Convert 1975 Afron Cherrypicker?

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

Post by antiscab » Sun, 27 Feb 2011, 04:39

Adverse Effects wrote: 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


no,
two important things to remember about gear reduction:

power out is *always* less than power in
only torque and rpm change (by roughly the same ratio).

so 1hp at the wheel takes more than 1hp at the motor.

on a 40:1 ratio, 40Nm at the wheel takes ~1Nm at the motor.

100A should be sufficient, but as with most things you won't know for certain until its all together.

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Convert 1975 Afron Cherrypicker?

Post by Electrocycle » Sun, 27 Feb 2011, 04:40

it's the torque that's amplified by the gear ratio, but the rpm is divided.
Power is torque x revs, so the power is the same (minus losses)

So basically, 1hp in is 1hp out, just at a lower speed.
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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Sun, 27 Feb 2011, 20:18

For anyone who's interested in seeing the machine in operation, I had to fix it this morning - turned out to be a disintegrated shaft key from the bodgy fitting of the 8HP Honda (not the original engine) - so while the gearbox cover was off I shot a short video showing how it produces the counter-rotating shafts for each side of the machine.

It also shows how damn loud that motor is Image

http://www.youtube.com/watch?v=D-7viCxVlfQ

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Convert 1975 Afron Cherrypicker?

Post by Electrocycle » Sun, 27 Feb 2011, 22:34

it'd definitely be a totally different experience with electric power!
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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Mon, 28 Feb 2011, 02:55

Electrocycle wrote: it'd definitely be a totally different experience with electric power!


That's a big part of the attraction to the conversion - silence :)

By my estimate it's going to cost about $4,000 for the conversion - plus the cost of the machine, assuming my neighbour is willing to sell it, which I expect they may as it hasn't been used for a long time - hence the poor state of the machine (I've already spent about $500 plus a lot of labour repairing various parts of it).

As part of the conversion, I'd remove some of the modifications - namely the air system that was added at some point (pump and tank) and all the gears, linkages etc. would go. I haven't weighed the machine (I will if I do convert it), but I expect the net result, even with the batteries, will have the machine being quite a bit lighter, which should improve manoeuvring, as there's a lot of weight on the castoring wheel at the moment.

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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Mon, 28 Feb 2011, 03:09

Adverse Effects wrote: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


That is a good point - I spent a while reading threads here trying to get a handle on what electric power really means compared to IC engines. The motor on the machine is 8hp, but it isn't the original engine - I don't know what size the original was - I might ask the manufacturer in Israel to see if they know.

The motor doesn't seem to load down too much when I engage the belts, so perhaps it's 8hp aren't really being used. I'm tempted to do a temporary bodge fitting of some kind of electric motor to see how it performs, perhaps a low-revving drill, but I'd need two of the same motor(drill), which is a bit tricky to come by.

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Convert 1975 Afron Cherrypicker?

Post by Adverse Effects » Mon, 28 Feb 2011, 21:53

try this
get a rock / brick / log what ever put it in front of one wheel then disconnect the drive shaft at the top end
now turn it by hand and watch the wheel climb over the item
it will take all most no effort on your part

i was just thinking you could mount the motors at the main part of the cheery picker and just drive the shafts you have all ready
mount the motors under the arms to straiten the drive line as much as possible this way you are not having to modify anything on the unit so it can be put back if needed

you may have to put a wider wheel on the back to take the added wight of the battery's as well

as for the speed it go's i think you will find the original motor that was on it spun faster giving you more travel speed

8Hp sounds about right for driving the hydrolics and 2 friction drives
i would say that the friction drives are stealing about 2HP from the motor
i would say you would need about 1/4HP high speed (electric)per wheel and about 2HP for the hydrolics and have it on a only when needed switch

its a pitty your not in Brisbane i would have loved to help on this as its the type of oddball project i love to do
Last edited by Adverse Effects on Mon, 28 Feb 2011, 11:05, edited 1 time in total.

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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Tue, 01 Mar 2011, 15:55

I think you underestimate how heavy this machine is - I haven't weighed it, but I'd say it's in excess of a tonne. There's no way you can turn the drive shafts by hand, but I have been thinking about attaching a lever and known weight to a shaft in order to determine the minimum torque required to turn the shaft, although I'm not sure if that'd extrapolate into anything useful.

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Convert 1975 Afron Cherrypicker?

