Randy's RCR40 MKI

[Brian Kissel]

Here are some pictures of the C8 parking brake calipers. As I said, I haven’t installed them yet. Search electric caliper and something should come up.

 

[Brian Kissel]

With very little effort I came across this. It was about a 2 minute search. There are others for sure. Look at page 24 post 464.

Restarting my SLC project in West Texas

Hi everybody. I am restarting my project after almost a two year hiatus. Had a little health issue that MD Anderson helped me leave behind. So pretty much have been working after my day job until 11 or 12pm every day for the last couple of months. I will post pictures of my progress. So far...

www.gt40s.com

Regards Brian

 

[Brian]

As you've seen, linear actuators and the electric parking brake calipers need more electronics than just full beans until it bottoms out.

You need to current limit the motor on the set direction, and stop when the voltage drops and current hits the peak. Then when reversing, you need to apply more max current, but timed. Maybe just a second or 2 after the current draw drops to freewheeling. You can run the linear actuator to the limit on release, but there is no limit switch in the parking calipers that I've seen. If you give it the beans for too long, you're liable to unscrew something internally, or bottom out the leadscrew and lock it up.

With the linear actuator, you could let it run to the limit but put a huge ass spring between the actuator and cable, like a mountain bike coil over that's 500 lbs/inch. I would go electronics on this.

I don't have any familiarity with the module you have, but unless it has adjustments I don't think it has the current limiting functions you need.


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I see Hector has the same Tesla calipers I bought playing around with the idea of adding them to the cobra. There was a recall a few years back and these Brembo made calipers removed for recalls could be had for $100/set. And I see he found a module for them.

 

[Brian Kissel]

That’s a deal. I paid $250.00 per set. These were take offs from zero miles C8’s. When the tornado swept through Bowling Green a couple years ago, several brand new Corvettes were destroyed. These were then sold and parted out. I was lucky enough to buy a couple sets.

Regards Brian

 

[Randy Folsom]

Brian K,
I saw Hector’s post but he’s working on an SLC. The shocks on the RCR40 unfortunately won’t allow for anything like the Tesla or C8 parking brake caliper. Wilwood sells a solution that will work, but the cost difference between my bespoke setup and the Wilwood is more than an order of magnitude.

Brian L,
You are correct that ideally there should be a means to prevent over loading, or stopping the actuator when certain conditions are met. However, it’s not hard to simply adjust the linkage such that the pads pinch the rotor before the actuator has reached its limit. There is a lot of flexing in the various parts to accommodate that. On the RCR40 it’s especially easy since the parking brake pads will not wear. On my Cobra, I included a spring compensation mechanism and added additional adjustments because there’s only one set of pads for both braking and parking.

The reality is, I can simply put the car in gear and it’s not going to roll away. I would never rely on my setup, or any other parking brake, for preventing the car from moving on a trailer or a hill in San Francisco. I will say, that the advantage of a hand operated parking brake with a manual transmission on a steep incline cannot be matched by any of the electronic brake solutions. Fortunately, I don’t live in San Francisco.

Cheers, Randy

 

[Brian]

So, these C8 and the Teslas Hector and I have are electric calipers. Instead of a hydraulic piston, there's an electric motor with planetary gears turning a lead screw or maybe just a ramp that clamps the shoes to the rotor.

The trick is you can't just jamb 12V to the motor until it starts smoking. You have to current limit the power to the motor. Torque is proportional to current independent of speed. I'm sure all of these calipers are different and will need different amounts of current to get enough pressure to the pad to lock the tire. You'll have to play with it to find what this current is.

 

[Randy Folsom]

So, these C8 and the Teslas Hector and I have are electric calipers. Instead of a hydraulic piston, there's an electric motor with planetary gears turning a lead screw or maybe just a ramp that clamps the shoes to the rotor.

The trick is you can't just jamb 12V to the motor until it starts smoking. You have to current limit the power to the motor. Torque is proportional to current independent of speed. I'm sure all of these calipers are different and will need different amounts of current to get enough pressure to the pad to lock the tire. You'll have to play with it to find what this current is.

Well it works, and the actuator is happy, so I guess I have played with it enough. It is quite easy to adjust the travel on the Wilwood calipers so that the pads are tight right at the end of the actuator travel. It also help that the actuator is capable of exerting a lot more pressure than needed to keep the rotors from moving.

 

[Joel K]

Those C8 calipers look nice. If I can’t get the provided SLC calipers to to work I may go down that route.

I plan on doing something similar to Randy. Haven’t tried it out yet, but figured I already have the calipers mounted so want to see if I can use them. I am running an electrical PDM with a built in reversing circuit so it will be easy to do a time/current based approach controlling the linear actuator.

I bought one of these linear actuator controllers to control a defroster valve which has a timer and Amperage detector built in. A nice little product. The amperage would need to match the upper limit of whatever actuator you are using.

Here is a link…

12V Reversible Motor Control Modules

AutoLöc's newest motor control module can be used to program up to 2 run times or distances for any 12 volt 2 wire reversible electric motor. 2 total presets available per unit.Easily program your linear actuator or other 12V motor to your specific preferences. Ideal for customizing the...

shop.autoloc.com

 

[Randy Folsom]

Those C8 calipers look nice. If I can’t get the provided SLC calipers to to work I may go down that route.

I plan on doing something similar to Randy. Haven’t tried it out yet, but figured I already have the calipers mounted so want to see if I can use them. I am running an electrical PDM with a built in reversing circuit so it will be easy to do a time/current based approach controlling the linear actuator.

I bought one of these linear actuator controllers to control a defroster valve which has a timer and Amperage detector built in. A nice little product. The amperage would need to match the upper limit of whatever actuator you are using.

Here is a link…

12V Reversible Motor Control Modules

AutoLöc's newest motor control module can be used to program up to 2 run times or distances for any 12 volt 2 wire reversible electric motor. 2 total presets available per unit.Easily program your linear actuator or other 12V motor to your specific preferences. Ideal for customizing the...

shop.autoloc.com

Joel, thx much for the link. I had searched for one of these unsuccessfully. I’m going to order one. Cheers, Randy

 

[Joel K]

Joel, thx much for the link. I had searched for one of these unsuccessfully. I’m going to order one. Cheers, Randy

Randy, they should have the instructions on the site posted somewhere. I should have mentioned this that it uses a pulse or momentary switch to trigger the motion. I would think a momentary rocker switch would work great, press one way to lock, the other way to unlock.