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It’s Working!!!!
Yesterday was a very busy day but late last night I gave the mountain wheelchair it’s first test-drive and it climbed up my sofa with complete ease:
https://vimeo.com/281047434
Keep in mind that it currently doesn’t have any brakes for the descent, but that’s proof of concept right there!
It’s also drives over car batteries and those boxes containing 5 packs of a A4 printer paper, also with incredible ease, hence putting a sofa in front of it. The rocky path up Snowdon should be a doddle 🙂
Large rocky steps (otherwise known as Granny Stoppers) on the Llanberis Path
The final rocky path towards the summit
As was to be expected though, not everything worked perfectly; it is incredibly difficult, in fact, it’s virtually impossible, to get the thing to steer. It could in part be due to a problem with one of the motor controllers (One of back motors is currently inoperable). Hopefully I can get that fixed today and then see what happens. It could also be due to a problem with the rocker bogie mechanism but I have implemented a solution to this in the smaller prototypes. Hopefully the same solution can be applied here. Failing that, I’m going to have to completely rethink the steering mechanism.
So on the downside, the steering is a big problem that could potentially take much time, effort and money to resolve (although it could also be a quick fix), but on the plus side, the wheelchair looks completely capable of getting up those rocky steps so often encountered in the mountains.
The Mountain Wheelchair Climbing My Sofa With Ease It's Working!!!! Yesterday was a very busy day but late last night I gave the mountain wheelchair it's first test-drive and it climbed up my sofa with complete ease:
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This is just a very quick post to demonstrate (how excited I am) that progress is being made on the wheelchair frame:
Mountain Wheelchair Frame Progress
Bits of it are cable-tied together at the moment, and one of my welds isn’t straight so I’ll have to redo that part again, but on the whole it’s starting to take shape. When you sit inside it, the dimensions feel perfect. Likewise, when you stand back and look at somebody else sat inside it, everything looks spot on. And my welds are getting better too:
Mountain Wheelchair Weld Improvement
There isn’t really a great deal that needs to be done before I can take it out for its first test drive.
It’s Starting to Look Like a Mountain Wheelchair! This is just a very quick post to demonstrate (how excited I am) that progress is being made on the wheelchair frame:
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At long last, I finally decided to go ahead and start building the mountain wheelchair frame.
For a long time I’ve been using a computer to create simulations of the wheelchair overcoming obstacles and different types of terrain. Every time I do, I notice something new which is going to create a problem. For this reason, I’ve been extremely reluctant to actually start the build process (in case I decide to revise the design).
Something changed the other day, I guess I felt like I was wasting time and it made more sense to get the thing built and see what happens. So with much trepidation, I cut into the forks:
Eek! Chopping the Wheelchair’s Forks!
Having finally cut them, this spurred on a wave of activity and by the end of the day I had built something that was starting to look like a Mountain Wheelchair Rocker Bogie:
Mountain Wheelchair Rocker Bogie
Wow! It’s actually coming together! And what’s more, I’m really pleased with how straight everything is and how well all of the angles have turned out. I don’t know what’s going to happen once it’s under load, but so far building the mountain wheelchair is going according to plan.
Building of the Mountain Wheelchair has Commenced At long last, I finally decided to go ahead and start building the mountain wheelchair frame.
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Whenever I’m sat at home and I turn on the TV, my first port of call is almost always The Discovery Chanel. Many of their shows feature experienced mechanics running beautiful welds as they build custom cars, bikes and such.
Unlike the splattered messes that I’ve been making with my arc welder, this weld is a thing of beauty:
Example of a perfect TIG welded bead
To achieve welds like this, a process called TIG welding (Tungsten Inert Gas) is used. As far as I know, TIG welding is also the only suitable method for welding alloy (the material which is being used to build the mountain wheelchair frame).
The only problem with this is that TIG is generally considered to be the most difficult welding process to learn.
