robot designed to move car on trolly

[cardboard]

Hi all,

i dont really know what to call this so if you can think of a better title do let me know and ill amend it! thats if you even understand my description!!  

Essentially i am trying to make transfer device.  I have attached a rough 3D model to aid in my explanation! the gold components i already have, the car sits on these and allow me to work around it easily.  however to move the car i have to push it.  what i want to do is attach something (like the silver component)  to the trolley that will move the car via remote control or by just holding a button on it and walking with it.

from my research so far i want the following to be incorporated in my robotic arm

1) i want to be able to attach and detach the "robotic arm" simply and easily

2) the maximum force required to start the system moving is about 80kg, consequently the robotic arm must weigh more (this affects point 1 above) or must have a means of using the weight of the vehicle to increase the pressure it exerts on the floor, a sort of jack or expansion system such that the load is spread between all three points of contact evenly.  The bending moments will be high with a design like this however??

3) all components for powering, moving, braking and guiding it need to be housed in it, including power, i would like it rechargeable. A simple remote control system could be implemented to control forward and backward motion or a button on the arm itself.  

4) i wouldn't mind a means of sensing how far the wall is from the front, much like car parking sensors?feasible?

i think some DC motors would have sufficient torque, ones used in golf buggies and wheelchair units but thats as far as ive got techincally.

My knowledge is limited in most of the above areas lol and im struggling to find relevant literature to progress my ideas. any advice you can give me or literature you can recommend in any area would be greatly appreciated.

[Fabian Munoz]

Welcome to the forum Cardboard



We just did a work a similar job but we were guiding the trolleys from the top .  You silver bracket will be at front sticking uplike 8 feet .

I'm going to try to post a picture tomorrow BUT we didn't use any robot (manipulator) to push it

Do you have one of them only and it goes through a small shop or there are 50 of them going through a huge building

I'm assuming they move very very slow.

You dont have to give us confidential details but the more you tell us the best we can do


somar

[cardboard]

Thanks for the quick response somar 

i appreciate your mention of confidentiality and will endeavor to give you as much detail as possible.  I am doing a research project based around this idea and the ultimate goal is to produce a working prototype in the middle of next year for testing.

i think i get what you are describing but this would require attachment to rails or something along the roof? this is not detachable? and i very much doubt it will be cost effective give the very low volume of product.  i am open to all suggestions however so will more than happily asses any idea for its applicability in my environment.

If you picture a production line 50 meters long then turning through 180 degrees on a radius of 5 meters and coming back along itself a further 50 meters with a station every 10 meters this is the room. 

the trolley will get lifted and consequently the robot must be detachable.  also it is only required when the trolley is too heavy to push and as such is only need at certain areas along the line, it can be pushed manually from all other stations.

i have very little support or knowledge in areas surrounding electric motors, charging, batteries, system integration etc so want to really buff up my knowledge on applicable components etc.  i need to produce a technical review mid january before we focus on final designs but i must cover all aspects of the design requirements.

I am currently reading a very interesting article on short circuiting electric motors to brake such systems which seems like quite a good idea!

i hope this helps some more! i realise that conversations like this are normally very challenging and an accurate picture of what i am trying to portray takes time to come across but i appreciate the time you have taken!

[SkyeFire]

Some more questions regarding the application:

1.  Does this trolley run on tracks or rails?  Or does it run on a flat floor?  If the trolley has to move through this path on an open floor, it will need to be much more complex -- steering, guidance, etc.

2.  What are the safety requirements?  Will people be in a position to possibly get run over by this trolley?  If so, you may need to add various safety devices to protect people operating near the trolley.

3.  What kind of surface would the drive mechanism be working against?  Concrete, metal rails?  Dirty, clean?  Smooth, bumpy?

A robot arm doesn't seem like what you need -- they don't have 50m reach.     I'm thinking of something like a geared-down electric motor turning a wheel that engages the floor.  Having sufficient friction against the floor would be an issue, unless your trolley runs on a track of some kind -- you could have the motor turn a gear, and have the gear engage a pinion that runs the length of the track.

This sort of task is a regular item in most Automotive production plants, and has many different solutions.  But the great majority of them depend on tracks and rails (like trains) to carry the weight and keep the cars on the correct path.  Often they use continous-loop chains that run the length of the line and drag the cars along.  Solutions that don't use rails generally use Autonomous Guided Vehicles (AGVs) that are like robotic trucks or forklifts and are quite complex and expensive.

[cardboard]

1) no it is a flat floor
2) the only safety requirement is that if it is user controlled and the user fails to stop it and its heading for a wall it senses it and stops, like parking sensors or something.
3) it would be a clean smooth stone floor

sorry my use of the word robotic arm is clearly misguided, the arm i have drawn of the trolley is what i am talking about this would only be 500mm high.  so far ive been trying to look at electric wheel chairs and so on.  the extra limb house batteries, and motors and yes if attached under the staple some sort of system would need to expand the arm such that the contact pressure increase through the arm to allow drive.

i have looked at AGV's but these do far too much in my opinion and are not cost effective. essentially i want to make my own AGV without all the unnecessary stuff!

