DIY Electric Car Forums banner
1 - 20 of 27 Posts

·
Registered
Joined
·
130 Posts
Discussion Starter · #1 ·
Working on a solution for a parking brake for my Tesla LDU powered Land Rover Series 109. With the conversion the LDU replaces both engine and transmission. In 1968 Land Rover had a drum brake style parking brake mounted on the transfer case so there is no current option on the wheels for any kind of cable actuated parking brake. The only solution I can see is to create a Pinion Brake. Mounted to either front or rear axle differential. I was talking about it over on the thread where I have been warning people not to buy from @PolyKup but I thought it would be nice to have a freestanding thread in the topic here.

There are a couple ways to go. Manual actuated pinion brake or why not use a Tesla Model S electric caliper?
 

·
Registered
Joined
·
130 Posts
Discussion Starter · #3 · (Edited)
For the cool factor the Tesla electric caliper is the way to go. The question is how to control it. It comes with 4 wires. 2 heavier ones, which when 12 v is applied will either activate or release the caliper piston depending on polarity. 2 fine wires are the main topic of discussion here.
Automotive tire Bumper Automotive wheel system Metalworking Auto part
 

·
Registered
Joined
·
130 Posts
Discussion Starter · #4 ·
To control the unit there is an off the shelf solution from Pantera Electronics the more I think about it it’s actually pretty robust and may be worth the money as it is feature complete.
Font Screenshot Web page Games Multimedia
 

·
Registered
Joined
·
130 Posts
Discussion Starter · #5 ·
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.

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.
 

·
Registered
Joined
·
130 Posts
Discussion Starter · #6 ·
My initial thought was, Why can’t I have two buttons, one that powered on the caliper by applying 12v and one that applied it in the reverse polarity to release and just call it good?

Remy_martian said
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.
 

·
Registered
Joined
·
130 Posts
Discussion Starter · #7 ·
Brian said


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.
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…
 

·
Registered
Joined
·
221 Posts
If you haven't experienced a driveshaft parking brake being applied while at speed, it is quite terrifying as the wheels hop and skitter all about the place. I'd suggest keeping it super simple, an electric window switch is about all you need. The increase in current when applied cuts off the power, just like when the window is fully up.
 

·
Registered
Joined
·
221 Posts
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.
 

·
Registered
Joined
·
124 Posts
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.
Nothing, not even tesla use a fully electric brake, Its always hydraulic. The electric component is only the handbrake. (and ibooster)
If your only using the caliper as a park brake, there are probably more compact options out there if you didn't want the use the whole bulky tesla caliper.
with it mounted as a pinion brake, were you planning on using the hydraulic part as well? or just keep the factory landrover drums? Willwood do a E brake caliper thats specifically for the park brake.

They also do a caliper control box, but not sure how it'd interface with anything non wilwood? The calipers look like they use the TRW motors, with the standard 2 pin plug

Also, as a thought to consider, Im helping my friend making a V8 SWB land rover. We had the same handbrake issue once we put the V8 in, the drum fouls on the mid chassis crossmember. He ended up using an off the shelf land rover disc brake handbrake conversion, Bought fromthe UK somewhere I think? That could be an option for you, as in the caliper bracket and mounting position?
Disc Handbrake Conversions - Paddock Spares - Paddock Spares (This one I think?)

Also, have you seen this thread?
They don't really talk much about the electric caliper, But there are pics of the X-Engineering brake caliper conversion
 

·
Registered
Joined
·
130 Posts
Discussion Starter · #12 ·
Some of these options still seem to use the original gearbox, this has been removed. The willwood options don’t have any particular cost savings so kinda puts me back to square one. I do appreciate all of the options tho. Nice to have everything in one thread….
 

·
Registered
Joined
·
130 Posts
Discussion Starter · #13 ·
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.
Seems like a simple 5 amp fuse could avoid catastrophe if the operator was unawares….
 

·
Registered
Joined
·
221 Posts

·
Registered
Joined
·
130 Posts
Discussion Starter · #17 ·
Ok so happy to report Sucess using a 10 amp resettable fuse and a 2 way toggle switch to reverse current polarity easily does the trick! I started with a 5 amp resettable switch. If you lean on that hard it will trip the fuse. Switching to the 10 amp fuse and leaning HARD until you obviously hear the brake fully clamping or releasing does not trip the fuse!
 

·
Registered
Joined
·
130 Posts
Discussion Starter · #19 ·
Boom. $300 bucks saved. Figured it out before window regulator switch even showed up using a more authentic looking old school switch I had laying around…. Cost $10 for an assortment of resettable fuses …. Making up for that $3600 that PolyKup shafted me for …. Not bitter….
 

·
Registered
Joined
·
2,984 Posts
Looks like the premium caliper senses the current for consistent clamping force.

My concern with your technique is not being able to release the parking brake with a lower 12V battery voltage than when you set the brake.

For your next experiment, clamp at 13V, release at 9V...if it does, Bob's your uncle.
 
1 - 20 of 27 Posts
Top