Last week, Dan from Coastal Welding very kindly gave up some of his time to help set up my welder and get me started with TIG welding.
It was clear from the off that Dan is a very skilled craftsman and he was instantly able to get perfect results. The same couldn’t be said for my efforts:
My first attempt at TIG welding
My first attempt at TIG welding
My first TIG welded joint
In amongst all of this mess, there are actually some welds which aren’t too bad. For a brief moment I almost felt like I knew what I was doing 🙂
Lots more practice required but this a big step towards building the actual frame for the mountain wheelchair.
Learning to TIG weld Whenever I'm sat at home and I turn on the TV, my first port of call is almost always The Discovery Chanel.
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Wow! It’s been over two months since I last updated the mountain wheelchair build log!
Several things have attributed to this. For one, I’ve been busy in work. Also, I bought a Land Rover Defender back in April as a means to get Ada back into the mountains. When I bought the Defender I didn’t realise how much of my time would be taken up trying to keep it running. I’ve had to replace so many parts that it’s almost an entirely different car. It’s been absolutely worth it though because thanks to the Defender I’ve been able to get Ada (and myself) back into the great outdoors.
Defender in the Mountains
Defender in the Snow
Defender with Broken Steering
Overlooking the Conwy Valley
Defender with a Canoe on the Roof
Asleep in the Defender
Thanks to the Defender we don’t have to walk far to get that mountain experience, which is good because Ada still gets very tired and whilst we’re out walking her legs will often give way without any warning.
When this happens it usually means that I have to carry her back to the car. This is not always an easy task and has lead to many improvised carrying devices using whatever is to hand at the time. Accordingly, we try to plan our adventures based on how much we think Ada is able to achieve but this can vary from one day to the next.
That being said though, her health is constantly improving and each month she is able to do more than the last. Having the Defender has, in my opinion, had a huge influence on this! It’s made getting outdoors much easier and spurred us on from one adventure to the next:
https://vimeo.com/276014986
Last week Ada did the biggest walk (6km) since being diagnosed with M.E. Compared to where we were this time last year, this is such an enormous change. It was only in December that we had tears of Joy when Ada was able to stand on her own two legs again.
As I proof-read this post, it’s great to see so many photos of Ada smiling again! Ada’s happy, she’s enjoying life, and that has always been the driving force behind the mountain wheelchair project. Having achieved that goal, where does this leave the mountain wheelchair?
We have been so incredibly lucky to see continued improvements but this isn’t the case for everybody. There are so many other people who could benefit from the wheelchair that it would be doing a tremendous disservice to discontinue the build. So with this in mind, watch this space…
Lots of Adventures, now back to the Wheelchair Wow! It's been over two months since I last updated the mountain wheelchair build log! Several things have attributed to this.
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All Six Motors for the Mountain Wheelchair are Working
All Six Motors for the Mountain Wheelchair are Working
There were a couple of tasks that had been causing me a bit of a mental block and preventing progress with the mountain wheelchair so it’s really pleasing to have them ‘done and dusted’ so that I can get back to it.
One task was to disassemble all of the wheels, make some modifications and then reassemble them all. Having done this, all of the spokes in the wheel rims are sitting far better than…
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As I’ve said many times before, my engineering background is extremely limited, yet this mountain wheelchair project demands experience in a wide range of engineering disciplines. As such, I have needed to spend considerable time in online forums seeking advice from people with more experience than myself. The forums, and the advice received, have been instrumental and I would not have been able to get this far without them. That being said, at times, some of the feedback I’ve received has been a little disheartening. For example:
“I don’t think I would let my daughter climb up a path like that in a vehicle on wheels and especially knowing she would need to roll down again”.
“Are you really planning on letting your daughter descent those steep parts on 6 bicycle disk brakes all the way down? That will be a workshop with a ‘steep’ learning curve in down hill biking”.
“The more I think this through the more I dislike the idea. Especially as you don’t seem to be very knowledgeable in this area (neither am I BTW) so it looks like this might end in tears. Please rethink this challenge and don’t risk your daughters health or worse with what seems a noble cause”.
