I disagree with the rc car vs ride on toy comparison, although I agree that the PW could be hard on the esc... mainly because the motors could be pushed to their stall limit.... which is a f course a bad deal for the esc. Dead shorting the load can smoke an otherwise capable system. But watts is watts. The esc doesn't know or care what type of work the motor is doing.... either it can handle the load or it can't. A stalled motor could fry an esc no matter how big it is.
The difference is that in a BPRO, the motors are working very hard all the time, no just during bursts of acceleration. I'm very well versed in RC, currently have 27 kits from 1/36 to 1/8, about half of them brushless EP. I've smoked 150A ESCs in my 12 lb truggy running them hard and continuously for 40 minutes to an hour (3-4 5,000 mAh 4S packs), which as you know, means on average not more than about 1/3 of the time at 50% or greater motor load. On a BPRO, the motor load will be at or above 50% the majority of the time, and in all likelihood much more than 30 minutes continuous.
It's heat dissipation that becomes the issue; those SMTs are smaller, and they do not have dedicated heat sinks, nor is the single heat sink on the ESC anywhere near the surface area of the multiple TO-220 heat sinks in larger general purpose PWM ESCs. As motor and transistor heat increases, component efficiency decreases, and amp draw goes up.
For those who aren't real familiar, let me show you the difference between two 60 amp ESCs, one mounted in my 3 lb RC10B3 buggy motivated by a 3,300 KV (10 turn; 3,300 RPM per volt) 380-cored 540 BLDC can, the other in my red Wrangler project, which is driving twin 68x92mm 320 RPM per volt PMDC motors:
You couldn't even fit 6 of the 16 transistor heat sinks from the BPRO ESC in the space occupied by the entire RC ESC.
but on the other hand, moving a 100lb ride on toy 5-10mph is not necessarily more difficult than moving a 10lb rc car 50-70mph
If you spend 80% of your run time at those speeds, you'll smoke either the motor, the ESC or the battery. Speed runs are high motor load, and things get hot. I've burned up BLDC motors (debonded the REM from the rotor), ESCs and LiPo packs doing speed runs without sufficient cooling or enough time between runs. Some of those that I fried should have been able to take it, such as the RC10GT chassis I E-converted and used a 2,000 KV Kyosho 42mm can, a couple of different 120A and 150A ESCs and 5,000 mAh 80C 4S packs. Again, it's heat. RC parts are just not designed for the continuous heavy load of a BPRO.
If you're into RC, you also know that the ESC manufacturers detail in finer print that the "150A 6S" rating requires the use of lower KV motors, higher final drive ratio and in a lighter weight vehicle. If you try to make a warranty claim on a 1/8 scale 150A ESC that you were running on 6S with a 2,600 KV motor, rockin' a 9:1 final drive ratio in an 11 lb truggy with 4.0" VTR tires, they're gonna laugh at you and tell you to pony up for a new one. The requirements to honor warranty running 6S in a kit that heavy would be something like ≤1,450 KV motor with a ≥12:1 FDR. What do you think happens when you're trying to push a 17 turn brushed motor in a 120 lb kit?
Let me offer another example; had to poke some holes in very hard, rock-filled concrete not long ago, started out with my Dewalt 5.4A 1/2" HD hammer drill. That thing was smokin' hot and noticeably losing power by the 7th hole. A friend lent me his Bosch 11224VSR, which is only 28% more powerful by the numbers. But this drill is meant for concrete work, and the motor and speed control are designed for that continuous heavy loading. That thing poked the other 33 holes without breaking a sweat.
BPROs with kids on them do
spend most of their time maxxed out, which is why manufacturers of RC speed controllers specifically tell you not to use them in ride on toys. Hobbyking's warning, for example:WARNING
This is an R/C plane/heli only ESC. Do not attempt to use it to power car, buggy, skateboard, go-kart or similar machines. The programming logic is only designed for R/C Planes and Heli and will burn if applied to other devices.
Looking at it from the other end of the system, a 24v 12ah gruber battery would only run about 10 minutes in one of my 1/8 rc cars
Aside from the fact that SLA and AGM batteries do not have the burst output capacity of LiPoly, that battery has much more total power than a standard 1/8 scale 4S 5,000 mAh pack. 4S 5,000 mAh = 14.8V 5Ah, or 74 watt hours. The 24V 12Ah SLA has 288 watt hours. In other words, about 4 times the juice. Trust me, the math works; the mean draw of a 1/8 scale RC on 4S on a track is about 25 amps; at 74 watt hours, that gives you .21 hours run time, or about 12 minutes. If you ran your car on the 24V 12Ah battery and metered your throttle to use the same wattage (more volts/less amps=same total power), you'd get around 45 minutes run time.
In the end, I'm not saying it can't or shouldn't be done, just trying to help some people understand that the manufacturers specs don't tell the whole story. Just as many a firearm design that'll run 20,000 rounds without a breakage in semi-auto might destroy itself after a couple thousand rounds of full auto, and just as a 1/2 ton truck can carry a ton and a half a few times in it's life but will smoke wheel bearings and axles if continuously loaded with 1 ton, an RC ESC that can handle very high amps for brief periods cannot take the kind of load it's ratings indicate it should when used in a BPRO or other application that causes the motors to operate at moderate to high loads most of the time.