The H-bridge module in the post #18 link (and I suspect many other H-bridge modules) is intended to receive two PWM drive signals. A standard analogue RC servo circuit would not provide those. As I understand it a digital servo does use some sort of PWM internally, but whether or not that would be suitable for driving the module in the link is debatable.
Standard RC servos have a potentiometer on the output shaft to provide positional feedback to the circuit. You may have to fudge a pseudo-position signal to fool the circuit.

 

The H-bridge module in the post #18 link (and I suspect many other H-bridge modules) is intended to receive two PWM drive signals. A standard analogue RC servo circuit would not provide those. As I understand it a digital servo does use some sort of PWM internally, but whether or not that would be suitable for driving the module in the link is debatable.
Standard RC servos have a potentiometer on the output shaft to provide positional feedback to the circuit. You may have to fudge a pseudo-position signal to fool the circuit.

Yes indeed. That is why I indicated he may have to dig for signals from the servo board itself. Meaning, gutting an "RC" servo for the H bridge drive signals.
I have not tried it but it may be possible. But the other way is to use the Arduino example that abound.
All in all, it is a bit of a dicey project that I can see many pitfalls in. A lot of fail safe provisions need to be built in.

 

A windscreen wiper motor could work very well, but all i have looked at have a plastic main gear. I think the constant load on the same few teeth would see if fail at the most inconvenient time.

 

Rc servos use a 1 to 2 ms pwm for position control, 1.5ms being centre.
And yes a potentiometer on the output shaft for position feedback.

I might have to bite the bullet and learn about programming an arduino!

 

If I had this to do I would likely consider using a pressure sensor on my towing vehicle to measure the master brake cylinder front brake pressure. While I have no idea what that is my light read is between 400 PSIG and 2000 PSIG depending on how hard we stand on the brake pedal, the force we apply. I would get a transducer with a voltage out with 0 to 5 Volts preferred. I would use an Arduino or similar uC (micro-controller) looking at pressure which should be proportional to the force I am applying to the brake pedal. I would then use the uC to drive my motor be it PWM or a Servo type output. While a mechanical linkage running a potentiometer could be used in the RV I would likely consider using a pressure sensor. I am just replacing the pot used in the link WIPER MOTOR AND ARDUINO MEGA SERVO with a pressure transducer. I am still not sure about backing the force off the vehicle in tow.

Ron

 

Not a bad idea there!
I think i will stay with using a potentiometer on the brake pedal as my source. In the unlikely event of tow vehicle brake failure i will still have a set of brakes behind me to pull up with.

 

I think you guys are over thinking this whole thing. Even though it is a vehicle being towed it is still in all actuality a trailer. To my knowledge surge braking normally used with a trailer isn't proportional, it is either on or off. Why do you think it is any different when it's a car being towed? I towed a Jeep for many years long ago with a tow bar, flat towing. And never had any problems with the Jeep not having working brakes while towing, so know it can be done.

To think there is a need for these proportional bakes makes it sound like the towing vehicle isn't big enough for the vehicle being towed. A very bad situation. If this ends up being built and it fails, what is the consequences, when the insurance company finds out there was a home built "brake control"??

 

Trust me i am doing this to comply with regulations and insurance requirements.

I came asking for help on an electronics question. All the other help while meaning well isnt required.

 

Trust me i am doing this to comply with regulations and insurance requirements.

If this is a requirement, then why are there no off the shelf articles available? And if they are available, why not reverse engineer one?

 

I can see here rather the problem that 40A is rather large PS, however voltage is laughful 6V. There would be interest to use an ATX 12V output for 20Amps and apply the down-converter producing 6V40A from 12V20A. One of such brilliant options is hip6301/hip6601 from pc core inner re-supply. One is controller and other is binded driver. Both together may easily produce even 240A with small transistors working in the 2phase, 3phase or 4phase regime. Thus, the I(ds max) one may overstep about 4-fold. Example of use is as well as at datasheet, as well at Danyk.cz circuitry page.

 

I can see here rather the problem that 40A is rather large PS, however voltage is laughful 6V. There would be interest to use an ATX 12V output for 20Amps and apply the down-converter producing 6V40A from 12V20A. One of such brilliant options is hip6301/hip6601 from pc core inner re-supply. One is controller and other is binded driver. Both together may easily produce even 240A with small transistors working in the 2phase, 3phase or 4phase regime. Thus, the I(ds max) one may overstep about 4-fold. Example of use is as well as at datasheet, as well at Danyk.cz circuitry page.

Huh? Did you read the original post which started the thread and any of the replies? Maybe I missed something but how do you power an ATX PSU in a towed vehicle? There is no need for 6 volts at any high current. The mentioned 6 volts is only a control voltage.

Ron

 

Reloadron: Yes, I didnt read whole. I read that there is need to get 6V from 12V and there ought be 40A. Its new for me that object is vehicle. Youre right.

 

For starters, an arduino and a model servo will wind up killing people in that application. The answer has already been given, which is a servo, which means a closed loop system. The simple approach would be a position servo, so that the more your brake pedal was pushed the more the servo would push the brakes in the towed vehicle. But you could also do that with a hand controller, where the farther you pushed the button in the harder the motor pushes the pedal. You would need to use a heavy compression spring to convert the position to force, but that would not be hard. And position servos are available both new and surplus, and probably even available down under. They are used in some farm implements as well, and so you may find exactly what you need ant a farm equipment dealer. AND, that product would work the first time and be reliable.

