RC ESC for EV motor - Page 1
Forum section: electronics / projects

author: firewalker
author_rank: Super Contributor
timestamp: July 19, 2023, 10:35:48 am
content: I was wondering if those ESCs for remote controlled cars are capable of driving a small EV motor. Load free. Just spin it for education purposes. Much safer than the real thing.I know those ESCs can control hundreds of amps.Alexander.

author: Berni
author_rank: Super Contributor
timestamp: July 19, 2023, 10:59:23 am
content: Yep they should be able to do it just fine.Bigger motors are typically easier to drive as they don't need as responsive of control, tho it is possible that one of those ESCs might be a bit unstable if its regulation loop is a bit too nervous for large motors.The specs of hundereds of amps on those RC ESCs are to be taken with a grain of salt tho. Yes they can do it, but not for very long and while doing it they are on the edge of blowing up. Quite common for high power RC ESCs to catch fire when pushed hard. But for just spinning a EV motor with no load it should only take 10s of amps at most.

author: langwadt
author_rank: Super Contributor
timestamp: July 19, 2023, 11:47:05 am
content: I'm sure that depends on what type of motor it is, and if the ESC is sensorless it might not start at all

author: Psi
author_rank: Super Contributor
timestamp: July 19, 2023, 11:50:55 am
content: Some RC ESCs are intended for high KV in-runner motors and may not work right on slow rotating motors. (They may give up waiting for the inductive kickback that indicates the motor has rotated because they expect it to happen within the typical timeframe of an RC motor) So you probably want an RC ESC that is suited for driving large low KV RC motors and one with lots of timing settings.Many RC ESCs have settings you can change. There's usually some timing settings in there and also a "soft start" setting which might have options of OFF, LOW, HIGH. I imagine you want HIGH for an EV motor.The settings are usually changed either from some digital protocol over the servo connection or from starting the ESC at max throttle and walking it through a menu of beep codes while reading the manual.Another option you could look at is ESCs for E-bikes and E-scooters.Some of them are pretty fancy with many timing options and PID adjustment

author: firewalker
author_rank: Super Contributor
timestamp: July 19, 2023, 12:19:31 pm
content: What is considered low KV rating for such an application?Alexander.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 19, 2023, 01:49:14 pm
content: I'm assuming the "small EV motor" is BLDC/PMAC type. If so, it's well possible it might work. Give it a try.

author: firewalker
author_rank: Super Contributor
timestamp: July 19, 2023, 02:01:58 pm
content: I failed to explain what EV means for my occasion. It means a four passenger vehicle. The motor could be a motor from a Nissan Leaf (3 phase synchronous) for example or from a Mitsubishi i-MiEV (PMAC). High voltage high power motors.I found the following video. This guy seems to drive it with a "flimsy" low voltage PSU and some beefy IGBTs.Alexander.

author: Benta
author_rank: Super Contributor
timestamp: July 19, 2023, 06:25:34 pm
content: With those kind of motors: no way.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 19, 2023, 06:33:11 pm
content: Quote from: Benta on July 19, 2023, 06:25:34 pmExactly why not? Largest RC motors are a few kilowatts with phase currents in over 100A. A "small EV motor" might be just a few times bigger in power or so. It would have higher nominal voltage but that would only translate to smaller maximum RPM. A lower-voltage ESC could still rotate it with low RPM. The only big question I can see is whether the ESC manages to do sensorless commutation properly.

author: Benta
author_rank: Super Contributor
timestamp: July 19, 2023, 08:04:32 pm
content: Quote from: Siwastaja on July 19, 2023, 06:33:11 pmDid you even read what the OP is referring to? i-miev is a 47 kW, 350 V system. Nissan Leaf is comparable. Please find me an RC ESC that will drive that. Thanks.

author: uer166
author_rank: Super Contributor
timestamp: July 20, 2023, 01:26:18 am
content: Quote from: Benta on July 19, 2023, 08:04:32 pmI'm sure he read it just fine. How much do you think a 47kW/350V motor consumes while free-spinning at low RPM on a desk?I'd say almost any 10s+ ESC, >50A would spin that. The challenge would be the start, since those motors have some kind of resolver, not the usual hall sensors. It's likely that some ESCs will start that anyway even if sensoreless though. Try and see, report back!

