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Sidecar: double A-Arm vs swinging arm configuration?

 
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Bandit Bill



Joined: 31 Jan 2005
Posts: 202
Location: Hamilton, Ontario, Canada

PostPosted: Fri Jul 22, 2005 4:17 am    Post subject: Sidecar: double A-Arm vs swinging arm configuration? Reply with quote

Just curious, is there a reason why most sidecars use a swinging arm suspension in either leading or (mostly) trailing link configuration vs an A-Arm suspension design, aside from perhaps the space considerations of the design?

Seems to me that once properly designed, an A-Arm setup would be more tuneable for alignment, and precision of handling due to the axle location never deviating fore and aft with suspension height changes. Is there something i am not getting, in terms of performance/safety considerations?

Edited: for sleep-typing the night before.
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Last edited by Bandit Bill on Fri Jul 22, 2005 2:13 pm; edited 1 time in total
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arbalest



Joined: 01 Feb 2005
Posts: 92
Location: Windham

PostPosted: Fri Jul 22, 2005 12:27 pm    Post subject: A-arm Reply with quote

Not to mention the fact that you might be able to find automotive parts that would work, either aftermarket or OEM. Seems like it would make the engineering a little easier.
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IanJ



Joined: 21 Jul 2005
Posts: 52
Location: Seattle, WA, USA

PostPosted: Fri Jul 22, 2005 5:09 pm    Post subject: Reply with quote

It seems very likely to me that, at least on the sidecar wheel, the double A-arm arrangement would take up a lot of "useful" space, right where you'd normally want to put the passenger seat or cargo area, as low as possible. As I recall, many A-arm designs also have a shock tower that extends above the height of the inboard pivots. A leading or trailing link, on the other hand, takes up much less volume, and that volume is concentrated on the outboard edge of the sidecar, where it doesn't take up as much useful space. I suspect that's why the system isn't in common sidecar use.

Personally, I find the A-arm arrangement much more appealing and elegant, as a suspension system.

I think a reasonably designed sidecar, frame and A-arm arrangement could get around these problems, or at least accomodate them. The "wasted" space taken up by the arm pivots could be extended across the width of the car's body, for instance, and used as a petrol tank. The A-arm system seems like a superior choice for a HP sidecar rig, where performance and adjustability may be valued over ideal passenger comfort/placement or cargo capacity.
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Bandit Bill



Joined: 31 Jan 2005
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Location: Hamilton, Ontario, Canada

PostPosted: Fri Jul 22, 2005 7:16 pm    Post subject: Reply with quote

Thanks for the input on this.

This is similar to my thinking. I'm leaning towards an A-Arm setup, over a swinging arm setup, as the boxed in section for the A-Arm would be well behind the passenger seat. What is behind the seat, is essentially wasted volume considering the use of the sidecar at present.

I need to plan on an auxilliary gas tank location also, so any space remaining - could be used for this purpose.
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swaybar2002



Joined: 26 Jan 2005
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Location: Central Pa.

PostPosted: Fri Jul 22, 2005 10:30 pm    Post subject: Reply with quote

>>>>why most sidecars use a swinging arm suspension in either leading or (mostly) trailing link configuration vs an A-Arm suspension design,<<<

My guess would be simplicity of construction and cost related to profit margin.
Example: Never could come up with any other reason why sidecars , as a rule, do not have the toe in adjustment out at the sidecar wheel instead of having to mess with the mounts.
There is a lot you could do with A-FRAME type suspension. Castor, static camber, toe-in, anti-dive,adjust camber curves..etc. could be adjusted at the wheel. If you wanted a steering sidecar wheel it would be a natural progression too. Complex? Yes ,but the end result may be very nice.
The early Motorvation Spyders had a nice similar suspension but now have 'PROGRESSED' to a simple trailing swingarm.
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Claude Stanley

Founder: Internet Sidecar Owners Klub
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2007
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irondad01



Joined: 26 Jul 2005
Posts: 7
Location: Osceola Mills,PA

PostPosted: Fri Jul 29, 2005 12:33 am    Post subject: Reply with quote

Just a thought but instead of an A arm could you make it a right triangle?That would put the wheel ahead of the pivot point so the pivot would be farther back in the cargo area. Carl
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IanJ



Joined: 21 Jul 2005
Posts: 52
Location: Seattle, WA, USA

PostPosted: Sat Jul 30, 2005 12:05 am    Post subject: Like this? Reply with quote

Are you talking about something like this? This would allow the pivot and structure to be built into the cargo compartment, while still allowing the passenger to sit right about inline with the wheel's axle.

