Hydraulic Differential for Rocker Bogie

Recently, whilst building the larger prototype, one of the things that has caused delay is one of 3D printers being busy with other projects and the other one completely out of action. I spent most of last week stripping it down and rebuilding it and gave the working printer an overhaul whilst I was at it. It was a huge relief once both printers were up and running again and the quality of the prints are now better than ever.

With both working printers I’ve been able to revisit the smaller prototype for which I had designed a hydraulic differential using syringes. It works! Sort of…

Although it works, the syringes aren’t perfect and small air bubbles are being drawn in. As a proof of concept though, it’s great, and I think it has more potential than both the differential gears and the differential bar. The reasons being that there is less wear and tear on the hydraulics (than the other proposed methods) and therefore less maintenance with increased reliability, but also it has a dampening affect which should result in smoother ride for Ada.

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.

Hydraulic Piston (Syringe) Mount

Today I finally decided to make the website public and posted it on Facebook. The response has been amazing and it’s fantastic to know that there’s so much support out there. I’ve started up Facebook groups previously which haven’t generated much interest so it’s a huge relief that this project has been received so warmly. So thanks to everyone for liking the page and sharing it on Social Media.

Although publicising the website is a huge step forwards, in terms of the actual wheelchair lots of parts have arrived in the post including some 4mm tube to make hydraulic pipes for the syringes. It’s just about time for bed so working out how to mount it to the frame will have to wait, but in the mean-time here’s the finished design for the hydraulic cylinder:

*update* Here’s the printed version.

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…


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