Hydraulic Syringe Mount Sorted

Few! Some progress was made today as I’ve just finished working out the details of how I’m going to mount a pair of syringes to the frame of the small prototype to act as a hydraulic differential. Just need to find a time where the 3D printers aren’t busy with other projects now :S

In other news, everything is sorted, booked and dotted lines signed for taking the engineering students up Snowdon next Thursday to take some measurements! Just need to keep fingers crossed for some mild weather.

Hydraulics Might be Better

My father has spent all of his adult life as a chief engineer in the merchant navy and although he’s now retired, I’m sure he still retains lots of useful information which I could tap into.¬†Yesterday he stopped by to drop off a birthday card and I introduced him to the project. I explained some of the difficulties I’d been having trying to find a balance between motor power and battery supply. He suggested using hydraulic motors.

With hydraulics, an electric motor powers a pump, which in turn drives oil at high pressure via flexible hoses to any number of hydraulic motors. The ship’s winches were powered in such a way.

Interestingly, shortly after he’d left I visited the endless-sphere forum where I’d been asking about how power is divided between motors and somebody else had also suggested using hydraulics.

This is a quick representation of what the system might look like:

Before my father mentioned it, I didn’t know there was such a thing as a hydraulic motor so I have lots of research to do. However, it seems a good investment of time because:

  • Gear ratio between motor and pump can easily be adjusted to get the right balance of speed torque
  • Hydraulic pumps in general have more torque
  • The motor can be kept spinning at its optimum range and increase the lifetime of the motor.
  • One motor means one battery
  • Hydraulic motors are cheaper than electric motors
  • Hydraulic motors seem easier to service
  • It removes the need for complex sprockets and chains to drive the wheels

First of all then, I need to make sure that such a system would still give the ability to have forwards and reverse on independent sides so that the wheelchair can turn on the spot, and when required that power could be delivered to individual wheels…

 

Some thoughts on Hydraulics

Last night I said the next thing I was going to do was explore ball joints, but as I was sat at a desk in work with no access to the physical parts or CAD software, I started thinking about hydraulics again and drew a quick sketch:

As I’ve mentioned, I think hydraulics have excellent potential. My only concern is that essentially the rocker bogie mechanism is inspired by NASA’s Mars rovers which employ a differential bar mechanism. Other methods I’ve seen use differential gears (and is the current method on the working prototype). I’ve never seen hydraulics being used for this purpose. Is this because it doesn’t work, or is it because nobody else has thought of it?

I know very little about hydraulics, much like all the other areas of this project ( :) ), but I can imagine that there’s likely to be some lag in the system as oil is pumped around and it won’t be as responsive as a geared system. Mind you this might not necessarily be a bad thing as it could potentially have a dampening effect which reduces the wobble in the driver’s chair even more?

It’s definitely worth exploring because if it does work, it presents far more freedom to position parts and the only part which needs to travel through the main body of the wheelchair is a flexible hose which connects the hydraulic cylinders on each side. This in turn gives you greater freedom to position seats, motors and batteries and the like as you’re note having to accommodate gears or bars but instead a flexible hose.

I also imagine that a hydraulic system will incur far less wear-and-tear than a geared differential, and less impact than a ball-jointed differential bar mechanism.

There other potential uses for hydraulics too but not knowing enough about hydraulics, a linear actuator might be better suited…

When overcoming obstacles such as steps, the front wheels are pushed into the step and with the traction created with all six wheels, the front wheels “drive” up the step. The problem is that the front wheels don’t always get traction.

To overcome this, you could use hydraulics (or a linear actuator), or perhaps even just the drive from the middle wheels, to lift the front wheels off the ground before approaching the obstacle:

This would greatly increase the chances of overcoming an obstacle. Without having done any research though, I imagine this would mean having to add the wight and power of some kind of hydraulic controller. Linear actuators on the other hand are just driven by electric motors so could use the power of the batteries (and perhaps even the motors) already attached. it is possible though that if you cut power to all of the wheels, then just delivered power to the middle wheels that the front wheels would automatically lift off the ground.

Another benefit of being able to do this is that it gives you a shorter wheelbase making it possible to turn in more confined spaces. It does however look a little unbalanced with the front wheels off the ground but the lifting up the middle wheel retains balance whilst still giving a shorter wheelbase:

Working Radio Control

It’s working!

I arrived home from work today to find that a number of parcels had been delivered by the postman. Amongst the parcels were metal ball joints for the rocker bogie system (more on this in another post) and the final components I needed to make a radio transmitter/receiver.

Essentially, this is a radio control with a forwards and backwards button for the each side of the vehicle. Once built into the prototype it should allow for a greater range of testing.

Getting this working has been extremely satisfying and I’m trying to put my finger on why that is. I guess that as I child I’d always wanted a radio controlled car and now as an adult I’ve built Ada’s little brother Eric a radio controlled lorry by commandeering a remote from another toy. This was also the case for the current working prototype. I guess that being able to make one from scratch just opens up a whole new world of opportunities for letting out the big kid in me.

In other news, it’s been a very productive day all around. The engineering students have started building their own prototypes (more on this later too) and being in class with them gave me the opportunity to splurge out all of the ideas that have been running around my mind.

I also had a chance meeting with another lecturer who suggested using hydraulics to equalise the rockers. I think this likely has great potential and needs to be looked into further. One of the advantages that I would expect is less wear and tear on moving parts and ultimately a more reliable wheelchair. I’m not sure how I’ll make a prototype, syringes maybe(?), but seeing as the metal ball joints arrived in the post today I’ll explore those first…

This page was last updated on April 18th, 2018 by .
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