[simspec]

If you arent going for an AGV (the safety stuff on AGV's are legally required to ensure that they dont run people over, which is why the safety stuff is complicated because it cant be allowed to fail).

Essentially you want something that will move a big heavy trolley (with the car on it), anywhere in a factory, with the guidance and control being supplied by a human operator and the motive power being supplied by the "thing".

 i am pretty sure they already have these (http://www.liftmate.co.uk/lemp10-semi-electric-pallet-truck) just take the forks off and replace with a towing hitch.

I think these things only move as long as the button is pressed down, which would take care of the running into walls problem (as the operator would splat into the wall first and let go of the button which will stop the car.

[cardboard]

yes i have actually looked at these but i am after a bespoke desgin design that integrates with the trolley system but essentially this is what i need packaged differently with some extra hardware.  i want to understand the internals though, and find literature on this so i can establish what is most applicable to the needs here.

many thanks tho for your suggestion

[simspec]

the internals are going to consist of:

power supply (battery)
electric motor & wheel (dont use a gearbox as it just add complexity)
some wire
switches (push & hold)
chassis to hold it together
handle to provide steering and hold buttons.

if i understand your picture correctly the upsidedown horseshoe shaped bits run from the front to the back of the car and the wheels on the bottom of the horse shows can go in any direction (like those on the bottom of a shopping trolley)?

if this is correct and you arent running on rails you will need to hook on to both of them with your "thing" (if not the thrust will be uneven and you will go around in circles).

i would also suggest that the wheels at the end which you are not towing from be locked so they only run forwards and backwards (and cant change direction - as if not control is going to be a nightmare  ---- imagine a very very heavy shopping trolley with a sticky wheel)

[cardboard]

your understanding is correct although only the front castors turn, the rear ones are fixed.

i realise that power will be uneven but this must be manageable by applying the drive at an angle to the direction of travel if the rear castors are fixed as apposed to using two machines.

how do i establish what batteries, charging systems, motors etc would be applicable? there must be technical papers somewhere?  also some form of expansion devise will be required to increase the contact pressure of the unit with the floor

[simspec]

I dont believe it will be controllable if power is applied on one side only - you would constantly have to adjust the steering (you would end up going in a zig-zag and wasting your battery).

Use one machine which is connected to both sides (see attached picture)

The chassis would be able to swivel independantly of the towbar thus giving you steering capability & the towbar would detach from the horseshoes so it can be used on more than one set of horseshoes.

I think for finding out the batteries, charger system, motor etc... go to   (http://www.liftmate.co.uk/lemp10-semi-electric-pallet-truck) and look up the specs for it, (see if they have a spares catalogue).

If you want to build one from scratch then you have to find out all the info to do with motors, batteries, charging systems, design it and then build it, which will be a lot of work and take a long time.
Or
It would be the simplest & quickest solution with fewest problems to get an electric pallet truck and replace the forks with the towbar / beam, as you will have to lift the front end of the horseshoes a couple of mm to put pressure on the "things" drive wheel to stop wheelspins. This could probably be done in a day.

Once you factor in the length of time required and the hourly rates of the people involved it would probably be cheaper to buy the electric pallet truck and modify it.

[cardboard]

This is an ideal solution. however the staples (upside down horseshoes) pass over lifts which lift the vehicle over head head consequently the pully "things" would collide with these ramps, however i wonder if we can redesign them a little instead! hmmmm

[simspec]

What direction does the car approach the lifts from?

Parallel to the direction of the staples (front of car or back of car?)?

OR

Perpendicular to the direction of the staples (side of car)?

Do the lifts touch the car or touch the staples when they lift the car?

[cardboard]

sorry i have been out of the country.

the lifts are inline with the direction of travel.  if a design like the one proposed by yourself (simspec) was used it would have to have to allow for vertical travel of three inches as it passes over the ramp.  it would have to maintain enough pressure on the floor to generate enough traction whilst absorbing the change in height, much the same way suspension on a road absorbs a speed bump?

any ideas how i would calculate the necessary motor and battery requirments?

thanks

[simspec]

For the motor and battery requirments look up spares / specs for the electric pallet truck and then i would suggest use comparable components.

Not sure i understand what you mean by "inline with direction of travel". Do you mean as indicated in attached pictures?

What size ramp / lift is it?  (wider or narrower than the staple separation)

[cardboard]

Hey simspec,

I been on the phone to electric pallet track repair people but they appear to only deal in small repairs.  all the units are built in asia they dont really know to much about the core internals. they appear to be more about switches and electrics fixes.

yes ramp2 is the most applicable.  this lifts the car from the trolley, work can be done at head height and the trolley's are left on the floor, they can be removed and the car is then lowered back down and it drives off.  there is however a substantial overhang over the front of the trolley.  the mount point is just behind the rear wheel and makes this method of dragging the vehicle complicated.

the next best solution i can think of is something like this