Hotrod

[copperhead]

I have seen some wonderful suspension setups on this list and I have a
question to anyone with experience building/using them (or anyone with
2c. they want to chip in).

I want to build a fast tank. I am in the process of reassembling the
gear boxes for my m-5 Stuart because it is too slow.

I want to make a robust chassis for an M-18 and wonder if running a
solid suspension (ie no suspension - axles attached directly to
chassis) would be acceptable.

I am under no illusions about firing on the move. I just want to be
able to move fast without throwing a track.

The tank will weight between 20 and 40 lbs when it is done.

Thanks,
martin h

[Steve Tyng]

How fast is fast?

Steve

[Susan Gutbrodt]

I would guess that fast is determined by how young/fit you are........

Kurt (old & semi-crippled, so slow is fast) G

[Paul Hilton]

I would think that a solid drivetrain would be less likely to throw a track
than a suspended one. As a matter of fact, I don't know if anyone has used
an actual suspension. This is not an easy thing to do. I'm quite sure that
most of the completed vehicles have, at best, a simulated suspension. By
simulated, I mean that the sprung portions are bottomed out in one direction
or the other. Either the vehicle rides on its stops untill presented with a
low spot, or it rides on its stops untill it encouters a high spot, if it
has springs at all. There are several that have pivots without springs. In
order to have a true suspension, the total sprung weight of the vehicle must
be known. I've found that this is a tall order to fill. One must build the
entire unsprung portion of the vehicle, weigh it, then determine the
strength and rate of the springs to be used. In a small vehicle (yes, a
1/6th scale vehicle is small), any difference in weight can cause your
"suspension" to bottom out in one direction or the other. J. Walter
Christie, in his original patents, stressed the need for some means of
adjustment to the springs to compensate for a change in the weight of the
vehicle. From my experience with the BT-7 suspension, I say build it a
simply as possible. You can always add a suspension later.

20 to 40 lbs seems awful light, Martin. My BT-7's wheels weigh 35lbs alone.
I've estimated a sprung weight of 100lbs for a 3ft tank with an unsprung
weight of 50 lbs (wheels and tracks). You may want to recalculate your
weight. I'm sure my batteries weigh more than 20lbs.

Paul H.

----- Original Message -----
From: "copperhead" <martin....@earthlink.net>
To: "R/C Tank Combat" <rctank...@googlegroups.com>

[George Mastoras]

My 2 cents on the topic would be to firstly establish what terrain you want
to go fast over. I would suggest firstly know what environment you want it
to work in and then work on a solution to achieve it.

George

[Cold comfort]

Hi there Paul, I am not sure I understand your definition of
suspension. I feel that all suspensions have a bottom out in both
directions. Altough I have not presented my tank here yet for
designation, it has a spring suspension like many I have seen on here,
and rests on spring tension alone, there are no mechanical stops at
all. The wheels will go up until the tank is resting on its bottom
hull, inversely if lifted up the wheels will hang and even pulled down
to the max length of of pivot arm. A nut on a bolt increases or
decreases resistence of the spring. Reading this post has given me
some food for thought, perhaps I should put in some kind of mechanical
stop so if ever the case should arise it wont bottom out on its hull.
Its seems unlikely put it could happen in theory. I haven't used any
calculations yet to figure out tension and such, as I add weight to
the tank I increase resistance on the springs or replace with larger
springs if its needed, in that area until the tank is level again and
at the clearence I want.
On another note, I personally have been trying to reduce the speed of
my tank to be porportional to the actual speed of the real tank. While
I find it really neat to watch Chris's tank videos and how fast his
tank is, I believe he has said that it is porportional to the real
thing. Watching say a tiger go this fast makes it look more toyish and
if all tanks on the battle field were flying around at cyber speed it
would lose a lot of appeal for me.

Greg

> > martin h- Hide quoted text -
>
> - Show quoted text -

[Chrysanthos Kanellopoulos]

Greg,

I had thought, when I first visited this website, that suspensions are an
overkill.

They make a huge difference, trust me. The vehicle runs smoothly, you can
climb obstacles no problem without overheating your motors, teh shocks on
the paintball gear and all are reduced considerably . IN order to cut
corners I devised bell crank suspensions in pairs, for all of my tanks,
although the original tanks did not emply this type of suspension. They
can't be really called active suspensions, like those that have springs, but
they work just fine for me. Bell crank type suspensions have been used by
other modellers in this list, before me. I am just passing you my own
experience. The track itself becomes teh spring.

