B&M Lift Motor Question

I have a question regarding B&M's lift motors. As far as I'm aware, B&M has been primarily been using DC motors for their coaster lift motors, as evident by an interview done with Monty Jasper years ago about Gatekeeper.

However I have noticed some coasters, specifically Bizarro, Superman @ Fiesta Texas, and Fenix @ Toverland seem to have hydraulic motors, or at least the videos I have seen on YouTube say they are (I know don't always trust the internet). The reason why I believe that they may be hydraulic systems is these coasters containing large reservoir tanks under the lift motors.

However, someone also mentioned to me that these tanks may be for the chain oiler pump, which these coasters also come equipped with, and the location of it varies. So my question is has B&M in fact used hydraulic systems coupled with the DC drive on some coasters, and if so why? It seems like for a company that's been so standard with their components wouldn't randomly switch for some projects unless there's a reason. Or maybe I'm overthinking it and these tanks are indeed just part of a oiling mechanism. I look forward to hearing some discussion on this!

My understanding is that B&M have 'stubbornly' stuck with DC motors even though AC drives have become far more efficient and in some cases more controllable.

Consider also that the tanks you see may also be a fuel tank for an emergency motor to drive the lift in the case of a power failure. I believe I recall seeing a system like that on Diamondback, where a combustion engine is installed inline with the drive gearbox so that if the electric lift motor is incapacitated the lift can still be operated to clear a train. It's been a while since I have seen one of these systems, so I may be more than a little wrong, but that's where my memory is taking me.

--Dave Althoff, Jr.

What is it about AC motors that make them "more controllable?" I'm sure the Internet could tell me why, but I was always surprised that Tesla used AC motors in their cars, given that the battery is obviously DC and that means they need an inverter.

Thank you for the insight Dave. I was certain that B&M had always used DC drive for their lifts, despite how others I know tried to discredit me.

It is curious that they still are using that technology despite how VFDs have pretty much taken over the industry. I know of at least three different rides that have blown a DC lift motor in the past few years, and you don't really hear about that happening for AC counterparts (at least as much).

As for controllability, AC motors coupled with variable frequency drives can be zeroed down to precise positions, much like a brushless DC motor. I'm not sure about the car aspect of it, but DC controllers basically convert AC phases to pulses with transistors that act in a similar manner to AC. Plus DC motors can deliver more consistent torque at different speeds, or at least that's what I was taught in Mechatronics.

AC drives can actually deliver full torque at zero speed, which is a really cool trick (and critical to the operation of a Segway).

Traditionally DC drives made the most sense because they offered better speed control and higher torque over a range of speeds, while AC motors basically couldn’t even get themselves started under load half the time. That’s why on just about any old ride with an AC motor you’re going to see that motor hooked through a V-belt to a fluid clutch (torque converter). That’s also why Arrow used DC motors on the Launched Loop...because you can abuse them and get massive torque out of them.
The new high frequency AC drives, though, are pretty amazing. It’s not uncommon now to see an AC motor coupled directly to the gearbox that runs the ride, with no clutch, because the drive can run that motor like a servo. Of course now DC motors are getting in on the act and the only real difference is whether or not the motor contains permanent magnets.

—Dave Althoff, Jr.

I can't really speak for efficiency, but with today's Variable Frequency Drives, AC motors can do pretty much anything you want. You can dial in any speed or torque profile that you want, and it will give it to you.

Well I know that. I've been driving EV's for years. ⚡