Dump Truck question

[Rishab N]

Hi guys

Currently I'm building a large dump truck, but I'm having some trouble with the lifting mechanism. Its not even able to lift the dump bed.

As of now i'm using this set up

Its an Xl motor geared down twice and then connected to the acuator. The Xl is connected to the axle connected to the 8 tooth gear. Also the axles for the 8 tooth and the grey gear are completely different

Here's another pic of my set up ( You can also see the dump bed in the background

So my question is how do I make the acuator strong enough to lift at least 1 kg or more? Should I change the positioning or the gearing?

[D3K]

You need to have more mechanical advantage! In effect; you need to attach the LA lower in the chassis!

[jorgeopesi]

A special linkage could work too.

[Cumulonimbus]

Allow me to explain some basic physics to give you insight in your design problem: Work is force times displacement. For a given amount of work (lifting the weight of the dump bed), you need to push the bed wth a certain force to a certain angle. As you probably figured out, the Lego LA's have a relatively short displacement in comparison with hydraulic cylinders of the real machines. You solved this by placing the LA closer to the pivot point, which decreased the required displacement. But because the work stays the same, the required force becomes higher.

You have two options: on one hand increasing the force by doubling the amount of actuators or choosing for pneumatics for example.

On the other hand you can increase the displacement of the actuator, which can be done with a linkage as jorgeopesi pointed out.

There are two common options found in the real world: MARREL-type linkage and GARWOOD-type linkage.

The following link shows you the difference: http://www.mitsubish...p/index.html?d2

In the following document they call it a scissor hoist: http://bb-truck.com/PDF/industrialhoists.pdf

You might need to create some room for it in your chassis though.

Good luck.

Edited July 19, 2014 by Cumulonimbus

[Rockbrick]

You may need another LA or use pneumatics....

[Hypo]

Hi,

i made this picture to tell you, that most of the power pushes between two pins which dont increase the torque. You lose too much power in pushing the two yellow pins (in the right).

SUM OF MOMENTS = SUM OF TORQUE (translation mistake, SORRY! )

i hope this will help you.

Greetings from germany,

Heiko

Edited July 19, 2014 by Hypo

[Rishab N]

Thanks guys before i try any special linkages( I'm still a really novice builder ) I'll try D3K and hypo's solution of changing the angle

More pics will be uploaded today

[jorgeopesi]

What an interesting topic, I am an autdidacta but it is nice to see there is science in that I learned it .

[Rishab N]

What an interesting topic, I am an autdidacta but it is nice to see there is science in that I learned it .

Yep i had no idea dump trucks were this complex

EDIT: I positioned the acuator as low as I could on the chassis, but it barely made a difference and it is still unable to lift the bed.

Here are some pics

The gears lead into two u joints which are connected to the acuator. The acuator is connected to 2 5x3 liftarms which are connected to the chassis

Heres another pic. Sorry for the quality I kinda rushed these as I was taking them with my phone. You can sort of make out the 5x3 liftarm its red and right above the axle. The lifting angle was obviously gonna be affected and I'm fine with that right now. Also as of now the rear of the chassis flexes a bit due to weight so I can't add in a second acuator as it would take away some of the support. So does anyone have any pics or ideas for a lego linkage mechanism like jorgeopesi and Cumulonimbus mentioned?

Thanks

Rishab

(OT but this is based off the lego 8258 and as of now its about 30 percent 8258 and 70 percent MOC. So would that be considered a MOC?)

Edited July 19, 2014 by Rishab N

[Cumulonimbus]

Sure, there are many examples:

To get an idea how this can be done in Technic, take a look at this topic: http://http://www.eu...showtopic=79396

It is not exactly the same mechanism, but the principle is identical.

Edited July 19, 2014 by Cumulonimbus

[VKTechnic]

That clutch gear might also be an issue. Linear actuators have built in "clutch" mechanisms, so get rid of that white clutch gear and you should get some more power going to the LA.

[aminnich]

That clutch gear might also be an issue. Linear actuators have built in "clutch" mechanisms, so get rid of that white clutch gear and you should get some more power going to the LA.

This would be the first thing I would try. The actuator won't do it's job if it is under a lot of force.

[Rishab N]

Sure, there are many examples:

To get an idea how this can be done in Technic, take a look at this topic: http://http://www.eu...showtopic=79396

It is not exactly the same mechanism, but the principle is identical.

For some reason that link doesnt work I'm guessing its to Zbljs dump truck? http://www.eurobrick...showtopic=79396 I was thinking of trying that too

That clutch gear might also be an issue. Linear actuators have built in "clutch" mechanisms, so get rid of that white clutch gear and you should get some more power going to the LA.

I thought only newer acuators had that. Didn't they revise them after the 8043?

Edited July 19, 2014 by Rishab N

[VKTechnic]

I thought only newer acuators had that. Didn't they revise them after the 8043?

Either way, you're losing a lot of power from that clutch gear.

[Rishab N]

Either way, you're losing a lot of power from that clutch gear.

