Sd Kfz 7 Sprocket question and partial model rebuild..

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Jeffrey Goff
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Re: Sd Kfz 7 Sprocket question and partial model rebuild..

Post by Jeffrey Goff »

Hi John, I put some rear windows in using soft clear plastic, I also made the detachable side curtains that rolled up and stored inside the seats
77104C49-06D0-4A4A-87B1-95EAF34B8F46.jpeg
Regards Jeff

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John Clarke
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Re: Sd Kfz 7 Sprocket question and partial model rebuild..

Post by John Clarke »

Jeffrey, your gifted like many on the forum 8)
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Jerry Carducci
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Re: Sd Kfz 7 Sprocket question and partial model rebuild..

Post by Jerry Carducci »

I appreciate all the replies gentlemen.

Some of the reasons I was (finally) attracted to 1/6 scale, after years of subtle prodding by Per Sonnervik and even Jacques Littlefield to go large(r) was that I came to realize that 1) there be amazingly talented modelers here who I can aspire to be half as good as 2) there's an after market of bits that is very impressive unlike that in smaller scales. The freedom of not having to make every last bit is wholly refreshing..

I fight the modeler's guilt of how many bits from others can I use and still claim "I made it myself". I think the older I become the less I wrestle with that. In my other long standing interest in 1/10 scale, the 3D printer revolution not withstanding, I had to make mostly everything. I was really only limited by available data, skill and patience. I try fiercely not to be critical of what I've done or risk never being done or worse never attempting a thing at all. Still I know the limits of my patience and skill is tempered by that.

If I can I will attempt to purchase parts for which my model will be adaptable. We'll see. I do like to see steady progress.

Jerry
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Jerry Carducci
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Re: Sd Kfz 7 Sprocket question and partial model rebuild..

Post by Jerry Carducci »

Having done most of the modifications that I've wanted to do I reassembled the model complete with electronics, batteries and had a go running the old girl in my yard.

Steering was atrocious. There's a tendency to execute a neutral turn if the control isn't approached carefully; if impatience takes over. I made a tactical
error of trying to execute a turn through an area from which I recently had a large tree removed making the ground in that area essentially mulch. Years ago while at an event wherein i ran multiple models from my collection I had occasion to run in a large planted area that was essentially mulch whereupon I broke the only track link I've ever broken in my entire time in this hobby. So bad idea. Still even on hard cement steering was unpredictable at best. Clearly the steering servo was not up to the task. I'd read about it but thought, "how bad can it really be?"

Some folks ask why I don't do more weathering. Well even though I consider myself a fairly experienced model 'driver', weathering just has a way of happening on its own... id est when driving back into my garage the combination of touchy steering and no very 'grippy' tracks caused a glancing encounter betwixt model and garage door...instant weathering.

Once I got the model back on the lift table I decided to take a look at this steering business. I first dismounted the wheels to examine the spindles and control linkages, considering what had been said in the previous forum thread on this model's steering assessment. It dawned on me that the steering on this model had been installed upside down originally and before paying attention I'd just followed that lead. Based on what I did next I beginning to think the inverse installation was on purpose to avoid some of the interference issues I see. I took it all apart and proceeded to remove the steering servo. I found it to be a Sanwa SRM-102 which I discovered has a torque rating of about 41.7 oz-in /3 kg-cm. Pretty anemic, I have low end Futaba servos from the 1980s with greater torque. I decided to dive into my servo collection of which there are many and I selected a Savöx Sa-1231SG which has a torque rating of 444.4 oz-in/ 42 kg-com. It should be an improvement. It required that I do a bit of machining on the servo mount and make a new interface arm to replace the brass one that's part of the kit- I just made a new one of the same thickness brass to conform to the hole spacing of new aluminum servo horn (arm) that I used on the new servo.

Next I looked over the steering linkages. Nothing here seems to really work in harmony, at least on my model. Depending on how bits are set up there's interference between the components. I haven't ruled out that they've been modified over the years but not having new parts to compare I can't say. I spent some time making new arms of different lengths and mounting the ball joints one way then another and there always seemed to be some interaction/ interference that would hinder or make the steering unreliable. In the end I used the supplied parts as a best compromise but with various 5mm shim washers ( .1- .3mm) to help with their relative positions. I haven't read of others have this sort of difficulty so I'm sure it's just me.

