Servo Operation

[Trailbiker]

Can someone please help me with the operation of servos. I'm having trouble getting the recoil on my Leopard 2 to work properly. I know how far I need the barrel to move (15mm approx.), but can't seem to get the movement of the servo to get this right. Have tried different arms and different positions but still it won't work properly. Have managed to write off two small servos and one recoil mechanism so far, so not doing very well ! I have videos/photos of other peoples Leopard 2 recoil working, but can't understand why mine won't. The new servo I've just bought is a Hi-Tec HS 311, which is identical to one in a photo I have from the net, but my one rotates the other direction to this, so I can't fit it exactly as per the photo. Can the direction be reversed, or do you have to just turn the servo around the other way ?
Still struggling with all this "model making " stuff.
Thanks for any help, Richard

[MichaelC]

Richard, what electronics are you using? If you are using Clark boards you just need to change the programming and switch the direction of the servo.

MichaelC.

[Tankbear]

Hi Richard you change the direction in the ibu2.ini file on the microsd card.

Regarding seeing other peoples recoil working are those the tamiya leopard? I don't think heng long have made a recoiling leopard.

Ian.

[MichaelC]

Ian,

HL doesn't sell one out of the box but the BB one is very easy to convert with the same barrel. Its almost like they made it so that if they need to do they just need to replace the BB unit with their recoil unit and then it is done. Here is mine with the HiTec 311 servo and also a little video. No mode what so ever on the barrel as I even use the BB as a frame.

https://www.youtube.com/watch?v=b0zatMuPQW4

MichaelC.

[Trailbiker]

Michael thanks for that. The photo and video are the ones I've copied and was using. That's where I got the idea of using the same servo as the one shown, but obviously yours in going the other way. So far I've managed to bugger two servos and one recoil unit, which I cut up. I'm now on my second recoil unit and this one isn't looking too healthy now either. I can't seem to get the movement just right. My HS 311 has a rotation of about 100 degrees approximately, certainly more than 90. It's converting this rotation into a straight forward linear movement that seems to be not working for me. I already filed out the mantlet for the barrel to slide in and out of, and then found somewhere on the net (may have been on this website) that someone had filed the flat on the barrel down further, and this stops the barrel from rotating. Mine has to rely on the BB recoil to keep it in line. Everytime the servo seems to pull awkwardly and jam it up. Another video I've seen, which seems to work really well, appears to be using a Tiger recoil unit, and not the one fitted to the Leopard. So long as you've got the tab for the gun elevation in the right place, I guess you can use any one.
How did you attach yours to the side ? I can't see any evidence of anything holding it on ?

[MichaelC]

Richard,

If you are ruining servos, I have couple of tricks that you can try. First of all, it sounds like you are using the frame of the BB, so you shouldn't have to worry about rotation pull since the BB piston is already secured linearly. Second, I love HiTec HS-311 but it is a large servo with tons of travel, so you really have to make sure that there is actually enough room in the BB frame for the servo pull otherwise you will kill the servo. Couple of things that you don't see in the picture but has to be done, one is you have to clear more space for the BB piston travel than what is in the cam. In otherwords, clear out as much travel as you can for the piston from the BB frame. At a minimum you will have to remove the "fin" from the piston that the BB unit has the spring hook up to. Second, you will need to clear the forward space of the BB unit so that the piston with the BB tube actually goes into the forward part of the BB frame (It does not if you don't enlarge the BB tube opening). I am assumming that you are keeping the BB aluminium tube so that you can attached the barrel, and that should be pushed into the BB piston and go in as much as can into the BB frame.

Another trick I do is that I don't attached the servo permanently for testing. I use a C-clamp and clamp the servo to the side of the BB frame for testing. This way if anything goes wrong I will know right away (servo direction, servo travel, linkage rod issue etc) and it won't rip anything apart, servo or otherwise. Once I get the right position, travel, angles of the linkage arms and servo pull arms etc, I then superglue it to the side of the BB frame. BTW, I also have to clear some plastic off the bottom of the turret so that the servo and the servo swing arm would clear it. You would only need to do this if you are using HS-311. If you are using micro servo you would be fine. If you don't it will either block the servo arm when you put the turret back together, or stop the elevation as the HS-311 won't clear the bottom of the turret.

