RCCrawler Forums

pantablo · 07-19-2008, 01:21 AM

I have an issue with the servo action...
YouTube - why is servo doing this to suspension?

why does it do that to the suspension. turning to the left (viewers right) it pulls the suspension down. turning right pushes it up.
WTF?

also note I tipped the servo so that the leading edge is lower than the back and also the servo horn is bent/angled a bit too...

Mnster · 07-19-2008, 01:30 AM

The steep angle of the steering link is doing it. The more level you can keep that link the better off you will be. Doesn't matter if the link is bent like that the motion is still transfered just the same.

If that isn't fixable a panhard link at the same angle would cancel it out. Of course at such a steep angle a panhard link may cause lots of unwanted suspension shifting.

pantablo · 07-19-2008, 01:39 AM

so the ideal solution is to bring the servo down so that the linkage is more level with the axle, right?
I can try that.

If I need to do a panhard I keep the same angle between the steering linkage ends and connect the panhard from axle to chassis, correct?

btw, thanks!

Mnster · 07-19-2008, 01:47 AM

Correct

Similar angles would be best.

pantablo · 07-19-2008, 02:01 AM

does the panhard need to be the same length rod end to rod end or just the same angle?

thanks again!
and btw, that build Jim did was so inspired. its the reason I narrowed my tlt's too.

Mnster · 07-19-2008, 02:09 AM

It's better to have the same or close to the same length of rod.

It basicly allows the suspension to compress and the tires stay straight. Otherwise when the suspesion is compressed the tires will turn slightly. (bump steer) It's not a enormously huge issue for crawlers cause we go so slow.

Thanks

pantablo · 07-19-2008, 02:36 AM

is it going to prevent my suspension moving up/down like it is though? If not I may have to rethink the shock setup.:-(

Mnster · 07-19-2008, 02:59 AM

The axle will swing with the panhard link. Doesn't limit the the up/down travel much at all if properly done. The suspesion should resist the side to side up down motion as now the frame has something to press against. Put it this way you will get much better transfer of firm servo power.

The stiffing the suspension and that the guys on scale 4x4 were talking about is mostly just a bandaid for the problem, although that would also help the up down.

Another idea is to increase your link triangulation as it would reduce the side to side steering slop motion. Like I said though panhard is your best bet.

Difuser · 07-19-2008, 08:59 AM

PT is you have done Delrin links you should have had to do similar to keep axle wrap in check. The force from the servo is taking the path of least resistance and that is to move the chassis. That and all the exellent comments from Mnstr.

I have built a "saddle" over the pumpkin using the top 2 holes on the TLT axle and used that as the tie-in point. You can use 2 of the TLT stays one on the chassis one on the saddle. I like to center mine up but it is not critical. I don;t have a great pic of it but if you look at the butt shot of the Brat you can see the saddle. Look to the left end of the chassis and you can see the post coming from the lower frame rail. This was for axle wrap but you get the idea

07-19-2008, 01:21 AM	#1
pantablo I wanna be Dave Join Date: Aug 2007 Location: santa monica Posts: 3,687	servo/chassis issue-please help I have an issue with the servo action... YouTube - why is servo doing this to suspension? why does it do that to the suspension. turning to the left (viewers right) it pulls the suspension down. turning right pushes it up. WTF? also note I tipped the servo so that the leading edge is lower than the back and also the servo horn is bent/angled a bit too...

07-19-2008, 01:30 AM	#2
Mnster MWRCA'er Join Date: Apr 2004 Location: Machesney Park IL Posts: 3,995	The steep angle of the steering link is doing it. The more level you can keep that link the better off you will be. Doesn't matter if the link is bent like that the motion is still transfered just the same. If that isn't fixable a panhard link at the same angle would cancel it out. Of course at such a steep angle a panhard link may cause lots of unwanted suspension shifting. Last edited by Mnster; 07-19-2008 at 01:32 AM.

07-19-2008, 02:09 AM	#6
Mnster MWRCA'er Join Date: Apr 2004 Location: Machesney Park IL Posts: 3,995	It's better to have the same or close to the same length of rod. It basicly allows the suspension to compress and the tires stay straight. Otherwise when the suspesion is compressed the tires will turn slightly. (bump steer) It's not a enormously huge issue for crawlers cause we go so slow. Thanks Last edited by Mnster; 07-19-2008 at 02:13 AM.

07-19-2008, 02:59 AM	#8
Mnster MWRCA'er Join Date: Apr 2004 Location: Machesney Park IL Posts: 3,995	The axle will swing with the panhard link. Doesn't limit the the up/down travel much at all if properly done. The suspesion should resist the side to side up down motion as now the frame has something to press against. Put it this way you will get much better transfer of firm servo power. The stiffing the suspension and that the guys on scale 4x4 were talking about is mostly just a bandaid for the problem, although that would also help the up down. Another idea is to increase your link triangulation as it would reduce the side to side steering slop motion. Like I said though panhard is your best bet. Last edited by Mnster; 07-19-2008 at 03:08 AM.

07-19-2008, 01:39 AM	#3
pantablo I wanna be Dave Join Date: Aug 2007 Location: santa monica Posts: 3,687	so the ideal solution is to bring the servo down so that the linkage is more level with the axle, right? I can try that. If I need to do a panhard I keep the same angle between the steering linkage ends and connect the panhard from axle to chassis, correct? btw, thanks!

07-19-2008, 01:47 AM	#4
Mnster MWRCA'er Join Date: Apr 2004 Location: Machesney Park IL Posts: 3,995	Correct Similar angles would be best.

07-19-2008, 02:01 AM	#5
pantablo I wanna be Dave Join Date: Aug 2007 Location: santa monica Posts: 3,687	does the panhard need to be the same length rod end to rod end or just the same angle? thanks again! and btw, that build Jim did was so inspired. its the reason I narrowed my tlt's too.

07-19-2008, 02:36 AM	#7
pantablo I wanna be Dave Join Date: Aug 2007 Location: santa monica Posts: 3,687	is it going to prevent my suspension moving up/down like it is though? If not I may have to rethink the shock setup.:-(

07-19-2008, 08:59 AM	#9
Difuser RCC Addict Join Date: Oct 2007 Location: Auburn Posts: 1,007	PT is you have done Delrin links you should have had to do similar to keep axle wrap in check. The force from the servo is taking the path of least resistance and that is to move the chassis. That and all the exellent comments from Mnstr. I have built a "saddle" over the pumpkin using the top 2 holes on the TLT axle and used that as the tie-in point. You can use 2 of the TLT stays one on the chassis one on the saddle. I like to center mine up but it is not critical. I don;t have a great pic of it but if you look at the butt shot of the Brat you can see the saddle. Look to the left end of the chassis and you can see the post coming from the lower frame rail. This was for axle wrap but you get the idea

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Thread: servo/chassis issue-please help