Whilst I’m able to shrug these comments off with what might be considered determined ignorance, Ada on the other hand hasn’t yet developed this skill and comments like this have somewhat diminished her sense of hope in the project.
Although these comments have no impact on my desire to keep pushing on, I have of late been coming home from work completely exhausted and finding it difficult to keep working on the wheelchair.
To try and reduce my workload, I had been questioning how useful this blog is. I mean, who actually reads it anyway? Less time blogging means more time for building right?
As chance would have it, just as thoughts of discontinuing the blog were starting to run through my mind, in quick succession we received a number of messages through our Facebook page. For example:
“I am watching what you are achieving with great interest”.
“I love reading your site. Keep it up! I’m 33 now and have grown up in a wheelchair my whole life. There is nothing I haven’t been able to do with a little bit of planning, effort and engineering”.
“I used to be a fell runner and miss getting out on the hills […] This wheelchair would give me the opportunity to get out and explore and enjoy the off beat track again. I want this chair! I love the design it is so upbeat and mountain cracking!”.
“Good luck with everything you are both inspirational”.
On top of this, in the very same week, I was sat at my desk in work when a colleague came in brandishing an envelope which she suspected belonged to me. I didn’t know of any other G Davidson in the college so I proceeded to open it. I was absolutely gobsmacked when I did! It was a letter of encouragement from the Welsh Assembly! The letter reads;
“Dear Mr and Miss Davidson, I am writing to congratulate you both on your inspiring ambition to create a specialised mountain wheelchair in order to continue your adventurous outdoor exploits.
I understand that Myalgic Encephalomyelities, or ME, can make it very difficult to continue pursuing a variety of activities, particularly as the models of mobility aids available are not designed for the rich and wild terrains that we have in [North Wales]. Therefore, your determination to continue pursuing the activities you enjoy, and think creatively to solve these problems is especially commendable, and should be a model for us all.
With all the hard work and gritty determination that you have both shown, I have every confidence that you will fulfil your ambition to reach the top of Snowdon, and i hope you take the time to reflect on your journey there when you do.”
Letter regarding the Mountain Wheelchair from the Welsh Assembly
The kind words both from the assembly member and from the followers on Facebook offered an immense boost in motivation and I’d like to thank you all for taking the time to write to us. It couldn’t have come at a better time for me and has given me the impetus to keep the blog going. When Ada read the messages her face lit up, then she walked away doing a little dance with a smug look look on her face 🙂
Whilst I’m here, I’d also like to say thank you to one person on Facebook who consistently shares all of my posts and helps to encourage interest in the mountain wheelchair project. If you’re reading this Mervyn, then thank you, your support is deeply appreciated.
What’s Next?
It’s Friday today and in a few hours the college will be breaking up for Easter. Hopefully this means a short break for myself to recharge my batteries and then it’s back to building the mountain wheelchair with renewed focus and fewer distractions. Lots of parts and tools have arrived from overseas so hopefully I’ll be able to make substantial progress. Watch this space…
Words of Encouragement for the Mountain Wheelchair As I've said many times before, my engineering background is extremely limited, yet this mountain wheelchair project demands experience in a wide range of engineering disciplines.
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Working Radio Controls for the Mountain Wheelchair
Working Radio Controls for the Mountain Wheelchair
At long last I managed to get the radio controls for the Mountain Wheelchair to work!
http://mountainwheelchair.com/wp-content/uploads/2018/03/MOV_1671.mp4
It’s taken so much and time and effort to get this to work. Not wanting to get too technical, I basically needed a way to convert an RC Receiver 1-2milisecond pulse to an analogue 0-5volts. I tried all sorts! In the end I found a very…
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At long last, I now have a Tube Bender! This means that I can actually start fabricating the frame for the Mountain Wheelchair!