The other thing that I know would kill the servo would be the wrong swing/linkage arm angle. If it is too wide you wouldn't get enough torque to push back and it will end up deflecting the angle outwards. I think if you can use mine as a reference you should be okay. The swing arm at rest is 90 degrees and the servo back is lined up with the back of the BB unit. You just then need to figure out the right length for the linkage arm so that you get the 90 degrees with the BB piston at the most forward position.

There is many ways to do this and I find this is probably the simplest since you don't have to deal constructing the frame, but using HS-311 is more difficult in my opinion as it is a large servo and has more travel, but I personally preferred it as it seems to be a tad slower and hence more realistic and I like long travel recoils.

Good luck. If you have a chance post some pictures and maybe I can give you more pointers along the way.

MichaelC.

[Trailbiker]

Michael, thanks for the info. The first two servos I used were micro ones, but with a pull of around 1.5 Kg, which I thought would be enough for the recoil. Because I spent so much time fiddling about with the first one, I managed to pull the insulation away from the wires inside it and hence caused a short circuit, which made the IBU board heat up and smell ! I tried to re-solder the wires onto the small pcb, but it was too difficult for me. The second one worked ok, until I reprogrammed the servo time for the firing. It was set a 4 seconds, which meant the gun barrel stayed in the mantlet for ages before it returned. It seemed to work fine when I tested it and put it all back together and ran it around my garden. Then it stopped working and when I looked at it, it appeared I'd burnt the motor out. I ordered two of the HS-311's as I had seen from your picture and was rather surprised when they dropped through the letterbox. I hadn't realised how big they were !
What I have done with the mantlet, is, to file a hole so the barrel slides in and out. I've put an extension rod on the back of the barrel, as it didn't reach the plastic piston properly. I've put the rod over the piston protrusion flush with the end, and the piston sits up against the end of its travel, before any movement backwards. The piston slides in and out of the BB casing and the grooves keep the whole lot from rotating. I've cut the tag off the piston, as you've suggested, and it travels the full length of the BB housing. The micro servo I was using, I fitted in the side of the BB housing, by cutting and filing a round hole. I thought that if the arm was inline with the centre of the piston, the pull/push would be linear and no twisting would occur. I now have a hole that is redundant and has further messed up the housing.
Thanks for the tip regarding clamping it on, until you know it's working properly. That's just the sort of help I need, as that hadn't occurred to me.

[MichaelC]

Richard,

Sounds like you are doing all the right things. If it helps I can post a video of the servo in motion and you can see how it works. It also sounds like the IBU has more options so it might be different than mine which is Clark. I cannot change the recoil timing or the recoil pull distance.

Michael.

[Trailbiker]

Michael, if you could post a video, that would be very helpful, thank you. I've been holding the servo in the position you have yours, and gauged that the arm will move a lot more than the 15mm I require, which will lead to it jamming. I need to clamp the servo to something and measure the distance the end of the arm moves, and then I can work out how to get it to move only 15mm for the recoil action. Judging by the fact it moves through more than 90 degrees, I'm sure it's a lot further than that. I think the only way to get the required result is to shorten the actuator rod, but we'll see !
I guess I should also try adjusting the time on the MicroSD card and running the servo without anything attached to see the results. I only guessed how much to reduce the time before, and wasn't really sure if it was the right one. There appear to be 3 different servo times that can be changed.
Richard

[MichaelC]

Richard, here you go. Hope this helps. Doesn't look like mine is moving more than 90 degrees. Perhaps this is something that can be adjusted on IBU ?

http://youtu.be/o9UPVl6qVmA

Michael.