Re: [DML] Solenoids vs actuators / Bob Zilla [long]

[Martin Gutkowski <webmaster@xxxx>]

Hi Bob

We haven't spoken before, and I should explain that my DeLorean is currently on
the "high seas" on its way to Southampton to meet me... I have not had any first
hand experience with the mechanicals in a DeLorean, but I have a lot of
experience with DC electric motors, actuators, solenoids, and I guess it's fair
to say, cars in general.

I want to take you to task over some of the things you've said - just for the
purpose of healthy debate, I promise!


> Actuators as a rule are not designed to output sufficient torque to open our
> doors which require an uncommon amount to do the job. EVERY actuator we've
> tested contained an EXTREMELY UNDERSIZED motor and had plastic gears.

And later:

> Upon internal inspection you discover, of the 6 very tiny gears, 3 are
> plastic. The motor is 1" long by 3/4" wide. Stop and draw a mental picture of
> this. The gear on the motor shaft is plastic with a 1/4" diameter. Let me
> remind you, you are opening your door with a 1/4" plastic gear.

Oh come on! Any engineer will agree that you can tow a bus with a motor that size
as long as it's geared down enough. Both a solenoid and a motor operate on the
same principle - electromagnet driving rare earth magnet. The difference is the
gearing. The power of a motor is given by its torque x speed. Now with an
actuator obviously it's the torque that matters most, so you gear it down and
reduce the speed. With a solenoid, you have no such gearing, so you have to make
that single acting electromagnet as chunky as possible. Disadvantage of the
actuator: it's slower...

Additionally, the enemy of any motor or coiled device of any sort is HEAT. What
damages a motor (or solenoid) is powering it and not allowing it to move - but if
you could keep it cool while you stop it moving, it'd never blow up. My point: An
actuator will work for a very small duty cycle - perhaps 1 second in half an hour
- and that's at a busy car show. I would be amazed if the motor inside got
anything more than slightly warm to the touch after several consecutive
actuations.

In fact, seeing as actuators are most often used on locks, I think you'll agree
that they are DESIGNED to be able to handle the torque of not being able to move
at all. Why? Because when popping the lock, the actuator must be supplied with
power for longer than it takes to pop the lock. Unless you employ some control
electronics.

So the fact that you "don't like the sound of the actuator labouring" is only
arguable from an aesthetic point of view - the device is designed to take being
stalled. It's just usually used in an application where it stalls instantly (as
the lock reaches the end of its travel) and you don't hear anything other than
the little "grunt" as the power is dropped and the gearbox relaxes.

> For those of us old enough to remember Audio Cassettes, I can tell you that
> these small DC motors that pulled the tape around failed with regularity.
> Product failure analysis was once my domain. There have been few ( if any )
> advancements in mini 12V DC brush driven motors in the last 30 years.

I would disagree with you strongly there, but the reason I know is not
DeLorean-related.

> So now, the goal is to generate enough torque with a Walkman size motor to
> open our doors for many many years ?

A walkman motor would be an S1 motor - ie designed to run constantly
(indefinitely) at a given power. For intermittent use, you can get a helluva lot
more torque from the same sized motor, but in S2/S3 configuration simply because
you know it can cool between uses. These have fatter coils and fatter brushes.

> The "Launch" solenoids we are
> using are Custom Made & particularly well suited to the task Insuring
> Longevity and the ability to open the door with Authority.

This I agree with - having a quality "thunk" rather than a whining gear driven
mechanism IS more pleasing :-)

> New or old technology ?
> There's nothing new about actuators. The concept dates back to the invention
> of the motor itself. Should someone ever create an actuator with all metal
> gears and a motor of reasonable size, then you've got something to get
> excited about. I'm not holding my breath till then as there doesn't seem to
> be a real market to sell it to.

Have a look at www.powerjacks.com - in "my other life" I build robots and
although I have not used these guys I have seen a gorgeous 500g screw actuator
capable of outputting over 2000N. Basically whatever application, large or small,
these guys will have an actuator for it. BTW these are linear actuators and not
the type we're discussing here.

> Actuators are filled with highly torqued plastic moving parts. A solenoid has
> exactly 1 hefty moving metal part and unlike actuators, it's action is
> instantaneous.
> Thoughts on Longevity anyone ?

All five actuators in my 12-year-old Citroen BX's central locking system are
still working after 180,000 miles. And they're REALLY cheap nasty plastic things.
And yes, all five stall for about half a second at every operation.

> No Modifications.
> As mentioned on a few occasions, our system does not require ANY headliner
> removal to achieve independent door control. No wires are cut or spliced. No
> wires are run in the headliner or through the door hinge. Everything just
> plugs in with the assistance of the "Launch Controller".

Erm, don't you need a torsion bar adjustment to cope with the extra weight?

> As soon as the work is completed on TranZilla ( the upcoming Shift Computer
> for automatics ) a new era in Toy Development will unfold.....

THIS I look forward to!!!

Best WIshes

Martin
#1458
DOC UK