DeBruce

My Super Astute Restoration (Complete Rebuild)

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Here is a picture of the differential. In the super astute it's a gear differential and you can see the internal gears in this picture. Again the diff is full of dirty grease but I found upon removing the gears, that they were in excellent condition, showing this gear diff, with a little grease, is tough and well up to its task. There was no evidence of wear on any of the gears.

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Also linked here is an excellent video for understanding how gear diffs actually work. It's from the 1930's but don't let that put you off. It's the first video I've seen that actually let me understand the mechanical principles.

 

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Nice progress !

Great to see you are back at it, the motor plate has come un really well and the gears themselves are in good condition. I put some tamiya anti wear grease in my SA diff to slow it down a bit and get more diff action and it works a treat. 

Keep up the good work !

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Thanks!

Next step is the assembly of the gearbox. I used new A tree parts as I want this new model to be very clean. Here you can see the new A parts tree.

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First job is the attach the motor plate which attaches to the side of the gear box with three long screws. I was able to reuse these from the original car.

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Next step is the build up the gear differential. Despite the original gears being in good condition, I bought a new gear set online which can be seen here. This was mainly because the main TTC clutch assembly and spur gear had been replaced in my car and I wanted to return to original condition. In the set I also got all the parts for the gear diff so it made sense to build this up as he picture below you can see the gear diff case and cover and the metal diff gears in a separate plastic bag.

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I used Tamiya TRF VG Gear Differential Grease, part 42212 to grease the diff. It's easy to build, with a lower central gear going in first, then the four surrounding gears and finally a top central gear which all drop into place in the gear casing. Then you add on the top cover and secure down with the four small screws. The finished assembly looks like this.

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Nice work, looking forward to seeing the end result!

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Next step was to rebuild the clutch assembly. In order to do this I had to buy a new gear set to get the correct spur gear, as well as a new clutch bag assembly to obtain the correct clutch parts.

The original main shaft on this car I found to be in good condition so I am reusing this part. From my clutch bag, I then added one of the new pressure plates which forms one side of the clutch assembly. Onto this is then added the clutch lining. The clutch assembly works by sandwiching this clutch lining between two clutch plates. On this side, the clutch plate is keyed to the main shaft using a hex shape in the plate that sits on the main shaft.

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On the other side of the clutch assembly we add the other clutch plate to the spur gear, which is keyed to that using three pips. There is also a brass bushing which ensures a snug fit of the main shaft into the spur gear. When completed, this part of the assembly looks like this.

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This assembly, when put together, allows the spur gear to transfer torque to the main shaft through the pressure plates and the clutch material. However it also allows the parts to 'slip'. The amount of slip is controlled by the spring assembly which exerts pressure between the spur gear and main shaft.

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Next the spur gear is added to the main shaft and then the spring assembly is added. This will exert the pressure between the spur gear and the main shaft with the other clutch plate.

The spring assembly is based on two conical disk springs which are squeezed together by a nut which is tightened onto a pressure disk. This disk squeezes the conical washer 'springs' down onto a pair of thrust washers which sandwich a ball thrust bearing. The inner of these two thrust washers transfers the force onto the spur gear the generate the clutch load. The weakness of this assembly is that a disk spring is very difficult to adjust and very little adjustment of the locking nut generates significant changes in the spring loading. This makes it very difficult to achieve the exact required loading on the clutch, resulting in too much slip or no slip at all.

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Next we build up the assembled parts into the gearbox. Firstly we add the two 1680 bearings onto the gear diff. Here throughout the gearbox I have used Apex Ceramic bearings. These bearings allow the entire clutch assembly to rotate in the gearbox. The diff assembly allows the outer diff casing to rotate on these two bearings and the two inner gears that drive the two output shafts will of course rotate with it, however through the action on the diff, they can rotate at different speeds.

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Next we push the diff into the gearbox case suitably greased, and then screw in place the lower cover which provides the base for the bearings to rotate on, holding the diff in place.

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Next we add the counter gear on its own two bearings (again ceramic). This connects the spur gear drive which is outside the gearbox case as we shall see, and transfers it to the diff by turning the entire diff assembly through the gear teeth on its outside. The counter gear is held in place by the black plastic A1 piece.

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Finally the main shaft and clutch assembly is added. The spur gear meshes with the counter gear here to transfer drive from the motor pinion into the gearbox. Note that in the pictures below you can see the conical shape of the two disk springs on the spur gear.