See the first, black and white photo of:
http://www.rctankcombat.com/tanks/T052/

Chrys

----- Original Message -----
From: "Cold comfort" <gfc...@hotmail.com>
To: "R/C Tank Combat" <rctank...@googlegroups.com>

Sent: Tuesday, July 22, 2008 3:28 PM
Subject: [TANKS] Re: Hotrod

>

> __________ NOD32 3287 (20080722) Information __________
>
> This message was checked by NOD32 antivirus system.
> http://www.eset.com
>
>

[copperhead]

Thanks for the input everyone.

The trade off between tracks staying put (solid suspension) vs
traction + drivetrain strain ("semi-suspension") is an interesting
tradeoff.

For the record, the semi-suspension that is used on some of the tanks
on the list is what I was thinking of when I talked about tank
suspensions ... "Fast" = I want to drag race Steve T's Cromwell when I
(eventually) make it up to Maryland :-)

I think I will build the tank with the wheels mounted solid and see
how it handles and then go from there.

The Hellcat is a cool looking tank but at 40/2, I will have to do the
same that the real tank did - hide and run.

- Martin



On Jul 22, 9:42 am, "Chrysanthos Kanellopoulos" <xchr...@otenet.gr>
wrote:

> >http://www.eset.com- Hide quoted text -

[Derek Engelhaupt]

Creating a working suspension was a difficult task for my non-math
oriented brain. Rather than rely on any calculations of any kind, I
guessed and guessed wrong in most cases. The final suspension on the
Sturmtiger is a mix of different spring rates and an almost solid rear
boggies. The last boggie set has less than 1/2" of suspension, but
will move forward (down) as needed. The biggest problem was guide
teeth in my opinion and not sprung or unsprung wheels. Since the
idler on the Tiger/Sturmtiger is so large, I had issues of the last
boggie wheel pushing up on the track causing the tracks to "derail".
After adding the guide teeth and making the rearmost boggie
semi-solid, the tracks seem to be fairly reliable now. I'm going to
take it out again soon to abuse the system a little more.

Derek

[Steve Tyng]

It's funny how these discussions start repeating themselves after
awhile.

http://www.rctankcombat.com/archive/2007-02/msg00121.html

Steve


PS: Frank, the Google search on the website is not picking up the old
archives. I found the above link on a Google cached archive search
page.

On Jul 22, 1:53 pm, "Derek Engelhaupt" <tan...@gmail.com> wrote:
> Creating a working suspension was a difficult task for my non-math
> oriented brain. Rather than rely on any calculations of any kind, I
> guessed and guessed wrong in most cases. The final suspension on the
> Sturmtiger is a mix of different spring rates and an almost solid rear
> boggies. The last boggie set has less than 1/2" of suspension, but
> will move forward (down) as needed. The biggest problem was guide
> teeth in my opinion and not sprung or unsprung wheels. Since the
> idler on the Tiger/Sturmtiger is so large, I had issues of the last
> boggie wheel pushing up on the track causing the tracks to "derail".
> After adding the guide teeth and making the rearmost boggie
> semi-solid, the tracks seem to be fairly reliable now. I'm going to
> take it out again soon to abuse the system a little more.
>
> Derek
>
> On Tue, Jul 22, 2008 at 10:04 AM, copperhead
>

> >> >http://www.eset.com-Hide quoted text -

[Steve Tyng]

Paul Hilton wrote:

> I would think that a solid drivetrain would be less likely to throw a track
> than a suspended one.

I've thrown track on the Cromwell exactly twice. The first time I was
doing a neutral turn on top of a pile of bricks (several guide teeth
broke off, since then have been reinforced). The second time was
right after a battle. I was towing my supplies back (extra batteries,
paint, water, etc.) with the Cromwell (pulling a little trailer just
for that purpose) when I made a quick turn and a track popped off. In
the first instance it's obvious the bricks were to much for the
system. In the second instance, I think dragging the loaded trailer
across the field had bottomed my suspension (thus a loose track) and
during the turn the track probably caught a rock or clump of grass
that redirected the track off the rear sprocket.

The point I'm trying to get at is that a well designed track will stay
on most of the time whether it's a solid suspension or not. And what
I mean by well designed is as large a guide tooth you can make work
and a rigid track (minimal side flex and twist).


Steve Tyng

[copperhead]

Thanks for the link Steve.

I remembered a post from last year but couldnt find it.

- martin

[Steve Hersey]

On Jul 22, 6:56 pm, Steve Tyng <Steve...@gmail.com> wrote:
> It's funny how these discussions start repeating themselves after
> awhile.
>
> http://www.rctankcombat.com/archive/2007-02/msg00121.html
>
> Steve

Rereading that post, something occurs to me about bottoming-out the
suspension vs fixed bottom limit stops. I'm not convinced the idea I
have in mind is a GOOD one, so I'd like your experienced feedback.

