Page 1 of 2 12 LastLast
Results 1 to 15 of 24
  1. #1
    Join Date
    Jun 2009
    Location
    Toowoomba QLD
    Posts
    71

    Default Engineering design question for tandem trailer

    I am wanting to make a tandem axle trailer that rides on air bags.

    I am not going the traditional route of independant arms like you see on most trailers with air bags or coils springs.

    I am going for a setup that will have each bag and the swingarm in a torsion type setup.

    I will need to draw a piccie I think that will show what I mean.

    But in the mean time, I am trying to work out the diameter of the shaft that will be under torsion, and whether I can get away with mild steel or if I need to go to high tensile.

    Is anyone here suitably qualified to help me out here?

    I can take a guess but that's it...a guess. I would prefer someone who can crunch numbers for me. I can pay if need be.

    Thanks

    Craig

  2. #2
    Join Date
    Jun 2009
    Location
    Toowoomba QLD
    Posts
    71

    Default

    ok here is my feable attempt at a piccie

    Does it make sense?

    http://i691.photobucket.com/albums/v...psoa2ksh5l.jpg

  3. #3
    Join Date
    May 2010
    Location
    Lower Lakes SA
    Age
    58
    Posts
    2,607

    Default

    Quote Originally Posted by surfin View Post
    ok here is my feable attempt at a piccie

    Does it make sense?
    Nope.

  4. #4
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
    Age
    71
    Posts
    5,942

    Default

    Hi Surfin,
    I'm not a number cruncher, I go from experience and what I've seen else where. From your drawing, the way I understand it, you propose to have a torsion bar assembly at the chassis level, and air bags under the chassis? My question is why would you want 2 types of suspension? I feel that they would counteract one another. One or the other would be fine, look at the Alko suspension system, works well, unless it is over loaded. Ideally for a tandem trailer the suspension should be load sharing, in SA registration of tandem trailer without, won't happen. I've seen a system used on an 80 - 100 series Land Cruiser that had air bags on the rear as load sharing, looked fantastic. A centre pivot point with approx 75 X 50 RHS beam running to both axles with air bags mounted above the axles, nice and simple. Your efforts though may well work, but I like the KISS principle, if it's too complicated there will be problems.
    Kryn

  5. #5
    Join Date
    Jun 2009
    Location
    Toowoomba QLD
    Posts
    71

    Default

    Quote Originally Posted by Bryan View Post
    Nope.
    I know it was a pretty crappy drawing. It was a pic of just one of the wheels and air bag setup.

  6. #6
    Join Date
    Jun 2009
    Location
    Toowoomba QLD
    Posts
    71

    Default

    Quote Originally Posted by KBs PensNmore View Post
    Hi Surfin,
    I'm not a number cruncher, I go from experience and what I've seen else where. From your drawing, the way I understand it, you propose to have a torsion bar assembly at the chassis level, and air bags under the chassis? My question is why would you want 2 types of suspension? I feel that they would counteract one another. One or the other would be fine, look at the Alko suspension system, works well, unless it is over loaded. Ideally for a tandem trailer the suspension should be load sharing, in SA registration of tandem trailer without, won't happen. I've seen a system used on an 80 - 100 series Land Cruiser that had air bags on the rear as load sharing, looked fantastic. A centre pivot point with approx 75 X 50 RHS beam running to both axles with air bags mounted above the axles, nice and simple. Your efforts though may well work, but I like the KISS principle, if it's too complicated there will be problems.
    Kryn
    The main idea of the design is so that the whole system can be aired down, and the trailer will sit flat on the ground for easy loading of the low car I am building.

    When I say it is a torsion type setup, that may not be correct exactly. The air bag mount and swinging arm are sharing the same length of steel at the pivot point, and it will experience a twisting on it (hence torsion) as the suspension cycles.

    I spoke to a person last night who I regard highly with his engineering design and he thinks a 40mm mild steel shaft would work ok for this weight of trailer (2000kg max).

    Any other comments or opinions?

