Stripping Down pt. 4 - Painting the Chassis

A whole bunch of cutting and grinding gets rid of the old motor and bearing mounts.

Then it's a matter of lifting the whole lot...

And flipping and painting the underside. I've added some 50mm angle iron to reinforce the area where the 240kg of batteries will sit.

Stripping Down pt. 3 - The Lifting Ram

I wasn't sure how to get the main lift ram out of the chassis - it's pretty heavy and in an awkward position. In the end a set of forks made the task pretty darn simple.

Stripping Down pt. 2 - The Main Gearbox

After removing many, many bolts, the main gearbox that generates the counter-rotating shafts is removed.

Stripping the chassis

The aim is to get rid of all the internal combustion related bits, so first, off with the engine.

There's oil and grease everywhere - once converted the machine will be much cleaner...





You can see in the above shot that the machine has a thick steel plate beneath it, which is basically dead weight for machine stability. Seeing as the batteries will weigh 240kg, there won't be much use for it.

Off she comes.

And onto the scales - 157kg.

Anatomy of a wheel gearbox.

The machine really hasn't been maintained as well as it might have over the last 36 years - pretty much everything leaks, including the oil seals on the gearbox. While I was pulling it to bits I thought I'd grab a shot of the internals.

Not really the most complex of gearboxes...

Wiring up the hydraulics

The neighbours who have so kindly donated the machine to me to convert also happened to have a collection of 12v deep-cycle batteries out of a telephone exchange which they offered as well. At 150 amp hours capacity, they'd be ideal for this machine. The only catch is that they're huge, and very heavy. This is the hydraulic pack wired up on the bench with the batteries next to it:

To start with I connected one 12v battery using 4 AWG cable and a 100A circuit breaker.

The wiring was a little tricky as while the motor was being supplied with 12v, the solenoid valves on the pack need 24v, so I used a pair of small gel-cells to supply the 24v - you can see them tucked in between the pack and the big batteries in the first pic.

With a bit of hose hooked up to the output and a lot of spilled oil, the thing works.

Next job was to remove the old engine-driven hydraulic unit:.

And fit the new unit along with batteries:

The little grey box with a switch is my control for lift or drop. The 12v supply worked well, but not as fast as I'd like, so I installed the second battery and adjusted the wiring:

It'll get some cable ties added to keep everything in place, despite this battery location being an interim measure - ultimately they'll be located where the engine is now, but I want to keep the machine as operational
as possible during the conversion. The downside with this location is the weight of the battery - I mentioned they were heavy: 60kg each, so that's 120kg sitting on the front.

The video below shows the hydraulic lift in action, with the difference between 12v and 24v:

The Hydraulic Power Pack

A bit of snuffling around on Ebay finally turned up what is hopefully a suitable replacement for the engine-driven hydraulic pump:

In a previous life it was in a stock-picker, a kind of forklift where the operator rides up in the air with the forks.

Popping it open reveals the gear pump and a fairly modest amount of filtering on the suction:

Which hopefully should be sufficient as it'll be permanently hooked up to the main ram, so not much scope for crap to get introduced. I don't know terribly much about hydraulics, so to be sure I wasn't going to hurt it, instead of using the normal general-purpose agricultural hydraulic fluid that I'd normally dump into a tractor, I went and got it some Caltex Rando HD 46, which is pretty much a straight mineral oil.

The unit came with this block of solenoids - it's set up to supply two "single-acting" circuits. I'll only be using the top one, which appears to have a bigger hole, and the black one at the bottom that allows the oil to drain back into the tank when the platform is dropping.

At the top of the block there's some kind of pressure sensor, which I'd love to do something clever with, but it has 3 wires coming out the top and no indication of how it should be wired, so I doubt I'll be able to work out how to use it.

It's a 24v motor rated at 2.2kW - next thing is to get some batteries, hook this bad boy up and start moving some oil.

How Much Power?

This machine has an ageing (and very loud) 8hp Honda motor powering it. It isn't the original - traces of the old engine are on the machine, including the electric start controls in the operator's platform - something that would have been very handy to save fuel and noise. At some point in the last 36 years, the original engine died and was replaced with this standard, bare-shaft Honda engine, which unfortunately has only a pull-start. Actually, I don't really know if there's only been two engines, there may have been more during its life.

