Convert 1975 Afron Cherrypicker?

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

Post by Trogdor! » Mon, 30 May 2011, 15:51

Yep, that's what I think I'll be doing - the shaft will be cut down to about 18" long with a universal at each end. As I understand it, I won't need an intermediate bearing to support the shaft.

Since I'll be recycling the shaft, the gearbox end is the correct fit, however the other end will require a new universal - are these things easy to come by? I'd need one designed to take the 7/8" shaft of the Mars motor with a 3/16 keyway.

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Convert 1975 Afron Cherrypicker?

Post by Adverse Effects » Tue, 31 May 2011, 00:21

why not just use 1 uni joint?
just mount the motor a a few degrees off line
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Post by Electrocycle » Tue, 31 May 2011, 00:22

I haven't bought any like that, but I'm sure they exist.
Worst case you could have some hubs made up to fit standard universals.

I'd be visiting a bearing shop with some of the parts and seeing what they have to suit.
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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Tue, 31 May 2011, 03:47

Thanks for the replies. I did consider putting the motor out to one side, but it becomes a lot more vulnerable as the wheels of the machine often poke in around the trunks of the trees. Also, with only one universal in the driveline, the machine would run rather strangely, accelerating and decelerating as the shaft rotated - that's why you always have to use 2 universals, or a constant-velocity (CV) joint.

I took one of the old driveshafts over to my friendly neighbourhood fitter & turner and he pointed out that the old universal's bearings are completely shot, which would mean it'd rattle and vibrate badly at high RPMs. Thus I'm going to need to use a new universal at each end - I did track some down - 7/8" bore and 1/4" keyway - he proposed fabricating a stepped key to slot into the motor's 3/16" keyway.

Unfortunately the four universals are $95 each adding even more dollars to this conversion...

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Convert 1975 Afron Cherrypicker?

Post by Tritium_James » Tue, 31 May 2011, 13:09

Can you turn the gearbox by 90° so that the motor shaft points straight up? You'd then be able to mount the motor directly to it with no universal joints.

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Convert 1975 Afron Cherrypicker?

Post by gttool » Tue, 31 May 2011, 13:32

Use a chain and sprockets and mount the motor on the gearbox
simple for alignment cheap easy to change ratio if needed
use taper lock sprockets

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Post by Trogdor! » Tue, 31 May 2011, 16:57

Tritium_James wrote: Can you turn the gearbox by 90° so that the motor shaft points straight up? You'd then be able to mount the motor directly to it with no universal joints.


90° isn't terribly easy, but 180° would be possible, with the motors out the front of the machine. However, it wouldn't change the fundamental problem in that these fat Mars motors would still be too wide to fit in next to the wheels.

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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Tue, 31 May 2011, 17:04

gttool wrote: Use a chain and sprockets and mount the motor on the gearbox
simple for alignment cheap easy to change ratio if needed
use taper lock sprockets


The issue is the motor being out the side and vulnerable to hitting trunks of trees etc - it certainly would be a good option in many respects, as looking at the torque curves for the motors I got, at 48v I'll likely be operating at 70% or lower efficiency - it seems if I was using 24v with gearing to get the RPMs up, I'd be up in the 85% range...

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Convert 1975 Afron Cherrypicker?

Post by Adverse Effects » Thu, 16 Jun 2011, 00:38

is that shaft comeing out of the box splined or keyway?

surly there has to be a CV joint that will fit it if it is splined

http://stores.ebay.com.au/suzukisuper/C ... b=12663787

as for the motor getting hit just make a nudge bar to go around it
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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Sun, 19 Jun 2011, 02:59

Well I've been proceeding along the path I've mentioned, and now am up to the bench test stage, and I've hit a problem. It's shown on my build blog here:
http://e-afron.blogspot.com/2011/06/motor-problems.html

Basically, the motor randomly stalls when changing direction. I've tried both controllers and both motors, one motor being worse than the other, and it's stalling more often when moving into reverse.

It also does it without the motor being connected to the gearbox, but it does it more when hooked up, despite the gearbox providing very little resistance. I hate to think how bad it could be when trying to move a tonne of machine Image

I've futzed with the controller settings without any improvement. The only thing I can think of trying is heavier cable between the controller and motor. At the moment I'm using fairly light cable, but when stalled the phase current hits 200A (the controller is set to limit motor current to 50%), so I'm thinking it could be due to excessive voltage drop?

I'll be contacting Kelly Controllers on Monday, but in the mean time I'm open to any suggestions???

