Convert 1975 Afron Cherrypicker?

Technical discussion on converting internal combustion to electric
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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Thu, 24 Feb 2011, 21:28

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The pics should tell the story well enough - it's an elevated work platform used in an apple orchard, it uses skid-steer with 2 driven wheels and a castoring one, and has a hydraulic ram for lifting the boom (ignore the air tank etc. it isn't used and I'd remove it as part of the conversion).

It strikes me as a good candidate for conversion as it spends most of the time stationary.

At the moment it has an 8hp motor and the travel speed of the machine is a bit slow (less than walking speed) whereas brisk walking speed would be preferred.

The pics show the pedal control system which uses rods down the boom to engage v-belts which send power down the shafts on each side to drive the worm reduction gear on each wheel. Obviously I'd look to mounting the motor (plus chain or gearbox if needed) direct to the input of the wheel gearbox. Being skid steer and driven in both directions, it'd need symmetrical speed control, which doesn't seem that common.

Any ideas on how feasible this is, or advice on how to ascertain what size motors I'd need on each wheel?

Last edited by Trogdor! on Thu, 24 Feb 2011, 10:53, edited 1 time in total.

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Convert 1975 Afron Cherrypicker?

Post by Electrocycle » Fri, 25 Feb 2011, 01:27

It'd be good to have some measurements of the input rpm to the gearboxes, or the tyre diameter and gear ratio, but I imagine you could put something like a Mars motor, ADC 6", or similar on each wheel.
You'd need a controller for each motor, and they need reverse - so the Mars brushless and Kelly or Sevcon combo would be good.
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Convert 1975 Afron Cherrypicker?

Post by Speedily » Fri, 25 Feb 2011, 01:45

what about one motor driving the pump with spool valves so the motor only goes when it needs to move

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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Fri, 25 Feb 2011, 02:19

Thanks for the comments so far - I did do some tests a month or two back and from memory the reduction at the wheel gear was about 40:1 and the wheels are 26" or 660mm dia, so a circumference of about 2m. At the moment it moves slower than walking speed, so maybe 3.5km/h which makes for an input rpm of about 1,200 rpm. Double this or more would be ideal.

From what I have read, 2kW on each wheel might do the job? The other tricky bit is the speed controller - I don't just need reverse, it needs to be symmetrical speed control in both directions - are there units that offer this?

As for just replacing the existing motor, it drives both a pump for the lifting ram and a set of v-belts that are engaged by the levers in the basket and drive the shafts to the wheels. This system requires quite a bit of physical effort to actuate (note this machine was made in 1975, modern units use hydraulic motors at the wheels). Part of the benefit of the conversion would be to improve the control system.

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Post by Electrocycle » Fri, 25 Feb 2011, 03:48

yeah I think two motors for drive and one to run the hydraulics would be the best bet (maybe replace the pump with an integrated electric pump as used in small electric fork lifts, etc)

2kw on each wheel would probably do the job for the current speed - but I think you'd want a bit more power for reliability and uneven ground.

The setup I used in my old bike would work ok for your wheel drives.

That was a Mars brushless motor and a Sevcon PMAC controller. It could do completely variable speed control to + and - 100%
That controller could only do 36v, but that would be enough. You should get about 2000rpm out of the motors.

If you went to 48v and ran the 48v Sevcon or Kelly controller you'd get heaps of power. (Kelly is easier to program, but the Sevcon is very robust and waterproof)
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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Fri, 25 Feb 2011, 03:49

Had another read of the Sevcon Millipak PMAC manual - it seems it's quite capable of 100% accel in either direction, though it requires a switch to change direction, which is not quite how a skid-steer vehicle operates (two levers, one per wheel), but perhaps an interface could be sorted out.

As Electrocycle suggested, a Mars brushless on each wheel and a pair of these Sevcon controllers could be the go...