So 8hp driving 2 wheels - 4hp a side? 4hp is about 3kW so that's what's needed one each wheel in converting it to electric. Simple.

Except for a couple of factors. When moving the machine, the engine rarely sounds like it's loading down - the only time it really seems to be working hard is when hoisting the boom - my previous calcs show that needs around 2kW, or about 2.6hp. So maybe it's using a great deal less than 3kW a side.

However, one big issue is that the machine is slow - I've measured the drive shafts to the wheels spinning at 1,200rpm - with the 40:1 reduction at the wheels, that's turning the wheels at 30rpm. The wheels are about 660mm in diameter, so for every revolution they move 2m. 30rpm x 2m = 3.6km/h, which is really slow (slower than walking pace).

This makes the machine very slow to move about the orchard. Ours is a small orchard, but to move 200m takes a very tedious 3 to 4 minutes. For any distance like this or further, it's faster to hook up a ride-on mower and tow it into position.

So while it may be using a lot less than 3kW on each side at the moment, a key goal is to increase travel speed - so the question remains, how much power, and therefore, how big a motor?

Testing Torque

In an attempt to apply some physics, I decided to try and measure the torque at the input to the wheel gearbox required to move the machine. Here are my torque measurement tools:

Yes, it may look like a couple of Chinese knock-off  Vise-Grips, a piece of DIN rail and a bucket of random bits of steel, but this might just give me some idea.

The setup is with the machine on level ground, and the other drive-wheel disengaged so it free-wheels. The third castoring wheel is pointing straight ahead. Then the measurement apparatus is attached like thus:

And more random bits of steel dropped into the bucket until this happens:

With the machine creeping forward ever so slightly.

Results

Torque is mass x distance. In this case the bucket ended up weighing 0.577Kg, the rod length was .835m and  itself weighed 0.121Kg. The torque applied by the bucket is just mass times distance, so:

0.577 x 9.8 x .835 = 4.7Nm

The 9.8 turns the Kg into newtons.

For the torque exerted by the rod, one treats it as the mass of the rod at half it's length, so:

0.121 x 9.8 x 0.468 = 0.5Nm

So the left wheel needed 5.2Nm of torque to move.

However the right wheel when tested the same way only needed 3.5Nm, supported by the fact that the left drive shaft seemed a lot stiffer to turn. I'll have to look into that - I previously replaced the axle shaft on the left gearbox, and am now wondering whether I buggered up a bearing position or something, causing binding.

Torque into Power

Ignoring the strange result for the left wheel, I can work on the basis that the machine needs 3.5Nm of torque to move forward. Digging up a  formula for power:

Power (kW) = torque x 2pi x rpm / 60,000

Plugging in our numbers, including the current drive shaft speed:

Power = 3.5 x 2pi x 1,200 / 60,000 = 0.44kW

Which frankly isn't a whole heap, making me think my torque measurement might be a bit flaky.

Forging on, though, as mentioned before, the machine is too slow. I'd like it to go 3 times as fast, so I want 1.3kW. That's 1.7hp. Still  not a great deal of power...

However, this is for the machine on the flat, the castor wheel pointing in the direction of travel. In many cases this machine will be on a slope, the platform raised and only one wheel driven in order to turn the machine, and quite possibly with the castoring wheel turned square to the way it needs to be. In that situation the torque requirement will be far greater, although the speed in that situation will be far less than needed for travelling to a new spot.

Conclusion

I'm not really sure where that leaves things. I certainly need to work out why one wheel needs almost twice the torque compared to the other, but I'm really not sure if a machine with an 8hp engine really only needs 440 watts of power (2/3hp) to move. Perhaps I need to try a different method for torque measurement...

The fact is that I've already semi-decided on what motors to use, and they are rated at 5kW continuous (15kW peak), so with one on each wheel, that's 10kW. Apart from the extra cost of the oversize motors, the other consideration is that if they end up operating at very low power, it's likely they'll be below their maximum efficiency, so I won't be getting the best bang for buck out of my batteries...

While I ponder that, I'll try and work out what's up with that left wheel gearbox.

