Ge­of­f­zone

NZ4WD - - CONTENTS -

Over the hol­i­day break I stayed home. In­stead of go­ing away I launched into a much needed com­plete 4WD strip- down and re­build. The old Rangie needed at­ten­tion. Body off, mo­tor and gear­box out. It took ages. Wheels off, man those big t yres take up some room when stacked! Sus­pen­sion apart, all joints checked, over­hauled, lubed. Both diffs over­hauled and ad­justed. CVs too, stripped and cleaned. Drive-shafts checked. Shock­ies opened and valv­ing mod­i­fied. Hubs cleaned up, new wheel-bear­ings all round. Power steer­ing up­graded. Mo­tor and gear­box re­placed. That was a mis­sion, choos­ing the best op­tions. Ra­tios too high or too low? Bal­anc­ing power against econ­omy, weight and size to fit avail­able space. Op­ti­mis­ing cool­ing. Mod­i­fy­ing wiring and con­nec­tors. Many hours were spent on my 3D CAD sys­tem match­ing up di­men­sions, work­ing out mods. In the end much of it worked out eas­ier than ex­pected. Ra­tios are spot on, power and con­trol are ex­cel­lent. The power steer­ing is per­fect. There are no signs of over­heat­ing. Noth­ing leaks, apart from some mo­men­tary smoke and a blown fuse. Low speed throt­tle con­trol when rock-crawl­ing is won­der­ful and the spring and shockie changes worked. With won­der­ful ap­proach and de­par­ture an­gles and belly clear­ance it sel­dom hangs up. It’ll climb a near ver­ti­cal face un­til it ’s about to fall over back­wards. No diff- locks yet so an ex­ces­sive cross-axle will stop it. It’s a real treat hav­ing it mo­bile again though. A few mods still on the list – a winch for starters. That will re­quire an up­grade to the ra­dio con­trol from t wo chan­nels to four to work the winch. Ah, there’s al­ways more to wish for. Good thing it ’s only a model! Some read­ers may re­mem­ber I wrote about this model Rangie in the mag ( 2001) when first built. It be­gan as a box of bits from a model shop. A Tamiya go-fast 4WD rac­ing buggy and some ex­tra parts. I short­ened the chas­sis, fit ted mon­ster truck wheels and t yres then made a re­duc­tion gear­box to fit a smaller mo­tor. The ob­ject was to make it a good rock- crawler. The orig­i­nal racer went very fast, had a lim­ited three- step speed con­trol and a bat­tery charge was gone in a cou­ple of min­utes. Speed con­trol was via vul­ner­a­ble and in­ef­fi­cient re­sis­tors that got very hot and tended to burn out. My orig­i­nal mods had kept that con­troller but was flat out at walk­ing pace and had rea­son­able low speed con­trol. Also the orig­i­nal steer­ing servo strug­gled to steer the big­ger wheels in rough ter­rain ( much like some full- size 4WDs!). One of the up­grades was to a cheap ESC ( Elec­tronic Speed Con­trol). These are vastly more ef­fi­cient as they don’t waste power into re­sis­tors and have step­less con­trol from zero to flat out. Ex­cel­lent at very low speeds. The steer­ing servo was re­placed with a high torque vari­ant, of which many are avail­able. It seems un­de­feat­able so far. The main rea­son be­hind a re­visit of the mo­tor-gear­box was ‘re­al­ism’. The orig­i­nal high-power mo­tor fit­ted side­ways into the chas­sis just ahead of the rear axle. There wasn’t much room to fit a dif­fer­ent mo­tor and a re­duc­tion box so I’d made a right-an­gled worm drive box with the smaller mo­tor ver­ti­cally above it. The ra­tio and mo­tor where ideal – it had enough power and a bat­tery charge would last an hour or so. I didn’t like that when pow­ered on or off it would lurch for­ward or stop in­stantly due to the worm drive. I’d al­ways wanted to change it to spur gears to re­move the lurch. This time I looked at many ways to re­power it and spent ages try­ing to adapt a t wospeed elec­tric screw­driver mo­tor to fit. They have very com­pact three stage epicyclic re­duc­tions of about the right ra­tios and would have al­lowed the pos­si­bil­ity to later give a Hi- Lo ra­tio switch via ra­dio. This, how­ever, en­tailed a quite com­plex gear­box build with bevel gears, new drive­shafts and bear­ings, etc, and lots of ma­chin­ing and fab­ri­ca­tion. I did make a test setup to check ra­tios – Lo was ex­cel­lent but Hi too slow. Then I dis­cov­ered some small in­dus­trial mo­tor- gear­box units from China. Bought one, tested it, wrong ra­tio. Bought an­other ( NZ$ 10!) and it ’s per­fect. It needed only a cou­ple of ba­sic adap­tors and works well with the ESC. Mo­tor is sweet and runs cool. So, a happy re­build, mostly done at my desk and with­out hav­ing to stress my back or scrabble around be­neath the ve­hi­cle chang­ing oils or bushes!

Scaled down Rangie pro­vides hours of fun.

Newspapers in English

Newspapers from New Zealand

© PressReader. All rights reserved.