EC750E Cylinder, linear actuators, pistons, etc...

The small cylinder problem. Lego linear actuators are 11 studs long, has an actuation length of 5 studs and a width of 2 studs. From the dimensions page for the EC750E the linear actuator (aka. cylinder) should be 19.5 studs long and 3 studs wide. This is clearly a grossly undersized cylinder. What if we could fuse two of them together. Would they still work? If connected plunger end to plunger end the new cylinder would be 22 studs long with a 10 stud actuation length. Unfortunately this does not work because the first cylinder can not spin around to activate the second cylinder. A simple solution to that is to let the driven end of the first cylinder to spin freely so that it can drive the second cylinder. This does work, but having the first cylinder not pull out from the driving axle becomes a problem if the cylinders are pulled out of instead of pushed into the axle. Another way to connect them is driven end to driven end. This leaves no shaft to drive, but this can be solved as whichever end will be driven simply has to be able to spin freely. There is another benefit to this arrangement, overall length is now 20 studs as one stud from each cylinder's driven end overlaps the other:

The overall extended length is 30 studs giving a better extended to retracted length ratio than the original cylinder.

Now the problem to solve is how to go about mounting this. The end that we choose to be the "plunger" end can be connected with a pin or axle as normal, but the "driven" end needs some way to be driven to spin around and handle both pull and push pressure just as the single cylinder's original mounting bracket. Thankfully Lego has a turntable that is just the right size for this.

The cylinder's driven end can be mounted to the geared portion of the turntable so as to be driven by gears or alternately the pictured grey axle connector with the 3L pin can be inserted so that it may be driven by an axle.

Lastly one could do both. That is have an axle and gear drive at the same time. For example one may need to drive a second cylinder from one axle source. Red axle powered by an XL motor drives a cylinder through an axle and the gear at the base of the cylinder drives the cylinder on the other side that lifts the boom.

This joint seems like it should work, but the small gears keep skipping because of the high stress of directly driving two cylinders under high load so this will have to be done in some other way.

Here is the overall view of how these double cylinders are used to mechanize the model's boom, arm, and bucket.

EC750E dimensions

Scale can be a tricky thing when modeling with Lego. We are beholden to the stud width and size of stock parts such as linear actuators. I initially chose a scale of 1 stud = 6 inches as it made for an easy mental conversion of all the dimensions in the Volvo brochure, but this has not worked so well for the arm thickness where it is supposed to be 2'6" (5 studs) over its entire length. This was not possible because bracing and structure have the arm width sticking out to 7 studs. This could have been because I tried to build the shortest arm and a longer one would have had more room to maneuver. The other problem with the scale was that the single cylinder(lineal actuator) or the arm for the bucket had a very short travel and while I got it to perform the necessary 180 degree bucket rotation it wasn't especially strong. The scale was based on the 2'6" grouser fitting nicely with the 5 stud Lego grouser. If we continue to use the grouser for determining scale, the smaller 26" grouser increases the scale slightly to 5.2" per stud. The scaling multiplication factor is now 2.3077. This makes the new arm width of 5.77 studs (6 is close enough). Bracing and structure could be changed to use some thin liftarms to bring the width down to 6 studs. At this point the scaling factor is no longer as easy to calculate. Using the metric measurements it is simple to take the real measurement given and divide by 130 to get the dimension in studs(s). Below are the Volvo dimensions in studs using the 1:26 scale.

Overall dimensions
A Width of superstructure	26.3
B Width of upper structure	33
C Height of cab	27
D Tail swing radius	32
E Height of diffuser	29.5
Height of guard rail	31
Height of engine hood	27
Height of rain cap	29
Height of cyclone	29.5
Height of oil bath	31.5
F Counterweight clearance	11.5
G Tumbler length	36.5
H Track length	46
I Track gauge	26.5
J Shoe width(650mm)	5
K Min. ground clearance	6.6

Overall dimensions
Boom	6.6m (50s)	7.7m (59s)
Arm	2.9m (22s)	2.9m (22s)	3.55m (27s)	4.2m (32s)
L Overall length	94	102.5	101.5	101
M Height of folded boom	37.3	35.5	35.5	38

Boom	6.6m (50s)	7.7m (59s)
Length	53.5	62
Height	19.5	17
Width	8.5	8.5

Arm	2.9m (22s)	3.55m (27s)	4.2m (32s)
Length	33	38	43
Height	11	11	10.5
Width	6	6	6

Cylinder
Length	Height	Width
19.5	4	3

Counterweight
Length	Height	Width	Weight
26.3	13.5	5	12100kg (scaled to 93kg ??? that can't be right)

Shoes 650mm (5s)
Length	Height	Overall Width	Weight
46	10.5	8.3	10600kg (?g)

Cab
Length	Height of cab	Height of diffuser	Width	Weight
42.7	20.5	23	26.5	23150kg (scaled to ??g)
height of rain cap	22.5
height of cyclone	23
height of oil bath	25

Cab with shoes (650mm/5s width)
Length	Height of diffuser	Weight
52	29.5	44350kg (?g)

Cab with shoes (650mm/5s width) and boom
Boom	Length	Height of diffuser	Weight
6.6m (50s)	78.5	29.5	53090kg (?g)
7.7m (59s)	87.3	29.5	53480kg (?g)

Boom	6.6m (50s)	7.7m (59s)
Arm	2.9m (22s)	2.9m (22s)	3.55m (27s)	4.2m (32s)
A Max digging reach	88	97	101	106
B Max digging reach on ground	86	94.5	99	106
C Max digging depth	55.5	59.5	64.5	69.5
D Max digging depth l 2.4m(19s)/8' level	54.5	58	63.5	68.5
E Max vertical wall depth	43.5	52	57	61.5
F Max cutting height	84	95.5	97	99
G Max dumping height	54	65	66.5	69
H Min front swing radius	39.5	42	41.5	42

EC750E proof of concept

The Lego set 42030 Volvo L350F is one of my favorite sets. So much so that I bought a second set to facilitate the creation of a Volvo A40E dump truck to accompany it. This leaves a large bucket lying around begging to have something made with it.

In comes the idea that maybe suck a large earth moving bucket could be used in an excavator such as the Volvo EC750E.

The first check is the bucket size. The L350F bucket is a spade nose rock bucket with teeth and segments. In real life this bucket is 13 feet wide and holds about 9 to 10 cubic yards. The EC750E's largest bucket is a general purpose earth moving bucket with a capacity of 9.34 cubic yards. It's width is unspecified, and while it will not be a spade nose bucket, the volume is close enough that maybe this could work.

Next is checking to see if and/or how it can be fitted to be used as an excavator bucket since it has the mounting points of a loading bucket. At the same time it would be good to see if the standard Lego linear actuator has enough length to it to rotate the bucket 180 degrees around a pivot. While I was at it I decided to start with a scale of 1 stud = 6 inches (roughly 1:30 scale). This makes the arm 28 studs long(9'6" arm) and the boom 53 studs long(25'3" boom).

Here is the initial proof of concept boom and arm plus bucket:

Here it is in comparison to the Lego set 42053 Volvo EW160E:

Since this seems to be feasible I'll continue the build. There will certainly be many problems to be solved along the way.