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Post by Trogdor! » Fri, 25 Feb 2011, 04:08

Seems I posted just after you did :)

Been thinking the same about the hydraulic lift, something like this (off a forklift):
http://cgi.ebay.com.au/Hydraulic-power- ... 1e61186bba

or slightly smaller would do the job. I think, as you suggest, I'd run a 48v pack of some kind, although the 24v for the hydraulics might cause a bit of imbalance on one half of the battery pack, but I suspect its intermittent use wouldn't be that much of a drama.

It's true that the machine does work a bit harder going up an incline, so some extra herbs on hand would be a good idea.

So the drive/control bit seems kind of sorted, but how do I work out how many AH of batts I need?

Also, are the Mars/Sevcon combos readily available in Australia? And reading the Sevcon manual, I think I'd need a programmer too.

Last edited by Trogdor! on Thu, 24 Feb 2011, 17:09, edited 1 time in total.

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Convert 1975 Afron Cherrypicker?

Post by coulomb » Fri, 25 Feb 2011, 04:39

Rather than separate DC motors on each wheel, why not just replace the ICE with an electric motor (DC would do) of twice the power? Well, same torque, up to twice the speed. Hopefully the gearbox can handle twice the speed from the motor/engine.

My understanding is that DC motors don't like to do symmetrical reverse. But the ICE never reverses, so the existing gearbox must do it. If you did decide on separate motors for each wheel, you'd possibly need to go to AC, or at least neutral timed DC motors (e.g. Kostovs) with reversing contactors. With one motor per wheel, you'd need one controller per wheel as well. I don't see the advantage (in one motor per wheel) when the mechanicals are there for you already.
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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Fri, 25 Feb 2011, 05:26

coulomb wrote: Rather than separate DC motors on each wheel, why not just replace the ICE with an electric motor (DC would do) of twice the power? Well, same torque, up to twice the speed. Hopefully the gearbox can handle twice the speed from the motor/engine.


Part of the issue with the machine is the archaic control mechanism. That 8HP Honda engine runs 2 things - the hydraulic pump that raises the boom, and a gearbox that outputs a set of counter-rotating v-pulleys.

To move the machine, you press pedals (or pull up levers for the opposite direction) in the operator's basket. These pedals/levers are connected by steel rods running down the boom to levers that move v-pulleys to apply tension to one of two v-belts and engage one of the counter-rotating drive pulleys, producing motion in the v-belt and sending drive to the wheel. Hard to describe, but the reality is that it requires considerable physical effort to operate the pedal or lever due to the friction in the connecting rods, and the fact that you are physically engaging a pulley to a v-belt to establish sufficient friction.

The system is workable, but, frankly, awful by today's standards. Newer machines (this was made in 1975) use a central hydraulic pump and hydraulic motors, as you'd kind of expect, so the actuation is effortless by comparison.

Apart from the awkward drive system, the unit works pretty damn well, but the attraction to electrification is 1. a much nicer control system, 2. elimination of the power loss in the pulley system and 3. silence for most of the time rather than an IC engine clattering away constantly.
My understanding is that DC motors don't like to do symmetrical reverse.
Possibly true for brushed motors, but I can't see why brushless motors should have issues running in reverse -they shouldn't know the difference?

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Convert 1975 Afron Cherrypicker?

Post by antiscab » Fri, 25 Feb 2011, 05:29

how much fuel does this thing use in a day?

just approximating battery size....
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Post by Electrocycle » Fri, 25 Feb 2011, 11:29

I'll have a look later for Mars / Sevcon availability. I bought mine from a robot parts shop :)

There are one or two around on this forum I think.

It's easy enough to make a throttle lever with direction switching so it'll work with normal skid steer style controls.

I have a sevcon programmer I could lend too. (might be cheaper to go Kelly controllers anyway)
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Post by Trogdor! » Sat, 26 Feb 2011, 00:28

antiscab wrote: how much fuel does this thing use in a day?
just approximating battery size....


I saw mention of that metric in another thread, however use of this machine tends to be quite erratic - you travel maybe 200m to get to a tree, you raise the boom and tweak the position to begin picking. At this point the IC motor is still running, but with electric everything would be turned off until you moved the machine or boom.