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The main shaft is locked in place with an e-clip and there you have the completed gearbox assembly.

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Thanks! I've actually done a lot more but I want to write it up methodically and its finding the time to do it!

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Time for the next update...

Next step was to prepare the main chassis plate. The old plate was perfectly usable but scuffed on the underneath so I purchased a new plate however the plate was an Astute and not Super Astute plate. The difference is the two additional holes required for the Super Astute forward battery holder. Using the old plate as a template, I marked, drilled and tapped these two holes. In the picture below you can see the old and new plates side by side.

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Next to the plastics...

Below are some images of the old plastics parts I removed from the chassis I received. You can see that the parts have had a hard life. The old front lower arms are badly scuffed underneath and one has a chunk missing. However we can see that they are clearly very tough and overall the is no evidence of cracking or splitting of these legs.

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Next the front bulkhead - again this has stood up very well. I could find no evidence of cracking or chaffing and in fact I could have reused this part. The only reason not to was the fact I had a new part available on the appropriate tree. This is evidence that the Super Astute brace works well to protect the bulkhead part from the stresses that splits it on the standard Astute

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Next the front bumper - as you can see this is severely scuffed and has cracked in one location where a screw was over tightened. This will be replaced with a new part.

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Here are the two titanium screws that hold the front bumper to the front bulkhead. Titanium is a very light metal which is excellent for use on RC cars, but is also very soft and so very prone to heads stripping if you are not very careful. For the new car I am using black 10.9 grade steel as it is easier to get hold of, however there will be a weight penalty for using it.

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Unfortunately I forget to take a picture of the front brace and will add one later. However it was in reasonably good shape although had cracked around one of the press nuts. This is a good illustration of the problems with these press nuts which, if over tightened, press outwards on the plastic too hard and can split it apart. Care must be used when tightening screws into these press nuts.

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Next the build...

Here you can see the new plastics parts trees to be used. First is the D parts tree which carries the front and rear bulkhead and the rear arm mounts, notorious weak points on this chassis.

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Next is the E parts tree which carries the front and rear bumpers.

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Finally the elusive B parts trees which hold the front and rear arms.

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First part of the build is to attach the rear arm mounts and rear bumper and the front bulkhead using the press nuts and 8mm black steel fixings to the new chassis plate. I worked the screws slowly tight, trying to work the press nuts gently into the plastic. 

Then the front bulkhead is attached using the front two fixing holes only. The rear two are used later to also hold the Super Astute brace in place. 

Once the front bulkhead is fixed into place I added the 730 bearings, four of the few left over from the original Astute design. However as per my previous build, in order to reduce weight I have used plastic bearings from the Carisma M14 3x7x3 which fit. Into these we secure the front lower Super Astute arms using the pin and an e-clip on either end.

Finally we add the front bumper and fit the two larger fixings in place with nyloc nuts on top to secure this part. The result at the end of this stage can be seen below.

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Next we add the rear arms using the rear hinge pins, which are held in place using e-clips. We must also add the rear strengthening brace which goes on the hinge pin before you add the forward e-clip. This braces the two rear arm mounts apart so that running forces do not twist and break the arms. Obviously this is only partially successful as breakages of these rear arm mounts are common.

We can also add the front shock tower. This is slotted onto the front bulkhead and then secured in place with two stepped screws which fit through the holes in the bulkhead and screw into two press nuts that fit into the shock tower itself. Here I am reusing the original shock tower - it would be nice to have a few original parts in this build! There is an additional fixing for the shock tower which also secures the bulkhead brace so we add this later when we add the brace itself.

Finally we can add the gearbox assembly itself to the chassis. This sits in the location on the chassis place between the rear arms and is then held in place with one self tapping screw and two threaded screws that secure into aluminium posts inserted into the gearbox plastics. On the original gearbox the self tapping screw had cracked the plastic so in this build I worked this screw very slowly in, working it backwards and forwards, so that the new thread was cut very slowly, the heating effect of working the screw helping to cut the thread. It's also worth noting that on my original Astute build, the two screws into the aluminium posts had become corroded in place. This is because the Aluminium and Titanium are about as dissimilar as it's possible to get and had promoted a galvanic reaction between the two metals, effectively welding the screws into place.

With the gearbox now held in place with its three fixings, the chassis now looks like this. Note that the aluminium posts at the front of the gearbox can be seen in the image below. These also provide two of the location mounting points for the rear bulkhead, as we shall see later.

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In the light of the new SA this post has new relevance, was this finished????

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