Heng Long 3958-1 IDF Merkava IV basic version to metal upgrade

[keilau]

So the Hooben sprocket hub "backspacing" is off slightly compared to the HL sprocket, but not enough to not work reasonable well.

This is a similar issue that the new CS metal Merkava sprockets have. Close enough to work, but not quite right at the same time.

The 1:16 scale plastic chassis RC tank is a light weight, low power toy. (Compared to an RC model airplane.) The most stressful part is the motor shaft-sprocket interface. The motor shaft OD is 7.88mm. A 8-10mm long contact is a good estimate. The 5mm length on the HL Merkava motor shaft is a little flimsy. I believe the Hooben sprocket is the correct configuration and a good match to the Hooben gearbox.

The problem of the HL Merkava was that the chassis designer did not move the gearbox mounting poles outboard to compensate for the wider chassis. They modified the sprocket to compensate for the shorter motor shaft. It works, but is not a good design approach.

[RichJohnson]

I had a machist make new longer shafts for my okmo DKlM m60a3 I built 6 years ago. First I had screwed extensions to my shafts, soldered them on and then turned in a lathe and it worked ok until the new shafts were made for me.

[keilau]

I had a machist make new longer shafts for my okmo DKlM m60a3 I built 6 years ago. First I had screwed extensions to my shafts, soldered them on and then turned in a lathe and it worked ok until the new shafts were made for me.

The 2 nylon rings give me the right amount of extension for the motor shaft. I changed the M3 mounting screw from 8mm to 12mm for the sprocket. With these mod, the HL Merkava with Hooben track is running very well indoor. When the weather gets warmer and the ground drier, I will take the Merkava outdoor.

I do not have access to a machinist so getting a longer motor shaft is out of the question. There are standard length motor shaft for sale on e-bay.
https://www.ebay.com/itm/40376773372...8QB3NS539AARE8

[Rubicon99]

The 1:16 scale plastic chassis RC tank is a light weight, low power toy. (Compared to an RC model airplane.) The most stressful part is the motor shaft-sprocket interface. The motor shaft OD is 7.88mm. A 8-10mm long contact is a good estimate. The 5mm length on the HL Merkava motor shaft is a little flimsy. I believe the Hooben sprocket is the correct configuration and a good match to the Hooben gearbox.

The problem of the HL Merkava was that the chassis designer did not move the gearbox mounting poles outboard to compensate for the wider chassis. They modified the sprocket to compensate for the shorter motor shaft. It works, but is not a good design approach.

Actually that is a very common engineering short cut for HL, Taigen, TongDe and even Tamiya. They all have to make things fit into a given size box with off the shelf components to make the price point obtainable by the vast majority of consumers. In a perfect world were money is no option you are correct, but the RC tank world is too small and to low margins to not take short cuts especially in areas the majority of people will never notice.

Personal I have run the snot out of my Merkavas and they have proven excellent out of the box tanks for reliability even with a the few short cuts taken in their design. I would rate the Merkava (with steel gearbox option) as the best all around HL modern tank for reliability right out of the box. It is even better running then my expense nicely engineered Tamiya Abrams, Leopards and M551.

[keilau]

Actually that is a very common engineering short cut for HL, Taigen, TongDe and even Tamiya. They all have to make things fit into a given size box with off the shelf components to make the price point obtainable by the vast majority of consumers. In a perfect world were money is no option you are correct, but the RC tank world is too small and to low margins to not take short cuts especially in areas the majority of people will never notice.

Personal I have run the snot out of my Merkavas and they have proven excellent out of the box tanks for reliability even with a the few short cuts taken in their design. I would rate the Merkava (with steel gearbox option) as the best all around HL modern tank for reliability right out of the box. It is even better running then my expense nicely engineered Tamiya Abrams, Leopards and M551.

I stand by my assessment that HL could have moved the gearbox mounting poles closer to the chassis sidewall. It will be a cheaper and sturdier approach for the HL Merkava. It will allow them to simplify the sprocket design. Let's agree to disagree.

[Rubicon99]

I stand by my assessment that HL could have moved the gearbox mounting poles closer to the chassis sidewall. It will be a cheaper and sturdier approach for the HL Merkava. It will allow them to simplify the sprocket design. Let's agree to disagree.

Absolutely its all good to disagree. We tend to agree more then we disagree. Disagreements are healthy and can be productive. My thoughts on your assessment of the current arrangement would be different if the current arrangement did not work exceptionally well, which it does. If it did not I would be inclined to agree with you.

It is pretty simple to understand their placement decisions though. Moving the gearboxes outward would require a different drive shaft length not currently available "on the shelf", aka increased cost. So then why not design the sprockets backspacing to accommodate a dive shaft that sticks out further from the hull. That is simple too because the further the driveshaft stick out from the hull the higher the chances for "wobbling" sprockets to occur (HL is not known for their precise made sprockets and drive shafts) and this increased potential for track related issues especially with "captive" track links like those used on the HL Merkava

So a short drive shaft and slightly wider sprocket was the cost and reliability compromise. Fortunately it works exceptionally well.