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Convert 1975 Afron Cherrypicker?

Post by Electrocycle » Sun, 19 Jun 2011, 03:05

The only thing I'd expect to cause that is excessive voltage drop on the supply side from the battery to the controller, or maybe interference causing the controller to crash / reset.
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Post by Trogdor! » Sun, 19 Jun 2011, 03:13

Electrocycle wrote: The only thing I'd expect to cause that is excessive voltage drop on the supply side from the battery to the controller, or maybe interference causing the controller to crash / reset.


The current on the supply side is only in the region of 10 to 20 amps (at 48v) it's the motor phase current that gets up to 200A (at low volts I assume), and the controller doesn't seem to crash as such - I can usually get the motor to un-stall immediately by engaging forward rotation, although with the first motor it sometimes stalled in both directions which could only be rectified by rotating the shaft a little.

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Post by Tritium_James » Sun, 19 Jun 2011, 03:32

Does the motor have position sensors (possibly halls?) or is it running sensorless?

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Post by Trogdor! » Sun, 19 Jun 2011, 03:46

Tritium_James wrote: Does the motor have position sensors (possibly halls?) or is it running sensorless?


It's got hall effect sensors. The only possible issue there is that the motor specs 12v for the sensors, but the Kelly controller supplies 5v for them - I'm not familiar enough with them to know whether that could be a problem?

I'm guessing the fundamental issue is that the motor is stopped in such a position such that the polarity supplied to the coils attracts rather than opposes the adjacent magnets?

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Convert 1975 Afron Cherrypicker?

Post by Electrocycle » Sun, 19 Jun 2011, 03:58

it should never get into that situation, unless the sensors are in the wrong positions.

Is it possible that the sensors are connected in the wrong order?
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Post by Trogdor! » Sun, 19 Jun 2011, 04:12

Electrocycle wrote: Is it possible that the sensors are connected in the wrong order?


I've tried swapping the sensor order, but then it just acts like a pork chop.

I'm wondering whether the special "joystick" firmware has a problem when changing from one direction to another?

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Post by Electrocycle » Sun, 19 Jun 2011, 04:40

It's possible.

Definitely sounds like you'll need to talk to Kelly about it.

There's a chance that the sensors have been installed in the wrong position in the motor, but it seems unlikely.
It should run the same in both directions, apart from the fan noise.
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Convert 1975 Afron Cherrypicker?

Post by coulomb » Sun, 19 Jun 2011, 23:44

Have you tried your other motor?

Are you sure that you are "swapping the sensor order" correctly? But surely it would not run as well as it does with the sensor wired incorrectly. I think TJ's suggestion of the sensor being rotated slightly makes the most sense.
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Post by Trogdor! » Mon, 20 Jun 2011, 01:10

coulomb wrote:Are you sure that you are "swapping the sensor order" correctly? But surely it would not run as well as it does with the sensor wired incorrectly.


I think that the fact that the motor did run reasonably well at least in one direction put me off the trail, as I had tried changing the sensor order, which had resulted in the motor's shaft just oscillating.

It turns out that, as mentioned in a thread I started in the Motor/Controller forum during my Period of Panic, the connection order was the problem.

So when hooked up correctly, the motor runs perfectly and pretty much identically in both directions, so it's onwards and upwards Image

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Post by Trogdor! » Mon, 04 Jul 2011, 19:18

So it's all back in one piece and working - the wiring is temporary - I'm using some thick-ish speaker wire for the moment - the wires to the motor get a bit warm, the wires from the batts to the controllers don't, as the max amps seems to be around the 20-40A mark, so 10A-20A per controller, which is fine for the wire used. It seems the current to the motor, particularly at low speeds, is much higher. I plan to cable it up with 4G wire when everything is sorted.

http://e-afron.blogspot.com/

However the one niggling thing to sort out is speed. The machine needs 2 speed ranges, fast for travelling and slow for manoeuvring. At 48v it's too fast. 36v is a good max travelling speed, while 24v is a good manoeuvring speed.

The Kelly controller has a "turbo" function that halves the speed when activated, but it has very little effect on the machine, probably because once moving, there's little torque required from the motors.

The controller also has a maximum speed setting, but this, it seems, just limits the output voltage rather than scaling the throttle input, so if I set it to 75% I'll get my max 36v output, but it also reduces the functional range of the joystick to 75% of its throw.

