Home » I Was A Tesla Engineer And This WWII Artillery Gun Suspension Design Blew Me Away

I Was A Tesla Engineer And This WWII Artillery Gun Suspension Design Blew Me Away

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On June 6, 1944, the largest military invasion ever attempted took place along the beaches of Normandy, France. Thousands of men landed on the coast, along with tanks, jeeps, and artillery and fought their way inland against relentless German resistance. One of those pieces of artillery was a Swedish designed portable cannon called a Bofors. It was a 40 mm anti-aircraft gun that was used in many different applications and mounted on many different vehicles, including ships. It also came mounted on a four-wheeled carriage which gave it the capability of being setup and ready to fire in as little as two minutes. While the gun was interesting, it was this carriage that caught my attention when I saw it in a museum in France.

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One of the main aspects of the design that allowed for such a rapid deployment was an extremely innovative suspension system that I have never seen before. The cannon has independent suspension at each corner consisting of equal length upper and lower control links attached to a rotating front and rear cross shafts that, when turned up to 140 degrees, lower the carriage onto pre-deployed support pads. The whole procedure looks like it could be accomplished in a matter of seconds. The suspensions at each corner are identical except that the front allows for steering.

Bofors Suspension 2

To fully understand how the system worked, I’ve built a computer model to show it in action. Here you can see the basic setup where the big fore/aft tube represents the body that the gun would be mounted on:

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Bofors Suspension Motion

or normal driving (or towing in this case) you can see how the double link suspensions allow the body to move up and down like any suspension would.

Once the gun reaches its desired position, the suspensions are rotated so the gun can be lowered onto its support pads. For the front suspension, this happens as follows. At first, the front suspension, which is attached to the tow bar, is in the driving position, meaning the body of the carriage is raised and ready for transport. The tow bar is horizontal and can be attached to a tow vehicle. Once the tow bar is un-hooked from the tow vehicle, it is then rotated to a vertical position. Since the tow bar is attached to the front suspension, rotating it rotates the entire front suspension anywhere up to 140 degrees depending on how much is needed to set the gun down on the pads.

Bofors Suspension 3

Due to the offset between the cross shaft and the wheel center, this rotation causes the carriage to drop. The rear suspension has the same mechanism but instead of a tow bar, it uses the gun support as its lever.

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Here you can see how this works in the model:

Bofors Suspension Rotation Gif

Once both front and rear suspensions have been rotated, and assuming the support pads have been deployed, the lowering of the carriage onto the pads means it is now supported in a stable position ready for firing. Super simple, super quick.

When the gun needs to be moved, pulling down on the tow bar and gun support reverses the whole procedure and the front and rear suspensions rotate back to their driving positions, thereby raising the carriage off the support pads which can then be returned to their transport positions. The gun is then ready to be moved to another location. Of course, a gun like this is very heavy and it wouldn’t be possible for a person or even a few soldiers to pull the tow bar down to raise the gun off it’s support pads. But the makers of the carriage have thought of that and provided a mechanism at the front and rear ends made up of springs housed inside the main carriage body actuated by levers and rods attached to the front and rear cross bars.

Bofors Rotation Spring

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Image via Bulletpicker

Rotating each suspension compresses the corresponding spring inside the carriage body which helps carry the weight of the entire gun, making it much easier to raise when needed.

With the front and rear suspensions in their driving positions, they become fairly simple though effective double wishbone designs with equal length links top and bottom. Parallel and equal length links mean the wheels always stay upright relative to the carriage without any change in camber and keeps things simple. Some of you may have noticed that neither my model nor the photos of the suspension show a spring. This is because the springs are housed inside the rotating tubes.

Bofors Suspension 4

Image via Bulletpicker

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As you can see from this cutaway, a coil spring is housed in the cross bar and is actuated by a lever attached to the upper links very similar to the mechanism that aids in lowering and raising the unit. As the suspension compresses, the upper links rotate and the lever pulls on the spring rod that extends through the spring and pulls on the spring plate, compressing the spring. Such a setup would make for a well controlled ride and allow the gun to be easily towed over rough terrain.

The last part of the mechanism are two steering tie rods connecting the front suspension to the tow bar. These rods allow for the front wheels to be steered around corners.

