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[luthj]

You can change the lever length ratio (pivot location) to change the overall motion ratio.

If you have a compass and a sheet of paper, you can design a linkage by hand pretty easily.

Use the compass to circumscribe an arc corresponding to he motion distance for each linear side, then a second arc to find the intersection of the displacement. Its hard to describe in text, but you should be able to work it out yourself, its pretty intuitive. Otherwise drop me a message and I can draw something up in CAD.

 

[Iain_U1250]

Just an update, thanks to help from @luthj and @DiploStrat I think I have a plan worked out. Luckily we are currently plugged into shore power (which doesn't happen very often) and the BMS with some assistance is slowly getting things balanced.

Now onto a bit of a challenge, I am revising our entry steps again. One of the goals with the new doors was to make the truck a bit more secure (I say a bit as we still have large windows). One of the other things we wished is we could retract the steps at night. This way more noise would need to be made to get in. So, I would like to add a DC linear actuator underneath the slide out platform (it is IP65 but I want to encase it in an aluminum shell to protect from elements). That is the easy bit, what would also be nice is if the same actuator could also angle the ladder in/out 22.5 degrees. This would require some sort of linkage which right now is escaping me how to accomplish. Forgive the rather crude drawing, but hopefully it will get the idea across. The challenge is when stowed the fuel tank is right below, so not a lot of room. I am considering building arms down each side of the platform inline with the ladder when stowed. A hinge could be built that would connect the ladder to these arms to hold the ladder out. So an up/down movement attached to the middle of the hinge could swing the ladder in/out. So getting the motion of the platform sliding out to cause a linkage to push down on the hinge would work. And obviously the reverse would be true. One thing is this is all exposed to the elements so simple would be the best. We are meeting with a welder/fabricator soon and he has a lathe and milling machine so we can make up most things.

View attachment 758079

The problem I can see is that the lever arm for the ladder trying to fold it in (assuming the lower step is on the bottom) is so much more than the lever arm length available to push the ladder out. It looks like at least 10:1 - so if I stood on it, my 82kg would exert 820kg onto the lever, which would mean the lever has to be very substantial. Pushing off from the ladder, the dynamic force would be 3-4 times that, and to have it not move much underfoot, about 5-6 times static load - which means you would need a very substantial hinge and lever. I could not make my steps strong enough with just the levers and linkages, so I added hard stops onto the frame, which each of the steps rest on.

Is the intent that the ladder no longer touches the ground with the new design? From this photo, it looks like you have a gap between the fuel tanks where you can fit a strut with a hinge in the middle with an actuator that folds back the ladder, but when extended, the strut locks straight, with the strut close to the bottom of the ladder the lever arm will be much less, and something like 25x25mm SHS will be more that strong enough. It will require two actuators, one for the platform, and one short one for the ladder, but that would be simpler than the reverse linkage I think. 12" is quite long for a linear actuator, so if you used another lever, you could have a shorter actuator push the platform out, which would be much quicker as well.

Just a few thoughts

 

[VerMonsterRV]

The problem I can see is that the lever arm for the ladder trying to fold it in (assuming the lower step is on the bottom) is so much more than the lever arm length available to push the ladder out. It looks like at least 10:1 - so if I stood on it, my 82kg would exert 820kg onto the lever, which would mean the lever has to be very substantial. Pushing off from the ladder, the dynamic force would be 3-4 times that, and to have it not move much underfoot, about 5-6 times static load - which means you would need a very substantial hinge and lever. I could not make my steps strong enough with just the levers and linkages, so I added hard stops onto the frame, which each of the steps rest on.

Is the intent that the ladder no longer touches the ground with the new design? From this photo, it looks like you have a gap between the fuel tanks where you can fit a strut with a hinge in the middle with an actuator that folds back the ladder, but when extended, the strut locks straight, with the strut close to the bottom of the ladder the lever arm will be much less, and something like 25x25mm SHS will be more that strong enough. It will require two actuators, one for the platform, and one short one for the ladder, but that would be simpler than the reverse linkage I think. 12" is quite long for a linear actuator, so if you used another lever, you could have a shorter actuator push the platform out, which would be much quicker as well.

Just a few thoughts

What you describe it pretty close to what I am planning and yes the ladder will not touch the ground (way cleaner that way). The 12" actuator will be mounted to the bottom of the habitat on one end and the bottom of the platform on the other. The mount on the habitat end will be custom and will include one end of the reverse motion linkage. The pivot point for that linkage will be on the underside of the platform. The local metal shop has an assortment of telescoping aluminum tube. I am hoping to use some as the bearing for the linkage (they have very little stainless, though stainless is still a possibility and I might just use it). If I use aluminum, it can all be welded to the platform which would be nice. Stainless I would have to bolt on.

