I know I have posted something similar earlier but I could not find it. The question however, is a bit different.
I have been doing a lot of testing with RC models. (yes, I will post the projects when it is working to my tast )
Anyway, I have created a "burnout" mode on one of my RC cars. Simply said, the arduino applies the discbrake on the front or rear wheels enough to make the other side spin its wheels.
No full throttle or full brake is applied because that would burn the motor controller instantly.
However, blocking (or nearly blocking) a 2800Watt motor on 25+ Volt can create high currents. And that is where the arduino should help.
I have multiple ESC's up to 120 and 150A. That should be more than enough but blocking can create currents that are way higher.
I would like to create a device that kills the whole ESC when reaching a certain current. For a 120A ESC, kill it at 110. 150, 140.
Is this even possible? I realise these are high values. Arduino just needs to flick the on/off switch when reaching the limits of the ESC. Or should I abandon the (sensational) idea to do burnout with my RC car?
If I want something to happen at a certain current or when a current is greater than a preset value it's not a problem. Since it's about current you need a means to measure current. Do you have any specific type current sensor in mind? It starts with a sensor and then what? Once I meet or exceed a threshold what do you want to happen and how?
Have you considered dynamic braking? Simply (I assume you are using H-Bridge) set both outputs either high or low. The current will start high and drop off rapidly as the motor slows down. I have no idea what ESC's are. This is how we stopped DC motors a few years back. I hope this helps.
ACS756 family of sensors might be useful here. Presumably you'd use pulseIn to read the throttle setting, analogRead() to sense the current, and modify the throttle setting and use the Servo library to push out the modified value.
This ESC is supplying the brushless motor with its voltages and currents. In my own current setup up to 80A when driving normally. But when I want to do burn-outs, it might be possible that I lock up the wheels and draw more than 150A. IF this happens, I want the arduino to just switch off the ESC by turning a pin to low or something. The ESC has a manual break/make switch so that part should not be very difficult.
But, With what kind of sensor can I measure these high currents without degrading the performance?
This all begins, as was mentioned, with your choice of current sensor and how deep your pockets are. Just as a few examples there are DC Current Shunts. Relatively inexpensive with a DC output volatge proportional to the actual current. Each method has good and not so good points. Just to explain a 0 to 200 Amp shunt may only have an output DC voltage of 0 to 50 mV so to become useful that really needs amplified requiring more hardware and parts. There are some basic current shunt amplifiers out there to be had.
Hall Effect type DC sensors are pretty cool and accurate and also have a price tag to match. Real nice is bi-directional current flow like a shunt but everything is onboard so a 0 to 200 Amp sensor can easily output 0 to +/- 5.0 volts or +/- 10.0 volts or even current loops like 4 to 20 mA.
Regardless of sensor you scale your code accordingly. You likely have an analog input proportional to the sensed current of volts so you scale that analog in to read out in Amps.
That done it's a matter of as already mentioned in your code. If my current is greater than then do something.
Shunts are fine. The downside is a need (normally) for amplification. There is no shortage of very inexpensive shunts pouring in from China. Not great but they work.
In this example the large bolts are the main current path and the small screws are the voltage signal out.
Using the above example with a full scale current of 200 Amps the Vout will be 75 mV. All we are really doing is measuring the voltage drop across a known resistance.
Something I have never tried would be use an Arduino Uno which only has a 10 bit ADC and add an ADS1115 AD converter with I2C. As seen the ADS 1115 can be had on a breakout board and affords programmable gain. I have used them with good results.
Is there a way to simulate these high currents outside my RC car? For testing purposes?
I could build a motorsupport and just block the outgoing shaft but I dont think that would do the motor any good.
I guess I have to use one big M****fu**er of a resistor?
The way this is normally done is to place a motor under test in a test fixture and apply a magnetic brake or any brake while measuring things like shaft RPM and torque but you start getting into expensive test systems. What is being done is the motor is being "loaded" and while under given loads the current is measured. All of this data is normally recorded and charted.
A Google of EDDY Current Brake or Mag Particle Brake will give you some idea.
You have heard of Dyno testing of cars and motorcycles? Think miniature scale.
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