Western Star 4900 SB - Bridge Inspection Truck

[BK9300]

A next project is not far off!  I do, however, need to finish the plow truck first, before I get fully into a new build. I’m thinking I couldn’t manage two at the same time.  My paint booth is out of commission for a week or two, so I thought I’d share my idea for this next project.

Going to be another highway maintenance vehicle for the scale, YRB fleet.  I’ve long wanted to build some kind of twin steer crane or boom truck, but they don’t really fit into the kind of equipment that YRB has.  The company does have hiab deck trucks, for smaller bridge work, but not any bigger boom trucks.  A few months ago, I was going through the company’s web site and saw a pic of a bridge inspection truck, owned by the Province of British Columbia, and that helped make the decision for my next project:

 

The equipment attached to the truck is a Paxton-Mitchell, PM-260B, ‘Snooper’ inspection unit.  The model number indicates it can reach, horizontally, 60’ under a bridge.  The truck that Paxton-Mitchell used, mostly, for this unit was a single steer, tri-drive, Volvo.  I have also seen quite a few similar inspection units online, and in particular, one made by Aspen Aerial – a model A-62T, on a Kenworth T880, twin steer, tandem drive plus a tag.  This unit can reach 62’ horizontally under a bridge, with no outriggers -

 

 

One of the searches also led me to this unit on Paxton-Mitchell’s website – a prototype Snooper, the PM-264 (64' horizontal reach under a bridge) -

 

 

I contacted the company to see if they would share any information or cad drawings on the PM-264, but they said it was a ‘one of a kind’, prototype vehicle, built in 2019, and no information could be shared.   So, back to looking for info on the PM-260B. The unit on YRB’s website is owned by the Province of British Columbia and, back in June, I found out it was going up for auction soon.  I was fortunate to be granted access to the unit, about 45 minutes from where I live, to take pics and measurements, and I spent two days gathering a bunch of details (700+ pics, lots of measurements and several short videos!).  Given the similarity of the Paxton and Aspen twin steer units, I decided to combine some features from each, into an inspection truck in YRB livery.

I want to make my cab and chassis based on Paxton Mitchell’s - a Western Star 4900 SB, twin steer, but with a tri-drive – no pusher or tag - and model the slightly smaller PM-260B (I did ask Paxton-Mitchell if a manual for the 260B was available – I was told I would need to own a Snooper before I could get a manual!).   I found it was extremely helpful to have designed my plow truck in Sketchup before building it, so, during the month of June, while the memories and pics were still fresh in mind, I made a Sketchup model of my vision for this build –

 

 

Outrigger down and booms lowered to basket 'entry' position -

 

Inspection underway! -

 

I have some parts already in hand – same two, Western Star kits I used for the plow truck, the tires and some steel, 2 and 5 hole wheels from M & R Wheels.  I am hoping that a bunch of what I learned doing the front end work on the plow truck will make the going much easier for modifying the hood for the set back, twin steer configuration of this truck.  Many other parts of this build should also be easier because of the plow truck build – that’s another reason to stick with the Western Star theme.

The Sketchup model’s parts are made as separate ‘groups’, so almost all the components – boom sections, hydraulic cylinders, outrigger arms, deck equipment, etc - are able to be isolated from all the others, and viewed from all angles (and posable for different renders, too).  I’ve spent a lot of time looking at the Snooper and complicated as it looks - from the tower support, the counterweights, to the boom sections - most pieces are made of lots of rectangular plate (need to get more styrene sheets!), square and round tubing, and lots of pins for pivoting parts.  I am hoping to use the 1/24th scale 3D model for dimensions and template patterns for cutting out parts from those styrene sheets.  I’ve not designed most of the Sketchup model to be printable – that’s a much more involved process - but some parts are.  The Snooper unit has two towers that rotate, to get the man basket under a bridge.  More thanks to @Bren, who agreed to do a test print for me of a sample outer ring gear of the slew ring that rotates the main tower behind the cab (the test ring gears below are 1.5 inches in diameter, with 120 teeth) –

 

The outer gear sample, which bolts to the lower, support portion of the main tower, needs to be modified to add the inner portion of the slew ring, which the upper tower portion bolts to, so the drive motor can rotate the rings around each other.  I just needed to see how the gear teeth would turn out on the test ring and they look good from the pics Bren emailed me.  He has sent me the actual rings, so should be able to check them out up close in a few days.