Bofors Suspension 5

As far as brakes go, there seem to have been two versions of this carriage: one with air brakes (like the one I saw) and others, which I presume came later, with electric brakes similar to what we have on trailers today. All used drum brakes on all 4 wheels.

From what I’ve been able to learn, the carriages for these guns were made by Firestone, although I don’t know if they were responsible for the design. If anyone knows anything about these, I would be very interested in learning more about the origins of this suspension.

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All in all, a very simple but effective and innovative design that made an already outstanding anti-aircraft gun even more versatile.

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Shrikant S Kamalapurkar
Shrikant S Kamalapurkar
8 months ago

Its a wonderful article with detailed content, Easy to understand the mechanism, Kudos to the Inventor, Thank you

STEPHEN WALTER GOSSIN
STEPHEN WALTER GOSSIN
9 months ago

Great read and thank you, Huibert!

I wonder what my grandfather thought of these as he passed them by on his way onshore on that day, and upon that French beach.

Kleinlowe
Kleinlowe
9 months ago

Oh wow, I have been wondering for *years* how these things worked! Thank you so much for the clear explanation and animation. I’m somewhat surprised this design hasn’t been resurrected for an overlanding trailer or something.

Twobox Designgineer
Twobox Designgineer
9 months ago

Hi Huibert
I enjoyed reading the article. Pretty clever use of mechanics in the design, and I’m glad to have learned about it.
It looks like maybe fixing the “upper” tow bar arm to the “lower” yoke-shaped portion with some pin (to hold it in a straight line) would enable the leverage necessary to hois the the chassis up off the firing support pads?
One small criticism (and forgive me if I missed the missing reference), but you repeatedly refer to “when rotated,” without first specifying which position was your base position and which was your “rotated” position, between transport/rolling/wheels-down position and steadied/firing/wheels-up position. It took me quite a few jumps back and forth from paragraph to earlier images and back to figure out your wording, and I’m an ME.

Last edited 9 months ago by Twobox Designgineer
CSRoad
CSRoad
9 months ago

Because this is Autopian I’m thinking a good ground clearance for an off-road trailer that then could be lowered to a more usable height.

CSRoad
CSRoad
9 months ago

Still currently in use.
The video shows them towed and folded up.
https://www.youtube.com/watch?v=SuItKslr60Q

CSRoad
CSRoad
9 months ago
Reply to  Huibert Mees

A durable, functional design and countries are pulling them out of storage primarily to shoot down drones in Ukraine.
It is a worthy museum piece for sure, sad that they are being used as intended once again.

Slow Joe Crow
Slow Joe Crow
9 months ago

This is a lot more convenient and clever than say an 88mm Flak 36 which deployed via winches in the axles which then had to be rolled away. I have seen a similar flip up axle on Russian 23mm AA guns.
Towed anti aircraft and anti tank guns that need 360 degree traverse have to have some way of lowering the mount to the ground and getting the wheels out of the way. This is the most elegant setup I’ve seen.

Hoonicus
Hoonicus
9 months ago

Reuben Garrett Lucius Goldberg was obviously the chief engineer on this. It is incredible, and I appreciate it, but wouldn’t effort be better spent on rapid deployment support pads system? Even 1930’s Rolls Royce had a service crank in the cab that lowered four hydraulic rams, lifting it off its wheels.

Cerberus
Cerberus
9 months ago
Reply to  Hoonicus

My guess is the answer lies with the major difference with this system: the pads are fixed to the chassis (adjustable, yes, but rigidly mounted). With deployable rams, the load would be variable, subject to wear and tear, and less stable against varying directional forces. How high a car is off the ground to change a tire isn’t so important as long as the tires are in the air and it doesn’t collapse and it is only working against gravity and maybe a small lateral load as the wheel is removed and replaced. For a gun carriage, in addition to the weight, it also needs to resist recoil and be stable enough that an aiming system can work.

Sensual Bugling Elk
Sensual Bugling Elk
9 months ago

Huibert, what software do you use for this modeling and animation? Very slick, and made the concept much easier to understand compared to labeled photos.

