Vantex M4A3 75mm Sherman

[Saracen]

I picked this Sherman up from Ebay last week. I've had a hankering for one of these gearbox drive models for a while but they don't seem to come up very often.

Overall everything worked apart from the steering servos, so once I'd won it I bought a pair of 30Kg Turnigy ones from Hobbyking.
The two batteries won't hold a charge either, but they're dated 2010 so not surprising. I've ordered a new pair from Hardware Express.

There are some frankly horrible bits of engineering in it though. The first change was the speed control. The ESC is from an electric scooter, so the speed control is a 50K pot, which is supposed to be turned by a servo:



I found this only worked some of the time, and was pretty on/off when it did work. To get some control over the motor, I have removed the 50K pot and replaced it with an Adafruit Trinket and MCP4725 DAC board, so that the response is fully programmable. Ultimately, I'll probably replace the whole motor control circuitry with a Syren 25 ESC unit but this will do for now.

Adria

[Saracen]

Another annoyance was that the turret is held in place by the traverse gear, using four M3 cap head bolts and nylock nuts. Three of these were OK to reach but the fourth was under the elevation motor and needed all sorts of faffing to remove it.

Once the screws were removed, the next snag I hit was that the elevation power lead passed through the centre of the traverse gear:



The plug was too big to fit through the hole in the gear and the gear was too big to fit through the hole in the hull !

In the end I removed the pins from the plug and managed to get it apart that way.

There seems to be some odd choices in the design. They've included roller bearings for the turret, something which was only recently introduced by Armortek with the Tiger 131 kit, but then they've smeared them with heavy grease, The turret is too light to overcome the stiction of the grease and so the balls don't turn as designed.



A little white spirit and the bearings clean up a treat:



The plan is to add a circular plate to the underside of the turret, to increase its overall thickness and to provide a decent surface for the bearings to run on. I'll also replace the centre boss on the turret so that it runs true, as at the moment it is too loose and the drive gear slips when traversing.

Adrian

Adrian.

[Luckylefty42]

I was just going to buy this same tank..you beat me by a day....I've found another and I'm planing on getting it next week..I'd love to get in touch with you in the future as I want o ass smoke and sound and haven't a clue what I'm doing..but I'm not scared to try so any help would be great..

[Saracen]

Where did you find the other one ?

I'm planning on adding sound and smoke to this one, but I want to get it running well to begin with.

I've ordered a set of clutch pads from Fuyuan, which cost £24 including shipping, so I'll need to strip the gearbox down at some stage to fit them.

I've also found the idler gears inside the gearbox are as loose as anything, so I'm going to machine a new set of mounting stubs for them. They have bearings fitted, so there's no reason they shouldn't run smoothly.

Adrian.

[Luckylefty42]

Text me on 07954:589395 lefty

[sassgrunt]

Just a thought on your turret bearings. The company Rubbermaid makes a large plastic turntable (maybe around 30cm; I don't have it to hand to measure) that has ball bearings in a captured circular framework that run in the plastic track of the upper piece. I found that it would fit in between the turret and hull of the Dragon M4A3 and allow the turret to turn smoothly.

[Saracen]

Thanks for the info. Once the roller bearings were cleaned up the turret turned really easily, so I'll probably stick with what's there already.

I've built a tank turntable using two bread boards and a "Lazy Susan" turntable. It makes working on 1/6th models so much easier.

Adrian.

[Luckylefty42]

I ordered a new one from tank zone..I know they have a bad rep..but so far they have been very helpful..and I will have the tank at the weekend..I hope