The linkage above is to move the platform out 12". With that same motion I want to use this linkage to move another linkage (the "Scott Russell" one which changes motion direction 90 degrees). This other linkage will be attached to either the center of a hinge (attached mid-way down the ladder to vertical arms welded to the platform) or a plate that will have hinges on the ladder. In the second scenario the non-hinge side of the plate will have guides on the vertical arms. I am thinking the latter would work better with the Scott Russell linkage as the motion would be vertical in straight line. I still need to work out the sliding bit, it would need to be mud tolerant and work without grease. I am thinking aluminum channel with plastic roller bearings with stainless shafts. So the vertical arms and the plate from above will take all the load from the ladder, the linkage would just be used to get things in place and hold it there.

I have 3 different actuators in reserve right now in case I need 2 to get what I want done. I would really like to get this all working with the single 200lb 12" one as it would be horizontal up under the platform. That way I could make a shield for it to keep as much mud off it as possible. I also need to be careful to not get too close to the fuel tanks. The subframe allows a bit of movement (though there is some extra room).

 

[Iain_U1250]

I never bothered with bearings on mine, just used normal zinc plated bolts with a tight fit - steel to steel and some occasional grease or spray oil. So far, I have never had to replace even one of the bolts, and give it a spray with some Ballistol every couple of months, especially when we have been driving down on the beach. I found that having something that works with loose tolerances is much better than any precision fit when it comes to being mud and dirt tolerant. It's not like it will see that many cycles in reality. I went with 8mm bolts to start, so could go up to 3/8", then 10mm, etc if it ever wore, there is enough metal to go up to 12mm, which at the present rate of wear will be many many years from now.

 

[RAM5500 CAMPERTHING]

We have been living on the batteries for the last 3 years. Back then there wasn't the options there are now for these better BMS's. I just swapped out my old BMS/balancers with this new JDB. Right now with a ~10 amp load at "99%" the batteries are within .013 v. But if I turn the charger on one of the 4P packs rises while the others don't. Then the BMS gets a cell over voltage and shuts down charging. I am using the Overkill Solar app to monitor, I am guessing when the "Bal" on the right of the cell graphs turns yellow balancing is occurring. I have yet to figure out how to get it to balance full time. It seems to turn off and on.

Sorry for delay, i have been out of town.

Sounds like you got it sorted.

Also, somewhere in the settings of the JDB software there is an option to balance "only when charging" mine was set on it by default, i changed it, so they are always balancing.

If i remember correctly, mine took about a week to get everything all balanced and working as it should, it did it all by itself

My .02

 

[Alloy]

What you describe it pretty close to what I am planning and yes the ladder will not touch the ground (way cleaner that way). The 12" actuator will be mounted to the bottom of the habitat on one end and the bottom of the platform on the other. The mount on the habitat end will be custom and will include one end of the reverse motion linkage. The pivot point for that linkage will be on the underside of the platform. The local metal shop has an assortment of telescoping aluminum tube. I am hoping to use some as the bearing for the linkage (they have very little stainless, though stainless is still a possibility and I might just use it). If I use aluminum, it can all be welded to the platform which would be nice. Stainless I would have to bolt on.

The linkage above is to move the platform out 12". With that same motion I want to use this linkage to move another linkage (the "Scott Russell" one which changes motion direction 90 degrees). This other linkage will be attached to either the center of a hinge (attached mid-way down the ladder to vertical arms welded to the platform) or a plate that will have hinges on the ladder. In the second scenario the non-hinge side of the plate will have guides on the vertical arms. I am thinking the latter would work better with the Scott Russell linkage as the motion would be vertical in straight line. I still need to work out the sliding bit, it would need to be mud tolerant and work without grease. I am thinking aluminum channel with plastic roller bearings with stainless shafts. So the vertical arms and the plate from above will take all the load from the ladder, the linkage would just be used to get things in place and hold it there.

I have 3 different actuators in reserve right now in case I need 2 to get what I want done. I would really like to get this all working with the single 200lb 12" one as it would be horizontal up under the platform. That way I could make a shield for it to keep as much mud off it as possible. I also need to be careful to not get too close to the fuel tanks. The subframe allows a bit of movement (though there is some extra room).

Aluminum, stainless, copper (non ferrous) gall so sliding/hinging them together is difficult to do. Even anodized aluminum will gall plus aluminum and stainless (non ferrous) work harden.