author: xavier60
author_rank: Super Contributor
timestamp: July 20, 2023, 03:42:06 am
content: Does anyone know how that resolver works? I don't see any rotary transformer.

author: xavier60
author_rank: Super Contributor
timestamp: July 20, 2023, 04:25:15 am
content: Quote from: xavier60 on July 20, 2023, 03:42:06 amIt appears to be the VR type Resolver.

author: Robotec
author_rank: Contributor
timestamp: July 20, 2023, 06:37:53 am
content: i dont see any problem in sensorless configuration, a freewheeling motor at low RPM should be fine with a ESC , obviously it wont have the power to drive it as the original driver but for show?, just fine.Setting the motot driver to rotate as a tension/frecuency controler should work just fine without resolver or encoder, the magnetic field will align in the startup as the magnetic field rotates, another option is going FOC.I would recommend VESC drivers the configuration program is straightforward and avoids reinventing the wheel.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 20, 2023, 08:55:28 am
content: Quote from: Benta on July 19, 2023, 08:04:32 pmI don't see any fundamental issue. 350V DC bus probably gets this motor into >5000RPM (without field weakening) so 35V should go to 500RPM or so, roughly. RC ESCs are common up to about 10s battery, or 42V DC bus. These motors have good bearings so you don't need a lot of torque to overcome friction, so even a few amperes should be enough to turn it. There is absolutely no fundamental reason (and I say this out of professional experience); all I'm worried about are those tiny little details like how the sensorless commutation algorithm works and whether it's tuned to certain kind of smaller motors.Now if the question was to use RC ESC to drive the motor while attached to Nissan Leaf, I would say "no way", because in a car you need a lot of torque right from standstill, and that's where sensorless commutation is going to suck in any case, and especially so with a seriously undersized controller. For example, helicopter/airplane ESCs do not need to give a damn about low-speed torque because torque required to turn a propeller goes up quadratically with speed.And yes. I have enough experience running large motors with serious undervoltages. You can still drive a 1000kg car, just up to 20-30km/h or so.

author: langwadt
author_rank: Super Contributor
timestamp: July 20, 2023, 10:15:47 am
content: Quote from: Siwastaja on July 20, 2023, 08:55:28 amthe hw is all there, but at a 10th of the voltage there won't be much for sensorless commutation algorithm to work with

author: Psi
author_rank: Super Contributor
timestamp: July 20, 2023, 11:28:42 am
content: I'm pretty sure it will work if the ESC doesn't give up due to timing being quite different to what it's used to.As previously stated, you need enough voltage so 10-14S battery and ESC is probably required.100A+ 10-14S ESC is what I would try

author: Siwastaja
author_rank: Super Contributor
timestamp: July 20, 2023, 11:37:59 am
content: Quote from: langwadt on July 20, 2023, 10:15:47 amBut it isn't 10th of the voltage. The motor has 10x the nominal voltage, and therefore produces ten times the BEMF voltage at given RPM. Then running at one tenth of nominal voltage decreases it back to 1x.In other words, if the controller detects say 3V BEMF amplitude which would be 10% of its 30V rating, and a 5000rpm@30V motor produces this 3V at 500rpm, then surely a 5000rpm@300V motor should produce the same 3V BEMF at 50rpm.But devil is always in details, that's why I say test it, I can't guarantee it works. I can't prove the absence of something I missed because motor control has a lot of tiny details.

author: langwadt
author_rank: Super Contributor
timestamp: July 20, 2023, 04:16:17 pm
content: Quote from: Siwastaja on July 20, 2023, 11:37:59 amofcourse you are right, high voltage motor higher emf per rpmso the only obvious potential issue is if the ESC will run slow enough, maybe something like the driver for a bicycle hub motor is a better fit?

author: firewalker
author_rank: Super Contributor
timestamp: July 20, 2023, 04:47:13 pm
content: Quote from: langwadt on July 20, 2023, 04:16:17 pmThis is what I was searching just now. For a 6s to 10s ESC from e-bike, e-scooters etc, but the ones for RC cars seems more powerful.Alexander.