A Tube Bender to build the frame for the Mountain Wheelchair
There were lots of tube benders to choose from, all of which were beyond on my budget, that is until I found this. This “Affordable Bender” came all the way from America, complete with dies to bend the two sizes of alloy tube I intend to use, and all for approx £500. Considering that the dies alone usually cost about £400, this was an absolute bargain!
I don’t expect this to last a lifetime, or to be able to produce complex bends, but it should be sufficient to get at least one Mountain Wheelchair built.
The Mountain Wheelchair Project now has a Tube Bender At long last, I now have a Tube Bender! This means that I can actually start fabricating the frame for the Mountain Wheelchair!
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Most of my time of late has been spent working on the electronics for the mountain wheelchair and more recently building the wheels, however, I have, for some time now, been thinking about the brakes…
When testing the smaller prototypes for the mountain wheelchair, I discovered that:
“When [the mountain wheelchair is] overcoming obstacles such as large 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 [and sometimes just wheel-spin, or even worse, get stuck]”.
To prevent this from happening, I had been thinking about using hydraulics or linear actuators to lift the front wheels off the ground before approaching the obstacle. A far simpler method is just to use the motors and brakes which are already on the wheelchair therefore requiring very few additional parts and reducing the overall weight of the wheelchair.
To demonstrate this; if you were to apply power to the front and middle wheels, whilst at the same time applying the brakes to the rear wheels, then the front wheels would lift off the ground resulting in an increased possibility to overcome large steps. Like so:
http://mountainwheelchair.com/wp-content/uploads/2018/03/Rocker-Bogie-Mountain-Wheelchair-Brakes.mp4
This seems incredibly easy to achieve from an engineering point of view, the problem is making it easy for the driver of the wheelchair to operate. If you only had rear brakes, then the wheelchair would skid under braking, so you need brakes on all wheels.
As I’m planning to use hydraulic disc brakes off a mountain bike, this does present some problems. These brakes usually have one brake lever for each brake caliper. For a six-wheel-drive wheelchair requiring six brakes, having six brake levers, I think, would be difficult to operate.
I have however found this hydraulic hose splitter made by Hope Tech. If I were to use these, then I could theoretically operate three brakes from one lever (one lever for the left, and one for the right). This way you could skid-steer the wheelchair down a mountain just by operating the left or right brakes.
Hope Tech Hydraulic Brake Splitter
If you have one lever to operate the three brakes on one side of the wheelchair, and another lever for the three brakes on the opposite side, how then do you apply the brakes to the rear wheels only? With a solenoid valve on the hydraulic lines which feed the front brakes perhaps?
Solenoid Valve for Mountain Wheelchair Hydraulic Braking System
At the flick of a switch, maybe a thumb operated switch on the top of the joystick, a solenoid valve would close, thus prevent the hydraulic fluid from reaching the front brakes. To help illustrate this, I made this (very) rough sketch:
Rough Sketch – One side of Mountain Wheelchair Braking System
As you can see in the sketch, I plan to have the brake lever upside down and mounted to the joystick levers (You can see this more clearly here). For testing purposes, I made this:
Mountain Wheelchair Disk Brake
As an aside, the picture above shows a disc brake on one of the motors. This is a very cheap disc brake that I found in the back of my shed, it’s about 20 years old and the pads are worn down. It does at least allow me to do some testing; if I squeeze the brake lever as hard as I can, the motor still has sufficient torque to keep turning. I’ve run the motor like this for five minutes trying to get it to overheat in order to test the thermal protection mechanism which I installed. After five minutes the disc brake was almost glowing hot and smoking, but the motor showed no signs of warming up. A positive outcome.
Anyway, back to the topic at hand…
Hydraulic brakes on a mountain bike have a reservoir built into the lever to hold the hydraulic fluid. When you squeeze the brake lever, the pressure moves the fluid from the reservoir to the brake calipers, thus forcing them to close. This is great, except that the levers are designed to operate one caliper only, not three. Actually, and this is where the gaps in my experience of engineering start to appear again, I’m not sure that it’s the reservoir that causes the problem, but rather the levers don’t create enough pressure to operate multiple calipers?
