Looking for help designing a circuit to control an actuator/motor

Thread Starter

David_Johnson87

Joined Oct 8, 2018
1
Hi there,

I'm brand new to this forum and I'm sure I will have posted this in the wrong place so I must apologise in advance because I'm unsure as to which topic to post the question under.

I'm wanting some help to design a 12V circuit to do carry out the following:-

- When a momentary switch is pressed, an actuator (or motor with gears and a stop to prevent it spinning continuously in either direction) runs in one direction until it reaches the end of its travel.
- When the momentary switch is released, the actuator/motor returns to its resting/original starting position.

I'm an automotive technician with a number of years experience in wiring and can read and understand schematics.

The circuit is to control an active air brake (rear spoiler) that will tilt upwards by pressing the brake pedal (a momentary switch will be placed underneath the pedal) and stop when the spoiler has reached its maximum upwards tilt angle (unsure how to achieve this). Once the foot is lifted off the brake pedal (and the momentary switch is released), the spoiler will return to its resting position (flat).

I've read up and familiarised myself with linkages etc so am able to control the mechanical side of things but need to be able to control it with input from the brake pedal.

Any help that can be offered would be greatly appreciated.

Thanks, David.
 

Hymie

Joined Mar 30, 2018
708
One possible solution is to use an electric motor with an encoder mounted on the shaft, using electronics to position the spoiler accordingly.
An alternative solution is to position limit switches on the spoiler and using these to control the motor movement.

But a simpler solution would be to detect that the spoiler had reached an end stop due to the motor stalling, resulting in an increased current draw in this state. With a simple circuit monitoring the motor current and cutting the power once above a pre-determined level. However using this solution you would need to ensure that the motor gearing/drive assembly could withstand the resultant motor stalled torque and not strip the gears or otherwise damage the spoiler movement mechanism in this state (for a second or so).
 

dendad

Joined Feb 20, 2016
2,977
Don't use end stops only, but limit switches.
The switches have diodes across them so when open, the motor can run the other way.
SpoilerMotor.jpg
The relay can be one double pole double throw unit, but 2 automotive relays may be easier.
Motor diodes need to be big enough to handle the motor stall current. Power bridge rectifiers use as diodes may be the way to go.
 

Attachments

dendad

Joined Feb 20, 2016
2,977
Bridge2.jpg
SpoilerMotor2.jpg
For the diodes, this is a bridge rectifier of the type I was referring to. Get a 35 Amp one.
 

mtonge

Joined Apr 19, 2016
87
How about servomotors? Gear driven, high torque, 180 degrees of travel, PWM controlled.
 

MaxHeadRoom

Joined Jul 18, 2013
18,995
- When a momentary switch is pressed, an actuator (or motor with gears and a stop to prevent it spinning continuously in either direction) runs in one direction until it reaches the end of its travel.
- When the momentary switch is released, the actuator/motor returns to its resting/original starting position.
Incidentally that is not a Momentary action, but a Push button in a maintained action mode.
@dendad is on the right track, but you can also get descrete power diodes that will do it.
Max..
 

Bernard

Joined Aug 7, 2008
5,252
All that post 3 needs is a DPDT switch, armatures go to + & _ power, cross strapped contacts go to actuator.
Normally the diodes are internal to the linear actuator.
 

MisterBill2

Joined Jan 23, 2018
3,847
One choice not mentioned is one of those relays used for power antenna control in years gone by. They run the antenna up when the radio switches on and then run it down when it switches off. That seems like exactly the functionality you are looking for. And the parts for that may be sitting on the back of a shelf in a shop, unless the shop is run by one of those fixated on disposing of all that is not needed at any particular instant. Of course it is still true that some limit switches would be needed to do it electrically.

If you can drive the air brake flap with an air cylinder the solution becomes very simple with off-the-shelf hardware: A double-acting air cylinder and a four or five way valve. Stepping on the brake operates the solenoid valve and the cylinder extends, releasing the brake releases the valve and the cylinder retracts. And flow controls on the 2 discharge ports of the 5-way valve allow some control of the speed of operation. And every bit of the hardware is fully mature products available from many different sources.
 

MisterBill2

Joined Jan 23, 2018
3,847
Are you talking RC servos? Don't think they have the power for this job, could be wrong though.
SB, MOST of the servos in the world are NOT those RC servos, but instead they are actual useful hardware instead of very specialized toys. RC servos have a unique control signal format not used anyplace else. Other servo systems do not use that strange pulse-width signal that is unique to RC systems.
 

shortbus

Joined Sep 30, 2009
6,968
SB, MOST of the servos in the world are NOT those RC servos, but instead they are actual useful hardware instead of very specialized toys. RC servos have a unique control signal format not used anyplace else. Other servo systems do not use that strange pulse-width signal that is unique to RC systems.
Oh, I know that coming from a industrial back round, but, most people coming here think that RC servos are the only type out there. And in the post I was answering it gave the most common way that RC servos are controlled. which isn't to my knowledge how a real industrial based servo is controlled.
 

MisterBill2

Joined Jan 23, 2018
3,847
I have designed several industrial servo systems, hydraulic, pneumatic, and electrical and electronic. The only part common with RC servos is the name.
And still, it seems that one of those relays used for the power antenna control would be fast, cheap, and easy to create. I had thought about that for the crazy idea of using the trunk lid as an air brake for my 1965 Barracuda street/race car. Use two convertible top cylinders and a compressed air tank. The flaw was that it would leave the trunk unsecured. Hydraulic drive would have been secure but way too slow.
 

MaxHeadRoom

Joined Jul 18, 2013
18,995
I think a industrial servo's system here would be way over-kill, it seems to me to be just a point-to-point system.
Max.
 

MisterBill2

Joined Jan 23, 2018
3,847
I think a industrial servo's system here would be way over-kill, it seems to me to be just a point-to-point system.
Max.
Correct you are, Max. That is why my first suggestion was, and still is, using that setup that extends the power antenna when the radio switches on, and retracts it when the radio switches off. It was a relay package with several contacts and connectors. And there were lots of them installed.
 

Bernard

Joined Aug 7, 2008
5,252
Operating from a brake switch implies a fast action is required like air cylinder. Look at " Surplus Center ",
Lincoln NE, USA. www.surpluscenter.com. Lifting a shooting target with an air cylinder takes about one sec.,
linear actuator around 1 sec/ cm.
 

noweare

Joined Jun 30, 2017
95
A small linear actuator would work I think they are expensive. No need to sense where the motor is.
 

MisterBill2

Joined Jan 23, 2018
3,847
I don't see any response from the thread starter. No comments about any of the suggestions. I didn't think that all of them were that far off, but it is possible that the requirements included something that nobody has addressed. What I saw was a request for a system to move to one position when operated and then return to the first position when released. And, of course, it has to have enough force to drive the air-brake flap, which is quite a bit for a real car, but much less for a model car, and in between for a go-kart type of car. And on a go-kart there is usually no electrical power available.
 
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