Hydraulics

I've decided to tackle converting the hydraulics to electric drive first. First thing to work out is how big a unit is required. That means taking a few measurements:

Flow

First thing to work out is the bore and stroke of the main ram. With the boom fully extended I measured this:

And came up with a stroke of 480mm and a rod diameter of 60mm. I'm not sure how the rod diameter relates to the internal cylinder diameter, but I'm going to guess it's maybe 65mm. That means the volume used to extend the cylinder fully is about 1.6 litres.It does this in about 9 seconds, so that's a flow rate of 10.7 litres per minute.

Pressure

To work out how much power is needed to lift the boom, I need to know the pressure required. If I knew the mass of the boom I could probably work it out theoretically, but I decided to go the direct route. This is the supply into the base of the ram:

The brass bit between the hose and the entry to the ram looks to be a flow restrictor - I assume it's there to limit the speed of the boom so it doesn't drop like a stone if the hydraulic hose bursts.

A quick trip to the hydraulic shop and:

With the gauge in place I was able to determine that the unladen operating pressure of the ram was 35bar, and with my 86kg on the operator's platform it goes up to 70bar, or 1,000psi, which is pretty low pressure for hydraulics.

Power

So knowing this info (flow and pressure) it seems there's a neato formula for determining the input power required. It's simply 

(flow x pressure) / (600 x eff)

The eff. term is the efficiency of the system and the answer is in kW. That gives me:

(10.7 x 70) / (600 x 0.7) = 1.8kW or 2.4hp

My term for system efficiency is totally made up. I assume hydraulic pumps are about 85% efficient and electric motors maybe 80%, that gives 70% total efficiency.

A bit of snuffling around Ebay turned up a 24v 2.2kW hydraulic power pack from a stock picker (a kind of forklift). I'm hoping it'll do the job - if the boom lift is a bit slower that's not a huge issue, as it's probably quicker than it needs to be at the moment.

First Measurements & Some surgery...

The plan for the conversion is to put an electric motor on each of the two drive wheels, and to replace the engine-driven hydraulic pump with an electric hydraulic unit for raising the boom. I also want to keep track of the weight of the machine to make sure it remains heavy enough to be stable, but not so heavy that it needs lots more power to move about.

So there's a few things to work out - how heavy is the machine, how much power is needed to move it (and can I get it to move faster) and how much hydraulics is needed to raise the boom?

1. Weight

Weighing this machine was a lot more tricky than I expected. The idea was to place each wheel on a dodgy set of digital scales while supporting the other two wheels to make sure the machine was level .

After a few life-threatening attempts with the machine spontaneously rolling and lurching off the scales, I came up with the following results:

• Front Left: 250kg
• Front Right: 190kg
• Rear Castor: 450kg
• Total: 890kg

There was 5kg of bits of scrap steel sitting on it, so that makes 885kg. I'm mystefied as to why one front wheel is 60kg heavier than the other.

2. Surgery

With the initial weight known, I was keen to remove a modification that a previous owner had made - they'd added an air compressor for operating pneumatic pruners - something I didn't plan to do (they scare the hell out of me) and the compressor added extra weight and stuck out from the back of the machine and knocking into branches when turning.

As the bits came off, they got weighed:

The total weight removed was about 76kg, so the machine weighs about 809kg.

The Idea

This is an Afron cherrypicker, or Elevated Work Platform. It's a bit different to many kinds of cherrypicker as it's able to move about while the platform is raised.

This particular unit was made in 1975 - I suspect most of that vintage were retired long ago - modern units are completely hydraulic, this one only uses hydraulics for the boom lift. The wheels are driven by shafts into gearboxes at the wheels:

The machine uses a system of gears, belts and shafts to send motive power from the centrally-mounted 8hp engine to the wheels with pedals and levers in the operators platform used to actuate drive to each wheel and thus steer it:

The system works, but it takes a lot of physical effort to engage the belts and move the machine. It's also very noisy with the engine running all the time. It's rather slow to move around - slower than walking pace, and pretty much all of the control gear and gearbox is worn - the main gearbox leaking oil constantly.

To give you a little idea of the machine as it is now, here's a video which also shows operation of the gearbox used to provide drive to the wheels:

In use, the machine is moved to one spot, the platform raised and then often stays in that position for quite a while, depending on what you're doing. During that time the engine is clattering away, using up fuel but not doing any useful work.

Converting to electric will:

• Make it much quieter
• Provide fingertip control
• Do away with all the control rods and gearbox
• Vastly reduce maintenance
• Hopefully increase the travel speed

And most importantly to me, breathe new life into an old machine!