The troubles were compounded by an issue I discovered on the left hand side of the axle. The spindle mounting, through which the king pin passes was terribly loose and could rotate at leas 5-6 degrees and I know that shouldn't be. It appears that the original method of fixing this brass piece was to use a tiny rivet pressed or driven in and held with Locktite. Clearly this didn't stand up as the rivet was badly mashed and loose to where I easily pulled it out by hand. The hole from which it came both in the brass mount and the steel axle tube were somewhat deformed, enlarged. I looked about for a
cure for this that didn't seem too extreme and I chose an SAE 2-56 screw. The existing hole was a bit large but I ran a 2-56 tap in it and installed a steel screw to replace the rivet. I can see that this isn't a permanent fix but is a little better than as I found it. As it's fairly easily accessible I can revise, refine this at a later date, but now my goal is to get this running again.

Having reconnected everything I tried the new servo and immediately it let its presence be known. The servo mount came loose! I realized I hadn't fully tightened everything down properly. I haven't yet tried it in the 'field' but I have to believe this will be an improvement although I still am of a mind that attempting to move these great big tires in place without moving remains a bad idea. When I tested it previously I had been using a 3 channel mix to control this servo without any direct interface defined- it only responds to what the tracks are doing. I think I will be tinkering with the two drive channel outputs for the tracks think that somewhere around 75% of maximum might be better and I think a standard proportional output curve for the steering is best.. This model doesn't look good in jackrabbit starts, turns and the like. Slow and majestic is the order of the day.

I've a ways to go yet.

Jerry
Attachments
tired old rivet and replacement screw.
tired old rivet and replacement screw.
The rivet replaced with a screw
The rivet replaced with a screw
One of the experimental (shorter) arms I made
One of the experimental (shorter) arms I made
Old and new servo
Old and new servo
New servo installed and replacement brass arm.
New servo installed and replacement brass arm.
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Jerry Carducci
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Re: Sd Kfz 7 Sprocket question and partial model rebuild..

Post by Jerry Carducci »

I wrestled with the steering on the model more than I would have expected. I did end up brazing the ctrol arms to the spindle on the left side.
The new servo has more than enough power to move the front wheels with purpose or break something I have no doubt. I have a Tonegawa- Seiki servo
but I can't imagine having to use it. Put another way if the servo I just upgraded to ever doesn't have the ability to turn the wheels then I'm not doing something right or something has let go somewhere... The turn radius of these things isn't small and I refuse to resort to a 'neutral' turn with a halftrack; that's just wrong...

I'm not happy with the engine compartment side panels. I'd sealed the screw holes early on and riveted the louvered sections to the steel panels at that time. I'd hoped magnets would retain these to give a clean look but then didn't. I think my aversion to cutting into body panels prevented that solution from working well. I resorted to (ugh) screws and I hate it. I will have to rethink this.

In the meantime I had a stab at making the headlights. I began with a piece of thin brass sheet. I used a set of doming punches and block to form the bodies with braised strips as needed. Making the lens rims was the worst part and while they're serviceable I'm not entirely happy with them. I of course want them to function; I plan to use soft while LEDs. After the forming was don and the mountings braised in I cleaned the parts and get them a nickle plate wash. The goal was to be able to polish the inside a bit to act as a reflector. This works ok. I'm using Poocher Mercedes 500 lenses. As they turned out they are nearly identical in size to the solid lead ones that came with the kit so I hope those were close! I painted the lamps this afternoon and I'll install them after the paint cures. Next I'll have a go at making the side (direction?) lamps and driver's searchlight. I'm hoping the smaller lamps will be a bit easier..?

I'm thinking I might want to make better seat cusions.....

That's it..
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S7_07222022_03.jpg
S7_07222022_02.jpg
S7_07222022_01.jpg
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John Clarke
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Re: Sd Kfz 7 Sprocket question and partial model rebuild..

Post by John Clarke »

I always wanted to drive my SdKfz7 like the posted video's you see on you tube. It looked effortless. But not seeing them in the flesh, never quite knew how it was being done.
I'm a lazy driver using single stick on tanks and wanted the same on the half track.
It was possible too get a three way mix on the old transmitter (futaba) using the steering as a slave output. Output percentage of the drive motors was reduced and it all worked well from the single stick.
Not fast and I got a turning circle of around 10 feet, but put it in reverse and the steering wheels went into "the wrong turn" for the direction I wanted to see them go. (Oh dear)
I came to the conclusion that the driving of the half track would need both sticks, steering on one, drive on the other, lots of concentration and thought for local surroundings.
I suppose now it can be solved with the PC based transmitters but I'm not smart enough. And even then not sure that its monoverablity would be that great in small areas.
Still, it's a great model. but definitely no skid turns. :D
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Jerry Carducci
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Re: Sd Kfz 7 Sprocket question and partial model rebuild..

