Servo for Remote Car Starter Throttle

by Bob
(Rochester, N.Y.)

I have a 1984 Towncar. I had a remote engine starter put on, but the engine will not start cold, unless you pump the pedal once to set up the throttle body.

I'd like to mount a servo and then connect it to the linkage. It would probably have to be a modified servo. I would like it to pull the linkage, as if the gas pedal had been depressed. Then I would need it to be able to reverse direction. I have to invent some type of mounting and linkage hookup. Not sure yet how much torque I need. I am completely new to servo's, transmitter, etc.

This should be a simple application, just used a few seconds a couple times a day in the Winter. One of the cheaper hand held transmitters would probably work, I'm guessing. Should only need 1 channel, if there is such a thing. Can you give me any advice on this. I will continue educating myself on the internet, will probably need to start visiting hobby stores.

Thank, Bob

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ADDITIONAL INFO
by: Bob

Not much room to work in.

Took a fish scale about 20 pounds to move the linkage at a 1 inch radius, so that puts this in the range of 320 in ounce torque or better. Total rotation required in one direction is about 60 degrees, maybe 70.

I do not think a modified unit would be required. If I can line up and center the shaft of a servo to the shaft the linkage rotates on, I could use one of those multi hole "X" mounts that they come with. Then, extend a drive pin on the needed radius that would rotate and push against a piece of linkage on the shaft. Then the servo could be returned to home position, out of the way of any linkage movement during driving.

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What Stroke is Required?
by: Matt

Hi Bob,

300 in-oz servos are available, but that's on the high end of availability. I've seen them up to 480 in-oz, that would run you around a couple hundred bucks for one servo...

What is the required stroke of the throttle linkage? Will it need to "pump" the throttle or simply engage the throttle for as specific amount of time?

Just thinking outside the box, maybe a 12 volt linear servo may be better? Maybe cheaper also and perhaps operate on 12 volts from your car battery? Would eliminate a need for a second battery?

As far as controlling it, would it be possible to wire it up to the existing remote starting mechanism that cranks the car? What type of voltage or signal causes it to begin to crank? Maybe find some type of relay that would also activate the servo, then retract the servo once the starter stops cranking?

This would save you the added expense of a second transmitter and receiver...

Just some food for thought...

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MORE INFO
by: Bob

The stroke is a little more than a inch, or a rotation of about 60 degrees. I have also started to think along the lines of a 12 volt servo that could run off the car battery. The servo must do the job of pumping the gas pedal once, all the way down, then back up, as if it was done with your foot.

Moving the linkage by using a servo would accomplish this. I've ordered a better fish scale so I can measure the required torque at 2 different points. One would be at a rotational point, the other would be at a point where I would hook on some straight linkage.

I don't know what kind of signal goes to the remote starter that was put on. It would be great if the servo could run off it, but that is beyond me, unless someone reading this knows how to make it work.

Thanks, I will keep thinking and investigating this. In the end, when I (we) have something that works, we can document it on this site for others.

Bob

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Info on Remote Starter?
by: Matt

Do you have any documentation on the remote starter? Did you install it yourself?

If you know the brand and model maybe we can look it up and get some more info on what signals are involved.

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Remote Starter
by: Bob

I have no info on the remote kit. Think I will need to keep the 2 systems separate. The linkage has to go thru its complete motion before you try to start.

Question #1: If I buy a 12v servo, how do you know what transmitter and receiver work with it.

Question #2: I see servo horns with tapped holes to connect to. What is the size of these threads, I cannot find it specified anywhere. I also see some without tapped holes.

Thank you,
Bob

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12v servo's
by: Bob

Can a 12 volt servo be controlled using the radio sets (transmitter and receiver) that are sold to control 4.8v and 6v servo's.
I want to hook up to a 12v car battery. Would the connections be any different. Am I better off buying the radio set where I buy the servo.
Thanks, Bob

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Getting Creative...
by: Anonymous

Bob, the receivers used for RC airplanes typically run on either 4.8 or 6 volts. I'm not really sure what would happen if you plugged a receiver into 12 volts. If you try it let us know!

Although I would highly recommend not doing it..

To be completely honest with you, I'm not sure using RC airplane radio equipment is the best solution for your project. Maybe, but it seems there must be a better solution.

If you DO go this route I'd suggest hopping over to eBay and look for the cheapest transmitter/receiver combo you can find. New or used, doesn't matter. Even toy grade equipment would work for what you're trying to do.

If you want to use a 12 volt linear servo with RC airplane radio equipment you'll need some sort relay switch controlled by the receiver (via the transmitter) to switch the 12 volts from the car battery on/off to the linear servo.

You'll also need to find a voltage regular to step the 12 volt car battery down to 6 volts to power the receiver.

Or you could get crafty and design your own mechanical relay by using a servo...

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MORE INFO
by: bob

Just no room to put anything near the throttle body linkage. Thinking of attaching an extra throttle cable, similar to the way the existing throttle cable and cruise control are connected. Then I could attach it to a servo and mount the servo where I want. So now I need to learn about throttle cables and ends.

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servo for throttle
by: Anonymous

I would rig up something using the recover and steering gear from a toycar to operate a toggle switch which controls a solenoid which operates the throttle on your carburetor. Is it really nesseccary to fully open the throttle or do you only need to open it far enough to engage the choke? Somethimg to consider when choosing a solenoid. A solenoid from an electric door lock mechanism might be all you need but if more effort is required you may have to rig up a starter solenoid.

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different way.
by: rodscot

I tried the same thing you are trying, in that I tried to move the carb linkage to actuate the fuel squirter in the carb so my car would start with the auto start. The servo size, as well as how well it would last if mounted next to the hot engine was also a consideration.

Also consider how safe it would be to have a servo mechanically connected to the accelerator linkage. I decided to tee off of the output of the fuel pump, and run that fuel line to the top side of the carb so the fuel would be dumped into the carb when the starter cranked, which is what a manual choke does. I work in a process-control shop, so I found a solenoid valve that operated from 12vdc and wired the solenoid so it was activated (porting fuel into the carb) whenever the start pulse from the auto start pulsed the starter.

On a cold morning, I activate the auto start, which pulses the starter for about a second, but while pulsing the starter, fuel is being dumped into the bowl.

Sometimes it starts on the first pulse, but it always starts on the second. I designed my first auto-start circuits back when I was in college so my car could warm up before or after class.

Another important consideration with cars is that you can't load down the battery with lots of active components when passive ones operate just as well but don't draw current. Instead of connecting a servo to the mechanical linkage, which could be a pain, you buy two "tees" and some gas line from the auto parts store, and a solenoid valve from ebay for ten bucks and the whole job takes an hour and works great since I've put these start systems on about a dozen cars with carbs.

I put the system in a triumph TR7, and since it had two carbs, I just dumped the fuel right into the intake manifold through a vacuum port. If you have fuel injection the whole process is easier because instead of a carb there is a throttle body.

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