Leveling revisited for MCI 102

[Jim Blackwood]

Well, that's certainly a valid question, but I never had any intention of running these by hand. And the reduction type units are taller. I bought three right hand units. No reducer. The idea being to do the reduction in the gearmotor. This test unit has a 100:1 reduction ratio, meaning it takes 3.4 seconds to make one revolution or about 18 rpm. Takes 4 cranks per inch of travel, so a minute to go 4-1/2". I do have a 1000:1 gearbox I can try just for a test but it's really going to be too slow for practical use. (Can you imaging spending 15 minutes to jack one corner?) It looks like the Jost gear reducer is very close to 10:1, so my requirement is probably going to be less than that. Anyway that should be a usable test. Provided that works, at an overall reduction of 100:1 I could expect to need a 5hp motor since that's 10 x 1/2hp. That should bracket the range nicely.

In messages with the Chinese manufacturer of jacking screws I was quoted a 3hp motor required to get something in the acceptable speed range. Because I had this test unit I decided to try it just to get a data point. Before this is over I may go back to that vendor for a price quote. However I suspect there may be other more competitive vendors and there is also the surplus market to explore.

It will be relatively simple to add the 10:1 unit for another test. I'm also relatively sure these light gearboxes will never hold up to this application so a test is all it will be.

IF the 1000:1 reduction works with the 1/2hp motor that does raise the possibility of using it with automatic controls such that on parking I could throw a switch and walk off and forget it, coming back in 15 minutes to a leveled coach. That could be workable. They are reasonably quiet.

The input torque required for the rated 62,500lb lifting capacity is given as 1000 ft/lbs. So about 300 ft/lbs for this application.  That means a fairly robust final stage on the reducer. A sprocket drive can give me about a 5:1 final ratio I believe, depending on the diameter of the driven sprocket. That would reduce the gearmotor output torque to 50 ft/lbs which is considerably more manageable. Maybe I'll go ahead and run that second test today.

Part of the problem is that although we think of worm drive speed reducers as being incredibly robust, in reality they are not, due to having a small area of contact on the ring gear. Wear and tooth breakage become real issues under heavy loads. The diameter of the ring gear has to increase rather dramatically as the torque requirements go up, and in the 300 ft/lb range it probably has to be around 5-6" making the case fairly large and heavy.

In retrospect getting the reducer units and paying the extra would probably have been advisable.

Jim

[Jim Blackwood]

OK that test was successful. The motor didn't sound like it was working at capacity but I'll have to stick an amp clamp on it to see what the current draw is and that will tell me how close I am to a full load.

It is very slow, but like I said if run as an automatic leveling system that shouldn't be very objectionable, and the big benefit is the ability to use my 900w inverters and switching relays that I already have for directional control. A current limiting relay could be used instead of limit switches also.

Jim

Just checked, running load is 6 amps, FLA is 7.2A so it's running at 83% of full load, a comfortable margin and just about where it should be. I think this speed should be acceptable. I can always upgrade later to 3600 rpm 1 hp motors without changing gearboxes to cut the leveling time in half.

[Jim Blackwood]

I'm now working on the major truss, the one at the rear that will support the side jacks, and I've had more time to think things through. I've reached the conclusion that the drive system on the front jack is usable but not very convenient. One of my options is to consider the use of 3-5hp motors. On the gearing side, it would appear that a 5hp would allow the use of about a 100:1 reduction ratio, increasing the speed by a factor of 10. This means that instead of taking 10-15 minutes to level the coach it would take 60-90 seconds which is much more in line with what we expect to see. Even allowing a 50% increase for the additional weight of the build-out that doesn't go much over 2 minutes.

On the power side, I believe this means about a 30 amp draw at 220vac but my 8kw genset should be able to handle that load, the key being not to try driving more than one loaded jack at one time. It also means careful management of power when running AC. But I think that is feasible.

