Foldable Workshop Crane Calculator LITE version
Foldable workshop crane calculator: cylinder force, stroke and boom kinematics
This free calculator sizes the hydraulic cylinder of a foldable workshop crane (engine crane): the cylinder force over the whole boom movement for every telescope position, the stroke and the retracted cylinder length, the hook height and the reach, all computed from the pin positions. Change the geometry, drag the cylinder mounts on the diagram or load one of four examples from 500 kg to 3000 kg; the 1100 kg and 2000 kg examples follow papacad crane designs.
Version Lite 1.0.0: the cylinder force is checked by two independent methods, and the kinematics was compared with the Inventor models of the papacad 1100 kg and 2000 kg cranes. Hook reach, hook height and cylinder lengths agree with the drawings to within 3 mm.
Key values at a glance
| Value | What it is | Why it matters |
|---|---|---|
| Max. cylinder force Fs | Largest push over the whole working range and all telescope positions | Sets the ram size and the pump pressure |
| Arm r | Distance from the boom pivot E to the cylinder axis | The force is inversely proportional to r |
| Distance E–F | Boom pivot to the upper cylinder mount | The main design lever: longer E–F, lower force, longer stroke |
| Required stroke | Change in pin distance from the transport position to the top | Needed to choose a cylinder from a catalogue |
| Pin distance in the transport position | Cylinder length with the boom folded down | The retracted cylinder L0 must fit into it |
| Hook height and reach | Floor to hook saddle; hook to pole base | What the crane can actually lift and how far out |
| Force margin | Available cylinder force / required force | Covers friction, pressure losses and start-up |
How to use the calculator
- Pick an example: 500, 1100, 2000 or 3000 kg.
- Move the boom position slider: the diagram, the readout and the force chart follow the boom from the transport position to the top. Buttons 1–3 under the slider select the telescope position.
- Show angle fields: the grey sector is the idle range (no load, down to transport), the orange sector is the working range with the load on the hook.
- Change the geometry: type values in the form, press Show dimensions and click a boxed dimension, or press Edit nodes and drag the points D, E and F.
- Read the checks: every check is marked OK, CHECK or NOT OK; the cards under Results and what they mean explain each value.
- Undo, Reset, Print: Undo (Ctrl+Z) steps back, Reset returns to the loaded example, Print / PDF gives an A4 summary with the input data, diagram, checks, chart and movement table.
All dimensions are in millimetres. The origin C is where the pole axis meets the top of the base, x points towards the hook, y up. Boom points (F, G, centres of gravity) are entered in the boom frame: from E along and across the telescope axis, measured with the boom horizontal.
How the cylinder force is calculated
The boom turns about pivot E. The cylinder pushes along the line D–F, and its moment about E must balance the moments of the load and the boom weight:
Fs · r = Q · xG + G1 · x1 + G2 · x2
where Q is the load on the hook, G1 and G2 are the weights of the sliding and the fixed boom, and x are their horizontal arms from E. The arm r is the perpendicular distance from E to the cylinder axis, r = EF · sin μ, with μ the angle between the cylinder and the line E–F. The calculator repeats this at every boom angle and checks it by virtual work, Fs · ds/dθ = Q · dyG/dθ + …, where ds/dθ = r.
For the 2000 kg crane the hook is about four times further from E than the upper cylinder mount (1564 mm against 396 mm), so the cylinder carries about four times the load plus the boom weight: 79.7 kN for 2000 kg. This is why workshop cranes rated at 2 t use rams of 8 t and more.
Why the force hardly changes over the boom movement
Unlike a scissor lift, a workshop crane has no position where the force runs away. Near horizontal both the load arm and the cylinder arm r change slowly. For the 2000 kg crane in telescope position 1:
| Boom angle θ | Arm r | Cylinder force Fs |
|---|---|---|
| −35° (lowest working position) | 350 mm | 78.3 kN |
| 8.6° (top) | 378 mm | 79.7 kN |
The force varies by about 2% over the working range. The largest force therefore depends mainly on the shortest telescope position with the full rated load, not on the boom angle.
Telescope positions
Each telescope position moves the hook out by one step (150 mm on the 2000 kg crane) and has its own rated capacity. The calculator computes the force for all positions and takes the largest.
| Position | Capacity | Max. reach from C | Max. cylinder force | Load moment about E |
|---|---|---|---|---|
| 1 | 2000 kg | 1388 mm | 79.7 kN | 30.9 kNm |
| 2 | 1500 kg | 1538 mm | 65.9 kN | 25.4 kNm |
| 3 | 1000 kg | 1687 mm | 48.1 kN | 18.4 kNm |
The capacities fall faster than the reach grows, so the load moment drops and position 1 sizes the cylinder. In position 3 the hook reaches 91 mm past the front wheel axle (1596 mm from C). A load ahead of the wheels is critical for tipping stability, which the calculator flags but does not compute.