Post by Jerry Carducci »

I took the old girl out for a test drive early this afternoon and I was actually pleased with her performance. Steering was difficult at times but accurate enough for me to be able to maneuver through some very tight spaces and allowed for turns with tracks and wheels in concert well enough to look the part. Reverse is serviceable but steering isn't as graceful and I'm unsure of the tires being in concert with the tracks or if the tracks are even turning in the right direction for left and right turns. The track slips dramatically on pavement in reverse which makes for marginal driving accuracy.

One odd occurrence was on first powering up the model today I discovered that both fuses for the drive motors had blown. These being 40 amp fuses I was concerned. These were as I received the model. I didn't have any 40 amp replacements so I replaced them both with 20 amp versions expecting them to fail quickly but I was able to drive all over my place with no problems. I'd checked for shorts in my wiring and added extra heat shrink tubing at the motor- power lead junctions because those spade connectors had made me nervous from whence I first saw them. Again my rather lengthy,, 20 minute drive went without incident, across my lawn ( I knew enough NOT to make sharp turns on my lawn), dirt, cement, asphalt (I drove across my street) and up my makeshift wooden ramp to my lift table. The track especially on the right side makes an unsettling clatter when making a turn but both do that to a degree but little to none in reverse. I don't see any signs of rubbing anywhere except for some under the mud guards. Track tension is moderate - loose but I think I may remove a link in the near future; I believe both side have a compliment of 54 links.

I wanted to make a video but it's awkward while operating the model and I was actually enjoying running it so phooey on that idea.

I'd wired up the winch and tested it. I need to make a shackle for it. For the time it took to wind up the (2mm) cable on it I was able to cook breakfast, eat it, finish two cups of coffee and read the news.. I need to finish my lamps and focus on those engine room side panels...
The more I look at those seats the more I want to swap them out. And there are a few more details for the dash. How I'll light up all the LEDs....there's still a 'to do' list....
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Re: Sd Kfz 7 Sprocket question and partial model rebuild..

Post by Jerry Carducci »

Just doing odds and ends on the model really. Made the two side marker lights although I didn't make the base as the originals so I might want to revisit those. They are functional with tiny soft white leds in them. Not sure I'll make the spotlight, perhaps. For the headlights I's originally used a pair of plastic Poocher lenses but as others reports these are delivered flat as I imagine they were on the Mercedes car of the period. My first attempt at putting in a slight dome resulted in a damaged lens so that was annoying; the failure occurred where the sprue originally met the part I imagine as this area was under stress. Ultimately I was able to get two lenses with a slight curvature by gently, at least as gently as I was able, heating them with a lower power hot air gun while pulling a vacuum on the opposite side with a small portable cordless vacuum. They'll work. I'd sent off for glass versions from a supplier here but he only delivered un-etched plain glass versions as he's had issues with the service he uses for glass printing/etching. He still owes me a printed set but they'll be just a bit smaller than I need anyway. There are many suppliers of 1mm thick watch glasses on ebay in all manner of diameters. All I need is a way to etch them myself. Having had experience with HF acid I don't really care to go down that path.

I'd been struggling with the engine room side panels. I had two criteria for a solution. 1) no screws 2) no clunky internal latch mechanisms added to the inside. It occurred that what was needed was just enough force to hold the radiator end of the panel up to the radiator housing as the rea of the panels were captured by a bolt head to the rear of the fender. What I came up with is a wonky but seemingly effective way to hold the panels in place that can't be seen from the outside. I drilled to #60 holes at a very shallow angle on the very front of the zinc louver panels. These I used to attach a expansion spring connecting the panels with just enough force to hold them flush. As these are zinc parts I don't know how long they will hold up but if and when the holes fail I'll make a small addition of steel to serve in their stead. Had I thought of this when initially assembling these panels I would have added this at that time. The next time I run the model I'll see how this idea holds up. There it is.

Going to do touch up and have a go at making the right rear brake lamp...

Jerry
Attachments
spring1.jpg
frnt02.jpg
frnt01.jpg
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