# Powered steps circuit

#### usafpol

Joined May 4, 2021
7
Hello I want to make powered steps for a vehicle. Think Powered RV steps, but with an alternative drive due to space limitations and also the double $600/ side cost of RV steps drives. I also want the design to be robust so it will withstand the elements. I was thinking about a latching relay to drive the motor in one direction A. In the circuit I would put a circuit breaker in the load side in the event I hit an obstacle the load would heat the circuit and break the latch thus eliminating damaging or hurting anything the step would encounter. To reverse the direction to B I would need to have an opposite circuit to drive the motor. I would suspect finding the circuit breaker would need to be trial and error and could be a problem depending on the weather conditions, seasons, and perhaps amount of grim collected on the links. Does any one have comments, is this too over simplified. I don't have any aversion to PWMs or other drive systems other than the learning curve to recall what was done in a year or two and maintenance is required #### LowQCab Joined Nov 6, 2012 2,364 You don't seem to have a grasp of just how in-hospitable the underside of a Car/Truck is. There are very good reasons why the commercial units cost ~$600.oo.

If you successfully create your own working model,
it probably won't last ~6-Months in Daily-Driver usage before it takes a dump,
for any one of a variety of reasons, mechanical or electrical.

This can apply to the commercial units too,
there are no guarantees,
but the commercial manufacturers have a reputation that they are "usually" trying to protect,
which means that they have "usually" come up with various solutions to
the most prevalent problems, that WILL OCCUR.

The Control Circuitry can be very simple and basic,
but must be protected from the weather inside a sealed box, or inside the Car/Truck.

Electronic Current Limiting / Auto Reversing, is easy to implement.
I would not use mechanical Circuit-Breakers, only a properly sized Fuse at the Battery.
Likewise, I would not use mechanical Relays either.
and will never fail if designed correctly.
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#### usafpol

Joined May 4, 2021
7
Feel free to share the circuit you are referring to.
The application details are to share the scope of the effort. I will address the environmental issues.

#### LowQCab

Joined Nov 6, 2012
2,364
There is no "The" Circuit.
The procedure of designing the "Control-System" depends on .......
the Actuator(s) that you choose,
the Limit-Switch configuration, or use of Current-Monitoring for stops / reversals, ( or both),
how you expect deployment and retraction to be initiated, and/or, inhibited,
Default-Timers, Safety-Loops, Manual-Controls, etc.

Tapping into an existing Remote-Control Alarm-System would be a huge bonus.
Tapping into the Car/Truck Wiring Harness is required.
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#### Bernard

Joined Aug 7, 2008
5,784
One or two steps per side ? I once made a second folding step on a 1972 Shasta MH which survived a brush with a mud cliff thanks to a tour bus on US 1, CA.

#### MisterBill2

Joined Jan 23, 2018
12,746
The TS needs to understand that the chalenge with powered vehicle steps is not the control system, it is the hardware. Of course if the goal is to have it be really cool like a show car, and never see rain or salt spray , then it is only a matter of money. A far better choice is to drive the steps extend/retract motion with a hydraulic cylinder. That can provide much more force in a much smaller package. Then tapoff either the power steering pump or use a separate hydraulic pump like as used for some convertible top mechanisms. It can be almost silent and not need switches or sensors to stop at the two positions. It will be great, but not cheap.

#### usafpol

Joined May 4, 2021
7
One or two steps per side ? I once made a second folding step on a 1972 Shasta MH which survived a brush with a mud cliff thanks to a tour bus on US 1, CA.
I will have one per side. They would act independently from each other as depending on the side you exit the step would extend and only when you needed it. I’ve designed gender and built a significant amount of projects in harsh conditions so the environment isn’t a concern. It can be resolved in a significant amount of ways. I have built circuits too but I want one that limits with current to stop from driving into items too hard

#### usafpol

Joined May 4, 2021
7
The TS needs to understand that the chalenge with powered vehicle steps is not the control system, it is the hardware. Of course if the goal is to have it be really cool like a show car, and never see rain or salt spray , then it is only a matter of money. A far better choice is to drive the steps extend/retract motion with a hydraulic cylinder. That can provide much more force in a much smaller package. Then tapoff either the power steering pump or use a separate hydraulic pump like as used for some convertible top mechanisms. It can be almost silent and not need switches or sensors to stop at the two positions. It will be great, but not cheap.
Yes thanks for the response. I’ve considered hydraulic as well. I have a few pumps around for convertible tops. Also pneumatic as I’ll have on board air. The environment isn’t too much of a challenge with the proper mechanical components. I’ve had a lot of success designing linear actuators for harsh environments. I had an ee controls guy working for me and he adressed the controls side. But he did so with ab components. Well beyond the scope of what I am looking for

#### MisterBill2

Joined Jan 23, 2018
12,746
One way to have a stop at the end positions would be to use the controller for the automatic opening of windows on a carit runs until it sees a current spike and then switches off. That is the function that is wanted for completing the extend and retract motion. I am not sure how it works, but it does what you are asking for. But it would need to be connected for both directions. A similar function exists for those powered van doors, but I am guessing hat is done by the master body control computer. BUT MAYBE NOT.