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: July 20, 2023, 05:25:34 pm
content: https://goldenmotor.bike/product/vector-500-series-72-volt-brushless-motor-controller/

author: firewalker
author_rank: Super Contributor
timestamp: July 20, 2023, 05:42:51 pm
content: The other thing more safe than having a high voltage/energy battery is to try a "simple" VFD via an isolation transformer. But I guess the large current will trip any "normally" sized VFD.Alexander.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 20, 2023, 06:09:53 pm
content: If the "simple VFD" has a BLDC/PMAC mode, then obviously yes.Isolation transformer does not make the VFD much safer, it still has dangerous voltages at its output.

author: Psi
author_rank: Super Contributor
timestamp: July 20, 2023, 11:03:25 pm
content: I guess it depends how much money you are willing to risk. Unless you can find someone who has lots of RC ESCs that you can test with.This ESC looks like it might be worth a try if you can justify the cost/risk.https://hobbyking.com/en_us/yep-120a-hv-4-14s-brushless-speed-controller-opto.htmlAnd you would want to also get the programming card to set it uphttps://hobbyking.com/en_us/yep-esc-programming-card.htmlIf you check out the programming card you can see that it has option for really slow startup (for helicopter main rotors) and has some PID options too.I would set the freewheel mode (FreeW) to "on", I don't think it's a good idea to have the ESC try to auto-brake that size motormight blow the fets.There's also more expensive version of the above ESC for 180Ahttps://hobbyking.com/en_us/yep-180a-hv-4-14s-brushless-speed-controller-opto.htmlBut I reckon 100A at 50V should be able to get a EV motor to spin with no load.There are more expensive ESCs for E-bikes and stuff that might be more likely to work but cost 4x the price.

author: thm_w
author_rank: Super Contributor
timestamp: July 21, 2023, 12:50:53 am
content: Oh man that YEP unit is comically small, 164 grams.Noname ebike units are cheaper, although they all have hall connections:https://www.aliexpress.us/item/3256804130980146.htmlhttps://www.aliexpress.us/item/2255800947428853.htmlhttps://www.aliexpress.us/item/3256804704639103.html

author: Psi
author_rank: Super Contributor
timestamp: July 21, 2023, 01:00:00 am
content: Quote from: thm_w on July 21, 2023, 12:50:53 amYes, it is small, but remember, it can pump out 51V at 100A or 5kW pretty much continues if you keep it cool.And this application only requires spinning an unloaded motor for educational purposes.And being set in Heli mode means it will slow start up, like the main rotor blades of a heli.Many small RC brushless motors will draw 2kW and are around the size of a golf ball.You cant really judge things by physical size when it comes to ESCs and motors.But i do agree that something for a Ebike/Escooter is a better fit especially if it has lots of motor settings for PID timing etc..And if it's also cheaper its a no-brainer.

author: Robotec
author_rank: Contributor
timestamp: July 21, 2023, 06:15:09 am
content: I would go for VESC, it is completely open source and can be configured with its own program through UART:https://vesc-project.com/example of device (84V 200 A MAx for 160 euros):https://es.aliexpress.com/item/1005005197381369.html?spm=a2g0o.productlist.main.47.139a7e34YfxN9u&algo_pvid=7811e574-9de7-48c1-aa1b-28b031c3ff5c&algo_exp_id=7811e574-9de7-48c1-aa1b-28b031c3ff5c-23&pdp_npi=3%40dis%21EUR%21215.07%21159.15%21%21%21234.00%21%21%402100b88516899196291956748d0775%2112000032097774746%21sea%21ES%21175983338&curPageLogUid=aAgdpRUvPdmbthere are hundreds of devices compatible with the project from chinese or you can go with the originals :https://trampaboards.com/1-x-vesc-6-mkvi---225-each--p-27529.html

author: Psi
author_rank: Super Contributor
timestamp: July 22, 2023, 03:10:25 am
content: open source VESC sounds like a good option, you can mess with the code/timing parameters.You don't have the potential problem where a closed source ESC might have all the hardware needed but the firmware enters an error state because off odd timing.I would start at a lower voltage than 84V though. There is a trade off were if you have too much voltage the inrush current will be too high for the ESC and the back EMF stronger than the ESC may be expecting.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 22, 2023, 05:23:56 am
content: Using very low voltages does not hurt if you just want to test/play around. I have rotated 400V rated motors with a 20V power supply just fine. Especially if the motor is efficient, like large motors usually are, it doesn't require much extra voltage beyond the BEMF (which is zero at 0RPM) to generate torque. RPM is of course very limited.Fundamentally, motor RPM linearly corresponds to voltage at the motor, e.g. a motor rated at 50V 5000 RPM requires 10V to run at 1000 RPM and 1V to run at 100RPM, assuming zero loss. Current that goes into the motor then defines the torque it generates, pretty much linearly.But because of losses, a little bit extra voltage is needed; motor can be mentally modeled as a voltage source with series resistance, so to actually drive non-zero current into it, you have to input more voltage than the motor's internal voltage source, as there is drop over the R. On highly efficient motors, this R is small so even small changes in input voltage lead to large changes in motor current, which is also why motor controllers should do current sense / active current limitation.

