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EDF Pinewood Derby Car

Richard HowardRichard Howard Club Members Posts: 1

New here and to the RC hobby. Building a pinewood derby car with a 40mm EDF. Have a BLHeli 30A esc and a 3s, 450 mAh 30C battery. Want to use a servo tester in place of a receiver and install a normally open switch in front that will be closed when the start gate pin is in the up position and the car is resting against it. I would like the fan to start as soon as the pin drops. Where in the circuitry would be the best spot to place the switch?

Thanks

Comments

  • Joe KareivisJoe Kareivis Club Members Posts: 8

    Richard... DId you build your car ? I'm working on the same set-up with the hinged roller switch on the front to lean against the start gate pin. My problem is I can't find any wiring schematics on the internet. I have a brushless EDF with ESC and a 3S LiPo battery. Trying to avoid receiver/transmitter hookup, and I have no idea how to deal with Arduinos or other boards, so I hoped I could use a servo tester.

    Leave it to me to do this at the last minute, but my race is this weekend, and if I gotta get any parts from ******* Prime, I need to place orders by tonight (3/5). If you could reply with a schematic that worked for your car, I'd appreciate it.

  • Joe KareivisJoe Kareivis Club Members Posts: 8

    Good morning Toby,

    I hope you are online and can respond quickly. I am building an "Unlimited" or "Outlaw" Pinewood Derby Car to race at my pack's event, and need help with wiring / component selection.

    I'm working on a setup where I want to use a hinged roller switch on the front to lean against the start gate pin to complete the circuit, rather than using a receiver/transmitter to drive the ESC. I have a brushless EDF with ESC and a 3S LiPo battery. I do not have the time to deal with Arduinos or other boards, so I hoped I could use a servo tester to run the ESC. attached is a schematic picture of what I'm working on.

    Leave it to me to do this at the last minute, but my race is this weekend, and if I gotta get any parts on quick-ship, I need to place orders by tonight (3/5). If you please look at the attached image, I need my schematic finished so I can wire up and take the checkered flag. feel free to make markups on the drawing where I need to connect stuff.

    If I need to do things like solder, wire or other stuff, i'm pretty handy that way, if it helps.

  • WTWUKWTWUK CornwallClub Members Posts: 13,360 ✭✭✭

    It may not work. You have no way to control the servo tester to get from zero to full throttle, as most, if not all ESC's usually will not arm at anything other than zero throttle.

    However, if you do happen to have one that will arm and run at anything other than zero throttle (unlikely?), you need to discard the direct Lipo to servo controller connection, as that would possibly fry the controller.

  • Joe KareivisJoe Kareivis Club Members Posts: 8

    Hello WTWUK,

    Thank you for commenting back to me. Here's a list of the parts I was going to incorporate:

    • EDF 50mm with 4300kV 4S motor
    • ESC Skywalker 40A 2~4S with BEC. Current:40A,Burst current(≤10s):50A,BEC mode:Switch,BEC Output:5V/3A
    • LiPo 4S 1550 mAh
    • RMRC Servo Tester with Manual/Neutral/Auto mode selector, 4.6 to 6V Input, three servo output, variable speed knob.

    The ESC and EDF were packaged together. The LiPo connects direct to the ESC using the Deans T-connector, and the remaining 3-pin JST connector on the ESC connects to one of the 3 outputs for the Servo Tester. The LiPo has a 5-pin JST-XHR connector on it. I believe it is supposed to be the input to the Servo Tester.

    My issue is that using the 4S LiPo gives me the two power outputs; the Deans one that feeds the ESC directly and the 5-pin JST with outputs from each cell. Can I abandon the middle three-pins of the JST and use the outer ones (+,-) and connect those to the inputs of the servo tester ? I basically want the fan to run constant.

    My other idea is to run the red (+) wire from the JST to a hinged roller micro-switch, then from the switch to the servo tester. The attached ".png" file shows how a microswitch is incorporated onto the car, so that when the start gate is lowered, the switch is sprung and completes the circuit.

    Please advise if this arrangement is sound

    Thank you.

