My homemade cycle lift table

[posplayr]

My comments are relevent considering where you decided to post your engineering analysis. Had you started a thread on how to properly engineer a motorcycle lift it would have been very educational reading. If you notice the OP of this thread has not paid much attention to your comments.

If you think that the interest in reading what I post is dependent in what thread it is posted, then I get the feeling you think I should have never posted to this thread.

Regardless of who reads my posts , it was entertaining for me. When I saw Chuck's lift, it appeared as if it would surely be quite wobbly. So I looked at how to improve it. Only after studying some of the other designs that Dale posted, did I realize where Chuck's lift get's it's stability from. I learned something and may incorporate various features in a design of my own.

I still think the cantilever is a fundamental detriment providing no utility and only risk as it creates a weak link that will bring the whole thing down. I don't want it to fall, and I would not want to be an "I told you so", but I also don't want it on my conscious for not mentioning something which is quite obvious.

Nobody is paying me and believe it or not I'm pretty used to people ignoring what I write.

[ptexotik]

What, if anything, can be done to improve on his design.

- 'Tie' the base together with plywood (like top platform) allowing to get the struts inside and braced a la Tkent.
- utilise kickstand platform for libation storage ONLY

[Mista M]

I agree, it definetly needs some support in the rear.
Chuck, I like the ingenuity and repurposing you did. My suggestion is to add two upright wood pieces at the rear of the table. Bolt them thru like the rest so they swing into place and attach some string to pull them when you bring the table down. Just don't want to see anyone get hurt. Cheap and effective solution

[JEEPRUSTY]

Sub the 2x4 with sub scrap channel iron
A bit o welding and bobs yer uncle

[tkent02]

Nah, we are overthinking this whle thing. Just put a fully loaded Wang on it and get up there and dance for a while. If it doesn't break you're good.

[rustybronco]

I agree, it definetly needs some support in the rear.

What about moving the 'locking' member further rearward and allow it to stand vertical then the table is lowered instead of locked on an angle. Then it would be a simple matter of adding another flip down set of legs near the jack. Of course both locking set of legs would need to have stops put into place to keep them from allowing the 'table' to collapse if it were allowed to over center.

[posplayr]

What about moving the 'locking' member further rearward and allow it to stand vertical then the table is lowered instead of locked on an angle. Then it would be a simple matter of adding another flip down set of legs near the jack. Of course both locking set of legs would need to have stops put into place to keep them from allowing the 'table' to collapse if it were allowed to over center.

The locking member is really a support member which is giving the whole lift most of it's stability. If the support was at the end and not cantilevered it would actually be very stiff.
As designed, the struts are only there to get the top box lifted before stabilizing it on the end lock.

As I proposed in my first post to this thread, the cantilever approach is more a detriment and I'm at a loss to figure out what could even be a benefit. Moving the "locking" member to the end would eliminate the cantilever and support the rear .

http://www.thegsresources.com/_forum/showpost.php?p=1929082&postcount=15

[Guest]

Nah, we are overthinking this whle thing. Just put a fully loaded Wang on it and get up there and dance for a while. If it doesn't break you're good.

All depends on which music one is dancing to.

[rustybronco]

If the support was at the end and not cantilevered it would actually be very stiff.

I don't grasp what 'you' mean by cantilevered? are you speaking of the difference in the length from the location of Chucks 'locking' legs to either end of the table?

What I'm suggesting is two sets of interlocked legs, one set on each end that would remain vertical when the table is lowered. Similar to how the legs on a folding table look when locked in place- using positive stops (wooded blocks) for them mounted in such a direction that the legs will not fold up if the table were to be pushed end to end.

[posplayr]

I don't grasp what 'you' mean by cantilevered? are you speaking of the difference in the length from the location of Chucks 'locking' legs to either end of the table?

What I'm suggesting is two sets of interlocked legs, one set on each end that would remain vertical when the table is lowered. Similar to how the legs on a folding table look when locked in place- using positive stops (wooded blocks) for them mounted in such a direction that the legs will not fold up if the table were to be pushed end to end.

I tried to draw in the motorcycle weight and supporting forces in the lift. It is not a full statics analysis as that would lose something in translation.

Chuck even called this a cantilever design. There is no support out at the rear wheel or at the center stand where most of the weight is. For talking purposes I'm assuming there is 500 lbs at the center stand and 50 lbs at the front wheel.

The "stop" is acting like a fulcrum supporting most of the weight. The lift and the 500 lbs weight are torquing the upper platform (which being made of 2"x6" is very stiff) is pulling the front strut in tension. Again the front strut is under tension it is not supporting any weight.

If the ends of the front strut split then the bolts and pipe will pull right through and it will collapse.



Moving the support to the back allows the load to be straddled by two supports and eliminates the cantilever.



As I described before the natural motion that the Jack has is a sweeping motion similar to a strut. This should be matched to avoid the jack moving with respect to the upper box. Once the upper platform loads the stop, the stop provides all of the load bearing for that side.

[rustybronco]

The locking member is really a support member which is giving the whole lift most of it's stability. If the support was at the end and not cantilevered it would actually be very stiff.
As designed, the struts are only there to get the top box lifted before stabilizing it on the end lock.

As I proposed in my first post to this thread, the cantilever approach is more a detriment and I'm at a loss to figure out what could even be a benefit. Moving the "locking" member to the end would eliminate the cantilever and support the rear .

What you have stated here is exactly what I was my thinking as well. I was always used to a cantilever being fixed on one end allowing the other end to have to support the weight being placed on it, not being considered a fulcrum.

Now I can see how the most of weight being placed on the end furthest from the jack could cause one or both of the front pivot bolts to split the end of the front strut allowing the rear to drop.

[chuck hahn]

Well Dale, the bikes at around 500ish and I am at 235...round up to 750 for a nice working number.

I roll the bike up and set it on the side stand. Then up on the center stand, strap it down, and lift it up. I have gotten up on the table with it extended and the bike on it for whatever reason it was..fiddling with the ignition switch I think. Anyway, it never tipped or broke with the extra weight added by me climbing aboard.

Im telling you guys its solid as can be....really.

[tkent02]

Im telling you guys its solid as can be....really.

So was the Titanic.

[posplayr]

What you have stated here is exactly what I was my thinking as well. I was always used to a cantilever being fixed on one end allowing the other end to have to support the weight being placed on it, not being considered a fulcrum.

Now I can see how the most of weight being placed on the end furthest from the jack could cause one or both of the front pivot bolts to split the end of the front strut allowing the rear to drop.

So now consider how much tension is on those front struts. Say the upper box weighs 75 lbs, with another 550 in the bike. so it takes at least 625 lbs out of the jack to get the lift up. that is at one end of the box with about a 2 ft moment arm. the other moment in the same direction is the weight concentrated at the center stand. (Figure the same 2 ft moment) So the total counter clockwise moment is 1125x2=2250 ft-lbs. the only thing to oppose this is the tension in the two front struts. The force is acting through a smaller moment arm (figure 1 ft). so there must be 1125 lbs tension in both front struts. How much is it going to take go split the end grain.

[tkent02]

How much is it going to take go split the end grain.

A lot with Chuck's hard head stuck in there.