I’ll admit this will be a very challenging build, and maybe as long as the plow truck build.  But doing more practice builds isn’t going to help.  Time is marching on and I can only hope that I maintain the ability to at least give this build a good go!  So, as soon as the plow truck is finished, I’ll start in on this one.  I’ve learned a bunch about these trucks, from the few month’s research I’ve done, from the time spent going over one in person and from making the digital model.  Lots of ‘how to’ stuff is figured out for the model already, but lots more to figure out yet.  And speaking of the Sketchup model, it’s also been fun to add a few other items to the model before rendering.  An ‘on the job’ situation –

I’m looking forward to getting started on modeling my version of the ‘Snooper’ - back in a few weeks!

Edited Thursday at 02:29 AM by BK9300
typo

[Biggu]

Boy am I looking forward to see Snoopy come together as this is lining up to be another world class build. Front row seat for me.  

[slusher]

What keeps it balance, that’s a lot of weight off to one side?

[BK9300]

12 hours ago, slusher said:

What keeps it balance, that’s a lot of weight off to one side?

Hey, Carl!  This truck has five counterweight plates that hang off the end of the main boom support, behind the main tower.  There are also stabilizer arms, one on each side, at the base of the main tower, with two wheels attached to each one.  I understand that the boom cannot be operated without the stabilizer arm extended and in contact with the pavement.  In two of the renders above, you can see the stabilizer arm and wheels lowered to the bridge deck.  The truck can also be moved, slowly, while the stabilizer arm is in contact with the pavement.  The stabilizer arm, and the counterweights keep the inspection unit balanced around the axis of the main tower.  Hope that helps!

Edited Thursday at 05:29 PM by BK9300
typo

[Gary Chastain]

Wow, now that will be a serious build right there. Will be watching

[bamadon]

I gotta watch this.

[BK9300]

12 hours ago, Biggu said:

Boy am I looking forward to see Snoopy come together as this is lining up to be another world class build. Front row seat for me.  

Glad to have you aboard for this one, too, Jeff!  I know it will take a bit of time before I start, but have lots of ideas brewing for what to do first - more decisions to make! 
 

3 hours ago, Gary Chastain said:

Wow, now that will be a serious build right there. Will be watching

Happy that you’ll be following, Gary, and looking forward to you getting back into your builds later this summer, too!
 

25 minutes ago, bamadon said:

I gotta watch this.

Thanks for having a look, Don!

[BK9300]

14 hours ago, slusher said:

What keeps it balance, that’s a lot of weight off to one side?

Hi again, Carl - thought a couple different views would show the counterweight and stabilizer arm/foot assembly better -

 

Back side of main tower, showing counterweight(s) - 

 

Stabilizer arm and rolling 'foot' assembly down in working position - there is a limit switch (not shown) on the stabilizer arm that I believe is activated when the arm's locking brace is in position.  In an Youtube video of an older model of Snooper, the operator says the stabilizer must be down and brace in place, before the electrical system to operate the boom(s) can be activated.

Edited Thursday at 07:10 PM by BK9300

[Firebuilder]

Wow, another great build to come, I will be watching this . Especially the boom part. I have wanted to build a Pittman Snorkel boom for a long time, but the task seems overwhelming for me.

[BK9300]

8 minutes ago, Firebuilder said:

Wow, another great build to come, I will be watching this . Especially the boom part. I have wanted to build a Pittman Snorkel boom for a long time, but the task seems overwhelming for me.

Thanks, Dom!  The boom(s) do look overwhelming at first, but they're starting to look doable after looking at them closely.  I'm learning along the way, so hope all this helps you, too.