Post by Adverse Effects » Tue, 01 Mar 2011, 16:21

i dont think i have

worm drives are a very interesting drive in the way they perform

give it a try Image

i have broken a 10 ton cable on a boat winch that was on my trailer trying to pull a demountable office on to it and i didnt even hear the motor slow down

i made the motor drive out of a Mini(the car) windscreen wiper motor with a worm drive driving the winch input

i can stop the motor by pinching the shaft its not very powerful at all

[EDIT] i do have to admit the cable was over 10 years old
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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Tue, 01 Mar 2011, 16:27

I just did a quick test - a 1kg 800mm rod attached to the drive shaft required a weight of 1.3Kg on the end to turn it, which I calculate to be a torque of 41.25Nm - that's from a static situation, so I'd expect it to be less than that once it's moving.

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Convert 1975 Afron Cherrypicker?

Post by Adverse Effects » Tue, 01 Mar 2011, 16:33

did you disconnect it from the drive system at the motor end?

the friction drive will take a bit to turn on its own

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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Tue, 01 Mar 2011, 17:11

Nope, but with no belts engaged, the friction drive pulley spins pretty easily - it's just a pulley in a bearing with the v-belts just draped loosely over it.

Also, I'm not sure of the use of a static measurement, as, doing some sums, it doesn't really equate to the power of the machine - if I was to assume it requires 40Nm of torque, to spin the shaft at the 1,200rpm I estimate, it'd require 5kW!

Also, my test was with the shaft and torque rod at an angle, so I can't be sure about my newtons. I'll have to think up a more meaningful test I think...

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Convert 1975 Afron Cherrypicker?

Post by Electrocycle » Tue, 01 Mar 2011, 21:59

that's a good starting point though, and about what I'd expect, having played with similar things before.

You really can't be sure about the power required until you actually do it, but it's always better to have more than you need available :)
The Mars motors are cheaper than most other options anyway too.
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Convert 1975 Afron Cherrypicker?

Post by Adverse Effects » Tue, 01 Mar 2011, 22:44

1200rpm sounds a little slow because the petrol engine is most likly spinning at more than that and you want more speed

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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Wed, 02 Mar 2011, 03:50

The 1200rpm is my estimate of the current drive shaft speed from guessing the machine's velocity and working backward from the wheel diameter and wheel gear reduction ratio. Given it's an 8HP engine, it achieves this giving 4HP to each wheel, or 3kW per wheel.

I'm under the impression that electric kW are more powerful than IC kW, but I'm not entirely sure what the reasoning is behind this :)

It's something I need to get right, otherwise after all the expense, the machine could end up being slower than it is now :(

The engine output shaft speed is indeed considerably faster, as the central gearbox reduces the speed, and the counter-rotating drive pulleys are smaller than the swinging pulley on the end of the drive shaft.

If I get a moment tomorrow I'll try an rig up a tacho to get a proper idea of the drive shafts' RPM.

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Convert 1975 Afron Cherrypicker?

Post by Adverse Effects » Wed, 02 Mar 2011, 09:00

easy way would be to work backwards

work out the speed you want to go then

find out the circumference of wheel

work out the RPM needed to get the speed required

multiplied that by the reduction gives you a shaft speed needed

i would also say that you will not need any more than 1/4HP for each wheel and you want something that will spin a bit faster than you want

how to make a geto tacho

start shaft spinning with a string tyed to it run it for 10 sec stop it count the turns do the math Image
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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Wed, 02 Mar 2011, 18:59

My plan for a tacho is to paint a white mark on the shaft in question and hook it up to a frequency counter and convert Hz to RPM.

Also, I can't see how 1/4HP on each wheel is going to perform better than the current setup that provides 4HP per wheel?

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Convert 1975 Afron Cherrypicker?

Post by Adverse Effects » Wed, 02 Mar 2011, 19:22

for starters putting power through a worm drive it totally different to putting it through a set of gears

through gears you can over power the motor and stop the drive or even turn it backwards but through a worm drive you carnt

you will see no difference putting 1HP(as long as 1HP can drive it to start with) at 2000RPM or 100HP at 2000RPM through a worm drive

where as doing the same thing through a pair of gears you will see a difference in performance

it could be sending 1HP to each wheel or it could be sending 400HP to each wheel

if the RPM is set to X speed you wont see the difference of 1HP or 400HP through a worm drive

think of it this way

the motor you have is 8HP

take off 1 HP for age of motor that is 7HP

take off friction loss say 2HP that is 5HP

ok 5HP when you are moving thee unit around dose the motor bog down and labor really hard ??     no?   

ok then your not useing anywhere near its output of 5HP so your running on less than 2.5HP per wheel

i dont know how to put in to words any better than that
but it is what i have learned in all most 30 years of being a motor mechanic
Last edited by Adverse Effects on Wed, 02 Mar 2011, 08:40, edited 1 time in total.

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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Thu, 03 Mar 2011, 02:54

I see your point - it's true that the machine runs at a pretty consistent RPM, although most of the operation is on level ground. The only time it loads down a bit is when raising the boom.

