Introduction: Mini Electric GoKart
There are quite a few GoKart Instructables here and in order to build mine I had to browse them all, The forums were also incredibly useful. What I will try to do here, is give a brief outline on how I built GoKart in the picture, provide the links from where I got the information and how I interpreted it, the equipment I bought "and" used and some key information in getting it to actually move.
I used aluminium extrusion throughout, it's more expensive but reusable and you don't need any water jets or CNC's to get it usable.
All in all the kart took several months, mainly because of work taking up mental and physical time, I should also explain now that I have a full workshop however I tried to keep the build as simple as possible and use as many generic parts as possible.
You may see prices in USD, SGD and GBP, I'm based Singapore so most of the time I had to look to specialist items else where. Just to note though.. USD and SGD are pretty similar, 100 USD + 1/3 will give you the SGD, double the GBP will give you the SGD, I could have got much cheaper equipment from Alibaba.com but what with so many potential issues, I decided to reduce the chance of error and stick with what others recommended.
Parts (mm unless stated)
Extruded Aluminium - 30*30*6000 - From 36SGD @ 5 metres
Aluminium Round Bar - 12mm Dia
Threaded Bar - M8 and M10 (Recommend Stainless Steel although pain to cut)
Brackets - came from same supplier as the extrusion 2.50 SGD per L includes the hex bolts and 'nuts' (expensive but reusable and adjustable
Nuts and Bolts - M6 up to M12 used Locktite should have gone with Nylocs
Bearings -SKF 12SGD per cassette. (needed to turn down the inner hub of each wheel for a snug fit but you can emery them down... not the bearings, the wheels)
Wheels - WBR250x60 12SGD each - http://bit.ly/2b8a8Gl
Seat - Old school chair from bin
Steering Wheel - OMP 11 inch Steering wheel https://mikimarketing.com/ (Prices online are wild!! but if you can visit the guy, and tell him your budget, ex display old stock goes very cheap)
Brakes - got cable disc brakes from chainreaction.co.uk
Throttle - THR-91Standard Steel Foot Pedal Throttle (THR-91) $29.95USD - http://bit.ly/2aUEDg0
Battery - 2x 12v Lead Acid.. absolute rubbish but cheap and quick to get going
Fuse - FUS-355ATO Fuse Holder with Cap (FUS-355) and 30 Amp ATO Blade Fuse (FUS-ATO30) $2.50USD
Speed Controllers - 2 x KBS48101X,40A,24-48V, Mini Brushless DC Controller () = $238.00USD (for the pair) High Speed Motor Option Unselected - http://bit.ly/2azS0j8
Motors -2x #SK3-6374-192/18129 Turnigy Aerodrive SK3 - 6374-192kv Brushless Outrunner Motor = $151.24 (for the pair) - http://bit.ly/2b3iD4L
Halls - HONEYWELL SS411A Hall Effect Sensor, Bipolar, 20 mA, TO-92, 3 Pins, 3.8 V, 30 V 5SGD each - http://bit.ly/2azRe5A
Terminals -terminal blocks for 240V rating
Jacks - DJ7091Y-2.3-11 - http://bit.ly/2b8bUHs DJ7061Y-2.3-11 - http://bit.ly/2aM8JCT DJ7091Y-2.3-11 http://bit.ly/2aM8JCT (Highly recommend you pick the corresponding male or female jacks depending on the connectors that come with your controller)
Driven Sprocket- 2* SPR-254747 Tooth Rear Sprocket For #25 Chain (SPR-2547) $15.95 USD each
Driver Sprocket -2* SPR-251212 Tooth 8mm Bore Sprocket For #25 Chain (SPR-2512) $9.95USD each
Chain - Style: 10ft min Riveted - Single StrandType: Roller chainPitch: 1/4"Specification: ASME/ANSI B29.1 - http://www.hikari.com.sg $30SGD
Relay - 12v - 240V
Diode - this comes with the Kelly controller
Pre Charged Resistor - this comes with the Kelly controller
Switch - Sparco would have been my number one choice but crazy price
Step 1: The Chassis
I owe all of this to extruded Aluminium, in fact extruded Aluminium makes up nearly every part of the chassis including the steering.
In order to make the most efficient use of the extrusion began the design process by sitting on the floor and using masking tape, mapped out an approximate chassis about my person. I had an old school chair, the legs had been bent, these were removed and the plastic seat decided where the reinforcements would go. I used 30*30 and about 6 metres of it, this was useful as it came in 6m lengths.
In retrospect I feel that the chassis may have been too small, the space for the electrics was pretty tight and you'll see the this led some of the terminal blocks to be mounted on the seat itself. Also by having a such a short chassis, the steering is hair raising to say the least. I also look like Donkey Kong in Mario Kart when driving it..
The frame was held together with the corresponding angles and brackets as pictured. These aren't the most cost effective, Chibikart (https://www.instructables.com/id/Chibikart-Rapid-Prototyping-a-Subminiature-Electr/) suggests, as do many of the other Mini-eGoKart designers that you use fabricated brackets, these are stronger and cheaper, however the more expensive brackets, usually available from the extrucion supplier can be reused and rearranged so as to provide you with more flexibility in your early designs. There's nothing stopping you from sorting yourself out with your own fabricated parts later on, it'd probable be a little safer as they'd be more reliable and hold stronger due to the increased moment within the holding structure... However for ease, I went with the prefab brackets.
