Does your tow vehicle produce enough vacuum to operate a vacuum powered brake controller in a useful manner? That would be my big concern. Also, there would need to be a fair sized tank on the towed vehicle to assure an adequate supply in case of repeated hard braking efforts. An electric servo would be simpler and smaller and it could run off of the towed vehicle battery. In addition, wiring is often simpler than hosing in a vacuum connection. And certainly towing a vehicle is indeed quite different from towing any large and heavy trailer. Both the weight distribution and the steering are totally different, the only similar part is the need for reliability and adequate control.
Another concept would be a hydraulic servo, pressure controlled, driving the towed vehicle's brake pedal from a small hydraulic cylinder. A small hydraulic pump and an accumulator and it could be very effective and quite reliable. And the technology for such is totally mature, all of the pieces are "off the shelf", produced by companies well experienced in the technology. Not as cheap, but very fast and effective. So there is another choice to think about.

 

I mentioned earlier that i have a 12v vacuum pump just finished for the towed vehicle.

The idea is to use a large servo control the braking.

ordering more parts at the moment!

 

A frame towing on the Vicroads website.

And again I ask did you read and understand what that rule says?

"The following requirements apply to the towing, with an
A-Frame, of an unbraked motor vehicle where the tare
mass of the towing vehicle exceeds 3.5 times the laden
mass of the towed vehicle.
Persons wishing to tow with a vehicle that has a tare
mass that is less than 3.5 times the laden mass of the
towed vehicle are required to have control of the brakes
on the towed vehicle. Such persons must seek further
advice from VicRoads or from a Vehicle Assessment
Signatory Scheme (VASS) Signatory. "

Those are the first two paragraphs of the rules. No one with any brains or respect for other people on or off the road would do something like that. Physics are just totally against you. The rules don't say you HAVE to HAVE remote brakes to tow a vehicle, they say you need to have them when doing something dumb. Like towing a car with a motorcycle.

This then begs the question, are you complying with the last paragraph of the rules?

"CertificationUnless the A-Frame is a proprietary item that has been
designed and is appropriately marked as being suitable
for the make and model of the towed vehicle, the AFrames and connecting hardware, including the
connection of the A-frame and safety chains to the
towed vehicle, must be certified by a VASS Signatory "

Meaning unless you have certification for your tow bar you are breaking the law.

 

invisibrake for example

That one didn't come up in the search I did. Did you look at how they do that? No proportional control just on or off, like regular surge type trailer brakes, but operated by the tow vehicles brake lights. And no motor they use an air cylinder.
https://www.truckcampermagazine.com/news/roadmaster-invisibrake-explained-installed-and-tested/3/

 

I mentioned earlier that i have a 12v vacuum pump just finished for the towed vehicle.

The idea is to use a large servo control the braking.

ordering more parts at the moment!

A vacuum actuator should be able to apply enough force but will it be fast enough. Air brakes on a big truck are strong enough, but there is enough delay that a driver needs air brake certification. Of course, if the vehicle already has vacuum assisted power brakes then it is just a matter of creating the means to apply the brakes with an external vacuum. My guess is that would be a bit of a challenge.

 

Shortbus , i have already consulted with a vass signatory.
If we all did what everyone else does there would be no progress full stop.
I am designing and building something superior.
I never ask for legal and safety advice. I have that covered. I came here asking an electronics question!

Misterbill,
Vacuum is only for brake booster on mastercylinder.

 

Shortbus , i have already consulted with a vass signatory.
If we all did what everyone else does there would be no progress full stop.
I am designing and building something superior.
I never ask for legal and safety advice. I have that covered. I came here asking an electronics question!

Misterbill,
Vacuum is only for brake booster on mastercylinder.

OK, that makes perfect sense then. Now I am waiting to hear what the final plan will be, it sounds quite interesting.

 

I came here asking an electronics question!

From the above posts it looks like the brake forces involved rule out them being directly generated by any reasonable sized electric motor. That means the role of a motor in your intended beefed-up servo would be limited to operating some actuator (e.g. proportional hydraulic valve) which in turn did the donkey work. So the choice of motor and its drive circuit would be dictated by the actuator characteristics.

 

Shortbus , i have already consulted with a vass signatory.
If we all did what everyone else does there would be no progress full stop.
I am designing and building something superior.
I never ask for legal and safety advice. I have that covered. I came here asking an electronics question!

Then I will ask a question on that. How do you propose to do this proportionally? With out a form of feedback from the towed vehicles brake system pressure it is just a glorified surge brake system.

 

The actuator could be as simple as a linear position servo loading a spring against the brake pedal, with the position command coming from the driver of the tow vehicle. AND, by the way, the surge brake system is proportional, with tow vehicle braking adding to the brake command and towed vehicle braking subtracting from the braking command. It is just very hard to get it exactly right, and also it sometimes brakes when one does not want it to brake..