Welding aluminum reduces the strength x 40%. This is dealt with by increasing the welded surface / adding gussets.

I noticed the flat bar hinges on the bottom of the stair platform. Flatbar on both sides or a (larger) pin running side to side reduces the torsion (wear/binding) on the aluminum. It's hard to beat a stainless hinge that is bolted on. The pins in stainless hinges are harden to resits galling.

 

[luthj]

Also, somewhere in the settings of the JDB software there is an option to balance "only when charging" mine was set on it by default, i changed it, so they are always balancing.

If you opt to do this, make sure the BMS doesn't balance below about 3.4Vpc, and that your target delta V is not any smaller than 10mV. Measurement error can drive the BMS to create an imbalance at 3.2-3.3V (flat are of the curve).

For those that charge at high rate (greater than 0.2C), setting the target delta V to ~20mv is a good idea in this situation, as contact/bus bar resistance can create apparent (not true) imbalance due to voltage drop, often on the order of 5-10mV. By setting the target delta-V higher, you prevent the BMS creating an imbalance. This is really only applicable to systems which primarily charge at rates greater than 0.2C, and often its not an issue if a holding/absorb period is available where the current tapers down pretty low.

 

[Alloy]

as contact/bus bar resistance can create apparent (not true) imbalance due to voltage drop

The aluminum terminals on the cells aren't very forgiving. Certainly not like lead / FLA that people are used to. I've seen cells in a bank where the resistance (heat) can be picked up with an infrared camera. I cringe when people try to remedy the differences in the buss bar/battery terminal resistance with carbon/graphite grease or copper paste. Neither should ever be used on aluminum.

 

[luthj]

carbon/graphite grease or copper paste. Neither should ever be used on aluminum.

Mg chemicals 847 paste works great, and they said it was fine on aluminum.

 

[VerMonsterRV]

The aluminum terminals on the cells aren't very forgiving. Certainly not like lead / FLA that people are used to. I've seen cells in a bank where the resistance (heat) can be picked up with an infrared camera. I cringe when people try to remedy the differences in the buss bar/battery terminal resistance with carbon/graphite grease or copper paste. Neither should ever be used on aluminum.

Just to add to what @Alloy says, living on a sailboat in saltwater galvanic corrosion was a constant battle, especially with aluminum. Below is a version of a chart that I would consult when combining metals. If you mix metals the higher metal on the list can become the sacrificial anode.

 

[Alloy]

Mg chemicals 847 paste works great, and they said it was fine on aluminum.

Yeah it's one I cringe at. Graphite is used to make it conductive. Grease contains water + Graphite + Aluminum =

An interesting study is to look at the number of NEC certified alum. to alum. wire connectors that have been removed from the market in the last 40 years.

This is better

NO-OX-ID Electrical Contact Grease- Conductive Lubricant | Sanchem, Inc.

NO-OX-ID electrical contact grease prevents the formation of corrosion deposits & keeps metals free from rust & corrosion. Buy electrical conductive lubricant now!

www.sanchem.com

NO-OX-ID A-Special Electrical Grade | Sanchem, Inc.

www.sanchem.com

Quoted from the PDF.
Fallacy of adding metals to increase Conductivity:
Many contact greases have copper, zinc or other metals blended into a grease to increase
conductivity. In a study for an aerospace company in 1985 it was concluded that putting a
metal into grease does not help conductivity. In many cases it reduces conductivity. The
United States Department of the Interior Bureau of Reclamation in their Facilities
instruction Journal Volume 3-3 Electrical Connections for power circuits states in Sec.
6.3.2 that "Use of grease with embedded zinc particles will cause a poorer connection due
to the lower conductivity of zinc".
Aluminum Oxide is one of the hardest substances known to man, just softer than
diamonds. How can a metal as soft as Zinc cut through it? It can't! Zinc metal can not
dissolve aluminum oxide either. The aluminum oxide that typically forms on an
aluminum connection is only 50-120 angstroms thick. Sanchem's NO-OX-ID penetrates
the oxide film by the chemical action of our corrosion inhibitor system.

 

[luthj]

Yeah it's one I cringe at. Graphite is used to make it conductive. Grease contains water + Graphite + Aluminum =

An interesting study is to look at the number of NEC certified alum. to alum. wire connectors that have been removed from the market in the last 40 years.

This is better

NO-OX-ID Electrical Contact Grease- Conductive Lubricant | Sanchem, Inc.