I spoke to Hope Tech and they’ve reassured me that their “Tech 3 Lever” will operate two of their “X2 calipers”, but not three. This is great for two reasons..
First of all, they both come in purple, so this will make Ada happy:
Hope Tech 3 Lever and X2 Caliper
Perhaps more importantly though, I think it might be better not to have brakes on the front wheels and I’ve made this video to help illustrate why. The video represents the wheelchair rolling down a hill and then applying the front brakes. As you watch the video, imagine what would happen next.
http://mountainwheelchair.com/wp-content/uploads/2018/03/mountain-wheelchair-rocker-bogie-front-brake-problem.mp4
Just like on a mountain bike, it would want to “throw you over the handle bars”. On the mountain wheelchair this effect is amplified because of the rocker-bogie suspension mechanism. In the video, it’s easy to imagine how the centre of gravity moves to the front of the wheelchair and would result in quite a nasty accident with the full weight of the wheelchair, its heavy motors, batteries and frame coming down on top of you.
Ultimately, I think this is going to be a trial and error thing during which time there are some other ideas which are worth exploring.
It would still be possible to have brakes on all six wheels, it would just have to be setup so that there wasn’t much braking force at the front wheels.
As well as this, the motors in the wheels have some resistance anyway; they act as generators which recharge the batteries. I plan to have a “knob” near the joysticks which lets the rider adjust how much regeneration the motors are doing. In effect, this dial would adjust the rolling resistance of the wheels. In this regard, perhaps brakes aren’t needed on the front wheels?
Perhaps the best solution though would be to replicate what happens on a bicycle. i.e. have one lever for the front brakes and one for the rear. This would give the rider complete control of the braking balance between front and rear wheels. In fact, this would then remove the need for the solenoid valve. To lift the front wheels off the ground, you would just have to squeeze the left brake lever (which would operate the rear brakes) and drive forwards. Far simpler than having to operate switches as well as brake and drive at the same time and for people who previously were passionate cyclists, this setup might be more familiar to them. The only problem with this is that it removes the ability to steer the wheelchair by operating the brakes. As I say, I think this is largely going to be trial and error.
The Mountain Wheelchair Braking System Most of my time of late has been spent working on the electronics for the mountain wheelchair and more recently building the wheels, however, I have, for some time now, been thinking about the brakes...
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Yesterday, when I got home from work, I was absolutely shattered and didn’t want to do much of anything other than lay down on the sofa and fall asleep, but as I lay there, struggling to keep my eyes open, I glanced over the mountain wheelchair parts and decided to crack on!
I’m really glad I did as I managed to get all six of the wheels laced. Ta-da! Six wheels for the mountain wheelchair!
Six Mountain Wheelchair Wheels
It’s taken quite a lot of modification for the wheel rims to accommodate the spokes. I think they might be motorbike or scooter spokes? By the time I’d finished the fifth and six wheels, I realised I’d done a much better job of these than I had the first and second wheel. With this in mind, I will definitely need to do two wheels again and perhaps even four. Still, I’m really happy with the result and the spokes look like they’re up to the task of transferring the motor torque to the wheels.
As I was tidying up the mess I’d made in my “living room” whilst lacing the wheels, I decided to throw out the boxes that the motors had arrived in. The sense of elation I got just from throwing out some boxes is, in a sense, quite funny. For me though it signified a step forward. No longer are the motors being kept in storage; I’ve actually started building this thing!
The really cool, yet at the same time worrying thing about having all of the wheels made is that in the process, I realised how quick and easy it would be to make a four-wheel-drive platform for testing purposes. Nothing complicated as I don’t want to waste too much time on it, just a plank of wood laid across four wheels would be sufficient. This would at least allow me to see if four of these motors are capable of carrying a heavy bloke like me up a hill. If not, then it will put a huge question mark over the entire Mountain Wheelchair project!
