Skelecs: Part 2 – The Layout

Work is over, I’ve had my summer holiday – holiday and I’m now home! Having unpacked literally a shed load of packages…

Bulk buying…?

…I eventually opened each and everyone (this is literally my equivalent of Christmas!), obviously most excited at the prospect of the hub motors, controllers and steel.

As I’d posted my “plans” in my previous post, I won’t repost the plans I will however show my layouts. The easiest way for me to envisage how the final items should look without committing to cut steel is to literally lay it out on the ground!

A laid out pair of Skelecs! Yep, the front casters are upside down, it’s just hard to put them the other way up when they want to move 24/7

Yep, the steel is oily as hell! On the other hand, kudos to Austen Knapman, they’ve done a great job with the custom cut steel, all of it within a nice tolerance!

Motor testing
Obviously, having received all the parts, I want to test them out, especially the wheels! This warrants a high performance test setup, by which I mean an unattached vice on my desk, my LiPo battery, Greentime controller, an old pot and some copper foil…

Since that video however, I have added a more safe permanent mod to each of the controllers consisting of an inline fuse and a proper XT60 connector for battery connection! No more need for random crocodile clips.

Minor motor mods, the majority of unused controller ports are tied together with cable ties.

Currently, I’m running the motor in sensorless mode which is supposedly all around less efficient, the only reason for this however was my initial match up of the hall effect sensor outputs/inputs (green to green, blue to blue, yellow to yellow and obviously power) seemed to run the motor in a really weird juddery action. Switching the hall effect connections round seemed to solve the problem, though after reading the motor controller operated sensorless-ly, I decided to take this route. Really, for <£11 these motor controllers are exceptional!

Braking! Who doesn’t want the ability to brake while careering down a pathway into an old lady and her trolley? Best way to get an asbo by assaulting old people? I think so! Unfortunately, in the real world, this would also likely end in the confiscation of my skelecs which I’m not so amused by the thought of. So! Solving this problem is actually relatively hard, I have no discs and the only way I could think of for mechanical braking would be to apply a plate on top of some of the wheels, increasing wheel wear and being generally uncool. Therefore, I’ve decided to take a look down the regenerative/dynamic braking route. According to the controller advert, my controllers should support “E-ABS” which I’ve read on the internet can generally be the Asian way of explaining regenerative braking. In theory, I love the idea of regenerative braking. Using your movement to recharge batteries and also bring you to a useful and electronically controllable stop. The problem I see here however is where that energy is dumped! In standard regenerative braking form, that energy is dumped back into the battery which in my eyes would be fine for an SLA or NiMH battery. My problem however is with the fact I’m using Li-PO batteries which not only scare the life out of me while they sit their doing nothing, scare me with the thought of me trying to dump 2kJ of energy back into them from me braking down a long hill! Therefore, as of yet, I’m looking down the dynamic braking route of essentially regenerative braking but instead of dumping the energy back into the batteries, dissipating it into a shunt regulator and burning it off as heat. Inefficient yes but much safer for my batteries and therefore me!

This is however and area that I need to look into more so hopefully my generic internet research will point me in the right direction… On the plus side, any Li-PO explosions will be pointed forward, backwards and outwards of my legs as the batteries will be contained in nice thick steel extruded U channel.

Adding by shoes gives a bit more perspective! I’m a size 8

Tomorrow (today, its post 12:00am), I’ll be getting started with the drilling! Unfortunately, drilling the double D shaft for the hub motors is a task a bit out of my ability if I want to get it done efficiently. Instead, my mums partner is a CNC operator and has offered to drill just the DD holes for me by the end of the week, wahoo!

Custom BLDC controllers
This was actually a relatively big deal and was one of the tasks I was most looking forward to with this project. After discovering however how efficient and high quality the greentime controllers are, I’ve but this project on the back burner and I’m currently concentrating on the wireless control and getting a base model built. Once the mechanical work is done, then I can start pimping out the controller with my own stuff! At least I now have some hub motors that I can scope out and figure out how on earth to drive, along with some MOSFETS and darlington transistors!

Keep tuned for further updates – this week should be packed with them!

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