Monday, 4 June 2012

Tiger Crawler rear axle repair

Our Tiger Crawler from Thunder Tiger has seen a lot of use lately. And it developed a few problems on the rear axle. With a bit of DIY, some scrap material and a fresh set of gears we got it running again in no time.


WARNING: This and other DIY projects are purely "at your own risk". If you are at all uncomfortable or inexperienced working with metal and platics, please reconsider doing the job yourself.

Axle hub dislodged

As written in our mini-review, the outer rear axle hub came off after the Tiger Crawler landed on the rear wheel when it was falling down some obstacles.
Initially it was an easy fix: just click it back on. However, the axle hub started to come off regularly when going over tough obstacles. Investigating the manner revealed that the locking tab that secures the axle hub to the main axle housing had snapped off.


We fixed this by jamming a small piece of soft plastic that we had saved from a toy packaging into the hole.


Right below the hole is a ball bearing where the plastic piece sits on. We cut the plastic piece so that It fits snugly into the gap, locking the axle hub to the main axle casing. We secured it with a bit of household glue so we can take the plastic piece out easily in case we need to open the axle case for other repairs. With this simple fix so far the axle hub never came off again, even going over the roughest terrain.


Inner axle strut mount broke

One Saturday evening I took the Tiger Crawler out of the cabinet to prepare for a crawling session with the SG Crawlers on Sunday. When I lifted up the Tiger Crawler I noticed the rear inner axle struts dangling down. The small tabs that hold the axle strut mount onto the main axle casing had snapped off. We do not know how and when this happened.



We tried an emergency repair with CA glue and Epoxy, but it only lasted for 3 minutes of crawling. The mounting tabs are very small considering the load they have to carry, so this is clearly a weak point of the Tiger Crawler's design. Luckily a bunch of guys from the SG Crawlers helped us by securing the axle strut mounting temporarily with a zip-tie. Lessen learned: never leave the house without zip-ties! It worked well and we crawled a full 2 hours in the rocks at Little Guilin.

Given that the mounting tabs are so tiny, a replacement of the rear axle case — even though inexpensive at SGD 5.60 — would not last long. We decided therefore to strengthen the axle strut mount. We used a 1mm aluminum plate that was originally a heat sink in a DVD recorder we found in the rubbish. It is thicker than necessary, but does the job. We cut and bent a new axle strut mount as shown in the images below. We started off with a paper template check for size.




The new axle strut mount is secured to the plate that sits on top of the axle. I think the original use of this plate is to allow for 4-wheel-steering conversion. We used 2.5mm screws and nuts for fastening. Make sure you drill the screw hole in front of the top plate so that the screws don't interfere with the axle housing.


For securing the struts to the new mount we used the original 2mm screws plus some 2mm nuts. You need some spring clips, Loctite or locking nuts so that assembly doesn't loosen during runs. We used normal, unsecured nuts at first and they came loose after 2 hours of drive.

The area on the main axle casing where the original axle strut mount was had a small hole. Make sure you close it with some glue, otherwise water and mud will go into the axle.


Gear stripping

The third problem we had was that the gears inside the rear axle started to strip. This happens when the Tiger Crawler gets stuck on tough, grippy obstacles and you apply too much power. Since there is no slipper clutch something in the system has to give: the gears themselves. On our car only the rear axle seems to have this problem, I guess it is because it receives most abuse during crawling.

When the gears strip you hear a loud click-click-click sound. Immediately go off the throttle and either go backwards or lift the Tiger Crawler out of its misery. The gears are actually quite tough. They don't strip completely, it is more that the top of the teeth "bends". When taking the axle off the vehicle and turning the drive shaft with your hands you can feel binding at places where the gear teeth are damaged.

Unfortunately there is no DIY fix I am aware of. I tried to file back the teeth a bit to reduce the binding, but it did not help much. The local hobby shop where we bought the crawler had spare gear sets in stock. A pack for SGD 10.50 contains 2 sets of axle gears. The gears are interchangeable front and rear, so assuming that only the rear axle will need replacements a single set lasts for 2 repairs.

Don't be discouraged

If you don't own a Thunder Tiger Tiger Crawler yet, don't let this blog post discourage you. For its size and price it is very durable. Spare parts are decently priced, just make sure they are available in case you need them. This tiny vehicle is a lot of fun!

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