At the moment the machine is being used mainly to put up netting on the orchard which often involves only intermittent use of the engine. I'll have to try and see how many hours I get from a tank (which is about 4l or so I think). When I think about it, some kind of counter could do the job...

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Post by Trogdor! » Sat, 26 Feb 2011, 02:23

Electrocycle wrote:(might be cheaper to go Kelly controllers anyway)


Thanks for the pointer - I finally had a moment to look at the Kelly controllers, and they might be the go - they do a 48v 100A continuous (200A peak) controller that I'm thinking should do the job? (that's with a Mars 3001 motor on each wheel) the nice thing is they offer a firmware upgrade that supports a centred throttle pot for skid-steer type operation.

This is the controller:
http://kellycontroller.com/kbl4820124v- ... p-256.html

And this the the throttle option I mentioned:
http://kellycontroller.com/stick-shift- ... p-627.html

They recommend a bigger unit for the Mars motor (150A cont 300A peak) but for my application I'm thinking I wouldn't be using that much power (100A = 4.8kW - I was expecting to need 2kW or so), or would I be making a mistake going for the smaller unit?

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Convert 1975 Afron Cherrypicker?

Post by coulomb » Sat, 26 Feb 2011, 03:14

Trogdor! wrote: Possibly true for brushed motors, but I can't see why brushless motors should have issues running in reverse -they shouldn't know the difference?

Sure, brushless DC motors can run in reverse all day. I think of brushless DC motors as really being AC.
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Post by Electrocycle » Sat, 26 Feb 2011, 13:41

I think the 100A controller would be ok. The Mars motor is only really rated for 100A continuous anyway.
I haven't personally tried that controller, but given the low gearing you have I don't think there'll be too much load on the motors.
It might be worth checking that the controller is ok driving a larger than ideal motor.

The skid steer throttle option is pretty handy! The price is also better than the Sevcon controllers so the Kelly is probably the way to go.

A small hydraulic power pack would definitely be the best option for the boom. You'd be able to simplify the hydraulics a lot and have better control.

The Mars motors are quite happy to run backwards, but they do have a cooling fan designed for one direction. It still works in reverse but not quite as well. I think there's a reverse fan option, but at the power levels you'll be running I don't think there will be any cooling issue anyway.
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Post by Adverse Effects » Sat, 26 Feb 2011, 16:42

you would be better off putting a motor on it that has a starter motor on it and just shut it down when your not useing the motor

will be way cheaper and i bet you would double or more the time it takes to use a tank of gas


[EDIT] not to mention if it runs out of power in the field how you going to get it back to the shed to charge it
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Post by Electrocycle » Sat, 26 Feb 2011, 17:34

the improvement in control gained by the electric conversion will make the machine much nicer to use though.

It doesn't sound like it'll be doing massive distances, so it'd be easy enough to tow it back or recharge if the batteries went flat (generator on a ute or wheelbarrow?)
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Post by Trogdor! » Sat, 26 Feb 2011, 17:45

Adverse Effects wrote: you would be better off putting a motor on it that has a starter motor on it and just shut it down when your not useing the motor

will be way cheaper and i bet you would double or more the time it takes to use a tank of gas
You are right - being able to shut down the engine and restart at will would save a lot of fuel. However there's a couple serious issues aside from that - with the power off, the hydraulic pump loses pressure resulting in the boom slowly dropping.

However the other big issue is the control system - I've mentioned it's appalling-ness a few times, but perhaps some more pics would make it clearer:
ImageImage
ImageImage

So to engage drive, you are physically moving rods to swing a pulley to engage v-belts. You can just stand on the foot pedals, but for the other direction, you need to pull up on the lever on each side. There's friction in the rod system as well as power losses in the v-belt system and the gearbox that provides the counter-rotating pulleys.

