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TheJoker
05-02-2012, 03:56 PM
Guys,

I'm a bit at a loss here. I've built this kick-stand for my cargo bike. Initially I thought I'd go for a standard centre stand by Hebie, but as the bike's a front-loader the stand simply is too far away from the load, so I started building a "proper stand".
First version bent, so I strengthened it. I now think it's strong enough, but I can't figure out the spring-system to keep the stand up or down. :rolleyes4: :confused:
I've got spring "hooks" to attach springs to. My initial spring wasn't strong enough and I ordered two more a bit on a whim trying to figure out what I needed. Apparently I failed.

Spring #1.
4218
Spring fact sheet. (http://www.assocspring.co.uk/p/16/extension_springs-stainless_steel/?min_1=12.70&max_1=12.70&min_2=1.91&max_2=1.91&min_3=114.30&max_3=114.30&PAGE_ID=1)
Part Number D0 (mm) d (mm) L0 (mm) L1 (mm) P (N) T (N) R (N/mm)
E05000754500S 12.70 1.91 114.30 171.96 113.05 10.19 1.78

Spring #2
4219
Spring fact sheet. (http://www.assocspring.co.uk/p/16/extension_springs-stainless_steel/?min_1=25.40&max_1=25.40&min_2=2.67&max_2=2.67&min_3=101.60&max_3=101.60&PAGE_ID=1)
Part Number D0 (mm) d (mm) L0 (mm) L1 (mm) P (N) T (N) R (N/mm)
E10001054000S 25.40 2.67 101.60 183.90 156.55 14.08 1.73

Photos of the stand configuration;
4220

Down position with the fat spring (25.4mm)
4221

One more in the next post...

However, I have no idea what to do now. I thought I had ordered strong enough springs, but apparently I didn't manage to do that.

Anyone have any good idea on what to do?!

TheJoker
05-02-2012, 03:58 PM
Here's the first pic again a bit bigger.
4222

And the last of the stand in the up-position.
4223

Heelp! :jester:

Petone_NZ
05-03-2012, 05:39 AM
I think the problem might be that there isn't enough difference in length between the two spring anchors as the stand starts to fall. Let me draw a couple of pictures to explain.

Here's what you've currently got (simplified) - the green shape is the stand in the "up" position and the red shape is the stand as it begins to lower:

http://i1260.photobucket.com/albums/ii576/nwmar2012/kickstand_diagrams/short_offset.gif

The dotted lines represent the length covered by the spring, and the critical issue is that they aren't very different in length. This indicates that the spring doesn't need much additional stretch to allow the stand to fall ... or to put it another way: the spring needs to be REALLY STRONG to resist stretching and stop the stand from falling.

Here's a slightly different design, with the stand pivot point lowered. (This would also require correspondingly shorter legs on the stand and therefore less suspended weight, but that's incidental.)

http://i1260.photobucket.com/albums/ii576/nwmar2012/kickstand_diagrams/long_offset.gif

Here the difference in spring lengths is greater as the stand begins to lower. This indicates that the spring needs more additional stretch to allow the stand to fall ... or doesn't need to be so strong to stop the stand from falling.

I'm not sure if it's practical to lower the pivot point like this - that may put it right in the knee-banging zone. But it will help if somehow you can rearrange the geometry so that the initial movement requires a greater variation in spring length.

Also, it's not the absolute difference in spring length that matters (i.e. number of inches or cm), but the percentage. If the spring is 30cm long when the stand is up and has to stretch to 36cm, that's only a 20% increase spread over the length of the spring. But if the spring is 12cm long and must stretch to 18cm, that's still a 6cm increase but it's also 50% (because the additional stretch must come out of a much shorter distance), so the spring will resist more strongly.

If any engineer zombies are reading this then please feel free to wrap some scientific explanation around it ... the above is simply garage-hacker logic.

Regards, Neville

yogensha
05-03-2012, 06:09 AM
Hi Nevile,

Stand style is like the old english front loading butchers/bread delivery bikes, they used friction and a clip retainer rather than springs so would drop sometimes if you hit a pothole!

Back to topic, can you adapt the method used by both motorbike centre stands and bicycle rear double kick stands.

What I mean is on both of this style of stand the spring is located infront of the pivot point with a spring plate attached to a plate at maybe 30 degrees to the stand on one side, this aids with retaining the stand in the up position, as both (stand and frame) spring anchor points on one side will be above the pivot point and on the opposite side a spring attached to the stand proper and the top hook in front of the pivot.

Here is a picture I found that shows the spring set up, the one on the far side is hard to see but its there.

4226 Found this image here http://www.oldbikes.ie/index.php?main_page=product_info&cPath=26&products_id=81

Hope this is useful?

regards
ANdy (UK)

TheJoker
05-03-2012, 06:17 AM
Thanks for that Neville!

I agree with you that there's a bit of an issue with the location points of the spring. Sadly altering the pivot point/legs will require major surgery (and the current design allows for a compact up-position).
I've created a straight line that goes from the leg-fastener on the leg when the leg is at 45 degrees, through the pivoting bolt to the top (frame mounted) fastener hook. This to allow the spring to pull the legs to both up-position and down-position.
Obviously adding a 2nd spring on the other side will help, but unless I a) correct any design problems (as you potentially pointed out, Neville) or b) know what springs to buy, then there's very little point in adding a 2nd spring.

I had however, not considered the percentages of the stretchings. :rolleyes4:

Let me place this on the slow-cooker in my head and see if something comes out. Thanks!!

PS, if there's an engineer out there that knows on what premises (numbers) one is to choose springs, I'd LOVE to know.

