1/8 Scale Nitro Monster Truck:

HPI Savage 21 - # 831 (Radio Controlled Model Review)

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History and Info:

Introduced by HPI (Hobby Products International) in 2002, the Savage 21 Monster Truck - # 831 - came pre-assembled RTR, with a pre-painted lexan polycarbonate Bodyshell, Nitro Star 21BB Engine and a Futaba Radio System. A number of other Savage versions were available (Check out our HPI Archive).

The 4WD model is shaft driven, on an alloy vertical frame chassis, with gear type differentials, 8 x coil spring over oil filled dampers, dogbone drive-shafts, 2-speed transmission and a full set of ball bearings.

HPI Savage 21 - # 831 Monster Truck

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To get the best from the HPI Savage 21, it needs to be fine tuned, to provide precise steering response and improve grip when cornering, so you don't slide off the track. Small changes can make huge advancements and our easy to understand guide will help you to the optimum Set-up for your individual driving style.

Savage 21
Manual

Savage 21
Exploded View

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Radio Controlled Model Accessories:

★ HPI Savage 21 Chassis ★

Buying a Used HPI Savage 21
Monster Truck (and What to look for)

There are essentially three reasons you might want to buy a used HPI Savage 21 Nitro Monster Truck; you may be a collector, looking to restore and display it; restore and sell for a profit; or simply restore and race an iconic vintage model. Personally, I used to get a buzz out of restoring an old clapped-out model, installing modern day electrics and maybe a few hop-ups, then showing the gang at our local club, just how competitive those old models could still be.

Cheap, pre-loved bargain models, parts and spares are always coming up for sale, but once you have made your purchase, the one thing you will always need, is an instruction manual. If not supplied with your purchase, they can often be downloaded from the HPI website, or purchased separately on eBay. With an instruction manual, any problems with your model Monster Truck you may discover, can easily be fixed.

Make a General Visual Inspection

Dampers
When you receive your used HPI Monster Truck, make a general visual inspection of the chassis, front and rear wishbones, suspension shock towers etc, for any broken parts that may need to be replaced. Then, take a screwdriver and box spanner and check each self tapping screw and nut for security, taking care not to over tighten.

Next, for those HPI models with oil filled shock absorbers, remove them from the chassis and dismantle the coil springs. The damper shafts should push in and pull out with a smooth action. If you feel a jolt as you change direction, this means the oil has leaked out and must be topped up. At the same time, change the O-Ring seals to prevent more leakage. Also check the damper shafts for damage. If they are scratched, change them as soon as possible.

Check the Body-Shell

If the body shell of your HPI Savage 21 is broken, ripped or damaged in any way, this can be easily repaired with rubber solution glue. Also, for added protection and if available for your Savage 21 model, fit an under guard to stop dirt and gravel entering the chassis.

Drive Shafts and Turnbuckles

Titanium Turnbuckles
Examine the drive shafts for wear and replace as required. If possible, change them for titanium. The steel shafts wear and bend too easily.

If you intend to race your Savage 21 Monster Truck model at a competitive level, I would also recommend you obtain and fit titanium pivot shafts, turnbuckles, tie rods and steering rods.

Examine the Drive System

The gearbox of your used Monster Truck should be opened up to check for gear wear and lubrication. A thin coat of grease is often used on internal gears and although this is fine for basic running around on the back yard, if you intend to race your Monster Truck at a higher level, this should be removed and replaced with racing oil (ZX1 or Teflon Oil). Of course, this should be reapplied after each race meeting.

Pinions and Spur Gears

Gears are a weakness on all Monster Truck RC models. Head on collisions can easily damage the gear teeth on nylon and plastic spur gears. Heavy impacts can also loosen the nuts or self tapping screws that hold the Nitro Engine in Position, allowing the pinion gear to pull out of mesh slightly and rip the tops off the teeth on your spur gear. To minimise this possibility, fit bolts with locking nuts to the Nitro Engine mount and remember to check them for security after every two or three runs.

Don't Neglect the Ball-Joints

Ball joints always cause problems. For top level Nitro Monster Truck racing, the plastic ball connectors should be checked and if deemed necessary changed after every meeting. A simple thing like a loose fitting connector popping off could easily end your race, so better safe than sorry.

Steering Servo and Servo-Saver

Servo Gears
The Savage 21 steering servo is also prone to damage. In high speed crash situations, the fragile gear teeth of the servo can be broken off, rendering your expensive servo useless, so be sure to obtain a good quality "Servo Saver". Check out my Servo Information article.