Four Wheels and a Plank
All of the Wheels are Laced… and a Big “?” Yesterday, when I got home from work, I was absolutely shattered and didn't want to do much of anything other than lay down on the sofa and fall asleep, but as I lay there, struggling to keep my eyes open, I glanced over the mountain wheelchair parts and decided to crack on!
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It’s taken me the best part of the day to filing away so that the motors fit onto the forks, but it’s done, and all six motors are now sitting in the forks. Shoulder aching, I decided to push on and managed to get another wheel laced, then much to Ada’s delight, mocked up part of the frame (a bogie) for the actual Mountain Wheelchair!
Mountain Wheelchair Bogie Mockup
Mountain Wheelchair Bogie Mockup It's taken me the best part of the day to filing away so that the motors fit onto the forks, but it's done, and all six motors are now sitting in the forks.
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Woohoo! It’s been a busy day in the shop. The spokes FINALLY arrived from China today and I managed to get the first wheel made.
It’s a motorised mountain wheelchair wheel!
First Motor Laced on a Mountain Wheelchair Wheel
Most of the the time was spent with a drill and file trying to get the separate parts to fit together, so although it’s a little bodged at the moment, it’s taken such a long time to get to this point that it feels like an important milestone.
I got Ada to control the throttle for a moment whilst I let the wheel roll on the floor. It’s much faster than it needs to be, but I think that will add to the fun of driving the wheelchair once it’s finished.
As well as the spokes, the “C Washers” which I had laser cut arrived today too and the guys at Microkerf did an excellent job. They’ve been extremely helpful and I’d definitely recommend them:
As I said in a previous post, I can’t be the only person who needs these washers so have listed them on eBay to try and raise some funds for the wheelchair.
E-Bike C Washers
Also currently on its way from the USA is a part which I hope will enable me to make the mountain wheelchair radio controlled – useful for testing purposes and driving it on/off trailers etc.
It’s also worth mentioning that Google doesn’t like us at the moment and we’re currently on page 3 for the search terms “mountain wheelchair”, however, on Bing at least, we are the very first result at the top of page 1.
All in all, a successful day! 😀
The Mountain Wheelchair has its first Wheel Woohoo! It's been a busy day in the shop. The spokes FINALLY arrived from China today and I managed to get the first wheel made.
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Composited 3D render of the Mountain Wheelchair
Composited 3D render of the Mountain Wheelchair
Just for fun, here’s a render with the mountain wheelchair composited onto a HDRI background.
3D render of Mountain Wheelchair
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Just a very brief post as I wanted to share an updated concept drawing of the Mountain Wheelchair:
Mountain Wheelchair Concept Drawing
Another Updated Concept Drawing of the Mountain Wheelchair Just a very brief post as I wanted to share an updated concept drawing of the Mountain Wheelchair:
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Some more parts arrived from China today which have enabled me to make some progress with the wiring for the mountain wheelchair:
Mountain Wheelchair Wiring
Put Simply
In simple terms, these components add some additional protection into the circuitry and much to Ada’s delight, the wheelchair now has a key ignition switch.
Detailed Version
In more detail, each controller should draw a maximum of 15 amps. With 6 controllers, that’s a peak of 90a (15 * 6). So the first component on the positive wire is a heavy duty 200a fuse.
The next component is the big red emergency stop key switch. This acts as a master switch and completely disconnects the battery.
Next is a keyed ignition switch which goes to the power switch on the controller. Although this is still operating at 48v, it only draws a maximum of 40ma so it is much easier to route cable so that the key is somewhere accessible. This also has an inline 2a fuse.
After this is a 200a main contactor. The key switch closes the contactor at which point the large capacitors in the controller draw a substantial amount of current. To prevent the contactor from welding closed as a result of arcing, there is a 1k Ohm 10w resistor across the main contacts. Because this resistor is in place, it meant that the controller was always connected to the battery (regardless of whether the contactor was closed or not), thus draining the battery. Hence the need for the big red eliminator.
