My Polar Research Vehicle (PRV) was inspired by the widely acclaimed Stilzkin Indrik Arctic Vehicle created by technical LEGOŽ magician Peer Kreuger, aka Mahjqa. After running across Kreuger's LEGOŽ Digital Designer (LDD) instructions for a single-track version of the Indrik chassis, I decided to build a larger vehicle with a different mission around an adaptation of the dual-track Indrik chassis featured in his must-see Indrik video on YouTube.
The PRV is basically an 8-passenger snowcat modeled after the expedition-class vehicles found in high-latitude, low-relief settings. (The smaller 2- or 4-passenger snowcats familiar from ski resorts are better suited to high-relief terrain.) As an Earth scientist, the polar research theme has a good bit of personal appeal, though I have no direct experience in that particular field.
Better yet, we get plenty of snow for PRV testing and playing here in Denver, Colorado. Colorado's high-country is world-renowned for its dry "Champagne powder", but the snow in Denver tends to vary a good bit in texture and water content. To date, the PRV has conquered every snow type tested with ease. Indeed, its play value in snow may well be its best feature. For that, most of the credit certainly goes to Kreuger, as it's mainly dual tracks front and rear and related mechanicals that keep the PRV moving with manageable sinkage -- even in the softest fresh powder.
Photos and text
PRV in its native habitat -- snow
Early-model PRV scouting for good places to collect cores from Arapahoe Bay's rapidly thinning ice shelf. Dwarfing the PRV at right is a massive NATO early-warning radar antenna array thinly disguised as a gigantic garden fence. Who do they think they're fooling?
Eastbound to a possible ice sampling site at the base of the rocky headland at 10 o'clock. Red rear doors were temporaries from one of the kids' early 1990s-vintage Lego train sets.
The PRV readily powers through axle-high snow and often prevails in snow over the tracks. However, snow build-up between front tracks can slow or halt forward progress at any sinkage level. The PRV easily backs out of such jams, but I later added a front snow dam that greatly reduced the frequency of these annoyances.
Westbound now in search of a safer ice sampling site. With no front snow dam yet, the snow is once again piling up between the front tracks, even though there's very little sinkage.
Two-way satellite radio is the only reliable form of telecommunication in typical PRV deployment scenarios. The steerable gimbal keeps the satellite dish pointed at the active satellite link regardless of the PRV's heading.
Nowadays, these angled passenger windows (from the observation car of one of the kids' early 1990s-vintage Lego train sets) go for $7-9 each on BrickLink. Good thing they were languishing in my basement, because I certainly wouldn't have purchased 8 of them for any MOC.
Before moving on to the next photo, note the steering pivot crosslinks below the center of the cabin.
When this photo was taken, an M motor under remote control steered the PRV by pivoting the front tracks in the desired direction. The crosslinks noted in the previous photo belong to a bow-tie (aka antiparallelogram) four-bar linkage that forces the rear tracks to pivot an equal but opposite amount so as to keep all tracks on the same turning circle. The M motor was more than adequate in most cases, certainly in snow, but an L motor does better on high-friction surfaces like carpet.
Tracking up trackless Arctic and Antarctic wastes is what the PRV does best. Mountain snowcats familiar from ski resorts seldom carry more than 4 passengers. The PRV's 8-passenger capacity is more typical of the larger expedition-class snowcats commonly used in high-latitude, low-relief settings.
Hatches and ladders provide roof access for observation and emergency purposes. Hatches may be the only safe egress in a polar bear boarding or after partial burial in large blizzard-driven snow drifts. Steerable rear floodlights extend precious work time into the long polar night.
Descending to another potential ice shelf access point in the gap in the low seacliffs at 1 o'clock. Note long mid-day shadows typical of high-latitude summer.
The large geared pivots above the front and rear track assemblies form the heart of the PRV's articulated steering system, which obviates the need to power the right and left track sets independently, as is usually done in tracked vehicles.
Bright reflections just aft of roof center mark ports for tandem infrared remote control (IRRC) receivers used to control propulsion, steering, and interior lighting. Unfortunately, the abundant IR in direct sunlight easily swamps incoming IRRC signals, making it very difficult to operate IRRC models outside, even with overcast.
Another IRRC limitation is the need for an unobstructed line of sight between transmitter and receiver. The large dish and gimbal blocking the camera's view of the IRRC ports here often hid the ports from my IRRC handset as well (think TV remote). Switching to a smaller dish and gimbal on later models helped a lot.
Oh, what I wouldn't give for an RF-based Power Functions remote control system!
From this late model on, the front light bar sat above bumper to improve night driving visiblility and reduce snow build-up between the front tracks.
The mugs visible through right front window glass occupy cup holders added in response to complaints from PRV drivers and navigators.
Black rear train doors have replaced the red temporaries seen in earlier photos. The open doors provide a glimpse of the high-torque XL motor powering the rear tracks. A separate XL motor drives front tracks, while a less powerful M or L motor suffices to power the steering pivots. Thanks to the XL motors, the PRV powers through this kind of sinkage without a hitch.
