Original actuators: dimensions, speeds and loads

Measuring current fake cylinders (in progress)
Upgrading the the cylinders is the fun part I definitely want to do myself. I have seen a lot of DIY upgrades (& builds) of very nice excavators on YouTube. The funny part is, everyone is claiming an increased loading capability, but no one actually come up with numbers. Even when buying 'Professional Metal Strength Main Arm Second Arm Bucket Arm Driving Rod' (about $50), it's unclear what you are buying.
Also useful basic information about cylinder travel and speeds are missing. Now my excavator arrived, it's time to measure!

Distances & speeds

So first I like to know more about the fake cylinders on the Huina toy:

Fake cylinder	Units	Boom	Digger	Bucket
Short *	mm	95	116	93
Long *	mm	183	183	138
Travel	mm	88	67	45
Time (Up&Down) **	sec	5.5	7	3.2
Speed	mm/sec	32	19	28

* Distances are measured between 'fake cylinder' pivot points.
** Time from moving an actuator to the other position and back till the rattling starts. So this time is including play of the system.
Apparently a 30 mm/sec cylinder seems to be a nice target speed.

Maximum lifting weights

Now we know the (no load) speeds, it's also interesting to know how much weight the 3 actuators could handle. All the motors have a torque limit gear system. That's where that rattle comes from, when hitting the end positions or trying to lift too big loads. So let's find out, when the torque limiter is activated.
So the measurements are easy, just add some weight on a rope and re position this, till the actuator starts to stall. Now note both the weight and the horizontal distance between pivot point and the rope.

Actuators:	Units	Boom	Stick	Bucket*
Distance	mm	210	210	60
Weight	gr	940	940	430
Force	N	9.2	9.2	4.2
Stall torque	Nmm	~2000	~2000	~250

The bucket actuator was tested with a printed gear (ABS), so this might influence a bit.
The final stall torques are rough indications anyway.

What does this mean for the cylinders?

Again it's interesting what load the fake cylinders would be. So let's calculate based on the motor torques. This is a little more tricky, since the distance perpendicular to the cylinder will change, when moving. So we want to know the shortest distance, which determines the minimum required force of the cylinder.

Actuators:	Units	Boom	Stick	Bucket
Min. distance	mm	32	37	26
Stall torque	Nmm	~2000	~2000	~250
Min. force	N	~62.5	~55.5	~80

So the cylinder specification would be at least: 80+ N (18lbs) and no-load speed of about 30 mm/sec.

Maximum tipping load

When doing the maximum lifting weight test, I also had to compensate some mass at the back of the excavator. The front wheels are lifted a bit, so the maximum load you want to lift, will give a falls indication, when the excavator is tipping a bit. This might also work a bit like a maximum load indicator.

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Next page: Upgrading Huina 560/1560