This week and next I'll be working to complete the major truss, get it installed, mount the jacks and trim out the installation. Then it's off to the scrap yard with me to see what sort of gearmotors I can find.

Jim

[richard5933]

Be careful you don't leave yourself stranded high and dry should your generator ever crap out on you. If you are relying on the 240v from your generator to run the motors, what will happen when you're out somewhere and your generator dies? Finding a 120v outlet would be easy, but a 240v one will be more difficult.

[chessie4905]

3 to 5 hp motor could trip breaker on 110 volts.

[buswarrior]

How often would you need to drive a loaded leg?

In practice, evaluate the terrain, lower legs freely under the air suspended bus to get 'em close, estimated to be where they need to be to be level, deflate air suspension, legs touch down in turn, coach is level.

Reverse method to raise free legs?

I'd be letting the air suspension do the lifting, let the gear motors just freely position the legs?

Happy coaching!
Buswarrior

[Jim Blackwood]

I think BW has it figured out, and in more ways than one.
Using the air ride to get to rough level is likely to be the quickest way of doing it. And it will almost always be able to unload the jacks. The exception would be when changing a tire.

I will probably be looking for 3 phase motors. They are generally capable of higher torque, and reversing is easier. Used, they tend to be cheap. But of course that means a VFD to drive each one. Still, there are VFDs that can use 110v and output 220vac 3 phase (how that's possible I don't know) and remote switching can be used for on/off, reversing, and speed control. Some are capable of approaching 150% overspeed under light load which could be handy.

I don't know yet what the unloaded amperage draw might be, but with soft start (from the VFD) it could be possible to drive an unloaded jack with the output from one of my 0.9kw inverters. If so that'd be an easy method of positioning so it's worth checking it out. And as BW suggested, level with the air bags, run the jacks down until they hit, and when leaving use the bags to lift the bus off the jacks. Later on of course I hope to be able to add a large inverter but as those are expensive, bulky and heavy I'd like to put that off for awhile.

Also, because I have a purge on the front and hope to add them to the sides, I hope to be able to drop the bus down to the bump stops before leveling it. (and the purge can be stopped at any point on the way down) Depending of course on how much of a slant there is. So just the way the bus rises up from the kneel position before moving off, the idea is to do the same at the rear. Meaning that on a reasonably level surface the bus can actually be moving while the jacks fully retract, and if there is a malfunction it can still be driven. Just how well that all will work remains to be seen of course, but I think the basic plan is solid.

Jim

[Busted Knuckle]

OK my 2 cents here (and for what it's worth. Add $5 to it and you might be able to get a cup of coffee at the local truck stop!)
I'd use little air actuators on each leveling valve like Setra did so you can raise the bus about 6" all the way around before leveling to give you plenty of "wiggle room" then I'd use the 2 speed gear boxes that are on most semi trailers for your jacks and it theory if needed you could use one of today's cordless impacts to drive the jacks!
Or use an air impact to drive them.
  BK 

[sledhead]

or just use the air bags in the coach to do all the leveling
works on the coach I have now and the M C I that I sold

dave

[Jim Blackwood]

Here's a shot of the major truss. It should go in today if there are no problems. What you can't see in the photo is that the top stringer is doubled, as it is offset to fit into the recess in the bulkhead.

What I was thinking was that I don't want to carry around a set of steps, so it made more sense to drop both ends as far as possible before leveling. Oh, and the torque requirement on those jacks is 1000ft/lbs at full load. That comes out to about 300 each on the bus. With the 10:1 factory reducer that gets dropped down to where the impact wrench could handle it I think. Worth a try anyway.

So sitting in the driver's seat watching the levels, I'd hit the purge valve(s) for whichever end is higher and bring that end down to the bump stops. Then if that is the rear, put some air back in the low side to get level side to side and then drop the front with the purge and stop it when it gets close and then level it. Then run down the jacks. If the front is highest, drop it to the bump stops, then drop the rear to hit level end-to-end, then level side-to-side, then lower the jacks. That way the entry will be as low as it can go and there should be no need for an extra step most of the time.