  7. #7
    Join Date
    Feb 2012
    Location
    mackay
    Posts
    17

    Default

    Surfin,
    I spent nearly 3 years designing/thinking of some sort ofairbag setup for my trailer. I really wanted to be able to lower it for loadingand adjust for different weights. The best I came up with was a smaller versionof what is fitted to the average airbag semi trailer, an axle with an arm eachside which is actually a leaf spring to allow for twisting moments of the axleas required. In the end I bought the average roller rocker spring setup becauseit is simple and the loading of the suspension is spread over 6 differentpoints. I'll have to find a different way to load it....
    However for your design, from reading between the lines, theshaft your saying is under torsion is not at all under torsion and is just a pivot.Either way, I hope your an awesome fabricator because welding up swing arms tobe straight and strong will be very hard. For the shaft I would envisage less downward loadto be on that shaft compared to the average axle (shared with the airbags) however sideway load would be greater as nowthe wheels have a lever to bend that shaft. Also you have to consider thepossible legal outcomes if something fails in your design causing an accident.
    Personally I would run a roller rocker setup but find thesmallest diameter wheels and tyres possible. Also consider drop axles as theymay suit better. Add a tilting drawbar and with the length of the trailer onlysmall ramps should be needed. I ran airbag helpers on my work cruiser ute (4.2tonne loaded) and simply got sick of having to keep adjusting air pressure dueto leaks.


    These are just my thoughts, hope they help in your decisions.
    Good luck, let us know how you go.
    Sean


  8. #8
    Join Date
    Oct 2011
    Location
    Norwood-ish, Adelaide
    Age
    59
    Posts
    6,541

    Default

    Quote Originally Posted by surfin View Post
    I am wanting to make a tandem axle trailer that rides on air bags... Is anyone here suitably qualified to help me out here?

    I can take a guess but that's it...a guess. I would prefer someone who can crunch numbers for me. I can pay if need be.
    Craig, as a general comment every so often someone puts up a post like yours asking for engineering advice. Problem is that if it is answered by someone who does this sort of stuff professionally and it goes wrong they are legally liable (doesn't matter if they did it as a favour or not - the legal view is that they should should know). Unless you pay full tote odds at an engineering consultancy I doubt you will get the level of answer you are looking for.

    Having thrown that into the mix, have you looked at the VW Razorback transporters? They drop the tray down while leaving the wheels/ suspension in one piece as far as I can see. Maybe another way to approach your problem.

    Michael

  9. #9
    Mobyturns's Avatar
    Mobyturns is offline In An Instant Your Life Can Change Forever
    Join Date
    Jul 2012
    Location
    "Brownsville" Nth QLD
    Age
    66
    Posts
    46

    Default

    Have you seen the Alko suspension system?
    Mobyturns

    In An Instant Your Life CanChange Forever

  10. #10
    Join Date
    Jun 2009
    Location
    Toowoomba QLD
    Posts
    71

    Default

    Quote Originally Posted by Michael G View Post
    Craig, as a general comment every so often someone puts up a post like yours asking for engineering advice. Problem is that if it is answered by someone who does this sort of stuff professionally and it goes wrong they are legally liable (doesn't matter if they did it as a favour or not - the legal view is that they should should know). Unless you pay full tote odds at an engineering consultancy I doubt you will get the level of answer you are looking for.

    Having thrown that into the mix, have you looked at the VW Razorback transporters? They drop the tray down while leaving the wheels/ suspension in one piece as far as I can see. Maybe another way to approach your problem.

    Michael
    That is a fair enough comment Michael. I will have a look at the VW setup and see if it does what I need

    Thanks for the input

  11. #11
    Join Date
    Jun 2009
    Location
    Toowoomba QLD
    Posts
    71

    Default

    Quote Originally Posted by Mobyturns View Post
    Have you seen the Alko suspension system?
    You mean the rubber mounted Alko independant suspension? If so, then yes I have. I need this design to enable the deck to sit totally flat on the ground, to drive a low clearance car straight on. then pump the bags up and the trailer goes up.

    Something similar to this, but a different design:


  12. #12
    Join Date
    Jul 2009
    Location
    Quorn
    Age
    53
    Posts
    35

    Default

    Quote Originally Posted by KBs PensNmore View Post
    Ideally for a tandem trailer the suspension should be load sharing, in SA registration of tandem trailer without, won't happen.
    Kryn
    Is there any substance to this. Having just looked at new trailers from several trailer manufacturers, there are a lot of brand new tandem trailers out there that don't have load sharing suspension.
    Cheers,
    Dion.