A more important question then the gearbox placement and sprocket arrangement is why the heck HL chose to go with torsion bars when the real Merkava uses external suspension springs. This was a huge mistake but one people accept. Why, because the suspension works well and you can't see the springs anyway, kind like the gearbox placement.

[keilau]

The first stage of the Hooben track and sprocket modifications took 3 days to complete (Post #79). The Hooben track is a tangible improvement over the Heng Long plastic track. The Hooben track runs steadily, but the amount of micro vibration is more than the Heng Long German Leopard 2A6 with similar gearbox.

After some investigation, I determined that the Merkava can be improved by a motor shaft ball bearing kit. HL put a nylon ring around the motor shaft. But it keeps falling out. I try to use RTV to fix the ring in place, but it did not work.

HL does not have a motor shaft bearing kit for the Merkava yet. I order a set of 8x12x3.5mm ball bearings from Amazon.

https://www.amazon.com/dp/B07TJQZBMX?ref=ppx_yo2ov_dt_b_product_details&th=1

It is a tight pressure fit to the motor shaft. I drilled a 3/8" hole on a 3/4" plywood to push the bearings in using a C-clamp. The bearings stay in place because of the tight fit. The Merkava now runs even smoother. The Merkava and the Leopard are the 2 best running HL RC tank in my small collection.

I changed the sprocket M3 machine mounting screws from 10mm to 12mm. It makes no difference to the sprocket mounting. It is just a feel good mod.

[tank_me]

Just as a side note to someone wanting to add their own shaft bearings, keep in mind that they do make flanged bearings in the same size.

[keilau]

Just as a side note to someone wanting to add their own shaft bearings, keep in mind that they do make flanged bearings in the same size.

As Rubicon99 review pointed out, the HL Merkava is a good runner as is. I cannot stand the look of the HL track's open pin look. Hooben nylon track is the only 3rd party option in town. It takes a little effort to figure out what I have to do to use the Hooben track. The final result is very rewarding. I hope to see more adaptation of the Hooben track and sprocket. The flanged ball bearing is a wonderful idea. I can see how it would reinforce the plastic motor cover with a few drop of CA glue.

[keilau]

The Merkava is a large MBT, making the metal upgrade very easy. The extra space allows the Heng Xin gearbox to drop into position easily. The metal sprocket is an easy drop-in replacement.

The plastic idler wheel has a brass insert. The brass to nickel alloy sleeve makes smooth rotation. The 2 ball bearings of the metal idler makes it even smoother.

To my disappointment, there is no provision to add bearings to the plastic road wheels. It is plastic sleeve over metal spindle, not a good combination. If you want bearings on road wheel, you need to get the metal road wheel set.

I broke down and purchased a set of metal road wheels for the Merkava from the Heng Long RC Store at AliExpress.
https://www.aliexpress.us/item/3256806433081717.html?spm=a2g0o.order_list.order_l ist_main.5.94601802HIXgoW&gatewayAdapt=glo2usa

Including shipping and tax, the total cost is about the same as US Store Toucan Hobby. I selected this seller because they explicitly state the components in the set with pictures. The shipping cost said "from China", but the ETA said from US. I will follow up when I receive the package.

[keilau]

The metal road wheel package arrived today. It was shipped from China and took 13 days to arrive.

In addition to the road wheels, it comes with ball bearings, caps and the return rollers. It does not have rubber rim. The road wheels are not painted except for the rims painted black. HL Merkava comes only with metal swing arms originally and can be used.

I changed my mind about metal road wheel because Heng Long do not allow user to add bearings to the metal road wheel. I first added ball bearing to the plastic road wheels on the Tongde M60A1 Patton. I found the Patton with the ball bearings runs like a whole different tank. I was able to purchase the metal road wheel set for the Merkava for about the same cost on the Patton bearings because HL do not allow bearing on the torsion bar end of the swing arm cutting the number of bearings to half. (24 bearings on Merkava vs. 48 bearings on Patton)

I shall start painting the road wheels tonight.

[quitcherbitchen]

What was the major difference with the bearings Vs no bearings

[keilau]

What was the major difference with the bearings Vs no bearings

With the ball bearings, the individual road wheels are all lined up much better with the chassis and move as one piece. Put a tank with bearing next to one without. Push each tank forward gentilely without power. It is very easy to tell the difference. The road wheels only moves up and down. I did not think that the bearing were important because the rotational motion is secondary. But I now have my mind improved. It is a moderate cost, high payoff upgrade.

I must admit that the road wheels ball bearings are super nice to have and change the RC tank's driving quality, but they are NOT an absolute necessity. On the other hand, the drive motor shaft ball bearings and the idler wheel ball bearings are "must have's"

[keilau]

The IDF Merkava metal road wheel kit (3958 Tanks Parts TH23641) that I purchased from Heng Long RC Store on AliExpress DOES NOT work. The kit is only half of the problem. The Heng Long 3958-1 IDF Merkava Mk4 RTR tank from Toucan Hobby Store (TH22634-QC-DZN1) was not designed to work with metal road wheels.