[ShakyCraftsman]

WOW! Brian this looks to be a very interesting build. Save me a front row seat. 🍺🍿👍😁

Ron G 

Edited Thursday at 09:54 PM by ShakyCraftsman

[BK9300]

6 minutes ago, ShakyCraftsman said:

WOW! Brian this looks to be a very interesting build. Save me a front row seat. 🍺🍿👍😁

Ron G 

Thanks, Ron, and saved!  I appreciate your interest in this, and I'm excited to get started, soon as I can.

[slusher]

Thanks Brian, I will follow your build..

[BK9300]

Getting my head around what this build is going to look like, I printed out some top and side, projection views of the Sketchup model.  Those printouts also allowed me to compare the plow truck to the Snooper truck, just for the heck of it.

It's going to be a tick over 22" long when finished -

 

I thought this was an interesting comparison, but Jeff reminded me if I was going to do any comparisons of the Snooper to the plow truck, I had to have the plow and sander in the pic, too.

 

All in, the plow truck will be bit longer -

 

Too much time on my hands, with my paint booth not available for a few more days yet!

Edited Friday at 05:12 PM by BK9300
typo

[gotnitro?]

Grabbing a seat for this one, especially after your epic plow 

Carry on! 

[BK9300]

9 hours ago, gotnitro? said:

Grabbing a seat for this one, especially after your epic plow 

Carry on! 

Thanks, Jeff - glad you’re checking in on this!

[vincen47]

This will be another masterpiece, for sure, and very unique. I haven’t seen a bridge inspection truck built in scale before.

[Jürgen M.]

This is gonna be a very interesting build Brian! 

First row once more! 👍

[BK9300]

18 hours ago, vincen47 said:

This will be another masterpiece, for sure, and very unique. I haven’t seen a bridge inspection truck built in scale before.

Thanks, Victor - unique for sure, and hoping to do it justice!

[BK9300]

3 hours ago, Jürgen M. said:

This is gonna be a very interesting build Brian! 

First row once more! 👍

Not to worry, Jürgen - lots of seats to go around!  I've got more than a few things to learn about this truck, and I hope it's as interesting a model as these trucks are in real life!

[BK9300]

Was doing some 'wandering' around in the Sketchup model today and there are a few things that are unresolved in my mind as to how to do them.  A couple standout more than others.  Firstly, I need to make four different sizes of hydraulic cylinders, for tilting and extending boom sections, and lowering/raising the stabilizer arms(legs?!)  I'm hoping to find a solution that allows me to manually pose the booms in different orientations, or extended positions, and have the cylinders hold the posed position.  Secondly, two of the three booms that extend have a 'Catrac' cable and hose carrier that I am unlikely to be able to make functional at scale.

 

This rendering shows portions of three of the boom cylinders and the two, Catrac carrier systems (at 1/24th scale the boom section that the top, Catrac system is part of, would be approx. 3/4 inch in height) - 

For the cylinders, I been thinking about making pistons from a suitably sized O-rings, sandwiched between two styrene discs, with a ram made from aluminum or brass tubing.  The piston/O-ring would need to fit snuggly enough into a cylinder of styrene tubing, to hopefully hold a pose, but not so stiff as to prevent the posing in the first place.  Then still need to figure out a packing gland of some sort, that would keep the ram aligned in the cylinder. 

I thought the sections of the Catrac carrier that are visible in the render above could be fashioned as fixed units, from thin styrene.  Then, instead of rolling and unrolling with a boom extension/retraction, the fixed unit would simply slide into the carrier housing when the boom extended, and reappear when the boom was retracted.  Might work ok, but won't know until I get there.  Lots of ideas floating around!

Edited 5 hours ago by BK9300
Typo

[ShakyCraftsman]

Hey Brian 

 I'm sure you'll figure it out. I use aluminum tubing for the cylinder rods because you can polish them to look like chrome.

Ron G 

[BK9300]

1 minute ago, ShakyCraftsman said:

Hey Brian 

 I'm sure you'll figure it out. I use aluminum tubing for the cylinder rods because you can polish them to look like chrome.

Ron G 

Keeping me thinking, for sure, Ron!  That sounds like a good idea - I just wonder if thin, aluminum rod would stand up to handling of posing.  I bent one shaft on the plow truck after just a couple of poses, so, not sure what the final solution for rams will be.  I appreciate the suggestion!