Terry,
I like your ideas. If I were building one, I'd keep the hefty pivot
brackets with their grease fittings. But, I'd mount them farther apart and
position the tread below the arms so it could stow right against the frame.
That would also allow the weldment going from the arm to the top of the
pivot to extend 'way out on the arm, triangulating it and making it more
rigid, even if left the same size.
For operation, I'd be inclined to use an air cylinder and solenoid valve.
They're compact, cheap, and relatively impervious to the hostile
environment, especially if you put a boot on the piston rod. Since we've
got 100 psi air available, why not use it? There's no uncertainty or
recurring adjustment of the travel. If you use the air to deploy the step,
the retained air pressure provides locking. If you use it for retraction,
then the springs probably can be strong enough to alleviate the need for
locking (not so with the weak vacuum actuator). I'd start with very small
orifices in the valves because fast deployment or retraction with the force
available could be dangerous. The fact that I have everything on hand from
some eBay purchases, and enjoy tinkering with them, are significant factors
in this choice.
The window regulator would be my close second choice. It would probably be
cheaper starting from scratch. The environment is more severe than they're
designed for, but a coat of undercoating or bed liner would probably correct
that. The switching complication is the main argument against it.
The lack of a known source for recently built vacuum cylinders is a major
argument against using them. My current cylinder is probably 3" diameter
with a 3" stroke; that's only 3.14*1.5*1.5*13.7*3/12= 24 ft-lb of energy
available to operate the step -- barely enough. I'd say about 4" diaphragm
diameter with 4" travel would be the minimum size I'd consider trying to use
(that's only 3.14*2*2*13.7*4/12=57 ft-lb of energy available vs
1*80*10/12=67 ft-lb from a cylinder with 1" area and 10" stroke. As much as
I like the simplicity of just hooking it to engine vacuum, as my current one
is, there are times the step should stay out with the engine running, so a
control valve is needed. I ran some numbers on the energy available from
different actuators:
Vacuum cylinder 3" dia. w/3" travel (about mine) --> 24 ft-lb
Vacuum cylinder 4" dia. w/3" travel (my design min.) --> 43 ft-lb
Air cylinder 1" area w/10" stroke & 80 psi air source --> 67 ft-lb
Air cylinder 1" bore w/8" stroke & 80 psi air source --> 41 ft-lb
That last air cylinder looks like a good choice to me.
In any case, I'd use the neutral safety switch for control -- perhaps with
overrides for some situations.
Have fun building it -- I'll get back to such projects soon, I hope.
Ken H.
P.S.: The mounting brackets DO need to be attached as close to the
crossmembers as possible, preferably with the same bolts. The frame rail
flexes too easily to depend on it much. KH
-----Original Message-----
Me either. That was why I started this thread. I like the heftiness of your
step and getting the wiggle would just take a little fine tuning. On the
other hand I like the window motor used in Bob Fletcher's step. It would
just take mounting the motor far enough away to make a "brake away" arm
feasible.
As to the door switch, it would be neat to have the step extend when the
door opens and retract when it closes. I suppose some sort of a power switch
just inside the door would be the way to go. And maybe a flashing red light
on the dash that would come on when the ign was turned on with the step
extended.
Whatdoyathink??..............Terry of Tacoma
--
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I like your ideas. If I were building one, I'd keep the hefty pivot
brackets with their grease fittings. But, I'd mount them farther apart and
position the tread below the arms so it could stow right against the frame.
That would also allow the weldment going from the arm to the top of the
pivot to extend 'way out on the arm, triangulating it and making it more
rigid, even if left the same size.
For operation, I'd be inclined to use an air cylinder and solenoid valve.
They're compact, cheap, and relatively impervious to the hostile
environment, especially if you put a boot on the piston rod. Since we've
got 100 psi air available, why not use it? There's no uncertainty or
recurring adjustment of the travel. If you use the air to deploy the step,
the retained air pressure provides locking. If you use it for retraction,
then the springs probably can be strong enough to alleviate the need for
locking (not so with the weak vacuum actuator). I'd start with very small
orifices in the valves because fast deployment or retraction with the force
available could be dangerous. The fact that I have everything on hand from
some eBay purchases, and enjoy tinkering with them, are significant factors
in this choice.
The window regulator would be my close second choice. It would probably be
cheaper starting from scratch. The environment is more severe than they're
designed for, but a coat of undercoating or bed liner would probably correct
that. The switching complication is the main argument against it.
The lack of a known source for recently built vacuum cylinders is a major
argument against using them. My current cylinder is probably 3" diameter
with a 3" stroke; that's only 3.14*1.5*1.5*13.7*3/12= 24 ft-lb of energy
available to operate the step -- barely enough. I'd say about 4" diaphragm
diameter with 4" travel would be the minimum size I'd consider trying to use
(that's only 3.14*2*2*13.7*4/12=57 ft-lb of energy available vs
1*80*10/12=67 ft-lb from a cylinder with 1" area and 10" stroke. As much as
I like the simplicity of just hooking it to engine vacuum, as my current one
is, there are times the step should stay out with the engine running, so a
control valve is needed. I ran some numbers on the energy available from
different actuators:
Vacuum cylinder 3" dia. w/3" travel (about mine) --> 24 ft-lb
Vacuum cylinder 4" dia. w/3" travel (my design min.) --> 43 ft-lb
Air cylinder 1" area w/10" stroke & 80 psi air source --> 67 ft-lb
Air cylinder 1" bore w/8" stroke & 80 psi air source --> 41 ft-lb
That last air cylinder looks like a good choice to me.
In any case, I'd use the neutral safety switch for control -- perhaps with
overrides for some situations.
Have fun building it -- I'll get back to such projects soon, I hope.
Ken H.
P.S.: The mounting brackets DO need to be attached as close to the
crossmembers as possible, preferably with the same bolts. The frame rail
flexes too easily to depend on it much. KH
-----Original Message-----
Me either. That was why I started this thread. I like the heftiness of your
step and getting the wiggle would just take a little fine tuning. On the
other hand I like the window motor used in Bob Fletcher's step. It would
just take mounting the motor far enough away to make a "brake away" arm
feasible.
As to the door switch, it would be neat to have the step extend when the
door opens and retract when it closes. I suppose some sort of a power switch
just inside the door would be the way to go. And maybe a flashing red light
on the dash that would come on when the ign was turned on with the step
extended.
Whatdoyathink??..............Terry of Tacoma
--
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Checked by AVG Anti-Virus.
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