 

The actuator could be as simple as a linear position servo loading a spring against the brake pedal

If we're talking about a 70lb force actuator and controlling it with the guts of a hobbyist RC servo, I think "simple" is a tad optimistic .

 

If we're talking about a 70lb force actuator and controlling it with the guts of a hobbyist RC servo, I think "simple" is a tad optimistic .

I would never consider an RC servo actuator for anything other than a hobby model. Hobby servo devices take a very starnge and hard to duplicate control signal. They are not good for other than hobby use, as I see it.

No, I mean a real servo-type linear actuator powered by the 12 volt system. And because it will not need to be super accurate it does not even need to be smooth. Just run to a position and stop, and then back off when that setpoint is given. The position signal would come from a potentiometer sensor and the electronics would be a window comparator and the3 modes would be advance, stop in the deadband, and retract.. No trimming the derivatige and gain terms, just setting the deadband just wide enough to keep it stable. And the controller could be a spring-return variable resistor in the drivers hand, or possibly even linked to the tow vehicle brake pedal.Probably a 10 to 15 amp DC motor with a medium pitch lead screw, having a 6 inch stroke in about 2 seconds, or maybe 5 seconds. Maybe the system would even have a backup manual control to drive the motor relay directly, in the event of an analog hardware failure.

 

The actuator could be as simple as a linear position servo loading a spring against the brake pedal, with the position command coming from the driver of the tow vehicle. AND, by the way, the surge brake system is proportional, with tow vehicle braking adding to the brake command and towed vehicle braking subtracting from the braking command. It is just very hard to get it exactly right, and also it sometimes brakes when one does not want it to brake..

Did you look at how they did it in my link in post #44? But the TS doen't want to 1.use a solenoid, 2. do it like any one else has before. They must have change surge brake controllers since I had one. They were never proportional before, just on or off. And just because the pedal in the towed vehicle moves the same amount as the one in the towing vehicle doesn't mean they are both applying the same brake pressure.

 

I did look at the "invisibrake" installation and it looked horribly complex. And it really did not give any details about how it actually worked, at least not as far as I could see. AND I never ever said that a solenoid would be a good choice, because it would not be a good choice.. There are a lot of different ways to use a motorized servo, and in a very recent discussion with an expert truck mechanic I found that such servo packages are available AND already approved for use on commercial trucks. Using a system that has already been certified is a handy way around a number of issues.

 

Perhaps something like this could be used for driving a linear actuator.

 

Thankyou Alec!

Could be just what im after. I have sent an email to enquire.
A linear actuator with position control is just a straight line version of a servo, being rotary.
Every cnc machine is controlled with servos.
I may use the servo to either pull a cable onto a small drum,rotary. Or to drive a ballscrew pulling the cable, linear.
Testing will decide which is more suitable.
I only need 2.5 inches of travel.
Said cable will be connected to brake pedal as this will be a permamently fitted unit.

 

A solution looking for a problem to solve. That is the only explanation for this thread.

 

Shortbus no idea what your problem is.
I quite enjoy developing things.

I will keep the rest of you updated with progress, your help is greatly appreciated .

 

Shortbus no idea what your problem is.

And I have no idea of what problem your trying to solve. The link you gave to the laws of your country seem to be what is valid any where in the free world. Works with any one using common sense. My self I wouldn't want to be liable for something "home made" having to do with braking or even steering for that matter. The companies doing the building of that type of thing need to be both bonded and insured, they don't do it their back yard shed, using cast off parts.

When you have a wreck and an injured party finds out you made the controller, do you really think your insurance company will stand behind you and pay?? I don't know about the history of other members that are posting, but do know mine. I've been involved with building home built motorsports vehicles most of my adult life in one way or another. And everything I've said comes from doing that. You have never said what type of "racing" vehicle your towing, but from where I'm from a dedicated racing vehicle is trailered, especially in this era. Not flat towed. I did back in the day because it was also a daily driver and took my family with me to camp. And I towed with a vehicle capable of doing the job.

 

Thankyou Alec!

Could be just what im after. I have sent an email to enquire.
A linear actuator with position control is just a straight line version of a servo, being rotary.
Every cnc machine is controlled with servos.
I may use the servo to either pull a cable onto a small drum,rotary. Or to drive a ballscrew pulling the cable, linear.
Testing will decide which is more suitable.
I only need 2.5 inches of travel.
Said cable will be connected to brake pedal as this will be a permamently fitted unit.

I suggest not using a cable for braking, based on my own experience of a cable reaching the end of it's useful service life while I was still using it for operating my two-wheeler brakes. I was very fortunate in that I was only inconvenienced and did not suffer any damage or injuries. Just offering what I learned so that you and others would not need to experience it.. And please note that none of my suggestions were considering anything permanently connected. Less convenient, certainly, but on the other hand, installing a system is one way to assure that all the parts are present and in place. So it will be very interesting to see what your final implementation looks like.