  • Joe KareivisJoe Kareivis Club Members Posts: 8

    I had another idea. What if I connect a battery pack to the 4.8-6V input of the servo tester to power it, which then can use the outputs for oscillating signal to the ESC for the EDP motor. I can leave the 5-pin JST-XHR balancing cordset from the LiPo unconnected and just run the 2-lead Deans T cable into the ESC for powering the motor.

  • Joe KareivisJoe Kareivis Club Members Posts: 8

    Update... I took a chance, an found that I could leave the balancing 5-pin JST lead un-connected. I attached the 3-wire (+,-,signal) lead from the ESC to the servo tester, and behold, I got the fan to run. All three modes on the servo tester worked great, and worked repeatedly (manual, neutral and auto cycle).

    I think if I cut the white signal wire that runs from the ESC to the servo tester, and splice in a microswitch, it will allow me to get the fan to turn on with the lowering of the starting gate pin

  • WTWUKWTWUK CornwallClub Members Posts: 13,360 ✭✭✭

    Ha! Had a reply ready but work got in the way and phone died! Haha!

    You discovered the contents of my reply lol!!

    However, with one exception. Not certain if you can cut the signal wire and incorporate a switch, as I suspect that will make the ESC think it is not connected to power. Try it though - nothing ventured and all that ...

  • Joe KareivisJoe Kareivis Club Members Posts: 8

    I have some good news. I did incorporate a switch by cutting the white signal wire that runs from the ESC to the Servo Tester; used a couple leads with butt-splicers and pin clips to attach to the microswitch. It works perfectly. When the hinged roller pin is pressed in, the EDF does not run, but the tester is powered. Once I release the roller pin, the circuit is made and the EDF turns on immediately. Then, when I press the roller pin back in, after a couple seconds, the EDF motor turns back off.

    Attached is a picture of the finished product. It's a bit rough in design. Gonna test run it on the track tomorrow night before race-day Saturday.

  • WTWUKWTWUK CornwallClub Members Posts: 13,360 ✭✭✭

    Hehe good stuff!!

    Now if you could mount the EDF at the rear and make and fit a thrust tube (effectively a funnel attached to the EDF - can be made from fizzy cola bottle plastic and tape!) to it, as is often used in model jets, you could really improve performance. A lot of thrust will be lost because of the battery etc. directly behind it.

  • Joe KareivisJoe Kareivis Club Members Posts: 8

    I had the same idea about reversing the layout, putting the fan at the back and the battery up front. My challenge is height limitation, as the car needs to completely pass under the finish line arch. I originally wanted to mount the fan on top of everything and keep the front and back free. My layout in the picture is because I wanted to keep the front of the fan clear, but maybe if I reverse the layout, and provide enough space for the fan in the back, it will be better. I'll also see if I can slice up a plastic water bottle to create a makeshift nacelle for the EDF.

  • WTWUKWTWUK CornwallClub Members Posts: 13,360 ✭✭✭
    edited March 8

    Stuff in the area in front of the fan, so long as it is not so close it is touching, is not anywhere near as critical as the rear end. You are not going to be going so fast to cause intake airflow issues you will notice, but everything in front has to be 100% secure or even that little 50mm fan will attempt to eat it!

    If you google 'edf thrust tube' you should find a shape calculator for cutting the correct pattern for the tube respective to your EDF size.

  • Joe KareivisJoe Kareivis Club Members Posts: 8

    Here's what I re-arranged and used a 20-oz water bottle as the shape for the nacelle. It only extends about 0.75 inches past the tip of the EDF motor, so it may not be the most efficient, but at least it provides a type of guard around the moving parts when we catch it at the finish line.

    After a lot of playing and testing, the battery drained out. Never charged it since I got it, so I have no idea about how long a full charge will last, but I'm betting it'll be more than four races down the track.

  • WTWUKWTWUK CornwallClub Members Posts: 13,360 ✭✭✭

    Hope you did not drain the battery to under 3.0V per cell or you will damage it. LiPos cannot be run absolutely flat like other batteries. Never run them under 3.2V per cell normally.

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