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Post by Trogdor! » Sat, 26 Feb 2011, 17:52

Electrocycle wrote: the improvement in control gained by the electric conversion will make the machine much nicer to use though.
Yup. Finger-tip joystick control would make a world of difference to using the machine.
It doesn't sound like it'll be doing massive distances, so it'd be easy enough to tow it back or recharge if the batteries went flat (generator on a ute or wheelbarrow?)
You can disengage the hubs of the wheels and tow the machine, which I often do with a ride-on mower as it's much quicker for any kind of distance.

That said, ours is a pretty tiny orchard - only 1Ha and maybe about 1,000 trees, and there's sources of mains at a number of locations.

However, conversion cost does look pretty steep - $1,000+ per side for motor & controller, plus whatever batts are needed + all the ancillary bits and pieces.

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Post by Adverse Effects » Sat, 26 Feb 2011, 22:38

if you want to spend money on it i would convert the drive system over to hydraulic drives and use that you would be able get rid of the pedals and the hand levers and just have a 3 gang hydraulic valve setup

outside 2 forward and back for each wheel and center one for up and down

as for it sinking when you turn the motor off you have a leaking valve somewhere
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Post by Adverse Effects » Sat, 26 Feb 2011, 22:49

you would not be able to use hub motors you would need to keep the hub reduction boxes

but it would not be hard to remove the drive shafts and make brackets for the electric motors or hydraulic drives

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Post by Trogdor! » Sun, 27 Feb 2011, 01:30

Adverse Effects wrote: if you want to spend money on it i would convert the drive system over to hydraulic drives and use that you would be able get rid of the pedals and the hand levers and just have a 3 gang hydraulic valve setup
Yeah, but at that point I think it'd probably be cheaper to buy a second-hand machine of a more recent vintage which is set up with hydraulic motors etc. That said, I haven't found too many units around, which is why I've been considering converting this one (it's on loan from a neighbour who I think would be happy to sell it).
as for it sinking when you turn the motor off you have a leaking valve somewhere
.

Yep, I assume it's probably in the spool valve that one of the rods actuates. If I convert it I'd probably just replace it with power pack from a forklift which would have solenoids on the valves - seems simpler than converting the current one to electric, fixing the valve and sorting out actuation of it.

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Post by Trogdor! » Sun, 27 Feb 2011, 01:36

Adverse Effects wrote: you would not be able to use hub motors you would need to keep the hub reduction boxes


Yeah, it actually seems the 40:1 reduction in the exiting gearboxes matches up well with the RPM of this Mars motor Electrocycle suggested.

Also, as the reduction box is a worm drive, it can't coast or drive the motor - once the motor stops spinning the wheel is essentially locked, so I won't get any kind of regen braking, but I also won't have to worry about braking either.
but it would not be hard to remove the drive shafts and make brackets for the electric motors or hydraulic drives


I've been looking at that - direct-coupling the motor to the gearbox input would be ideal, though I'm not sure what kind of coupling is normally used? Also the input shaft on the wheel gear is about 100mm below the bottom of the arm it's mounted too - I'm not sure if the Mars motor will line up OK.

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Post by Electrocycle » Sun, 27 Feb 2011, 03:40

The Mars motors are around 200mm in diameter, and have threaded bolt holes on the face (where the shaft comes out).
I would probably keep the universal joint, cut the shaft short, and weld a coupling for the motor shaft in the end (motor mounted somewhere close to the picture above)

The price is a bit hard to get away from since it needs two motors and controller, but you could get away with second hand lead acid batteries I think, so the battery cost would be low.
Once it's proven you could upgrade the battery pack for more range.
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Post by Adverse Effects » Sun, 27 Feb 2011, 03:57

its a 40 to 1 drive
so to get 1Hp at the wheel you only need about 1/39th(allowing a bit for friction) of a hp at the motor . ok maby a bit more

and 100 amp is most likely way to much

considering a golf buggy has about a 1/8 hp motor runing through a bout a 4 to 1 diff and it can get up to around 40Kmph

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