  13. #13
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
    Age
    71
    Posts
    5,942

    Default

    Quote Originally Posted by Wahoon View Post
    Is there any substance to this. Having just looked at new trailers from several trailer manufacturers, there are a lot of brand new tandem trailers out there that don't have load sharing suspension.
    ADR INFORMATION

    Australian Design Rules (ADRs) now apply to the building of Caravans, Trailers and most trailed vehicles. It is your responsibility, whether you are a manufacturer or a private one-off builder, to conform to these regulations. Our staff at SA Trailer & Chassis Equipment Pty Ltd will be able to help you with general ADR enquiries on Brakes, Suspensions, Trailer Plates, Lights, Wheels, Tyres and Chains etc.
    For specific ADR information and copies of the current ADR regulations, please contact the Department of Road Transport in your state.
    GENERAL POINTS ON ADRs FOR TRAILERS

    BRAKING


    1. Trailers up to 750kg Gross Trailer Mass (GTM) - No brakes required.
    2. Trailers with GTM from 750kg to 1999kg - Brakes required on at least two wheels.
      "Efficient" override brakes, electric brakes or power-assisted brakes are acceptable.
    3. Trailers with a GTM from 2000kg to 4499kg - Brakes required on all road wheels.
      Must be independent brakes in either electric, vacuum or compressed air-assisted, with control via foot and hand controller from the driver's seat, with a breakaway system to automatically apply the trailer brakes fully for at least 15 minutes should be vehicle accidentally disconnect from the towing vehicle.
    4. Trailers with a GTM of 4500kg and over - Require fully ADR-approved axles with "S" Cam Brakes, Load Sharing Suspensions and Compressed Air Brake Operating and Breakaway Kits.
      Kit Approval Numbers supplied on purchase of approved running kits to make registration easier.
    SUSPENSIONS

    1. Trailers up to Gross Trailer Mass (GTM) of 1999kg - Can use Slipper, Shackle or Rocker Springs, or Independent Suspensions.
    2. Trailers with GTM from 2000kg to 4499kg - Require a Load-Sharing Suspension when in tandem or tri-axle configuration.
    3. Trailers with GTM fro 4500kg and over - Require ADR-Approved Suspension Kits.




    Sorry about that I had been misinformed.
    Kryn

  14. #14
    Join Date
    Jul 2009
    Location
    Quorn
    Age
    53
    Posts
    35

    Default

    Another reference I found, stipulated that load sharing not required if axle trammel distance is less than 1m for tandem, 2m for triaxle and 3.2m for quad's. Doesn't directly say anything about GTM.
    One of the best trailer suspension mods I had ever been done was to change a flat bed trailer, which had two axles at about 1.5m apart changed over to single point suspension. Great in the bush.
    My own 7x4 tandem, which is due for major rebuild as the floor is rotted out, will also have both axles treated with single point suspension.
    Cheers,
    Dion.

  15. #15
    Join Date
    Aug 2010
    Location
    Horsham Victoria
    Posts
    113

    Default

    Following with interest. What are the advantages of variou axle suspension and some pics would be good

    Dave TTC
    Turning Wood Into Art

Page 1 of 2 12 LastLast

Similar Threads

  1. Brake controller for tandem trailer
    By chambezio in forum TRAILERS & OTHER FABRICATED STUFF
    Replies: 5
    Last Post: 11th Jan 2013, 11:05 AM
  2. Tandem Box trailer questions
    By Dan in forum TRAILERS & OTHER FABRICATED STUFF
    Replies: 11
    Last Post: 3rd Sep 2012, 12:19 AM
  3. Tandem Trailer Spring Bushes
    By chambezio in forum TRAILERS & OTHER FABRICATED STUFF
    Replies: 1
    Last Post: 27th Jul 2011, 10:44 PM
  4. Tandem Trailer Build
    By Bad Fruit in forum TRAILERS & OTHER FABRICATED STUFF
    Replies: 2
    Last Post: 9th Mar 2011, 06:39 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •