Mother-Daughter Carts

What is a Mother-Daughter Cart?

A mother-daughter cart concept is a solution by which you are able to place smaller carts within a larger frame for more efficient use. A mother cart is a cart or frame that holds daughter carts within it, therefore creating a mother-daughter cart solution. The benefit of this is that operators are able to leave the daughter carts at different work stations and assembly areas. Also, it means that not all carts need to be equipped with a tow bar.

Why Buy a FlexQube Mother-Daughter Cart?

The Mother-Daughter cart concept with the FlexQube system (or Routenzug in German) is the most versatile and flexible solution on the market. The carts and trolleys can be integrated with many of the different mother-daughter systems on the market including the STILL LiftRunner E-frame, B-frame or C-frame system and the Linde Tugger Train with e.g. the Bridge Type design. FlexQube also offers other types of mother-daughter systems including frames for small carts. These can include 1, 2, 3, 4 or 6 daughter carts in the same mother frame. These solutions make it possible to disconnect the daughter cart from the mother cart and place it at work stations or at the assembly line in a quick and ergonomic way. The daughter carts are also easily pushed onto the mother carts and locked into position.

The carts are lighter than welded carts and lock safely and quickly into the mother cart frame.
While other companies provide standard-sized mother frames and solutions, FlexQube can offer custom-made designs using the LEGO® inspired building block system.

Since the beginning of FlexQube we have spent much time and effort not only into setting up the most versatile cart system but also into designing state-of-the-art and modern material handling solutions including durable, efficient and ergonomically required mother-daughter cart systems.

Our daughter carts and trolleys are either transported on the floor with no need to push them up a ramp which is heavy and sometimes impossible to do for some operators. The unloading of daughter carts from other mother cart systems on the market where the carts are rolled onto an angled ramp is very dangerous if the operator tripped or fell and their legs collide with a 2000 lbs (approx. 910 kg) container cart. This is not the case with the FlexQube mother-daughter cart systems. We also integrate our carts with the STILL LiftRunner system where the carts are raised off the floor using a hydraulic or pneumatic system.

Choosing between a tongue and hitch tugger train system and a mother-daughter type can be tricky. Below we offer some pros and cons with both concepts. FlexQube can supply carts and dollies that would work with both a tongue and hitch setup, as well with different mother-daughter cart concepts.

If you connect the carts together with a tow bar, it is possible to create what we at FlexQube refer to as a ‘low rider’ (sometimes referred to as a lowboy cart); a cart that has a very low loading height (short distance from floor to the loading deck). That makes it possible to stack taller loads (bring more material at the same time and hence gain in productivity) on the cart and still have the material presented in an ergonomic height for the operators. With great quality and proven heavy duty 5 inch (125 mm) polyurethane casters that are integrated into the cart base, the steel deck will sit just about 5.5 inches (135 mm) off the ground. With the high-quality casters, the carts run silently around the plant and work perfectly on many floors, even those in a less good condition.

Since there is no frame that limits the size of the dollies, as in a tugger system based on separate frames, the possibility to mix and match carts in different sizes in the train is unlimited. That allows great flexibility to use different sized containers and types of carts; kit carts, pallet carts or shelf carts, in the same train set, mixed differently on each route.

By being independent of the frames, the number of carts in each tugger train is also adjustable/flexible. Run 1, 2, 3, 4, 5, 6, 7, 8 carts (or more depending on your fork lift aisle width) in the same train and connect and disconnect as you wish since there are no frames setting the limit for the number of carts at the same time. Just as well as there will be no empty slots in the train if you only need to run two carts but have four frames, where two will be empty if you use the mother-daughter type concept.

Most of the mother-daughter frame systems today only allow release on one side of the frame. One exception to this is the B-frame sold by STILL GmbH that FlexQube has an official partnership with. This means that the routes must be planned in such a way that the frames are set to open to the side where the material is needed. Since there is a need for a handlebar, most of the times to allow an ergonomic handling of the dollies for the operator, the dollies need to be rotated 180 degrees when taken off the train and placed at the work station. That kind of movement is one of the worst from an ergonomic standpoint for the human body and something that HSE (Health, Safety and Environment) officers often complain about.

Using a tongue and hitch system with fixed casters placed at the centre of the cart allows release from the train to both sides of the aisle. It is also much easier to turn the cart to its intended position at the line since it only needs to be turned 90 degrees. And anyone who has tried to move a cart with four swivel casters compared to a cart with fixed casters at the centre of the cart and swivel casters in the short ends, knows how much easier this is.

Release cart and turn to either side of the aisle with fixed casters at centre of the cart.
Fixed casters at the centre of the cart and tongue and hitch setup allows release to both sides of the aisle.

A natural benefit that is always included in the FlexQube concept is the use of more lightweight carts compared to welded carts. As a matter of fact, in a direct comparison between FlexQube and competing cart suppliers on the US market, one of our customers found the FlexQube cart to be 40% lighter. This cart holds 2000 lbs. (approx. 910 kg) and the customer has been using 100 of these carts for three years now.

Another important aspect concerning the release of the carts is the angled ramp or slope that some tugger train suppliers use. The ramp has a slight incline allowing the daughter cart to be connected to the mother cart without having the casters of the daughter cart touching the ground during transport. This means that heavy carts must be pushed up a ramp, against gravity, something that can be difficult for operators to handle. The greater risk though lies in the fact that upon release of the daughter cart from the mother frame, the daughter carts slides off the ramp in a motion that could cause injuries if operators trip and the cart hits them. This specific risk has also been identified by some of our clients, causing them to prohibit this kind of push up mother-daughter cart system in their plants, just from a safety perspective.

Heraclitus, who lived about 500 BC, already then realised one important thing that is the core of the FlexQube concept; ‘Change is the only constant’. Even 2,500 years back Heraclitus got it right; nothing will stay the same forever, everything changes. And nowadays that is more true than ever.

Volumes change, mix change, products change. More and more often.

FlexQube believes that making welded carts in this market environment is a bad idea. Using a fixed mother cart frame system in an environment where mix is high and products and things change rapidly could be a bad idea as well. But keeping a standard frame set could also be something that limits the variation and sets the boundaries for the logistics system. But, in that case, make sure to have the flexibility built into your carts instead.

With the FlexQube concept, the daughter carts can be adapted to new mother frame brands, new sizes and so on. The way of moving the carts can also be changed over time, it could just as well start out as carts to be used in a mother-daughter tugger system but later change to an AGV or Robot integration. With the modularity in the FlexQube concept, this is possible at a whole other level compared to welded solutions.