Tamiya KV-1 turret rotation problem...

[DonCarlos]

I'm new here having just built the Tamiya KV-1 kit. Thought I'd do something fun during lockdown.
I'm using Futaba T6L radio gear. It seemed a good basic entry level set and is a brand I remember from when I last was into RC models in the, erm, 1970's.
My problem is that all the functions on the tank work OK except for the turret, which will only rotate one way. Anticlockwise, viewed from above. If I move the stick to the right I get nothing. Motor not even trying to budge. I've swapped the radio channels around for turret and gun elevation to check that the radio is all working OK, and it is. Tried the Tx trim at both extremes, still nothing.
I've tried resetting the DMD to factory defaults but still no joy.
Is this something anyone has come across before or do I have a DMD problem?
Any suggestions?

[Model Builder 4]

Hi DC,

I had a similar problem with my tamiya pershing unit, it worked as normal one way when I pushed the stick fully to the left but I got nothing when pushing the stick fully in the opposite direction What I then found though is if I moved the stick ever so slightly and slowly instead of pushing it fully across it worked as it should not that this is an answer or a fix but its something you can try to see if you get any response from it that way

Cheers,Lee.

[Tiger6]

Did you follow the calibration procedure in the manual? and have you centered the trim tab?
After that I would be trying to check the stick is functioning correctly - I had this issue fairly recently, which tracked back to a faulty potentiometer on the stick. My radio has a lcd screen so checking travel vs input signal was an easy thing to do, I'm not familar with your model tho.

[General Jumbo01]

Having had a quick look at Tamiya's build manual the turret rotation motor is powered from the DMD mfu but it's not clear how as l can only see one orange lead. I wonder if the Futaba radio stick trim is so far off centre that it's only allowing one direction to work?

[DonCarlos]

Thanks for the feedback so far. In reply:
I have followed the calibration in the manual.
I've eliminated any problem with the RC Tx and Rx by swapping channels so I know the LH stick horizantal axis works fine.
All trims are currently centered, and I have tried with them at all extremes.
The turret motor has two wires to it from the DMD, so it must switch the polarity of the voltage to the motor to reverse it. I will try checking voltage to that plug with a meter to see if there is zero or just insufficient voltage for the motor.
I'll also try moving the stick more gradually.

[Tiger6]

Have you tested by plugging the motor into the elevation lead and vice versa? Not sure how the circuit is set up, but its possible that the motor is controlled by a pair of transistors - one driving one way, and one the other, and one of them is faulty... (in that case a cheap RC truck esc could be hooked up in place of that DMD channel if there was no other solution)

Also have you checked the motor with the turret removed to eliminate any possibility of binding?

Starting to scrap the bottom of the 'possible cause' barrel here...

[Harry Serpent]

I had this problem with my Tamiya JS-2 turret rotation unit
And just replaced it with a new one
Tamiya have a Quality control problem

[DonCarlos]

I tried swapping over the gun elevation and turret rotation connectors, as suggested. Good idea!
Guess what? The turret work fine both ways when I used the gun elevation stick, but the gun would only go down and not up. To me, that shows it has to be a DMD problem. I'm pursuing it with the Tamiya agents in the UK as a warranty problem. Worst case I can leave them swapped over as turret rotation is a more useful (or impressive?) function than gun elevation, but that seems a shame on a new kit that originally retailed for £970! Thanks for the suggestions.
BTW, I'm already thinking I need lower geared drive motors for a nearer scale speed. It accelerates way too fast...and top speed is crazy. What would a real KV-1 do? 30 kph maybe? That's 2 KPH roughly for the model. Oh dear. Slippery slope...

[silversurfer1947]

It might be worth contacting the vendor that you purchased from.

[General Jumbo01]

£970 Tamiya toy! Said it before but I'll say it again. If you want hobby grade models you have to pay and buy a Henglong

Okay, just joking but things really have moved on in our hobby with maybe Taigen moving the boundaries first forcing HL to follow. Still like Tamiya's 1/16 tank crews though.

Sounds as though you've cracked your turret problem. That's good news.