The plan is to have one key ignition and one contactor to supply power to all six controllers.
Although not shown here, I’ve also successfully wired a thermistor inside the motor housing. The manufacturers have suggested a theoretical max operating temp of 120℃ for the motor. To allow some wiggle room, the controller will cut power to the motors if they reach 90℃.
What’s Next?
The next job in terms of wiring is to include a watt meter. To this end, I’ve purchased a really cool Eagle Tree E-Logger. Not only does it monitor and record power consumption, temperature, speed and altitude, but also plots all of this into graphs and with an additional GPS unit, can display all of this data alongside a satellite map of the route you’ve taken. This sounds extremely useful because it will allow me to see where spikes in temperature and power consumption have occurred, as well as providing the tools I need to make far more accurate estimations of battery capacity needs. Although it’s intended for radio controlled aeroplanes, it’s good for up to 80v and 150a so should be perfect for the mountain wheelchair.
Eagle Tree E-Logger V4
Wiring for the Mountain Wheelchair is Coming Along Some more parts arrived from China today which have enabled me to make some progress with the wiring for the mountain wheelchair:
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I finally bit the bullet last week and outsourced the manufacturing of parts for the first time.
The mountain wheelchair frame is in part being made using BMX bicycle forks. The parts at the end of the forks, where the motor axles sit, are called dropouts. Looking at the image below, you can see that there is a circular indentation in the dropout where the motor axle sits.
Mountain Wheelchair Lawyer’s Lips
This indentation is intended for quick release wheels. If the cyclist doesn’t tighten up their quick release wheels properly, then this raised edge will help to prevent the wheel from falling off. The common term given to the raised edge is a “Lawyer’s Lip”. I believe this is because they were added for legal reasons.
For the mountain wheelchair a quick release mechanism isn’t needed. In fact, it creates a problem; because the axle isn’t perfectly centred in the dropout, this means I don’t have a washer to fit, and therefore the nuts which hold the wheel in place will only press against the raised edge. The front forks on BMX bikes were designed for any amount of torque; they just hold the front wheel in place whilst all the drive comes from the back wheel. Considering the torque produced by the wheelchair motors, this becomes quite a large problem. If the nuts holding the wheel in place only press against this raised edge, then it’s quite likely that the wheels would fall off whilst driving the wheelchair in the mountains.
To help prevent this from happening, I decided to design a washer which would fit the void where the quick release mechanism is supposed to sit. To begin with, I 3D printed the part to ensure a good fit:
Mountain Wheelchair 3D Printed Lawyer’s Lips Washer
Safe in the knowledge that my measurements were correct, I started looking for quotes to laser cut the washers from stainless steel. The first quote for 20 washers was £150! Eek! That’s a lot of money just for a few washers.
The following day, another quote arrived for £80. Looking through the pricing structure, I realised that the £80 was a minimum fee, and that my parts were actually only costing £12. After discussing this with them, I discovered that I can order 150 washers for the same price as 20, so this is what I decided to do. Hopefully I can sell these on eBay and recover the costs. After all, I can’t be the only person having to overcome this problem.
The company have sent me a sample before placing the order and they seem perfect:
Mountain Wheelchair laser Cut Stainless Steel Lawyer’s Lips Washer
As I say, this is important for the mountain wheelchair because it will go some way to preventing the wheels from falling off, and it’s my first experience of outsourcing some of the work.
As said though, the forks aren’t designed for high torque motors, so whilst this will help to stop the wheels from slipping off, it does nothing to prevent the forks from snapping. I do have an idea for this, but this will have to wait for the moment as I have plenty of other things to be getting on with.
First Outsourced Parts for the Mountain Wheelchair Arrived I finally bit the bullet last week and outsourced the manufacturing of parts for the first time.
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