 

Have you looked at a commercial electric brake system? The controller is a proportional PWM driver and usually has an inertia sensor so if you slow rapidly the trailer brakes come on. As well as link to the towing vehicle's brakes, it will have manual override too. This will be usable on a normal caravan or trailer and a linear power solenoid could be added to the brake pedal of your towed car.

 

Have you looked at a commercial electric brake system? The controller is a proportional PWM driver and usually has an inertia sensor so if you slow rapidly the trailer brakes come on. As well as link to the towing vehicle's brakes, it will have manual override too. This will be usable on a normal caravan or trailer and a linear power solenoid could be added to the brake pedal of your towed car.

I have a commercial electric brake system on my travel trailer, and while it does in fact control electromagnets, they do NOT directly apply the brakes. Instead, the electromagnets are on the ends of levers and they ride against the side wall of the brake drums so that as the attraction is increased the motion of the wheel pulls harder against the wall, increasing the drag and thus the applied force through the lever. Solenoid force is far to non-linear to smoothly control braking, while the constant air-gap of the sliding electromagnet allows a linear change in braking effort with the change in current.
Thus the construction of those drum brakes is totally different from the construction of regular vehicle brakes. They are not at all similar.

 

Do you have any idea what the force required to move the brake pedal will be?
I was thinking of something like these...
http://www.pneutrolspares.com/media/specs/Deltrol_Controls_MED24x2-4_Tubular_Frame_Solenoid_PIL.pdf
A solenoid similar to these could be mounted to the towed car's brake pedal with a removable pin, or even left there if it moves freely while un-powered. I just do not know if they come in a strong enough version. It does depend on how the brakes work.
Whatever system you use, it will be non linear so tuning will be required. And you need to be able to adjust the amount of braking applied to the car.
It does sound like an interesting project. I hope you get it going ok.

 

Do you have any idea what the force required to move the brake pedal will be?
I was thinking of something like these...
http://www.pneutrolspares.com/media/specs/Deltrol_Controls_MED24x2-4_Tubular_Frame_Solenoid_PIL.pdf
A solenoid similar to these could be mounted to the towed car's brake pedal with a removable pin, or even left there if it moves freely while un-powered. I just do not know if they come in a strong enough version. It does depend on how the brakes work.
Whatever system you use, it will be non linear so tuning will be required. And you need to be able to adjust the amount of braking applied to the car.
It does sound like an interesting project. I hope you get it going ok.

If the brake system on the vehicle is a power-brake system but the engine is off so that there is no assist power, the brake force can easily reach 20 pounds. You are not going to get that much force from any reasonable solenoid with a stroke of three inches or more. In addition, a solenoid big enough to apply that much force near the start of the stroke will take a whole lot of power. I suggest that you look at a service document for an electric trailer brake system to learn why it is not adaptable to a towed vehicle.

You need a position servo system with a spring to be able to control the force in a reasonable manner. A force servo would be even better but that is a lot more complex and it would cost more and be less reliable.
One more possible choice is a motor driven two-position servo, so that when operated it would move to apply some level of braking that was preset, and when released would back off completely on the brakes.

 

Do you have any idea what the force required to move the brake pedal will be?
I was thinking of something like these..

If the brake system on the vehicle is a power-brake system but the engine is off so that there is no assist power, the brake force can easily reach 20 pounds.

From what I can find online, the force(maximum) on the brake pedal for power brakes is ~70 pounds. You guys are telling him something the TS doesn't want to hear. He hasn't been back since I told him the same type of thing. He wants to do this his way with things he already has. The solenoid was something I suggested earlier.

He says that this is something required by insurance and law for a towed vehicle. But there are none of these for sale that I could find. So I doubt that statement very much. As someone that flat towed a Jeep for many years, the prime thing with doing that is picking a tow vehicle that is big enough to do the job. You don't tow a dump truck with a Yugo for good reasons. Even around here they won't rent an empty trailer to you if the tow vehicle isn't up to the loaded weight limit of the trailer. It all comes down to physics in the end.

 

From what I can find online, the force(maximum) on the brake pedal for power brakes is ~70 pounds. You guys are telling him something the TS doesn't want to hear. He hasn't been back since I told him the same type of thing. He wants to do this his way with things he already has. The solenoid was something I suggested earlier.

He says that this is something required by insurance and law for a towed vehicle. But there are none of these for sale that I could find. So I doubt that statement very much. As someone that flat towed a Jeep for many years, the prime thing with doing that is picking a tow vehicle that is big enough to do the job. You don't tow a dump truck with a Yugo for good reasons. Even around here they won't rent an empty trailer to you if the tow vehicle isn't up to the loaded weight limit of the trailer. It all comes down to physics in the end.

Yes, max force can be a lot higher than 20 pounds, but for assisting in handling it can be less. The rental places are so very conservative because of the history of courts awarding huge amounts to stupid people. I won't put that into more polite terms!
AND, it is not the thread starter who keeps suggesting the solenoid. That is another participant. A fairly fast position servo that is able to provide enough force to push the pedal will still be a fairly big deal, though. One more thing is that for trailers with brakes it is important to have something to apply the brakes if the trailer becomes disconnected from the tow vehicle. That is even more important with a jeep type that could coast a very long distance if it came loose.

 

Im still about!
just had a big weekend race meeting i organised to run.

There are remote braking units available, invisibrake for example. it is vacuum actuated tho.
There will be a breakaway switch fitted in the event of vehicle disconnection that applies the brakes.
For those so worried about the rules, lookup A frame towing on the Vicroads website.
A frame towing is completely different to towing a caravan as far as there concerned.