#### usafpol

Joined May 4, 2021
7
One way to have a stop at the end positions would be to use the controller for the automatic opening of windows on a carit runs until it sees a current spike and then switches off. That is the function that is wanted for completing the extend and retract motion. I am not sure how it works, but it does what you are asking for. But it would need to be connected for both directions. A similar function exists for those powered van doors, but I am guessing hat is done by the master body control computer. BUT MAYBE NOT.
Yes good point that is a good starting point. Cars are broken into circuits and systems like aircraft. I’ll look into that. I would image the older ones 60/70’s had a thermal breaker that would drop the circuit as a form of load control. That was the foundation of my original thought

#### Tonyr1084

Joined Sep 24, 2015
6,971
Personally I'm thinking the pneumatic system would be best. Have the ram extend to a stop. So what if air pressure remains on the cylinder; won't harm anything. When retracting - reverse the direction of the air pressure and the cylinder will retract to its full retracted position. Having it in the full retracted position when you want the step retracted will also keep the cylinder piston shaft away from the elements. Eventually you'll probably have to deal with a little rust issues, but nothing lasts forever.

#### usafpol

Joined May 4, 2021
7
Yes good point that is a good starting point. Cars are broken into circuits and systems like aircraft. I’ll look into that. I would image the older ones 60/70’s had a thermal breaker that would drop the circuit as a form of load control. That was the foundation of my original thought
Thanks for the help with a little searching I found a circuit to try.

#### LowQCab

Joined Nov 6, 2012
2,364
Motors ramp-up to speed smoothly.
Lots of input options.
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#### MisterBill2

Joined Jan 23, 2018
12,746
How about a warning buzzer if the vehicle is taken out of park or neutral and the step is extended? Using the existing neutral safety switch. Since I once drove away with a step extended I can recommend that.

#### usafpol

Joined May 4, 2021
7
How about a warning buzzer if the vehicle is taken out of park or neutral and the step is extended? Using the existing neutral safety switch. Since I once drove away with a step extended I can recommend that.
Good Point . My rv cyles the steps in when I turn on the key and have the door closed. Its like a by pass to the up switch. It would energize the up circuit when the key is turned on.

#### MisterBill2

Joined Jan 23, 2018
12,746
I do like the concept of a pneumatic cylinder driving the steps because it is very happy to msit stalled at the end of a stroke. And it could be lighter a well. And if you get the thin cheap ones they will be much lighter. Probably the vehicle does not have air brakes, but it may have a compressor for an air horn, almost as good. If it has an emission ytems air pump that would be another option. In desperation an engine vacuum powered compressor could also keep a tank charged with enough pressure to extend and retract the step. BUT with a cylinder you will need a latch for the retracted position. You could also use medium pressure hydraulics and a much skinnier cylinder, using some power steering fluid pressure. But that would mean you needed the engine running to move the steps,

#### Tonyr1084

Joined Sep 24, 2015
6,971
with a cylinder you will need a latch for the retracted position.
Or a spring to retract the cylinder when not pressurized. In the case of a failed air supply the step would default to the fully retracted position - provided there's a way to depressurize the system. Air pressure to extend, lack of pressure to retract.

I, too, think the air cylinder is the way to go. Hydraulics gets complicated and you have to deal with messy leaks. An air leak is an annoyance and typically easily repaired.

#### LowQCab

Joined Nov 6, 2012
2,364
I disagree with the Pneumatic idea.
Just the superior "motion-control" of a Linear-Actuator is enough to convince me.
A Pneumatic System is very simple, (other than the Compressor and Storage-Tank),
but I've never seen a Pneumatic system that wasn't jerky and noisy.

On the other hand, a Motor Driven Screw / Linear-Actuator will always be quite smooth,
and most are extremely quiet, and they are usually much stronger than Pneumatic.

No "Hydraulics" need to be involved, there's no need for that much potential Force.

Ride on a City-Bus for a day, sit right next to the main-Front-Door, it's fully Pneumatic.
Then decide if you want anything on your Car or Truck to operate like that.
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#### MisterBill2

Joined Jan 23, 2018
12,746
I designed the controls for MANY machines that used pneumatics, and hydraulics, and NONE of the pneumatic motions were noisy or jerky. And those machines were mostly production equipment running one cycle per minute or faster. The city busses suffer from a severe lack of service and from incorrect adjustment by a mechanic who has no clue, supervised by a foreman who does not care.
And how smooth and precisely controlled does a step need to be when it is either extended to a stop or retracted hard against a stop? And a lead screw is not the sort of thing that should be stuck below a vehicle, except possibly a serious show car. AND, for that smooth control it really needs an encoder to slow it for the ends of the travel. Suddenly the system gets complex.