Now granted, there is no reason why that method won't work with using a battery impact to put the jacks down. And that makes a lot of sense. Plus when you go to drive away the bus will come up to standard ride height by itself and lift the jacks off the ground most of the time. But I didn't buy the jacks with the 10:1 boxes, and I planned all along to use gearmotors. Might as well stick with the plan. The only real variable is what gearmotors to use.

Jim

[Jim Blackwood]

Installed the truss today and got the four top bolts in. I'll try to get the bottom two in tomorrow. Here is how it fits: The rear bulkhead is pretty thick stainless and has a 4-1/2" channel near the top that is 1" deep. The truss has two top stringers made from 1 x 2 x 3/16" rectangle tubing welded with a 1/2" overlap and then there are spacer blocks below that so that when the doubler on the top stringer goes into the offset the blocks hold it to the top of the offset, then four bolts go through the top stringer and the doubler and into the suspension subframe which is formed of 3/8" thick steel.

The ends of the bulkhead are welded into the framework of the body and the top forms part of the floor support system so it is  very tightly tied in and the top 6" or so of the bulkhead is pretty stiff, especially out near the ends. The recess allows the load to be transferred to the doubler, from there to the top stringer, and from there to the downlegs that the jack is bolted to.

In addition, the truss itself transfers loading from the six 1/2" attachment bolts and the central section of the recess out to the jack mounts. To resist twisting, the jack mount sections will have four 5/16" bolts per end clamping it to the bulkhead panel, and the floor trim will include a containment collar to secure the lower end of the jack and prevent lateral movement in two axis. The side bracing and floor will add to the rigidity provided by another stringer running along the base of the bulkhead and bolted to the suspension frame in two places.

I used the leveling jacks to lift the truss up into position and it fit like a glove. Probably weighs somewhere in the neighborhood of a hundred pounds, but I think along with the support provided by the bulkhead that it will do the trick. The minor truss looks beefier, but I don't think it is any stronger. Still there is some risk with any cantilevered construction. The true test will be to see how solid it feels with all the tires off the ground. Probably won't be to that point for another couple of weeks.

Jim

[Jim Blackwood]

So I went to the local scrapyard and scored three gearmotors yesterday which I do believe I can press into service here. Unfortunately I doubt I can use the motors but the gearboxes were well worth the $75 each I paid for them. (a new gearmotor to serve this purpose could easily cost over $2k each)

The center one is a SEW/Eurodrive with a 541:1 ratio and a 1/2hp motor. That one has a hollow shaft and can hang on the input of the front jack, and MIGHT have enough power to lift the bus without help. If not it will at least give me another datapoint. I plan to swap that motor for a 1-1/2 to 2hp 3450 rpm one which will double the speed, effectively cutting the ratio to 270. If it is capable of lifting the bus as it is that will mean I can use a 1hp replacement motor and it will help me in sizing the rear ones as well.

The other two gearboxes are 80:1 and 60:1 respectively, have a solid shaft output, and will need a chain drive, meaning additional reduction there. With a 3:1 and a 4:1 chain drive I can achieve a 240:1 ratio, nearly matching the front so the same hp motors but in 1725rpm should apply.
For a perfect match the chain reduction would be 3.375 and  4.5 respectively, certainly feasible with available sprocket sizes. Rather than hanging off the input shafts directly the boxes will have to hang alongside, which is why this had to be done before the waste tanks.

The other photos show the side jacks in place mounted on the rear or major truss. Although in the photos it may look a bit spindly, it is solidly attached to the rear suspension frame and the bulkhead and tied into the side frames as well and is designed to transfer load directly to the upper offset of the bulkhead so I think it will hold up the bus. It is built along the lines of a bridge truss design.