Yea that does sound true I'll try that next

[Zerobricks]

Maybe the linkage i used in my dumptruck might help:

http://www.eurobricks.com/forum/index.php?showtopic=79396

[Cumulonimbus]

Here is what I'm thinking about:

It's the same principle, but it's a bit easier to build in Technic than the ones in the photo's I showed earlier. By changing the length of the green and the lime parts and the position of their pivots (shown in red) you can influence the distance this mechanism will travel, how much the mechanism will amplify (or reduce) the travel of the LA and thus the force it will require to lift it.

You should build a quick and dirty mock-up with real bricks similar as what I did in the image above, but with the same dimensions as your truck. By playing around with the things I mentioned above, you will quickly find a ratio that will work for you.

Edited July 19, 2014 by Cumulonimbus

[Rishab N]

Alright so I replaced the clutch gear in my second design and it lifts the bed with a bit a struggling. I'm going to try cumulonimbus's design in a little while and see how it goes. I also like Zblj's mechanism but I would have to redesign the entire middle section for the move of the motor and the acuator

Thanks for the help guys

[Zimix]

In Madoca's Dump Truck the lifting is solved like this

Pivot point of the dump bin is on the green axle

this pic should be turned to the right and it would show about it correctly. This is just to show that under the bin there is an arm which folds. And where on this arm the LA is fixed.

[Blakbird]

Note that adding an extra actuator adds absolutely no additional force because it is powered by the same motor.

[Rishab N]

Alright well i tried out Cumulonimbus's linkage and Zblj's linkage

Here's my rendition of Zblij's

This has a nice angle of tip

However the problem is here as it cannot fold up at all

I tried adding a 4 axle to the LA to try and solve that but it wouldn't change

Onto the other linkage

This one also has an excellent angle for the tip

But it too suffers the same fate of not closing

So what should i try next? Also thank you everyone who's helped so far I'm really sorry but I just started MOCing and I don't know what I'm doing

Note that adding an extra actuator adds absolutely no additional force because it is powered by the same motor.

One of my earlier designs had two acuators and it changed nothing

Edited July 19, 2014 by Rishab N

[hrontos]

These linkages are ok just find the poper lengths of those yellow beams. Do it in closed position and try to see if the open version gives good angle for tipping. It is mainly about lengths and pivot points. They have influence on the max. angle and force. You can also reduce gear ratio. Tipping will be slow, but stronger. If you reach limit of one LA, add another one. Two of the do not have more energy, but can provide more force before their clutch will be activated. More force you can get only by changing gear ratio or by adding another motor.

[Cumulonimbus]

These linkages are ok just find the poper lengths of those yellow beams. Do it in closed position and try to see if the open version gives good angle for tipping. It is mainly about lengths and pivot points. They have influence on the max. angle and force. You can also reduce gear ratio. Tipping will be slow, but stronger. If you reach limit of one LA, add another one. Two of the do not have more energy, but can provide more force before their clutch will be activated. More force you can get only by changing gear ratio or by adding another motor.

Yes, I completely agree with this. You need to realise that there is no universal solution. What I was trying to say, is that although the physics and the principle of the mechanisms is the same, each situation requires it's own custom 'version' of the linkage. If you don't have the experience yet, trial and error with real bricks will give you the most insight.

There is a graphical method to determine the correct shape of the linkage, but explaining this through this medium is not really feasible. You are entering the world of 4-bar linkages, invest some time to learn how it works and you will be amazed about the potential this mechanism has.

If you are interested, a good place to start is the wikipedia page (http://en.wikipedia....our-bar_linkage) and this fun site: http://www.mekanizma.../fourbar01.html

Edited July 19, 2014 by Cumulonimbus

[Rishab N]

Yes, I completely agree with this. You need to realise that there is no universal solution. What I was trying to say, is that although the physics and the principle of the mechanisms is the same, each situation requires it's own custom 'version' of the linkage. If you don't have the experience yet, trial and error with real bricks will give you the most insight.

There is a graphical method to determine the correct shape of the linkage, but explaining this through this medium is not really feasible. You are entering the world of 4-bar linkages, invest some time to learn how it works and you will be amazed about the potential this mechanism has.

If you are interested, a good place to start is the wikipedia page (http://en.wikipedia....our-bar_linkage) and this fun site: http://www.mekanizma.../fourbar01.html

Thanks for the links

Yea I totally get what you're saying. I think I found a good linkage but i still have to weight test it

[jorgeopesi]

These linkages are ok just find the poper lengths of those yellow beams. Do it in closed position and try to see if the open version gives good angle for tipping. It is mainly about lengths and pivot points. They have influence on the max. angle and force. You can also reduce gear ratio. Tipping will be slow, but stronger. If you reach limit of one LA, add another one. Two of the do not have more energy, but can provide more force before their clutch will be activated. More force you can get only by changing gear ratio or by adding another motor.

I agree again, I spent hours doing tests to get the maximum arm movement to my caterpillar 6090 but spent even more with the z-linkage for my komatsu wa-800, one millimeter can make the difference.