author: Berni
author_rank: Super Contributor
timestamp: July 24, 2023, 05:56:54 am
content: Yep there is no point in going to high voltages if you don't need to spin the motor fast.Brushless motors this huge have very low resistance windings so applying only a few volts can already send many 10s of amps of current trough them. It is only when the motor starts spinning at a decent RPM and starts generating its own back EMF, that's when you need the higher voltage to overcome the EMF and continue pushing current into the motor.The voltage required at a given RPM is the Kv rating for the motor, this is the voltage constant, it tells you how many RPM per Volt of input you can get. Hence why running at near 0 RPM needs near 0 Volts. (However you can squeeze even more RPM than Kv would suggest, using field weakening methods)Similarly BLDC motors also have a Kt, this is the torque constant. It tells you how many Nm of torque you get for every Ampere of input current. Motors can be designed to optimize for one or the other of these. If you use weak magnets and low number of turns you get a motor with a high Kv that can spin really fast but not produce lots of torque. Conversely you can use stronger magnets, more turns on coils, more poles...etc to get a high Kt motor that will produce a lot of toque, but will also have a low Kv so it won't spin very fast.In general an EV car motor will be designed for more of a high Kt because it needs the torque, while the low Kv can be compensated for by using a very high battery pack voltage. Such low Kv motors are easier to drive since the current control loop does not need to be as fast (lots of turns means lots of inductance, hence slow current change) and since they tend to have high Kt, they will pull the rotor alignment using less current during sensorless startup.Electric bike ESCs are indeed a good fit since bikes also use high Kt motors, but since they don't need to spin as fast (heck a bike wheel would probably explode at 5000 rpm) means they can get away with much lower battery pack voltages in the 24V to 90V range (since some people want to go unreasonably fast on a bike).

author: langwadt
author_rank: Super Contributor
timestamp: July 24, 2023, 01:39:40 pm
content: Quote from: Berni on July 24, 2023, 05:56:54 amif EVs didn't use low Kv motors and high voltage batteries the currents needed would be sky high, the powerstage would be quite the challenge and wires would need to be the size of fireshoses

author: Siwastaja
author_rank: Super Contributor
timestamp: July 25, 2023, 03:17:40 pm
content: Quote from: Berni on July 24, 2023, 05:56:54 amI think EV motors are balanced designs between speed and torque, where maximum efficiency and minimum motor weight are the targets, and speed/torque will be what it is. This is because torque is not exactly important as there will always be a gearbox. High rpm (6000-8000) + gearing it down for wheels (<1000rpm or so) gives overall minimum weight and maximum efficiency even if you count in the weight and efficiency of the gearbox (which in an EV is a simple fixed reduction gear, much simpler than ICE gearbox, automatic or manual.)Direct wheel drive motors are different, but they are not usual in normal EVs. They are just very heavy as a lot of iron is required for the torque, and due to that weight you can't really mount them to the wheels directly but need CV joints to decouple the unsprung mass, and once you have that adding a tiny gearbox at the end of the motor is not a big deal anymore and makes the motor so much smaller.Choosing the voltage/current relationship in a motor is trivial and does not affect the torque/speed characteristics except that multiplier value. It's exactly like when winding a transformer, you just choose number of turns according to voltage you want and the wire gauge (or total section when using parallel wires) according to current, while trying to maximize the fill rate within the available window. You can rewind a motor to a different voltage by just changing this relationship and a 400V 10A motor becomes a 100V 40A motor and nothing else much changes.