Step 2: Rolling Chassis
Wheels - http://bit.ly/2aGr8kd
I think I went a little over kill on the wheels, however these were unwanted items due to the large internal dia. The good thing about these pneumatic castors was that they were held together by 4 removable bolts, the holes enables me to map out the holes required to secure the drive sprocket. (Will go into this later) Due to the larger axle holes I had to bore them out a micron and place two sealed bearings into the central axle hole.
Bearings - SKF 10mm internal diameter
These weren't cost effective but I had saved on the castors so it was necessary. The internal dia of the bearing was 10mm this was due to choosing 10mm threaded bar as the axles on both front and rear sets of wheels. The front steering assembly is explained later, the rear wheels are very simply held in place using the 90 deg angled brackets
Step 3: Steering and Brakes
Steering rack - The steering was assembled using the same extrusion 30*30 and the accompanying brackets. The aluminium is very soft so it can be cut easily however be warned the wear upon the parts that move against the threads could quick easy jepodise the kart's integrity.. However as long as you know this, you'll hopefully be looking out for it. I used mild steel threaded bar, and although this has worked out I'm mindful that it's beginning to bend under the dynamic loads when in use.. I'm looking into machine bolts and stainless steel threaded bar. (The later is a pain to cut without machines though.. so be warned)
Steering column - The steering column itself is an aluminium rod, 12mm dia, I turned it down towards the end to 11.5mm (lathe) this was to prevent it from slipping through the angled bracket, this can be seen fixed to the two uprights towards the fron of the seat. There's no reason why you couldn't use a nylon cable tie or aluminium collar cut from a lightly larger tube and pressed into the rod via a hammer and centre punch.
The end of the rod has been flattened on the tangent and a D shaped hole was made in perforate Aluminium sheet so as to form the moment arm for the steering rods. (This actually failed during a test run, the metal was too soft for the turning force and the steering rod ripped through the plate. I am currently working on a similar design to the bracket that holds the steering wheel in place.)
On trial, the steering is hairy, spins on a dime and the G force hurts. This kart needs to be longer and the steering needs to be more merciful.
Braking systems - what went wrong
Originally I had purchased 2 Hydraulic Disc Brakes from Chain reaction cycles these were going cheap at 19GBP each, no longer at this price ( http://bit.ly/2aVyqyt) I really don't recommend these. They have been a pain to calibrate since delivery, constantly pinching the discs and really slowing the wheels. I've since bought a bleeding kit, spent hours calibrating and they still refuse to let go once the brakes have been activated. A few days ago I gave up on them altogether and have moved onto mechanised, cable activated disc brakes from amazon. I've seen others use the cable brakes and now I understand why. Spring loaded calipers should release the pads instantly and you wont need the extra equipment to trim them. The original brakes actually ripped one of the discs out of the wheels, you really get some torque with the motors listed used in this build.
Step 4: Drive Sprocket and Rear Wheel and Motor
Because of the extrusion and the fact that you can adjust and tune the brackets, attaching the drives to the chassis was easy. in order to be able to tune the brake discs and driven sprockets everything is connected via threaded bar and nuts and locktite. this means you can use washers or shim to adjust the ride.
Step 5: Electrics
This was by far the most confusing at first glance, however everything revolves around the controllers. I opted for the Kelly Controllers which had a good user base and reputation, and so far I've not had an issue with them. The first part was to download the data sheet or spec outline for the particular model.
Follow the schematic as if you were building the Lego Deathstar or whatever. I used a laser cutter to not only cut out the wooden board for the electronics to sit on, but I also use it to raster (etch) the circuit schematic, that way I simply needed to follow the wires and fix the components where they were mapped. I used a lot of cable ties.
The Kelly controllers can take a huge amount of voltage but need at least 24V to work.. Having exactly 24V in the two Lead Acids meant that they needed to be fully and utterly charged before I would get any response. Those blinking red lights! I tried to connect the system to a 36V LiPo from an old e.Bike but although the motors spun, under load they did nothing at all.
Step 6: Calibrating the Hall Sensors
This was a pain, I had originally created an adapter in fusion 360 and 3d printed it out, but it was the for a much larger outrunner dia, weeks of watching the motor stutter and finally gave in and found some online. Just before they arrived I was messing about with one of those clamps you get in science, holding the hall sensors at different distances from the motor and it suddenly kicked into high speed. And what speed! Back on fusion I redesigned the bracket, allowing it to be twisted and pulled for fine turning. The STL's are attached. they are for the Turnigy featured in this kart though.
I never did use the ones I bought, funnily enough they had also been 3d printed! Some clever people know how to make money.
Step 7: Finishing Up
Once the turnigy motor were kicking in, everything else was very simple. Although I used locktite (Blue and Red) I should have gone with Nylocs or even castle and pins. The lack of suspension knocks the chassis around something crazy and within 5mins you're sitting on the floor with just a steering wheel in your hands.
The drive sprockets on the Turnigy spindles will come off, they're held with tiny lugs that can't resist any torque or shear. I had to use the holes (two) on each sprocket and mark two dots on the Turnigy drive shaft, then use a Dremel and a conical abrasive head to work dents into the shaft, this will give the lugs (once you've sharpened them a bit, something to grip into.
The first photo and the 2 vids are of my gokart, the others are located at SUTD in Singapore.. I'm not sure they still do the Chibukart project with MIT , I think they've moved onto the Shell Eco Challenge or something..
All in all this was an expensive project and it really takes it out of you. But once you've done it, everything else is just a piece of .... pie? Originally I had thought of turning this into a school activity but it's far too fiddly. Instead we now make 3 wheel gokarts from extrusion and front wheel drive eScooters.. Will post that up later.
Good Luck if you're trying this, if you need any of the original Fusion 360 Files or more information let me know, otherwise I'm closing this one.