Col Lingus
Col Lingus
9 months ago

Just a genius design. After watching the animations it started the thoughts about use as chassis for a real SUV. Low center of gravity on the street, off road capable.
Maybe better used for EV off roading?
Just very cool.
Good stuff here, thank you.

Last edited 9 months ago by Col Lingus
Col Lingus
Col Lingus
9 months ago
Reply to  Huibert Mees

<My bad. As a product of the pubic school system I plead no contest. Understanding is hard, or it could be the heat?

Mark Tucker
Mark Tucker
9 months ago

Wow, that is clever! And as a bonus, now I know where Tamiya got the front suspension arm/internal spring design for their Frog off-road RC buggy from.

Canopysaurus
Canopysaurus
9 months ago

From what I could find, Bofors designed/developed the I carriage in 1935.

This write up is attributed to Saab.com which bought Bofors’ parent company in 2000:

“Bofors also developed a towable carriage, which was displayed at a show in Belgium in April 1935. That mount allowed the gun to be fired from the carriage with no set-up required, although it had limited accuracy. If time was available for set-up, the gunners used the tow-bar and muzzle lock as levers, raising the wheels off the ground and so lowering the gun onto supporting pads. Two additional legs folded out to the sides, and the platform was then levelled with hand cranks. The entire set-up process could be completed in under a minute.”

Bofors artillery and carriage designs were licensed by many countries, including the U.S. during WW II. Chrysler used 12 plants and over 300 subcontractors to manufacture 60,000 Bofors 40mm cannons and munitions. I couldn’t find a reference for Firestone and the carriage, but it’s a likely probability they were involved.

Last edited 9 months ago by Canopysaurus
Marc Fuhrman
Marc Fuhrman
9 months ago

OK, that is insanely clever. Is there anything still in production that utilizes a similar setup?

R Rr
R Rr
9 months ago
Reply to  Huibert Mees

Looking at the spring setup, first, it looks clever both for packaging constraints and for protection (housing the suspension inside the transverse tube) and second, is this the first time anyone has used horizontal damping/springs, decades before they started using them in sportscars?

Bizness Comma Nunya
Bizness Comma Nunya
9 months ago

I absolutely love learning about interesting/odd suspension designs. I never knew about this one, but I’m also fascinated by this. Thank you for sharing!

Speedway Sammy
Speedway Sammy
9 months ago

It’s like all the technology of its era…and most of the moon shot stuff…designed with slide rules, drawn on vellum with pencil, and fabricated by high school grads running manually controlled machine tools. 😉

Hoonicus
Hoonicus
9 months ago
Reply to  Huibert Mees

You do a fine job with your animated models, as always, much appreciated.
side-note; are you still answering ask an engineer inquiries ?

Man With A Reliable Jeep
Man With A Reliable Jeep
9 months ago
Reply to  Speedway Sammy

File this under “they don’t build ’em like they used to,” but I feel oftentimes, simple (relatively speaking) and robust engineering as exemplified by this, is overlooked in lieu of using technology instead of creativity. Technology is great, but it does have a way of breeding apathy in engineering when ingenuity is the superior, albeit more difficult, solution to a problem.

Just Jeepin’
Just Jeepin’
9 months ago

Constraints are amazingly valuable when problem solving, and they had a lot of constraints to fight through.

Paul B
Paul B
9 months ago

It seems to me that if the towbar was hinged along it’s length, you could the power of the tow vehicle to rotate the pivot point for raising and lowering.

Imagine a tow bar with a lockable hinge.

Drive up to where you want to setup, unlock the hinge and drive backwards and then unhitch.

Picking up is the process in reverse.

Some over centering and springs would make it an easy and reliable process with minimal force applied by the operators.

Sean O'Brien
Sean O'Brien
9 months ago
Reply to  Huibert Mees

If we went the route of using the vehicle to lift and lower the gun, you have a suspension that locked the brakes and, when a pin was pulled, allowed the suspension to rotate and the carriage to ‘sit’ down on its supports by backing up. Pulling forward would lift it back off. Mechanisms like this were very common on horse-drawn and pre-hydraulics farm equipment.

05LGT
05LGT
9 months ago
Reply to  Paul B

Seems like the type of thing someone would have tested and discovered the not immediately obvious problem with.

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