NO-OX-ID electrical contact grease prevents the formation of corrosion deposits & keeps metals free from rust & corrosion. Buy electrical conductive lubricant now!

www.sanchem.com

NO-OX-ID A-Special Electrical Grade | Sanchem, Inc.

www.sanchem.com

Quoted from the PDF.
Fallacy of adding metals to increase Conductivity:
Many contact greases have copper, zinc or other metals blended into a grease to increase
conductivity. In a study for an aerospace company in 1985 it was concluded that putting a
metal into grease does not help conductivity. In many cases it reduces conductivity. The
United States Department of the Interior Bureau of Reclamation in their Facilities
instruction Journal Volume 3-3 Electrical Connections for power circuits states in Sec.
6.3.2 that "Use of grease with embedded zinc particles will cause a poorer connection due
to the lower conductivity of zinc".
Aluminum Oxide is one of the hardest substances known to man, just softer than
diamonds. How can a metal as soft as Zinc cut through it? It can't! Zinc metal can not
dissolve aluminum oxide either. The aluminum oxide that typically forms on an
aluminum connection is only 50-120 angstroms thick. Sanchem's NO-OX-ID penetrates
the oxide film by the chemical action of our corrosion inhibitor system.

I understand the general advice, and its good. However I contacted the MG chemicals support, and they indicated this product is fine for use in this application. I can also confirm that it does reduce contact resistance for connections like this (have have measured on two packs compared to just dielectric grease). I wouldn't be recommending it if I hadn't had a system in daily service for two years with it.

The reason its so effective in this application is that the clamping force is quite small, and there can be lateral forces on the terminals. Normally a well clamped joint will conform, and have lower resistance, but that isn't possible with soft aluminum terminal bosses.

Obviously if this was a wet compartment, I would be more concerned.

 

[Alloy]

I understand the general advice, and its good. However I contacted the MG chemicals support, and they indicated this product is fine for use in this application. I can also confirm that it does reduce contact resistance for connections like this (have have measured on two packs compared to just dielectric grease). I wouldn't be recommending it if I hadn't had a system in daily service for two years with it.

The reason its so effective in this application is that the clamping force is quite small, and there can be lateral forces on the terminals. Normally a well clamped joint will conform, and have lower resistance, but that isn't possible with soft aluminum terminal bosses.

Obviously if this was a wet compartment, I would be more concerned.

It is possible if both surfaces are aluminum
- the terminals are on the same plane
- oxide is removed from the terminals with a SS wire cup brush
- oxide is sanded (lapped) off the (4mm) aluminum buss bars so the contact surface is flat.
- after removing the oxide assembly is done ASAP with NO-OX-IS.


There is no need to use a material that's at the opposite end of the galvanic scale contained in a paste that reacts with water. The MG is #3 (moderate) on the SKF Emcor Test which is only 1 week long.
.


FYI..Couple of weeks ago I looked at a Lithium bank that was in a dry compartment. The bank was covered (here on the B.C. Raincoast) in condensation.

 

[luthj]

The MG is #3 (moderate) on the SKF Emcor Test which is only 1 week long.

Can you point me to the testing in question? I looked up that particular test, and it appears to involve a rotating bearing assembly which is intermittently sprayed with water. At first glance I am not sure how representative it is of a static electrical application. If I have some time I will make up a test coupon with 847 and a aluminum bar stock. However it will be some time before I can consider disassembling for results.

The bank was covered (here on the B.C. Raincoast) in condensation.

Sure, if a person operates in a continuously condensing environment (that location is on the extreme end of condensing situations). There is not a single perfect solution, and general advice is general!

 

[Alloy]

Can you point me to the testing in question? I looked up that particular test, and it appears to involve a rotating bearing assembly which is intermittently sprayed with water. At first glance I am not sure how representative it is of a static electrical application. If I have some time I will make up a test coupon with 847 and a aluminum bar stock. However it will be some time before I can consider disassembling for results.

Sure, if a person operates in a continuously condensing environment (that location is on the extreme end of condensing situations). There is not a single perfect solution, and general advice is general!

This from the datasheet. Not sure if this is what you're looking for? The test is only useful in this discussion to show it "moderately" resists corrosion.



I've worked with aluminum for decades and seen every way aluminum can corrode. Each time was an eye opener. There's no perfect solution but mixing graphite and aluminum is a ways from it.

Aluminium Corrosion | 13 Types Explained | Fractory

Aluminium corrosion comes in many forms and types. We are looking at all of them in-depth to make sure you know what to keep an eye on.

fractory.com