You're right, driving them with the typical sensorless, back EMF position feedback ESCs that the RC people use doesn't give good results at low speed, high torque as, with the exception of one or two very expensive ESCs, they tend to lose sync and often have poor start-up algorithms. There are some fairly good ESCs about that do work very well though. Those from Castle Creations, particularly their HV160 50 volt, 160 amp high power unit, seem able to give exceptional performance up to motor power levels of around 6 to 8kW though. Several people on the ES forum have used these controllers to drive the cheap Turnigy HXT 80-100 motors (these: http://www.hobbycity.com/hobbyking/stor ... oduct=5142
) at power levels of around 5 to 6kW on electric bikes quite successfully. In fact,the stator of that cheap motor is the same as the one on the motors I've just bought - they come from the same Chinese manufacturer.
Driving these motors with a typical cheap Chinese BLDC ebike motor controller, after having fitted Hall position sensors at 120 deg to generate the three phase position feedback signals needed, is dead easy though, and gives excellent performance from a standstill to max rpm at any load. I've been using a 3,250 watt outrunner motor like this (one of these: http://www.hobbycity.com/hobbyking/stor ... oduct=7870
) to run my milling machine for a while now and it makes an excellent variable speed, high torque spindle drive motor.
I've also been using smaller, 2,800 watt outrunner motors on my electric boat drives. One of these has successfully driven an 18ft day sailer at hull speed without getting warm. For a controller I used a cheap ($45 inc shipping) electric bicycle BLDC controller and modified the motor by fitting internal Hall sensors between the stator slots.
The BLDC controller circuit board shown in the picture of the FETs is a multifunction, microcontroller based, design that can be programmed via a connection to an ordinary PC, to vary things like max current, phase current, rpm limits, cruise control setting, electric brake settings, regeneration level, low voltage cut-off point etc. The boards, as shown in the picture, are a little bigger than a credit card and cost about $20 each including shipping from China. They are normally fitted with 6 TO220 FETs and used to drive motors up to around 500 watts directly, but can easily be modified to just provide the FET drive signals to external FETs/drivers, which is what I'm doing.
Pretty much all the parts in these outrunner motors are specifically made for them. The stator laminations are typically much larger, with a higher slot count, than brushed motor rotors and tend to use thinner iron laminations to reduce eddy losses from the somewhat higher frequency they operate at (maximum commutation frequency for a typical controller will be around 2000 to 3000Hz). The magnets are usually Neodymium, bonded directly to the steel can. Measurements of external flux leakage I've made shows that the poorer motors do indeed leak a few % of the magnet flux through the thin steel can, but the better motors tend to keep this leakage down below 1%, which is really negligible in terms of performance loss. Typical efficiency at the peak operating point will be around 90% or so. My 3,250 watt motor on the milling machine barely gets warm after an hour or so of hard work, but then it is running in free air. The motor design is such that air is naturally drawn through the intakes in the base mount and around the annular gap between the rotor and the base and expelled through the top of the rotor. Even with no fan the airflow from the milling machine motor is quite substantial, which helps keep the stator cool.
The main issue is getting used to working with motors that need a relatively high ratio reduction drive to deliver good power. I will be spinning my motor at upwards of 8000rpm, probably three times as fast as the much heavier and larger brush motor it will be replacing. The drive design isn't hard, using off-the-shelf HTD toothed belts, but there is a noise issue to be addressed - these big three phase motors howl a bit when running at high speeds.