Thick towing eyes below rear bumper greatly extend PRV endurance and range away from base by allowing extra fuel and supplies to be carried on cargo sleds.
Near-final trim changes visible from this vantage: (i) New whip antenna for better short-range radio communication with away teams. (ii) Protective wind-break just forward of whip and dish antennas. (iii) Otherwise cleaner roofline. Original dish and gimbal remain.
PRV in near-final trim rechecking east shore of Arapahoe Bay for additional ice sampling sites. Rocky headland in the distance has acquired a thick blanket of fresh snow since the 1st photos in this album.
A last look at Arapahoe Bay before the long twilight drive back to base. LED headlights and tail lights double as much needed-reminders to turn off the battery box. The original AA box shown on this page made for rather labor-intensive battery changes.
The remaining outdoor shots show the PRV getting around quite well in 10 inches of rather soft, dry powder fallen the night before and still without ice crust. However, totally hidden scattered pockets of exceptionally soft snow caused some problems. The PRV dug deep trenches in 3 failed attempts to power through the 1st of the day's 4 hidden "traps". Eventually, it backed out and went around, as shown above.
Thanks to the PRV's very low average ground pressure (total weight divided by total ground contact area), sinkage between traps was generally insignifcant -- even in fresh powder sans ice crust.
Probing another hidden soft snow trap for a way through. After 2 more tries, the PRV once again had to back its way out and make a wide end run. The utter lack of surface cues WRT trap boundaries kept the end runs interesting.
The 4th and final trap came with a twist -- a deep sinkhole that opened suddenly after very little digging in. After 6 long test runs on a variety of snow surfaces, this was the only time the PRV required divine intervention.
PRV up close
For scale, the light-colored floor tiles were 12x12 in before the corner cuts were made.
Open rear doors reveal the XL motor driving the rear track assembly.
An away-team and cameraman headed out for a day of ice sampling.
A look inside the cockpit with the roof removed: Driver's console on left, navigator's console and computer on right. The navigator never shuts up.
The cockpit dome light is under remote control. In the foreground below it is the XL motor driving the front track assembly.
A look through the front windows with the cockpit dome light on. The front snow dam at bottom center was surprisingly effective in reducing disabling snow build-ups between the front tracks. The navigator's still talking.
The forward motor compartment: The XL motor just above center drives the front track assembly. At 5 o'clock from the XL is the steering L motor, which powers the steering worm drive to its left. The dual IRRC receivers are at bottom center. The L motor here was an experiment and will be replaced with the original M motor, as the added torque of the L is seldom necessary. L motors have better things to do.
Kreuger's original design called for a standard PF AA battery box, here hidden beneath the yellow studded roof support just below the dual IRRC receivers. However, battery replacement proved to be a royal pain, and the much smaller and longer-lived PF rechargeable battery was later substituted. The PRV would probably benefit from V2 receivers, as total current draws can get quite when maneuvering with the tracks buried in snow.
Should blizzard-driven snow drifts cover the front windows, the dual periscopes above them (at bottom, here retracted) offer some hope of backup visibility from within the PRV.
The left rear seat (here at bottom right) was a real squeeze with the AA battery box in place, and nobody would to sit there voluntarily. That effectively reduced the PRV's science team capacity to 7 but did have the advantage of opening up a spot where misbehaving scientists could be sent for time-outs. Geophysicists spent the most time there, because they just couldn't keep their corny jokes to themselves. The seat became useable again when the AA box was replaced by the much smaller PF rechargeable battery, but the time-out spot was sorely missed.
And the navigator's still talking.
For some odd reason, the driver, the navigator, and the passengers on the right drink coffee incessantly, ...
... while the passengers on the left are always glued to their binoculars -- even when the scenery's on the other side. Nobody's having a time-out at the moment.
Table of features and stats
313 x 227 x 116 mm (11.9 x 9.0 x 4.2 in) in LxWxH
1.8 kg (4.0 lb)
Studded bodywork, mostly studless chassis
3 in all -- 1 PF-XL each on front and rear track sets; 1 PF-L for steering
3 PF LED pairs: Headlights, tail lights, dome light in cockpit
IR receiver connections:
4 -- 1 for each motor; 1 for cockpit dome lights
Initially, 1 PF AA batter pack; later, 1 rechargable battery or AAA battery box
That is just simply one of the coolest things ever! Very Syd Mead in design, completely utilitarian and totally awesome. The interior looks righteously crammed full of cohesive detail as well as research equipment/motors and gearing. I am highly impressed. Perfect!
Quoting clayton Marchetti
Awesome! Those windows look great . Looks like a load of fun in the snow.
Thanks for the kind words. I think the observation windows really make body design pop, and they fit the theme well. Sure glad I turned out to have 8 in my basement, because I wouldn't have coughed up for even 4 of them at current prices.