Your typical electric go kart build... maybe?
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JPEG Image - 3.31 MB - 05/05/2021 at 17:34
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It's alive! We're rollin and in this update we get mostly all wired up to do some test driving. Initial verdict? It's fast! Like, scary fast. I've had to dial down the battery power output to 40% (initially started at 75%). At 75% I saw a peak draw on the BMS of 200 amps and I wasn't even full throttle! 40% is a more reasonable and controllable peak of about 175 amps.
So, how did we get here since last update? Well, lots of little things! First, we finished up a bunch of things on the back panel including the throttle cable mount block, throttle cable pivot, and 24 volt output to the BMS. Now the BMS and controller have power from the DC-DC converter.
The 3D printed pieces for the control panel and display also arrived with the throttle cable mount and contactor and BMS brackets. I had mostly finished the wiring for the front panel so this was mostly just plugging the LEDs and switches into the holes and shoving all the wiring and board into the back. The display bracket doesn't fit perfectly on the steering top tube but it is good enough. Control panel fits nicely. Both cinched down with hose clamps.
While waiting for the 3D printed parts to arrive I got impatient and purchased my own 3D printer! I used it to print the new battery cradle design.
This new cradle design works out a bit better than the box. The battery straps to the cradle with nylon and plastic cam buckles.
The first drive worked out great. The brakes could use some work and steering is a little twitchy and can be hard to turn at slow speeds. I think this is mostly due to the weight being mostly in the rear of the kart.
Check out the video for some footage of the drive. We've sent the cut off for powder coating and when it comes back we will do a full bill video to outline everything. I imagine that video will be really long and detailed. So, if you've been looking for the ultimate detailed video stay tune for that one!
So what have I been up to in the last two weeks? Well, not too much. But did hit an important milestone. The motor is spinning!
I did some work to wire up the DC-DC converter and throttle body. Then connected the battery up to the converter and controller (using a resistor to limit current to charge the controller capacitors first).
I did receive my acrylic panels for the battery box and glued them together. It looks nice. But the fitment with the packs large 2 AWG battery cables is not good. It also feels much more fragile than I would've expected. I'm thinking I'm going to scrap this idea and go for a cradle design instead.
This cradle would allow the front and sides to be exposed for easier cable routing. The battery will be strapped to the cradle with nylon straps. I'm planning to 3D print this part myself with a 3D printer that is on the way. Really exciting!
The other bit I have worked is getting the axle parts all aligned and tightened down for the belt drive. It looks like everything should fit but I will need a really thin wrench to get to the bolts between the motor and pulley. This is because the quick disconnect bushing needs to be mounted facing the motor. The shaft is not long enough to make contact with the bushing if mounted the other direction.
That is all for this update. Everything is still looking pretty good and should be able to get it moving in the next couple weeks. I'm still waiting on 3D printed parts for the display, controls, and throttle cable holder.
The battery cells and hardware have finally arrived. I spent the week building the battery pack and testing functions of the front panel wiring.
As previously mentioned the battery is a 20S2P configuration. Nominal voltage should be 64V and peak charged voltage should be 73V. The individual cells are a 6 Ah which in a a 2P configuration means we have 16 Ah capacity. The pack can put out a continuous 5C which means we can do 80 A no problem. Peak is rated for 15C or 240 A!
The battery pack is taped up with Kapton tape to help prevent any accidental short circuits. It's wired up with the Chargery BMS24T balance cable and temperature sensors.
I'm waiting on some additional screw hardware to fasten up these beefy battery cables before I can test out the pack. These are 2 AWG wire which should be good for up to 210 A according to the manufacturer. The connectors are Anderson SB175 and are good for up to 280 A. One pair of plugs will be for the battery to the contactor and current shunt and the other pair will be for the controller to the other side of the contactor and current shunt. This will allow us to unplug the controller and plug in the charger.
I've also started working on the wiring harness. Here is the start of the switches and LEDs which will live in the control panel. This will have a connector that connects to the main wiring harness and goes back to the controller and BMS main module.
This quick wiring harness and control panel set up is working! I was able to verify that the controller is seeing a switch inputs and also tested out the motor data cable adapter which is showing data from the motor.
I have parts ordered for the battery box and other 3D printed parts such as the display and control panel. I'm still waiting on a couple more fasteners and then we should be just about finished with orders and can start throwing everything together. Hopefully in the next video we will have the motor spinning. Cross your fingers!
The motor is mounted! Big thanks to Matt for helping us out in his shop. We were able to cut out our aluminum panel for the controller mounting and weld up the motor brackets.
The mount is a piece of 2" x 1" rectangle tubing between the seat cross tube and end of the brake caliper bracket. There are two pieces of 1-1/2" angle perpendicular to the tube which we drilled holes to mount the motor plate. Everything feels very sturdy.
We also got the rear panel cut and mounted. Instead of the pipe clamps Matt suggested we use some self-tapping steel screws into the frame. This should work out nicely and I'll later add some rubber washers and trim to the panel to cut down on vibration.
Less interesting but still relevant is a small adapter I made that connects up the motor signal wires (sine, cosine, temp) to the controller. This is a Metri-Pack 150 8-way male pin to DJ7061Y-2.3-21.
The frame mount changes have been added to the CAD drawings and I rearranged some parts for better fit. I'm now thinking that the contactor and BMS will go on the side of the battery box and the throttle POT will go where I originally had the BMS.
I've finalized most of the control panel and ordered parts to start wiring it. But hard to get length of harness without the battery box in place. Still waiting on the batteries!
That's all for now. Stay tuned for battery build and more electrical updates soon!
The project now has legs.... or rather, wheels!
We have ordered parts and I made the 7 hour trip to Keller, TX to pick up the vintage kart kit.
In addition to the frame we have the other major parts ordered as I finally settled on a setup I hope will work well:
There are still a lot of parts left on the list (wiring, terminals, mounting plates, 3D printed parts, fasteners, etc). But these are the major cost components and they are en route!
In addition to gathering parts I've been spending a ton of time in OnShape trying to model up how everything will fit together. There are a couple custom parts to be made:
That is it for this update. Parts start arriving next week so stay tuned!
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