I found my cord to tie into the 3 phase and will be testing 2 of the three motors later (one is 440v only which I don't have) and then I'll need a bore adapter for the eurodrive but once I have that I can proceed to the next test. In the meantime, I have used a ratchet and extension to take some load on one of the side jacks but I don't have the tire off the ground yet. In hindsight, the 10:1 built in reducer would have been a good thing but there really wasn't room for it in the front. It would have greatly simplified things at the back though.

Jim

[Jim Blackwood]

Are you guys still interested in this? If you aren't that's OK, just one less thing for me to do. I do realize it's drifting into the more arcane part of things what with gear ratios and current draw and whatnot. Sometimes it breaks my brain to think about it.
But anyway, yesterday I ordered sprockets for the two side jacks. I was fortunate enough to find what I needed on ebay and was able to get all four for around a hundred bucks so that was a pretty good deal. The chain I have enough of. It's motorcycle chain so I may have to thin the teeth a little but that's easy to do. It's 40 pitch which has a 1/2" spacing between the pins. For this application I think it'll be fine although nominally it might look a little on the skimpy side. It has to handle about a 750 lb pull and I think the rating is about 525 lbs. I found two 60 tooth sprockets with a 1" hub and those will fit the available space. For the reducers I found one 13 tooth 1-1/4" bore sprocket  for the 60:1 reducer and a 17 tooth 1-1/2" bore sprocket for the 80:1 reducer. That should put me close to 280:1  on both sides. The front is 541:1 with a 1725 rpm motor so if I switch to a 3450 rpm motor it will double the speed. That is roughly equivalent to cutting the ratio in half which would be 270:1, meaning that the front and side jacks will then be running at the same speed.

The question then becomes the horsepower requirement which based on earlier testing should be no more than 2 hp per motor and the next test using 3 phase power will nail that down more closely.

Now then, 3 phase power on a bus you ask? Yes well, things have gotten more inexpensive you see. Today you can buy a VFD drive that will run on 220vac for about $65 and power a 2 hp (1.5kw) 3 phase motor so it's reached the point of affordability. And that drive is easily reversed with an external switch and also has some pretty sophisticated electronic controls. Like soft start which we find useful. It may even be able to run the motor at a higher speed under no load conditions. So a simple up/down switch on the console ought to do the trick. It also lends itself well to an automatic leveler that can be added later.

To power that VFD (and at the 1/2 hp level they can run on 110vac which can be very useful sometimes) all that is needed is a 2kw inverter. You can buy those with a sine wave output all day long for about $35 each, meaning the jacks can run on battery power if needed. Or the generator, or the shore line. That takes care of that.

The motors may be a bit expensive but there are quite a few available for under $100 so hopefully I can find the right combination of rating, shaft size, speed, voltage, mount type, and size in that price range. If not, the cost of new is not prohibitive. Even so I think I still have a pretty good chance of keeping my total cost under $2000 which is exceptional for such a robust leveling system.

Jim

[6805eagleguy]

Jim, very interesting knowledge. I am impressed. Keep it coming

[Jim Blackwood]

OK, I'll keep going with it. One thought I did have if anyone wants to try this, you should be able to run it with a garage door opener. I know that sounds far fetched but all you'd need is a jack with the 10:1 reducer, a 1/2 hp opener, and 100:1 reduction from the motor to the jack. It'd be slow but it'd work. A typical opener has a 20:1 reduction and a 10 tooth drive sprocket meaning the driven sprocket would need to have 50 teeth. 10x20x5=1000:1

It'd be a light duty drive of course, but also light and inexpensive. The heavy part of the reduction would be at the jack itself, reducing the torque requirement from 300 ft/lbs to 30 and then the chain reducing it further to 6 ft/lbs at which point the plastic gears of the opener take over. At the motor the torque requirement is around 4 inch pounds, plus losses. The only reason I didn't try this approach is because I didn't think of it.

Jim