TheJoker
05-03-2012, 06:24 AM
Hi Andy,

I don't really understand what you mean? :( I can see from the pic that the stand has got different spring setups on the different sides. From what I can see though is that the pivoting mechanism is pretty similar to mine (albeit mine is calculated by throwing darts in a blackeded out the garage). I do have two motorcycles that I can check and the Hebie stand too, but as far as I can tell, they're all very similar.
What am I missing? :rolleyes4:

yogensha
05-03-2012, 07:16 AM
Hi Andy,

I don't really understand what you mean? :( I can see from the pic that the stand has got different spring setups on the different sides. From what I can see though is that the pivoting mechanism is pretty similar to mine (albeit mine is calculated by throwing darts in a blackeded out the garage). I do have two motorcycles that I can check and the Hebie stand too, but as far as I can tell, they're all very similar.
What am I missing? :rolleyes4:

Sorry about that, the pivot could be made from a plate, then attached at the same position, as was show in one drawing the pivot was extended lower.

Describing ideas was never my strong point, so i drew it, see below, and I hope what I was thinking comes across.

The idea is that by attaching the spring to a plate at an angle to the stand it better supports the stand in the up position, length of the stand comes into play because the longer it is the stronger the spring needs to be to keep it up.

The angled spring brace act as a lever on the stand, like undoing a wheel nut on a car the longer the lever the easier its is to undo.

A triangular plate carrying the pivot point and spring mount in one this might make more sense, it's not perfect though:-

4228

Andy

TheJoker
05-03-2012, 08:39 AM
Ah! I think I get it, now another question; is the spring brace (sticky out bit from the stand) solid, i.e it does not move at all?

I wish I had Lego Technic at hand! :jester:

yogensha
05-04-2012, 06:50 AM
Ah! I think I get it, now another question; is the spring brace (sticky out bit from the stand) solid, i.e it does not move at all?

I wish I had Lego Technic at hand! :jester:

Yep it is welded to the stand, bad choice of drawing it as wire rod, switched it to a plate, probably better and an end view.

As you said similar to yours but switching where the top of the spring attaches to the frame, benefit is that when the stand is down the line of the spring is in front of the pivot point giving enough pull to keep stand down, and the reverse when stand is up.

42334234

Andy

go1000go
05-04-2012, 01:17 PM
Brilliant timing.
I was just going to start looking at what I needed for my current "back seat driver" build, as I will need similar stand
Thanks, I will use the same on my tandem,cargo,rear stear bike.

TheJoker
05-04-2012, 01:24 PM
Thanks for that Andy! I will have to have a look at the bike. If I could do that modification, I don't believe it would actually solve my problem. I believe that I need to know more about springs and get the right type of spring. And this is where my knowledge is close to non-existing.

Any spring-engineers around? Hello? :rolleyes4: :jester:

macka
02-10-2013, 11:57 AM
What about deleting the springs altogether? Use a prop rod to hold the stand in place when extended, and a tie down to hold it too the frame?

Ticktock
02-10-2013, 09:30 PM
Hi,
This topic can be a night mare, because it looks so simple, and often is not.
Take a look at these three pics of my LWB side stand.
622062216222
NOtice that when the stand is down, the spring is pulling it down, and when its up, it pulls it up.
How do you get this right?
Well the secret is in the middle photo--its half way up (or down). At this point, the spring is stretched to maximum, The key point is that the spring attatchment to the frame must be in a straight line with the stand at this point. It is also "above" the pivot point of the stand.
From this point, the spring wants to pull the stand up or down, depending which way you move it. A longer (within reason) spring is easier to set up than a short one. It does not need much tension to hold the stand up, but the more the spring holds it down the better it is .
Make sure that your stand is swinging down far enough (past vertical) so that the weight of the bike locks it down.
The closer the spring attachment is to the pivot point, the less the spring will help. The further away the attachment point is , the more it will help. It is a very small range over which it will work properly. I will try to kock up a drawing that may help more.
Steve G

Ticktock
02-10-2013, 10:36 PM
Hope this works, heres the sketch . I think it explains itself fairly well.
If not , just ask.6227
Steve G
There is an "S" in useful--you just can't see it!

TheJoker
02-11-2013, 09:31 AM
Thanks for the input guys, but this was solved a long time ago. :) It too me (us) about 4 sets of spring strengths to figure it out, and I could do with a bit stronger springs at the moment, but the ones I have, are good enough. In the up-position the stand bounces a bit, but it won't fall down.
https://lh4.googleusercontent.com/-Z4tU7FVFstI/UOl23_oP2GI/AAAAAAAAKYw/L6vJR5Ganys/s800/2013_%25201_%25206_13_%25206.jpg

And yes, the secret to pull-up and pull-down is exactly how Ticktock explains it. Much harder finding info on how strong the springs need to be. :jester:

TheJoker
02-11-2013, 09:32 AM
Another pic; https://lh5.googleusercontent.com/-vaSHyqBntyI/UOl3FLE7KdI/AAAAAAAAKZA/-nJORWipsUk/s800/2013_%25201_%25206_13_%25207.jpg

Ticktock
02-11-2013, 10:29 AM
Uhm, you don't have much room between the pivot and the platform! If you need a stronger spring effect, and if the spring you have will allow, just put another hook a little further down the leg of the stand. I guess in this case forward is up?
That spring looks like it would take a bit more stretch if you really want it to!.
Nice looking bike--very practical, and very "normal" to ride.
Ste

TheJoker
02-11-2013, 10:33 AM
Thanks! Yes, there's not much room above the pivot, but it works almost perfectly now. Very easy to flick down and up.