Please pardon my inexpert CAD work, this is literally the first thing I've ever tried to make in BRL-CAD that wasn't a tutorial exercise (and I picked a hard one Wink )



Particularly if you built the A-arms with "elbows" in them (which is beyond my skills in the program right now), you could probably have an arrangement that would be nicely adjustable and still leave the passenger enough room.

Interesting thought. I wonder how the "leading" design would affect the suspension's performance, if at all.

[edit]

Actually, there's nothing to prevent you from using the same style of leading-A-arm suspension people are using for CHS rigs, with the pivots running perpendicular to the above picture, across the width of the sidecar. If they can do it for the front wheel of the rig, it's definitely strong enough for the sidecar.
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irondad01



Joined: 26 Jul 2005
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Location: Osceola Mills,PA

PostPosted: Sat Jul 30, 2005 12:55 pm    Post subject: Reply with quote

Yep. Your picture is just what I was talking about.
Carl
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swaybar2002



Joined: 26 Jan 2005
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PostPosted: Sat Jul 30, 2005 9:24 pm    Post subject: Reply with quote

This is a link to some very basic suspension stuff but may be of interest.
http://tinyurl.com/d4ew3
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Claude Stanley

Founder: Internet Sidecar Owners Klub
http://autos.groups.yahoo.com/group/SCT/

2007
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First full weekend in August!! Thursday through Sunday!!
Weikert, Pa ..more details coming
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Bandit Bill



Joined: 31 Jan 2005
Posts: 202
Location: Hamilton, Ontario, Canada

PostPosted: Sun Jul 31, 2005 10:57 pm    Post subject: Reply with quote

Thanks for the input all .. and for the site, Claude. That site confirmed a number of issues that i think i've identified with my particular (peculiar?) setup, and pretty well confirms that double A-arm is the way to go, if i am going to change out the sidecar suspension.

About the only thing i'd be concerned about an offset A-arm setup, is that a tendancy for the A-arms to 'twist' under load would appear. the longer side of the A-arm setup i think would need to be of a heavier guage of tubing than the shorter A-arm side, to resist twisting of the A-arms.

I had a semi-brilliant idea for the sidecar setup, i'm currently contemplating - going back to the SMART car, which uses a 145 series 15" on the front and a 175 series on the back, and both rims can fit on front and back hubs (on SMART car, rear is drum brake, front is 280mm rotor).
My thought is that to keep the fender wheel well changes down to the minimum required for the sidecar body, i can run the 145 series tire. Take the body off, put on an aluminum monkey platform (to be built yet Smile ) and the 175 series for additional traction, and I've got a versatile rig. In theory anyway.
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IanJ



Joined: 21 Jul 2005
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Location: Seattle, WA, USA

PostPosted: Mon Aug 01, 2005 6:22 am    Post subject: Reply with quote

I agree that the diagram I posted would be a terrible "actual" design for an A-arm system, but it got the idea across. Smile

I think there's some merit in studying the leading-link front A-arm, CHS systems which have the pivot axis running perpendicular to the direction of travel. These systems will already have twisting worked out, and could easily (well, "easily") be adapted for a non-steering wheel on the other side. It would just take reconfiguring the arms and building up a beefy enough mounting point.

Of course, if you're not worried about passenger seating comfort, a simple, inline A-arm suspension would be the best choice.
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swaybar2002



Joined: 26 Jan 2005
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PostPosted: Mon Aug 01, 2005 8:10 am    Post subject: Reply with quote

One nice thing about an a-frame suspension is the adjustability of it. This can be good or bad in some ways as it does add complexity to the construction of it. My present project has a kingpin (pretty old school huh?) on the trailing swing arm that allows toe in to be a simple adjustment at the wheel area. On an a frame system you could do the adjustment at the sidecar wheel as well. You can also adjust the camber of the sidecar wheel and if you plan ahead you could even incorporate a steering sidecar wheel into the design at a later date.
If doing this properly there will be many other things to consider such as scrub radius, possible ackerman, how much do you really want it to turn, bump steer etc.. (MAYBE we can agree that from now on we can refer to a 'BAG OF WORMS' with the letters 'BOW'?...How does a
'BOW alert' sound).
Anyhow , here is a link to a site that may be of interst:
http://campus.umr.edu/fsae/library/sae_paper/paper.html

Just a thought but has anyone ever considered how fast the F1 sidecar rigs corner and how flat the cornering stance of them is? What suspension do they have on the sidecar wheel? Pretty darn simple. They are rigid!!

Maybe a rigid sidecar suspension and a sprung body would be the simple answer?
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Claude Stanley

Founder: Internet Sidecar Owners Klub
http://autos.groups.yahoo.com/group/SCT/

2007
I.S.O.K Sidecar RON-DEE-VOO III ..
First full weekend in August!! Thursday through Sunday!!
Weikert, Pa ..more details coming
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