I checked the RPM of one of the drive shafts - 1,200RPM, which surprises me a bit as that is what I'd estimated. Through a 40:1 reduction gearbox it's turning the wheel at 30RPM, which with a 2m circumference has it travelling at 3.6km/h.

As you say though, this doesn't really help much. I think the thing to do is hook up some kind of electric motor to one wheel (I can dis-engage the hub on the other so it free-wheels) and see what it does for the motor kW and RPM.


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Convert 1975 Afron Cherrypicker?

Post by Adverse Effects » Thu, 03 Mar 2011, 04:23

nice guess on the RPM Image

the good thing about making it electric would be you can make it run faster than you need and just control the speed you go with the joystick

so its spinning at 1200 then you want about 2400 to 3000 RPM would make it really usable

if the motor bogs down raising the boom then you are going to need about a 5HP for the pump

or change the pump for a smaller volume higher PSI pump and run it on a smaller motor

if it was me i would fix the leaking valve and then rig the petrol motor to run it only with a remote start stop ability

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Post by Trogdor! » Fri, 04 Mar 2011, 17:32

Did a quick test last night while the machine was near a shed - I removed one drive shaft and found a 22mm socket fitted nicely over the input shaft to the wheel gearbox - a piece of drill bit dropped into the keyway was enough to make it lock. I then plugged in a 1/2" to hex adaptor in a 550W Makita drill and was able to get the machine to move (with the other wheel's hub disengaged). The drill was operating well below its normal revs causing it to heat up after a few seconds. I'll have to see if I can make some meaningful measurements without burning out the drill.

One thing that did become apparent is that due to the worm drive, as soon as I released the trigger on the drill, the wheel came to a very abrupt stop, causing the machine to judder and the boom to swing. This kind of behaviour is not desirable for this machine, so I'll have to see if there's some kind of ramping option in the speed controller.



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Convert 1975 Afron Cherrypicker?

Post by Adverse Effects » Fri, 04 Mar 2011, 18:13

well here is your controller
i have played alot with controllers like this they are fantastic you can also have between 3 and 5 preset control mappings
CLICK THE PIC and go to wheelchairs

nice and cheep and very configurable

you can set all types of ramp up and ramp down

Wheelchair Joystick Controller -- IM-50A

# All-in-One, programmable Controller
# 24Vdc/36Vdc, Maximum 50Amps
# 5 Speed Ranges
# Regenerative Braking NOT NEEDED
# Parking Brake Open Circuit Detection
# Parking Brake Manual Release Microswitch Detection
# Including all connectors to motors and charger
# Exchangeable to other common joystick controllers



Image
Last edited by Adverse Effects on Fri, 04 Mar 2011, 07:20, edited 1 time in total.

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Convert 1975 Afron Cherrypicker?

Post by Electrocycle » Sat, 05 Mar 2011, 01:33

Trogdor! wrote: so I'll have to see if there's some kind of ramping option in the speed controller.


Yep, the controllers generally have ramping options and different levels of braking, so you can make it slow down nicely or output zero torque to let it spin down nicely.
I think it would require a bit of tuning to get the control super smooth, but it's definitely doable.

Your drill experiment is about what I'd expect, given the weight of the machine and friction in the gearboxes.
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Post by Trogdor! » Sat, 05 Mar 2011, 03:04

I had a look at the screenshots of the Kelly programmer, and it does seem to offer ramping. Braking is kind of irrelevant, as the wheels can't return drive the motor by virtue of the worm drive, so no regen for me :(

I have thought about fitting some solar panels to the boom though :)

As for that wheelchair controller, it looks like a very neat solution, however I'm not convinced it'd have the herbs to drive this machine. At it's max spec of 36v and 50 amps, that's 1,800 watts which I assume is shared between the two motors, so 900 watts a side, factor in 80% motor efficiency and that's 720 watts at the shaft. 550 watts from my drill moved the machine, but not with a great deal of authority.

The drive has to be up to the worst-case scenario, which would be turning the machine up an incline with one wheel stationary and the castoring wheel out of alignment to the turn, requiring extra effort to get it to rotate into the right line. The motor as fitted can do this, and I don't want to go backwards in the conversion.

Can't argue with the price though!

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Convert 1975 Afron Cherrypicker?

Post by Electrocycle » Sat, 05 Mar 2011, 03:46

yep, you definitely need to go a bit overkill I think to make sure it'll be usable.
It's no use having to do it twice!

It might even be worth doing a temporary installation with a motor to test how well it'll work. I'm not sure if anyone has one kicking around any more, but it might be possible to find something comparable.
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