author: Berni
author_rank: Super Contributor
timestamp: July 25, 2023, 04:11:07 pm
content: The motors in EVs can get most of the gear reduction already in the differential. Since usually they have one motor they need a diff to power 2 driven wheels, you can then choose the gears in the diff to get a desired reduction ratio for free. This is why internal combustion cars tend to have the gearbox be a direct drive 1:1 ratio in 4th or 5th gear and yet the tires don't hit 5000 rpm.But yeah EV motors tend to spin at about 2x the typical RPM of internal combustion engines since higher RPM means more total power out of a smaller and lighter motor (So they do sometimes have gearboxes for when the ratio is too big for the diff alone to provide). But they are still fairly low Kv since running at ever higher RPM can present other challenges like how to make reliable long lasting bearings and gearboxes to handle that RPM while being low cost and efficient. The motor construction might become more complicated at some point to avoid the rotor tearing itself apart, the core losses etc... So in the end you end up with a Kv that is close to the slow spinning ebike motors.The high Kv motors are the tiny motors in model aircraft and drones. They don't have a lot of Volts in the battery pack to work with since having 100 cell batteries is not practical, but they do want a lot of power from a light weight motor. So they often go for insane RPM, they don't need a gearbox since they can directly spin a propeller, as a bonus a high RPM propeller is also smaller. As a result they pump insane amounts of current into the motors to get any meaningful torque out of them, the ESCs even have to be specially designed for high Kv motors as they need to have very fast regulation loops to keep up. That is why those ESCs are not that well suited.

author: macboy
author_rank: Super Contributor
timestamp: July 27, 2023, 09:22:10 am
content: RC Drone or plane ESCs never need to spin the motor especially slowly but an RC car ESC does. Not all do it equally well, but some can drive the car very slowly. It works out to much less than 1000 RPM, and that's on a 2 pole motor no less.

author: Psi
author_rank: Super Contributor
timestamp: July 27, 2023, 11:28:00 am
content: A lot of RC ESCs can handle anything from like a 160KV pancake outrunner motor designed to spin a 22 inch prop on a large quad, all the way up to like a 6000KV inrunner designed to spin a 2.5inch prop on a small foamy and scream across the sky at 200kph. And i've seen up to 11000KV and as low as 80KV in the RC industryThere are ESCs intended for a specific purpose, but in general they are quite forgiving with KV ranges. You just have to set them up right.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 27, 2023, 12:50:42 pm
content: Quote from: Psi on July 27, 2023, 11:28:00 amThis causes so much physical pain to my eyes, there are these normal SI units for things you know, 160kV WTF? That would be definitely outside of radio control toys by four order of magnitudes. Or maybe you mean 160V/rpm or what? 200kph is what? Knots per hour? Or maybe km/h, if that, then say so? (Sorry for a blunt rant.) And when did that kilovolt become a kelvin-volt?

author: Psi
author_rank: Super Contributor
timestamp: July 27, 2023, 12:53:23 pm
content: Sorry, i'm much more used to writing kV than KV.Fixed.But there's nothing wrong with kph

author: langwadt
author_rank: Super Contributor
timestamp: July 27, 2023, 03:00:27 pm
content: Quote from: Siwastaja on July 27, 2023, 12:50:42 pmshort hand for KvK for constant and v for velocity, messy but that's how it is

author: Siwastaja
author_rank: Super Contributor
timestamp: July 27, 2023, 03:42:24 pm
content: Note the difference between symbol and unit. One does not write current is 5I, just because I is symbol for current; instead, I = 5A. Similarly, Kv= 100 rpm/V, where rpm/V is the unit. KV = kelvin*volt, which makes absolutely no sense.There is nothing messy in the symbol Kvand it follows the practice of using K for constants like this, where units are then application-specific. But it's a symbol, not an unit. If you want to be concise, just don't use the symbol at all, the unit obviously tells the reader what it's all about, just like we say "1000W heater", not "P=1000W heater" or, incorrectly, "1000P heater".Note that SI system reuses same letters in both symbols and units. V as symbol is volume, V as unit is volt for example.

author: langwadt
author_rank: Super Contributor
timestamp: July 27, 2023, 04:06:23 pm
content: Quote from: Siwastaja on July 27, 2023, 03:42:24 pmsure, but it is when written as Kv when you don't have subscript

author: Siwastaja
author_rank: Super Contributor
timestamp: July 27, 2023, 04:12:08 pm
content: Quote from: langwadt on July 27, 2023, 04:06:23 pmYeah, but it's never written after a number, because it's not an unit.Using standard 7-bit ASCII is not a big sin IMHO. Programmers are for example limited to such symbols in their code, so Kv is fine for a symbol (but still not unit).