Stabilizers

If body roll on your HPI Savage 21 is a problem, handling can be improved with the use of stabilizers, anti roll or sway bars, stiffer tuning springs and, or, thicker silicone oil in the dampers.

Don't Forget those Bearings

If your used HPI Monster Truck comes with plastic and sintered brass bushings (ring type bearings), check the shafts that run in them for wear. Dust and grit can get into these bearings and abrade the shafts. Therefore, you should replace them all with shielded ball bearings. If the model has been run with ring type bearings, you may have to change all the axles and driveshafts. For more information, take a look at my article, How to get the best from your Bearings.

Finally, good luck with your Savage 21 model and good racing.

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Manufacturers and Brands Catalogued and Listed by RC-Scrapyard.

At present, the RC Model Manufacturers, Brands and Distributors covered by us are: ABC Hobby, Academy, Acme Racing, Agama Racing, Amewi, Ansmann Racing, ARRMA, Team Associated, Atomic RC, Axial, AYK, Bolink, BSD Racing, Capricorn, Carisma, Carson, Caster Racing, Cen, Corally, Custom Works, Durango, Duratrax, ECX - Electrix, Exceed RC, FG Modellsport, FS-Racing, FTX, Fujimi, Gmade, GS-Racing, Harm, HBX, Helion, Heng Long, Himoto Racing, Hirobo, Hitari, Hobao, Hong-Nor, Hot Bodies, HPI, HSP, Intech, Integy, Jamara, JQ Products, Kawada, Kyosho, Losi, LRP, Maisto, Mardave, Marui, Maverick, MCD Racing, Megatech, Mugen, New Bright, Nichimo, Nikko, Nkok, Ofna, Pro-Pulse, Protech, PTI, RC4WD, Redcat Racing, RJ-Speed, Robitronic, Schumacher, Seben, Serpent, Smartech, Sportwerks, Step-Up, Tamiya, Team-C Racing, Team Magic, Thunder Tiger, Tomy, Top Racing, Traxxas, Trinity, Tyco, Vaterra RC, Venom, VRX Racing, WLToys, X-Factory, Xmods, Xpress, Xray, XTM, Yankee RC, Yokomo, ZD Racing and Zipzaps.

This is an ongoing project, with new and "lost in time" RC Models and Brands being added as they are found and although most of those listed above have been covered in relative detail, some are still being researched and will be completed in the near future.

RC Information and Advice:

Hints, Tips and Information

Wheel Caster Explained

   Caster is basically the angle the steering kingpins or steering pivot points, leans back in relation to the horizontal when viewed from the side of the chassis.

   To test the effectiveness of your cars caster, place your model on a flat surface, point the front wheels straight ahead, and push the chassis over to one side to simulate body roll when cornering. You will notice that as the car leans over, all four wheels also lean over in the same direction. Tires provide the most grip when the wheels are perfectly vertical and the full width of each tire is flat on the ground. Body roll pushes the wheels past the vertical and reduces the amount of tire contact. Now, if you turn the front wheels as if cornering, and again push the chassis over, you will see that in this position, the front wheels are now more vertical, giving you better ground contact and therefore improved grip.

   Another effect of caster can be seen by disconnecting your steering servo and pushing your car along the floor. Because of caster and the kingpins leaning back, your car will naturally roll straight ahead.

   Obviously, the more body roll your car induces, the more positive caster you need to counter it.

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Hints, Tips and Information

Toe Angle - for Steering and Straight Line Stability

   When you first build your RC model car, you will no doubt have made all the settings advised in the manufacturers' manual and will take it out on the back yard not thinking of things like camber, caster or toe-in - I know I did. It's only when you get competitive that you start learning about these things and just what a big difference they can make to the handling of your car. One of the more effective of these adjustments is Toe-in.

   The term, toe-in, toe-out, or toe-angle, refers to the alignment of the front or rear wheels, when viewed from above. Front toe-angle is easily adjusted via the track rods or turnbuckles that link to the steering mechanism or directly to the steering servo horn. At the rear, some models like the Schumacher Mi1 can be adjusted by turnbuckles, but most models, on and off-road, have a set of hub carriers to provide the desired toe angle.

   Front toe-in reduces steering when entering a corner, but improves steering response on corner exit under acceleration.

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