I found a 1990’s ‘Muddy Fox’ mountain bike to use for the basis of this electric bike conversion. Old steel frames have some advantages over modern aluminium frames when it comes to wedging large motors in them.
The original coilgun circuit used a relay which quickly suffered from contact problems due to the large current flow so I have replaced it with a thyristor.
I’m using a FS2514MH thyristor with an non-repetitive on-state current rating of 330A.
A simple 5V DC battery power supply was built using an L7805 linear voltage regulator and a PP3 9V battery. This certainly isn’t a good way of doing things but I have a large supply of lighly used PP3 batteries so it’s what I’m going with.
SPICE Simulation of 5V regulator.
Later on, during the PCB design, I shall use a buck/boost topology and a more suitable battery.
With the new reflector fitted everything was looking great however I soon discovered that all the ports such as HDMI, Audio Out and USB were blocked by the large heatsink keeping the new LED array cool.
I had 3 options :
Unsolder the HDMI connector and extend it.
Move the PCB to outside of the projector housing.Find a smaller heatsink.
I choose to simply move the PCB and so 2 slots were cut into the top housing to allow the flat flex LCD cable and control panel cable through. Along with this I also added perspex standoffs to mount the PCB and give clearance to the components on the bottom.
And in the image below it can be seen mounted in the turret frame with some protective packaging on the flat flex cable.
At some point I shall strip the projector down and clean it out with compressed air and polish all the lenses etc as a lot of debris has entered during the modifications
I made this simple wooden test bed to hold all the parts of the coilgun securely. When firing there is some recoil so it’s good to keep everything in place.
The small PCB on the bottom left is a mystery chinese DC-DC boost converter. The control chip had it’s part numbers ground off but I manged to read them under a bright light and it’s a flyback based design. Takes 5V in and gives a nice 300-400V which is perfect for capacitor charging.
I made this tool so I could discharge the large capacitors I’m using in a controlled maner as just shorting them with a screwdriver leads to big sparks and contact errosion.
It’s simply a 10 Ohm 50 Watt power resistor attached to a nice thick cable and some crocodile clips all with plenty of heatshrink. I settled on 10 Ohms after doing a few rough calculations given the level of voltage I’d be using it at.
Here is a brief update on the portal turret. I’ve talked about it at each open day but I’ve finally designed and 3d printed a reflector that matches the new LED array to the Fresnel lens and LCD.
Side by side you can see the extra length required match up with the new LED.
Coating the inside of the new reflector I’ve done some quick tests in a bright room and the output seems considerably brighter but the real test will be when it’s all bolted back in the turret frame.
Next task shall be relocating the HDMI connector and fixing the LED array and heatsink permanently to the projector housing.
The speaker is held in place by the clamping pressure from a few nuts and bolts.
Here you can also see the radio band dial also mounted in the same manner.
I’m not sure how well this style of linkage will work but that’s what experimentation is for.