The thought that occurs to me is this: instead of lower stops, set the
springs on all roadwheels to be stronger than needed to hold the
vehicle at the midpoint of suspension travel. Then, shorten the track
so that it is fully tensioned at the midpoint of suspension travel.
Thus, on a level surface, the springs would be strong enough to raise
the chassis further, except that the tension of the track holds the
chassis down. In effect, the track tension provides the lower limit
stop for the roadwheels as a group. The track should still adapt to
bumps or potholes, but the chassis can't bounce. In addition, the fact
that the extra-strong springs keep the track tensioned should help
keep it from being thrown.

So much for the theory; does anyone have any real-world experience
with this method? It's not a purely theoretical question, as I'm
getting close to finishing Sancho Panzer's drive sprockets and idlers,
which will be followed by TTS track fabrication and installation, at
which point I will need to set-up the torsion springs. At that point,
I may be able to report some experience of my own on this point...


-- Steve H.

[Frank Pittelli]

Steve Tyng wrote:
> PS: Frank, the Google search on the website is not picking up the old
> archives. I found the above link on a Google cached archive search
> page.

I'll take a look and see why Google isn't behaving as expected. All the
messages are still there, so I can always put the local search back
online if necessary.

Frank P.

[Doug Conn]

This is pretty much how my tank's suspension works. I do have stops, but
they are to prevent the suspension arms from rotating too far forward under
some conditions (like reversing over bumpy terrain). The tank doesn't rest
on the stops.

I have the occasional track throwing problem. I'm addressing it by
increasing the track tension, making a better fit between the road wheels
and track, and adding more rugged adjusters to my torsion springs. Some
people in the forum have warned against track tensioning because they
believe it will lead to inefficient drive. There's probably such a thing as
an 'over tensioned' track, but I think it's a pretty extreme case.

- Doug

------------------------------------------

[Odyssey...@aol.com]

In a message dated 7/22/2008 6:57:07 P.M. Eastern Daylight Time, Stev...@gmail.com writes:

It's funny how these discussions start repeating themselves after
awhile.

http://www.rctankcombat.com/archive/2007-02/msg00121.html

Steve

PS:  Frank, the Google search on the website is not picking up the old
archives.  I found the above link on a Google cached archive search
page.

 

it's like teaching at a school, same subject, different class of students - asking the same questions that and I (or someone) might pick up on something overlooked before

---

Get fantasy football with free live scoring. Sign up for FanHouse Fantasy Football today.

[George Mastoras]

> Rereading that post, something occurs to me about bottoming-out the
> suspension vs fixed bottom limit stops. I'm not convinced the idea I
> have in mind is a GOOD one, so I'd like your experienced feedback.
>
> The thought that occurs to me is this: instead of lower stops, set the
> springs on all roadwheels to be stronger than needed to hold the
> vehicle at the midpoint of suspension travel. Then, shorten the track
> so that it is fully tensioned at the midpoint of suspension travel.
> Thus, on a level surface, the springs would be strong enough to raise
> the chassis further, except that the tension of the track holds the
> chassis down. In effect, the track tension provides the lower limit
> stop for the roadwheels as a group. The track should still adapt to
> bumps or potholes, but the chassis can't bounce. In addition, the fact
> that the extra-strong springs keep the track tensioned should help
> keep it from being thrown.
>
> So much for the theory; does anyone have any real-world experience
> with this method?
>

> -- Steve H.
>

My very first tank, a T34 was done with a similar method. In my case the
reason I did something similar was because I did not have any method to
tension the tracks and I didn't have any guide horns so the spring tension
on the arms had to account for the weight of the tank when stationary as
well as the track tension. Had to set it a few times before it was right but
it does work. As soon as the tank moved tension was released so had to start
with some extra tension on the tracks.

My first tank was half the size of your tank so I just put the tank on its
back and pressed down the arms to loosen the tracks and then connect the
tracks up, when released they would tighten up, when put on the ground the
weight of the vehicle released some tension and it worked fine after that.

My first track used bike chain, rubber blocks and bolts so it was fairly
easy to break and join it at any point, with a TTS you will need to be able
to get the track on and then tension up the springs from the inside, I
didn't have that luxury at the time.

I also remember that rather than adding stronger springs I set the arms in a
lower position to increase the tension. There is probably a few ways to do
this but you will probably have to experiment a few times to get it right.
Just remembered also that I had used double the springs on the first and
last road wheels, these where the most important in hindsight to stop some
of the dipping and they sort of acted as shock absorbers. This also allowed
me to have softer springs on the middle wheels.

George (Its fiddly but do-able)