I was wondering how many people were using power expanders and what combination of motor types they were using with them.
We are using a power expander with all high strength motors. Since the high strengths draw more power, We find it best to keep as many on their own battery as possible. We’ve never actually tested any of this though, so we may be completely wrong lol.
Not much sense in using anything other than 393’s in my opinion. A power expander makes huge different, We divide the load between the Cortex and the power expander usually putting 1/2 of our drive motors on each.
With the possible exception for 3-wire Servos, we’re going to be using 10 393 Motors on each of our robots with a Power Expander. I can’t honestly see a use for the small motors any more. If anyone knows one, would you mind sharing? We just use them on robots we’re building for demonstrations.
We’re using eight 393s and two 269s without a power expander, but with a back up battery. Did they come out with something to replace the expanders yet?
I’m confused by your question. Why would they need a part that replaces the power expander? It already does exactly what it’s supposed to.
last i checked, they stopped the production of power expanders. Since it’s a useful part in competition, they would replace it with something else to stimulate profits. Kind of like how certain kits were shut down and other kits were brought up as replacements
Nope. Still for sale. Obviously you need another battery to go with it, but you just buy that separately.
yeah your right, i didnt stay updated on this thread. Silly me:p
https://vexforum.com/t/vex-power-expander-discontinued/22959/1&highlight=power+expander
I can’t see any reason, aside from cost, to not use 393s and an expander. Maybe if you had a really funky design, the slightly smaller profile of the 269 would become necessary.
There are uses for them, at least in theory. They’re better for applications that require low power output or low current draw. Any time you want a motor to output up to 2.4W of power while using the minimum possible current, or to output the maximum possible power on less than 1.1A of current, you should use a 269.
Here is the full current vs power chart for both motors (based on the specs on their product pages along with some theoretical calculations):
Of course, one could argue that by using motors for low power applications you aren’t making the best use of your 10-motor allowance and that a robot should be designed to output as much power as the rules allow.
Any time when you don’t need a high strength is a good time to use the low strength. The 269’s are smaller, lighter and cheaper. If there is any subsystem that needs little torque, a 269 is your most efficient option. For example, a claw doesn’t need to have much torque at all, so you save space and weight on the lift, as well as spend less money.
well usually money would be the #1 reason 
if we all have infinite monies and can all have fresh overcharged batteries every single match, we would happily take it over whatever recharge rotation system we have in place now
and yes, the 269 has a smaller profile as well
Does anyone who uses all 393 and a power expander have problems with brownouts ( otherwise known as lagging or motors overheating)? I know some teams in my club have had issues, but I never have. Is it just a poor design causing this (my opinion) or does it happen to others as well?
We had 10 393 motors the whole Sack Attack season and we never tripped a breaker or had a ‘brownout’. We did have our drive motors stall because of pushing constantly, but that’s it. We were using a power expander for half of the season.
A combination of poor design (ie high friction drive chain) and driving (ie pushing battles)
If you’re having issues, I suggest taking a look at a programming solution: https://vexforum.com/t/smart-motor-library/22282/1
The programming solution, however, isn’t a substitute for good engineering, but rather a compliment to it.
Yah. Thats what I thought. I have planed to use the programing solution and obviously i will try to minimize the friction and the other causes…
At worlds with my sack attack robot I was using 10 393 motors on high speed without a power expander. 8 of these motors were running constantly at once. I never tripped a cortex breaker even when under full load (pushing people). My toss up demo robot right now is using 10 393s all 10 on high speed.
It saves a bit of weight running with only one battery. It also ensures all your motors have the same voltage which is important considering in sack attack I had a drive to lift transmission.
And actually yes I took the expander off because I noticed a lot more brown outs on the motors hooked to the expander.
I am a big fan of power expanders, but if you don’t think out your placement of motors the voltage difference can be an issue. Somehow we had gotten wires mixed up on our first Sack Attack robot which had 4 motors for the lift, and instead of one from each side being on the Cortex and the other being on the power expander they ended up divided left and right. It was easy to see the effects of this mistake when one side lifted better than the other.
Power expanders are great, but make sure the loads are divided properly not only for circuit protection, but also for continued function in the event of a tripped breaker. If you are dividing 4 drive motors off of 2 breakers make sure they are divided front/back and not left/right.
Thanks for the help everyone!