1. I expect that the ball bearing ID to be pressure fit to the swing arm and the OD to pressure fit to the road wheel pockets. They are not. They are both very loose. In another word, the ball bearings are used as loose bushings.
2. I expect HL to use machine screw to mount the road wheels to the metal swing arms of the torsion bar suspension. HL used self-taping screw instead.
3. I cannot remove the screws to remove the return rollers. The screws just keep turning. Not sure how they are fixed to what.

I will like to hear from others who tried the metal road wheel upgrade on the IDF Merkava. Are other HL tank and road wheel kit similar?

I painted the road wheel kit pieces this morning. I guess I will have to write off the loss.

[Rubicon99]

The IDF Merkava metal road wheel kit (3958 Tanks Parts TH23641) that I purchased from Heng Long RC Store on AliExpress DOES NOT work. The kit is only half of the problem. The Heng Long 3958-1 IDF Merkava Mk4 RTR tank from Toucan Hobby Store (TH22634-QC-DZN1) was not designed to work with metal road wheels.

1. I expect that the ball bearing ID to be pressure fit to the swing arm and the OD to pressure fit to the road wheel pockets. They are not. They are both very loose. In another word, the ball bearings are used as loose bushings.
2. I expect HL to use machine screw to mount the road wheels to the metal swing arms of the torsion bar suspension. HL used self-taping screw instead.
3. I cannot remove the screws to remove the return rollers. The screws just keep turning. Not sure how they are fixed to what.

I will like to hear from others who tried the metal road wheel upgrade on the IDF Merkava. Are other HL tank and road wheel kit similar?

I painted the road wheel kit pieces this morning. I guess I will have to write off the loss.

It is not uncommon that HL uses two different metal suspension arms sizes for their tanks. One sized to fit the plastic wheels hubs and one for the metal bearing wheels. Sounds like that is the case here. You would then need to buy the correct suspension arms.

I only buy HL metal wheel upgrades as a package that includes the suspension arms because of this reason.

[keilau]

It is not uncommon that HL uses two different metal suspension arms sizes for their tanks. One sized to fit the plastic wheels hubs and one for the metal bearing wheels. Sounds like that is the case here. You would then need to buy the correct suspension arms.

I only buy HL metal wheel upgrades as a package that includes the suspension arms because of this reason.

I spent serval hours searching for IDF Merkava metal road wheel package with suspension arms, but failed to find any. Other tank models do have such package.

I did find 2 sources for Merkava suspension arms, one at AliExpress and one at UK ebay. The ball bearings that come with the road wheel are 5x9x3mm. There is no information on the suspension arm set except that they are metal. I ordered one from the unknown AliExpress seller whom seems to be the only game in town. If the arm works, I may CA glue the bearings to the road wheel.

I am very puzzled by HL's 2 suspension arm approach. From the engineering and business prespective, it would be more economical to make one metal suspension arm. They can easily mold the plastic road wheel axle hole diameter just a hair bigger for rotation.

[keilau]

The IDF Merkava metal road wheel kit (3958 Tanks Parts TH23641) that I purchased from Heng Long RC Store on AliExpress DOES NOT work. The kit is only half of the problem. The Heng Long 3958-1 IDF Merkava Mk4 RTR tank from Toucan Hobby Store (TH22634-QC-DZN1) was not designed to work with metal road wheels.

1. I cannot remove the screws to remove the return rollers. The screws just keep turning. Not sure how they are fixed to what.

I will like to hear from others who tried the metal road wheel upgrade on the IDF Merkava. Are other HL tank and road wheel kit similar?

I painted the road wheel kit pieces this morning. I guess I will have to write off the loss.

Lesson I learned: I must use the correct tool to turn a screw.

I tried many times to turn the return roller with a Philips screw driver. The return rollers are mounted on a hex head screw. I kept trying for 2 days without looking. Once I realized my mistake, the screws came off easily.

[keilau]

The return rollers:

30mil sticky copper foil on road wheel axle:

[keilau]

The tip from Max-U52 works wonderfully. The road wheel bearings are standard 5mm ID ball bearings which needs a 5.03mm axle to fit properly. The HL suspension arm axle has a 4.85mm diameter for the plastic road wheel. The metal road wheel should come with its own suspension arms, but they did not. I found some spare suspension arms on AliExpress, but they are the same 4.85mm OD.

I get a roll of 30mil (0.003mm) brass foil. I tried various number of layers. I ended up cutting 2mmx1mm pieces of sticky foil. Remove the backing and wrap the foil around the suspension arm axle. I get the slight pressure fit that I am looking for. The fit is very secure.

https://www.amazon.com/dp/B0CGF6DDCX?psc=1&ref=ppx_yo2ov_dt_b_product_details