is a 3000 battery (which is freshly charged) … and when we switch we plug the other one in … but the 2000 mah is reserved for testing really, we found that it discharged very fast at our last competition (all the motors)
another problem we always have is with the chargers at competitons, whenever we charge anything at nationals the batteries get mixed even though the charger and batteries are all labeled, we dont mind other teams using them but when we are expecting a battery to be on charge and someone unplugs it, it gets on our nerves, this year we are gonna have a team member supervise the battery when it is charging to prevent chaos again
but back to my original question, would you buy a power expander ?
With your motor set up I wouldn’t recommend using a power expander because then you wouldn’t have a second battery and because alot of teams used 4 393s and 6 269s without a power expander and they didn’t have any problems my team included.
A power expander is nearly always a good move. First it shares the robot power consumption between two batteries. This may not seem like a big deal, but over the course of an entire competition it means your batteries will stay closer to fully charged. Second the power expander gives the robot a third circuit breaker. This allows for better distribution of the loading on each power circuit. This will help the breakers stay cooler longer. Remember the breakers are thermal protection device. They trip when they get too hot. During a match the ambient temperature in the case is slowly rising. So after the first trip the breaker will trip faster each successive time because it can’t shed its heat as quickly. At some point the temperature in the case will keep the breaker from resetting until the match is over.
Our team is planning on using 10 HS motors with a power expander. What would you guys recommend for Cortex/expander distribution for an 8 motor drive and 2 motor arm? I was thinking four drive on the expander and the rest on the Cortex. Also, we will have to be driving and lifting the arm simultaneously at times – will this cause issues with drawing too much current (assuming gearing isn’t extremely aggressive)?
I would put the “left” drive motors 2-5 and the “right” drive 6-9" and put the arm on the power expander. You are going to have 4 motors some were but this ways allows the least stress on everything if you do stall.
I would say to spread the drive out as evenly as possible, as drive motors always stress the system out the most. Put 2 drive motors on the power expander, 3 somewhere in ports 1-5 of the cortex, and the other 3 somewhere in ports 6-10 of the cortex. The arm can also go on the power expander.