Servos and brakes

[Graham P Hough]

Just a warning to those like me who didn't read the instructions properly, the manual gives a clear image on how to fix the brake arm to the servo, I did it wrong and burnt out a servo.
Also does anybody who knows these things know if the Caunter Scheme would be appropriate for my UC? I want to paint it desert colours anyway to match my 25pdr.
Also I expect many have passed this stage but I have had to remove the back plate that the tow bar is fixed to, inorder to remove and refix the rear drive unit.
I do love this kit congratulations to Monique and Kian and their team for an excellent model, I just wish I had read the instructions properly

[Dennis Jones]

I also had to remove drive unit with back plate in place but when I reassembled it I drilled a small hole in the drive sprocket level with the screw holes and then reversed the fixing bolts so that the nuts were on the inside and an allen key can be inserted through the hole, makes fixing easier and the cap heads can't be seen anyway as they are behind the drive sprocket.

Dennis.

[Graham P Hough]

So what am I doing wrong? I have burnt out two servos so far trying to get the brakes working. Can some kind person spell it out, as if you were talking to an old person like me, how to set them up. Do the link pieces have to be able to move in the slot? Please explain setup before I loose it even more.

[Armortek]

So what am I doing wrong? I have burnt out two servos so far trying to get the brakes working. Can some kind person spell it out, as if you were talking to an old person like me, how to set them up. Do the link pieces have to be able to move in the slot? Please explain setup before I loose it even more.

Before the servos are installed, they should be powered up so that the servo arms can centre. If you do not do this then the servo will always be under strain and will have a significantly shorter life.
To do the above - the easiest thing to do is to bench test the electronics - as part of that the servos will be central.

Once that is done then the servos should be installed WITHOUT moving the servo arms. This position will be the un-braked position. Activating the servo in either direction will now either push the pad onto the disk or pull it back slightly.

What you should also do (on your transmitter) is limit the travel of the servo. Because the connecting rod needs so little travel before engaging or retracting the brakes you do not need the full range of servo travel. Normally the travel of the servos is set to 100%, but you can probably reduce this to 40-50%. Will need some experimentation depending on your transmitter.

Finally, once set up, and you are doing your tests, frequently check is the servos are getting hot - if they are then they are under strain and will have a shorter life.

[Graham P Hough]

Thank you for the advice I will do that.

[David Merritt]

I have just powered up my system to set up the servos for the brake steering and reading all of the posts on the subject decided give the servos more movement and see what happens.

I replaced the two nuts holding the servo arm extension ER1609 with nylock nuts and tightened them just tight enough to allow the extension to swing in the slot and then installed the servos as per the instructions, ensuring that the springs could retract the brakes easily.

I then powered up the system and everything worked well. The holes that the servo arms pass through are sufficiently large to allow the increased movement of the servo arms without fouling and the free play in the servo arm increases the dead band through which the servos operate and with a little bit of adjustment of the attachment of the arm to the servo it was possible to enable the idle servo to still be operating in the dead band when the other servo was applying the brakes so no load was on the idle servo.

This change has increased the available servo movement by over 100% but does require the spring to retract the brakes as the servo will no longer do this due to the free movement of the extension arm on the servo, it can only apply pressure to the brake.

I hope this is clear if not please let me know and I will try again to explain what I have done.

David