gunthn said:
I don't have a good understanding of elec rpm and power, but if the limit is a stict cutoff, like a rev limiter in an IC, then why should it affect power if most of the power is produced in the upper middle rpms? Overall the hxt is about at 7000 so is the last 1300 important?
From what ive read, most RC motors produce peak power/efficiency at ~80>90% of no-load RPM. If your HXT 80-100 has a no load speed of 7000RPM @ 48V, then that would equate to an ideal operating speed of ~5600>6300RPM.
Yes, a controller's speed limitation (electrical RPM) is usually based upon the microprocessor clock speed divided by the number clock cycles per electrical RPM cycle. Potentially it could be limited by the switching times of the power FET's but not normally. Yes, it is like a rev limiter on a car. The phase wires simply cant be switched any faster than the maximum speed that the microcontroller can process the feedback signal's from the hall-effect sensors.
The 5833RPM controller limit (for a 12 pole motor) i mentioned referred to the special
Kelly controller BMC geared hub motor intended unit that i posted a link to. NOT the Cyclone/Headline controller. I was trying to say that to be sure that you would be able to spin your HXT fast enough to be usable, you may have to upgrade to something like one of these expensive Kelly controllers which would deny the benefit of using the Cyclone/Headline controller you already have.
The Cyclone/Headline controller is likely limited to a
lower electrical rpm than would be needed to utilize the
higher power/more efficient part of the HXT's powerband. Yes, 5833RPM of the special Kelly controller would probably be enough speed get into the better part of the HXT's powerband that can sustain continuous heavy loading, but 3500~4000RPM - which the Cyclone/Headline controller could be limited to as low as - would be too low meaning the motor would get critically hot due to the lower efficiency.
The reason i say that the Cyclone/Headline controller is
likely limited to a lower speed, is because most sensored controllers are designed with integrated microcontrollers that are selected to be
just fast enough to run with the intended motor that they will power. Maybe with a bit of headroom/tolerance, but the point is it's a design measure. Faster microcontrollers cost more money and if there is no need to use a faster version- from the manufacturers point of view, then they likely won't. The best of the cyclone motors powerband is <3500RPM, so they wouldn't need to have their controller's run much faster than this. Some members of this forum have increased the clock frequency timing that feeds the microcontroller within other makes of sensored controllers so as to 'overclock' the electrical RPM capabilities. This is only possible if the microcontroller in question has more speed capability than it is clocked to in it's standard setup, so these 'hacks' must be taken on a case by case basis. Although im an electronics technician by profession, i wouldn't even attempt to hack the Cyclone/Headline controller without a circuit schematic or a datsheet for the microcontoller (I can't even tell what microcontroller they use as they are an unmarked IC).
Finding this out seems improbable as in my experience Headline electric are unhelpful to 'small fry' customers like us, whereas they probably bend over backwards for Paco at Cyclone when he rings up to order another 1000 units.
So in a nutshell, whilst i can't say for sure what the Cyclone/Headline electrical RPM limit is I was just trying to warn you that there is no guarantee of success using these controllers with a fast outrunner. This doesn't mean you shouldn't try - Hell i'd be glad to see the results of your experiment - but you should be aware of what's going on.