Simple kinematic simulation of a TreppenSchlepper

After getting in touch with HotInt (see previous post), it was time to try a little TreppenSchlepper multibody dynamics model myself. After a few hours of try & error (and a little help from HotInt support; these guys a very quick and supportive, really great!) a TreppenSchlepper model Version 0.1 was ready to be simulated. 

 Ok, even "0.1" is quite exaggerated, because it just consists of 3 parts: the FootPlate, an OuterShell and a SpringDamper in between.

The SpingDamper is just a simple substitute for the ElevatorCylinder which would be really needed, but it at least links the other two parts and provides the damper for that link. The elevation itself is currently done by a load (called ElevatingForce) defined for the z-Axis and acting on OuterShell. A Contact1D acts as coordinate constraint, making sure the OuterShell can move up but not into or below ground.  

FootPlate is fixed to ground with a RigidJoint element. The model (a text file with extension .hmc, to be fed directly into HotInt) can be found here (Filename TreppenSchlepperV0.1.hmc), while a simple up/down simulation animation is here.

The blue part (OuterShell) is modelled having a mass of 30kg , which gets lifted by a force F(t), plus gravity and spring force counter-acting.

I'm not a mechanical engineer, so if you are or know an expert: help is greatly appreciated. Just mail me at treppenschlepper@gmail.com

What could be the next steps?

1. Model a SlidingInnerShell:
   This crucial part is currently missing in the TreppenSchlepper. The SlidingInnerShell sits between the ElevatorCylinder and the OuterShell. It is needed to allow TreppenSchlepper to move forward onto the next step once it is elevated enough.
2. Model a stair
   At least a LowTread -> Rise -> HighTread for the beginning, to have something TreppenSchlepper can start to climb up
3. Model the ElevatorCylinder
   Currently it is only a SpringDamper, but eventually this should become the actuator doing the actual lifting. Probably that's a part which needs to connect to some kind of controller (to be modelled as IOModule in Hotint ?).
4. Add wheels to OuterShell
   This allows TreppenSchlepper to move on flat surfaces, like the floor, and to position itself correctly in front of a step.

As a summary, the simple TreppenSchlepper consists of

• FootPlate
• ElevatorCylinder (currently simplified with a SpringDamper)
• SlidingInnerShell (we really need that!)
• OuterShell + wheels

Then we should be able to simulate different phases during operation of TreppenSchlepper, like

#	Phase	remarks
1	move to starting position in front of step	Under control of path planning algorithm
2	Elevation
3	slide to upper level of step	actually, this will be a quite interesting phase. We need to make sure nothing gets out of balance
4	Lift, fetch and retract FootPlate

As always, comments and feedback (and help!) is appreciated, contact me treppenschlepper@gmail.com or directly via commenting this post below.