The distance E–F: the main design lever
Moving the upper cylinder mount F further from the boom pivot E increases the arm r and lowers the force, but the cylinder must then travel further. For the 2000 kg crane, changing only the position of F along the boom:
| Distance E–F | Max. cylinder force | Required stroke | Pin distance, transport |
|---|---|---|---|
| 302 mm | 105.7 kN | 309 mm | 918 mm |
| 352 mm | 89.5 kN | 362 mm | 873 mm |
| 396 mm (WC-2000) | 79.7 kN | 410 mm | 833 mm |
| 451 mm | 70.7 kN | 473 mm | 783 mm |
| 501 mm | 64.4 kN | 530 mm | 740 mm |
The force falls roughly in proportion to E–F, the stroke grows in proportion, and the pin distance in the transport position gets shorter. At 501 mm the 743 mm cylinder of the WC-2000 no longer folds down to the transport position, and its 500 mm stroke is too short.
Working range and idle range
A foldable crane needs more cylinder travel than it uses with a load. Below the lowest working position the boom folds down for transport, without a load. The calculator splits the movement into two fields:
- working range θmin to θmax: load on the hook, sizes the cylinder force;
- idle range θfold to θmin: no hook load, the cylinder carries only the boom weight (at most 1.3 kN on the 2000 kg crane) and the result does not enter the force sizing.
The transport position θfold sets the retracted cylinder length; θmax sets the extended length. On the 2000 kg crane the full movement needs 410 mm of stroke, of which the working range uses 293 mm.
Fitting the cylinder
A catalogue cylinder fits when two conditions hold:
- the retracted pin length L0 is not more than the pin distance D–F in the transport position, otherwise the boom cannot fold;
- L0 plus the stroke H reaches the pin distance at θmax, otherwise the boom cannot rise to the top.
The WC-2000 cylinder has L0 = 743 mm and H = 500 mm. Extended it measures 1243 mm, exactly the pin distance at the top position, and folded it leaves 90 mm in the transport position (833 mm).
Worked example: 1100 kg and 2000 kg papacad cranes
Both cranes use the same cylinder (L0 = 743 mm, H = 500 mm). The ram bore and pressure are an assumption for the comparison: Ø45 mm at 630 bar, 100.2 kN.
| Result | 1100 kg | 2000 kg |
|---|---|---|
| Distance E–F | 358 mm | 396 mm |
| Max. cylinder force | 47.4 kN | 79.7 kN |
| Required pressure (Ø45 ram) | 298 bar | 501 bar |
| Force margin at 630 bar | 2.11 | 1.26 |
| Pin distance, transport → top | 836 → 1243 mm | 833 → 1243 mm |
| Hook height, working range (telescope in) | 562 → 1720 mm | 567 → 1728 mm |
| Boom angle, transport / working range | −70.8° / −35° to 9.7° | −58.4° / −35° to 8.6° |
Result: the same cylinder serves both cranes. On the 1100 kg crane it has more than twice the required force; on the 2000 kg crane the margin is 1.26 at 630 bar.
Limitations of the model
- Kinematics and cylinder force only: tipping stability, strength of the boom, pole and legs, pins, welds and rod buckling are not calculated.
- Rigid members, no pin clearance or elastic deflection; the load hangs vertically from the hook pin.
- Cylinder self-weight and friction are not included; the force margin covers them.
- Boom masses, centres of gravity and the ram bore and pressure in the examples are estimates.
- The angle limit μ is a design-practice value and can be edited.
- The requirements of standards for portable floor cranes are not checked.
FAQ
How much force does a workshop crane cylinder need?
About four times the rated load plus the boom weight for a typical geometry. The papacad 2000 kg crane needs 79.7 kN at the shortest telescope position, the 1100 kg crane 47.4 kN.
Why does a 2-ton engine crane use an 8-ton ram?
The hook is about four times further from the boom pivot than the upper cylinder mount, so the cylinder force is about four times the load. For 2000 kg that is about 80 kN, which needs a ram rated at 8 t or more.
Where in the boom movement is the cylinder force highest?
With the shortest telescope position and the full rated load. Over the boom angle the force changes little: on the 2000 kg crane it varies by about 2% between −35° and the top position.
How do I choose the cylinder stroke and retracted length?
The retracted pin length must fit into the pin distance with the boom folded for transport, and the retracted length plus the stroke must reach the pin distance at the top boom position. The calculator gives both distances.
Why does the capacity drop when the telescope is extended?
The load moment about the boom pivot grows with the reach. The rated capacities of the telescope positions keep the moment, and so the cylinder force, at or below the value of the shortest position, and they limit how far the load sits ahead of the wheels.
Does the calculator check tipping stability?
No. It flags when the hook reaches past the front wheel axle, but stability, member strength and pins are part of the Pro version.
Further reading
- R. C. Hibbeler, Engineering Mechanics: Statics: moment equilibrium and virtual work.
- ASME PALD, Portable Automotive Lifting Devices: safety requirements that include portable floor cranes.
Need a workshop crane designed?
papacad.com offers ready-to-build CAD projects of foldable workshop cranes (Autodesk Inventor 3D assemblies, STEP files, 2D production drawings and BOMs) and takes custom engineering commissions. CAD projects · Contact