electric calipers aren't that simple. I've seen someone use a pair of automatic power window close modules to operate their caliper. On the bench, its great, works perfectly. It was enough to convince me it was feasible to fit electric calipers as part of my diy.
There are things that need to be considered in its operation.
When engaging (clamping) you need to sense the motor current. The current draw when the motor is running is fairly constant, but when it finally clamps and builds pressure, the current spikes as the motor is loaded up. When it spikes, you need to cut the power to the motors, otherwise you risk burning them out. The e brake motor module used on a lot of Japanese and Euro calipers (TRW?) seems to be a fairly common fail point, so they are probably quite susceptible to over current burning them out over their normal operating life.
When disengaging the caliper, the motor has slightly more current as it starts, then drops to its regular level as the clamping pressure drops and the pads move away from the rotor. Nothing really needs to be measured electronically there. The catch is that its the time retracting the pads that is really important. If you pull the pads too far back away from the rotor, you then have to use a lot of pedal travel to put those pads back there. It may only be the first time you put your foot on the brake, but it still needs to be done. When do you put your foot on the brake when you first start driving? when you approach the first stop sign/intersection... A time you really want your brakes to work.
If the pads are only pulled off the rotor a mm or so, you'll never notice it. If they are pulled several mm off the rotor, the pedal will feel like that time you changed your pads and fluid, then forgot to pump the brakes back up afterwards (You only ever do that once)
In the Tesla calipers, they have 4 pins per caliper. From what i've figured out 2 are for the motor, reverse polarity to run the motor in the other direction. The other 2 are a sensor wire of some description, perhaps pad location? motor step position? I'm not overly sure as im not using Tesla calipers so I haven't spent a huge amount of time learning about them in particular.
The Euro/Jap TRW E caliper generally only has 2 pins, Just the motor. I suspect the controller is monitoring the current output and cutting it as it spikes and simply being a timed thing when disengaging.
There is also a 'roadworthy' saftey requirement in many places, where you cannot disengage the calipers unless there is a brake pedal signal as well (Holding the brake pedal on)
Here in Australia, to be considered roadworthy and pass engineering, you must have the ebrake only able to disengage while holding the brake pedal, so using something like a power window auto close module would be a big no no here. Somewhere where the rules are a lot more lax, maybe its a possible option?
There is also the consideration to be made if you are creating your own circuit, This is a saftey item, It must work properly at all times, It has to fail in a safe way, You don't want it accidentally engaging while you drive or accidentally releasing while your parked etc.
Maybe put a diode and power resistor on the actuate direction to make sure it'll release. Or maybe that's built into the mechanism.
Early Model S had a separate ebrake caliper. Newer has it built in to the hydraulic one.
Great video. I’m getting interested in arduinos. Also liked the idea of adding an obd2 dongle to access the canbus info and display it on a phone or tablet. May be a great substitute for the $3500 unit I paid PolyKup for but never received. Oh wait that’s a different thread…It might seem that way, but it's not that simple. Here's SuperfastMatt's take on the subject, illustrating what TeZla explained:
Tesla-Jag Gets The Red Carpet Treatment
There are different versions of parking brake controls in different Teslas, possibly even within the same physical caliper design.
Nothing, not even tesla use a fully electric brake, Its always hydraulic. The electric component is only the handbrake. (and ibooster)In the discussion started on the other thread TeZla had some great points. The only thing I would say was I was only looking for a parking brake. I wouldn’t want to rely on the unit as my only source of braking. I actually am thinking of an iBooster down the road as a separate project.
Seems like a simple 5 amp fuse could avoid catastrophe if the operator was unawares….worth a shot for twelve bucks. There are a heap of different ways the current is cut off in the automatic systems so it might need more than just the basic switch to have it automatic. I read about somebody doing it with a window switch but can't find the reference now.
Could also use it as simple human-in-the-loop but that would require a small amount of operator awareness since it would be possible to both leave the brake partially on and also burn out the motor from holding the switch on for a long period.