I'll contact Kelly Controllers to see if they have any suggestions, but my current thinking is to implement a low-speed mode by switching the voltages to the joysticks, ie. rather than 0-5v, supply, say, 1.5-3.5v, this would maintain the full range of movement for the joysticks while limiting the max speed in either direction.

Any thoughts?


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Post by Tritium_James » Mon, 04 Jul 2011, 20:16

Sounds like you really want a logarithmic response on the throttle levers.

If they're potentiometers, your high/low can probably just be an extra resistor you switch in series with one end of the pot.

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Post by Trogdor! » Mon, 04 Jul 2011, 20:43

Tritium_James wrote: If they're potentiometers, your high/low can probably just be an extra resistor you switch in series with one end of the pot.


That was my first idea. And it almost killed me Image

I put in a switch to add in a 3k3 resistor on the 5v side of the joystick pot. I turned on the machine in my new "slow" mode but the controllers flashed an error. Not really thinking, I turned it all off, flicked the switch to "fast" (ie. no extra resistor) and turned it on.

All good - no error lights on the controller. Without thinking, I flicked it to "slow". The machine immediately charged forward smashing into a wall, destroying a heavy old wooden bench in the process. It was only luck that it moved away from me, not over me, as suspect I'd come off second best with a tonne of machine involved Image

The first lesson there was to always disengage the wheel hubs after messing with the controller, the second was that the controller expects 2.5v from the joystick when centred, and gives a fault if it's different when switched on. Adding the 3k3 resistor moved that "centred" point to about 3.5v. So flicking that switch in the second instance changed the throttle signal from 2.5v (ie. still), to 3.5v (about 40% throttle).

I then tried putting a 3k3 resistor on both the 0 and 5v sides of the pot, but because there's 2 joysticks, adjusting one has the effect of pulling the reference voltages back and forth and thus changing the signal coming off the other joystick, leading to unpredictable behaviour.

As far as I can work out, there's 2 options - one is to use regulators to supply the pot voltages, the other is to use resistors, but with separate 5v supplies for each controller signal.


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Convert 1975 Afron Cherrypicker?

Post by Adverse Effects » Mon, 04 Jul 2011, 22:03

why not go the simple path

make your battery packs 2 X 24 volt and put in a set of relays that will switch between 24 parallel and 48 seres

but then again if you had gone for my first idea for a controller (140 amp wheel chair controller) it would have been ample for what you need and 5 speed settings

i have to say that is an awesome looking conversion and it almost looks like it was made in the factory and a nice clean control box to
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Convert 1975 Afron Cherrypicker?

Post by Trogdor! » Wed, 06 Jul 2011, 01:32

If I was doing an experimental machine, I certainly would have gone down the path of low-cost alternatives. However, the situation is that with the IC engine in place, the machine was a working, functional tool, and in converting it, I had to ensure that it was just as capable, functional and reliable, and quickly as the machine has work to do.

It's also worth noting that it does need considerable grunt when in worst-case positions, such as on a slope with the castoring wheel square to the desired direction of movement. With half a tonne resting on it, it takes a great deal of torque to get it to move and rotate to the right direction.

Thanks for the feedback regarding the conversion - dismantling it completely was an opportunity to expose and identify parts that were at risk of rusting through, or unlubricated due to lack of ongoing care and maintenance.

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Post by Trogdor! » Wed, 06 Jul 2011, 01:44

I thought a bit longer about the speed issue - I had considered the 24/48 battery switching, but it would have required things like break-before-make contactors, and some consideration of the state of the battery config before hooking up the charger. This machine will be lent out to various people, so it's operation and charging has to be foolproof.

I thunk a little longer about adding resistance to the joystick pots, and realised there was a simpler solution that should work. Basically, each pot gets a resistor added to both the 0v and 5v ends, and I have a switch to change between 2 sets of resistors.

I decided to use multi-turn pots so that I could ensure some level of accuracy and adjustment, and ended up with a board containing 8 pots and a 4 pole double-throw switch to change between the two. When I get a moment I'll take a pic of the setup.

Bottom line is, it works well, meaning I can run the unit on 48v, so I'll now order a 48v charger (up until now I've been using a 12v charger on each batt. Very boring).

At the moment the hydraulic lift runs on 24v off 2 of the batts - drawing about 80A, I'm concerned about the asymmetric draw off the set of 4 batts, so I have a third 48v speed controller that I plan to drive the lift motor with (voltage limited of course), along with a special joystick that will add speed control to the lift.

When I say special, this joystick has about 8 wires coming off it...

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