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Post by don on Feb 8, 2012 6:54:39 GMT -5
Crossbow plans are finally available!... www.diyden.netPlease have a look at the free preview and I will be available to discuss the design if anyone is interested.. Regards Don |
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Post by scooterrebel on Feb 12, 2012 19:24:11 GMT -5
Looks nice to me, I admit I do not fully understand the front suspension by looking at the preview plans. The nose on the body reminds me a lot of a Honda Helix scooter, not particularly fond of that.  |
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Post by don on Feb 13, 2012 1:31:49 GMT -5
That's not a pretty scooter!  The Crossbow styling is a suggested easy to build option, I intend doing some more options, and interested parties are also welcome to offer suggestions... The front suspension is zero roll, similiar to the Sportcycle, but operated with bottom rocker wishbones and pullrods. The real innovation is reverse castor which causes a into the curve jacking or slight tilt, and that thereby results in camber gain on the rear tyre. (Castor effect is gained back by placing the spindle behind the upright axis- like a shopping trolley castor wheel) |
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Post by scooterrebel on Feb 13, 2012 2:07:40 GMT -5
What do you think the weight limit is on the suspension.
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Post by scooterrebel on Feb 13, 2012 23:24:09 GMT -5
With the single front spring doesn't that keep it from having an independent front suspension? Sorry, I'm not a mechanical engineer. Do you have a projected cost of the build? I'm curious also about the price of getting the custom parts cut out, I wouldn't even know where to go and ask about getting it done, I wouldn't think the mom and pop machine shop would have a laser cutter.  |
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Post by Deleted on Feb 14, 2012 9:31:20 GMT -5
With the single front spring doesn't that keep it from having an independent front suspension? Sorry, I'm not a mechanical engineer. Do you have a projected cost of the build? I'm curious also about the price of getting the custom parts cut out, I wouldn't even know where to go and ask about getting it done, I wouldn't think the mom and pop machine shop would have a laser cutter. I was thinking the samething. Unless I'm missing something, if both lower arms are connected to 1 rocker shaft that move the same coilover, how could each side work independent from each other. Seems like if one wheel dropped in a pot hole it would try to pull the other side suspension down also, creating a bind, or bending the rod that would connect the arm to rocker shaft, and also creating a strange or unpredicable felling to the steering. |
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Post by woodsmith on Feb 14, 2012 12:01:48 GMT -5
I have a slightly different design for a front suspension that achieves the same result.
The result is that the front hubs both move together, up and down, and so the chassis is controlled against leaning when cornering.
During cornering the outer wheel will load up, the chassis will want to roll outwards, but in attempting to do so it will unload the inner wheel and transfer the load to the outer wheel. That shifts the roll center from the center line of the chassis to the outer wheel.
With bumps across the front axle the spring will absorb the bump as normal but with a single wheel bump the chassis will tip side to side.
Not sure yet what effect that would have on handling until I have built and tried it.
However with my set up I am using two springs/damper units and I can 'disconnect' the set up if it proves problematic.
Having said that I have driven a RT with another form of non lean suspension and it was fine, absolutely flat around corners and not weird when driving over bumps.
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Post by Deleted on Feb 15, 2012 1:10:34 GMT -5
If the idea is to resist lean in the corner and not have the tires independant from each other, then why not just use a single axle beam suspension with a single leaf spring like a Ford model A setup? Heck, a model A front axle and hubs don't weigh much, might be a good front suspension setup.
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Post by woodsmith on Feb 15, 2012 9:24:30 GMT -5
Because a beam axle will still allow lean, quite a lot of lean unless constrained by an anti-roll bar.
The trick is to assemble a trick pile of rods and linkages that allow the chassis to have vertical movement in bounce, relative to the wheels and the road, but not allow the chassis to roll side to side.
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Post by Deleted on Feb 15, 2012 9:50:09 GMT -5
This might be a dumb question, but why do you not want any lean or roll on a reverse trike? I'm new to this idea and here to learn. Anywhere online to read up on some theory?
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Post by woodsmith on Feb 15, 2012 14:19:06 GMT -5
I suppose for the same reason as any other sporty car.
The problem with a reverse trike is one of stability. The idea senario is to lean into the curve, like a motorbike, but with three wheels on the road the trike will lean outwards, like a car. This shifts the centre of gravity outwards and can cause the trike to tip over in extreme conditions.
Reducing the amount of lean keeps the centre of gravity closer to the centre of the trike's foot print and makes it better able to resist the tipping over forces.
If you drew a line joining the footprint of each tyre you get a triangle. The centre of gravity needs to be inside that triangle for the trike to be stable. When cornering centripital force acts to vector the centre of gravity outwards. When it falls outside the triangle the trike tips over.
By leaning the body the centre of gravity of the body moves outwards, adding that to the centripital force makes it more likely that the trike will tip over.
This is more of an issue in a 'sit astride' trike, as in the OP's design, as the centre of gravity is higher and any lean will shift it out further then a low riding kart type trike.
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Post by woodsmith on Feb 15, 2012 14:36:27 GMT -5
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Post by Deleted on Feb 16, 2012 10:03:48 GMT -5
Thanks for the links. I'll have to do some reading.
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Post by don on Apr 25, 2012 0:53:58 GMT -5
The reason I have designed no lean into the front suspension is because lean will cause positive camber on the rear wheel, and with such a wide tyre will cause a severe loss in traction. You actually want the chassis to lean slightly into the turn, to cause some camber gain... This is the principle behind the Crossbow's unique reverse castor suspension design.
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Post by Deleted on Apr 27, 2012 5:39:18 GMT -5
fantastic looking project
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Post by Deleted on Jan 14, 2014 3:33:43 GMT -5
I just purchased the plans ( I'm in California ) I expect to get going on this one in a few weeks. I will be making some changes. I have a tubing bender and notched so round dom rather than Sq tube. Also going to use a ducati 748 single sided swingarm. Was going to use a Mc tire but after some reading I think I'll go with the widest car tire that will fit my wheel. Also I am paralyzed from the chest down so all controls are going to be via hand. Will use the normal bike front brake to a Slave that actuates a small sand rail master with a proportioning valve to adjust f/r bias. I've built a few sand rails so this should be a cakewalk I have a 6 ft strong hand welding table with a harbor freight truck bed crane on one corner.
I'm just not the fastest builder now since my injury. But once i start ill keep the pictures coming.
Any questions feel free to ask.
Don
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Post by ion on Apr 11, 2014 23:20:48 GMT -5
Hey aaxiss. How is the project going? Did you start yet because I was really looking forward to seeing one built. I hope all is well with you.
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Post by ShogunTX on Jun 21, 2015 2:56:32 GMT -5
Hey aaxiss. How is the project going? Did you start yet because I was really looking forward to seeing one built. I hope all is well with you. Any updates on the build? |
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The Crossbow styling is a suggested easy to build option, I intend doing some more options, and interested parties are also welcome to offer suggestions... The front suspension is zero roll, similiar to the Sportcycle, but operated with bottom rocker wishbones and pullrods.
