35 posts in this topic

Posted (edited)

Starting and turning are the most difficult things to do. I found it was easiest when I put the rear foot on first, had the front foot ready over the board, started the wheel and put the front foot down before I started going backwards. I suspect I will be able to ride backwards and frontwards once I get used to the surfing position xD 

@esaj Thanks! That cleared up things. Darned charge/discharge cycles will probably mess too much with the flow of current and the stability of the voltagecurve... Conclusion is I would need several kilograms of capacitors as well as too many batteries than practical. Perhaps a solution could be a main powerbank with max discharge ability at or above 20A and a few auxilliary powerbanks in parallell made from cheap 4A discharge batteries. Wired so aux batteries can only engage when the current is below 4A

Edited by Cryptonitor
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Posted (edited)

2 hours ago, esaj said:

I'm still not sure if I just misunderstand what you're actually trying to achieve.

If you mean to power the wheel from the capacitor banks alone, with some kind of separate circuitry disconnecting and connecting them between the batteries and the mainboard/motor, I doubt it's going to work. You'd need battery packs capable of charging the banks faster than they're being discharged, so that the other bank(s) has/have always charged up before it switches over, and the switch-over needs to happen in a way that at no point in time is the mainboard and motor left without power. Even with relatively large banks, you likely need to switch at least once per second, if not several times per second, for smaller capacitances, hundreds if not thousands of times per second. There's likely going to be all kinds of noise, rush currents and voltage transients in the system, that can play havoc with the mainboard components or the software (it would probably see the battery voltage "all over the place"). If the batteries aren't capable of charging the bank(s) fast enough, when the switch over happens, it'll be connecting only partially charged bank and it will run out of juice before the next switch, or even if the switch is voltage-based, in the next period it will connect a partially charged bank ..? The mainboard will shutdown or the motor will run out of torque. I see this simply as an unnecessary new point of failures introduced into the system.

If you already have battery packs capable of charging the banks faster than what the wheel uses at peak power, why bother with the banks in the first place? Just stick the batteries directly into the wheel and be done with it? Less space needed than with the banks and less points of failures ;) Of course you could put bypass capacitors there, but always keep the batteries directly connected...

But, I could be wrong :P  There's a bunch of actual electronics/electrical engineers, or at least otherwise far more advanced people in this field at this board who probably could shed more light into the issues. @lizardmech ? @Christoph Zens? @electric_vehicle_lover? @zlymex? @DaveThomasPilot? @Slaughthammer? Probably others I don't remember right now...

Have to study this in greater detail and do some simulations of the circuits I had in mind. Unsure of the names of the components in english and how the behaviour of the powersupply would affect the controlboard. So far it seems this will be too heavy to be practical, but I might build it anyway so it can be done without adding so much weight when the technology catches up (slower discharge capacitors and batteries with higher energydensity being researched). Simply put I was thinking the capacitor banks would only engage when the load was higher than 4A (to increase batterylife of the mainpack 20A max discharge), and one/several cheap, low capacity (4A max discharge) batterypacks would be coupled in parallell to facilitate the charging of the capacitorbanks and increasing Ah rating of the total powersupply. Seems like a pretty bad idea with the current technology in batteries and capacitors

Edited by Cryptonitor
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Posted (edited)

Delaying making of low-cost battery solution for now.. I'll just get a 20A pack and be done with it. I'd rather focus my efforts on making the surfboard add-on look like something from Back To The Future, with a "hood" ontop to replace the shattered shell.  http://www.instructables.com/id/How-to-build-scale-Hoverboards-from-Back-to-the-fu/

Edited by Cryptonitor
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Posted (edited)

2 hours ago, Cryptonitor said:

Starting and turning are the most difficult things to do. I found it was easiest when I put the rear foot on first, had the front foot ready over the board, started the wheel and put the front foot down before I started going backwards. I suspect I will be able to ride backwards and frontwards once I get used to the surfing position xD 

@esaj Thanks! That cleared up things. Darned charge/discharge cycles will probably mess too much with the flow of current and the stability of the voltagecurve... Conclusion is I would need several kilograms of capacitors as well as too many batteries than practical. Perhaps a solution could be a main powerbank with max discharge ability at or above 20A and a few auxilliary powerbanks in parallell made from cheap 4A discharge batteries. Wired so aux batteries can only engage when the current is below 4A

 

1 hour ago, Cryptonitor said:

Have to study this in greater detail and do some simulations of the circuits I had in mind. Unsure of the names of the components in english and how the behaviour of the powersupply would affect the controlboard. So far it seems this will be too heavy to be practical, but I might build it anyway so it can be done without adding so much weight when the technology catches up (slower discharge capacitors and batteries with higher energydensity being researched). Simply put I was thinking the capacitor banks would only engage when the load was higher than 4A (to increase batterylife of the mainpack 20A max discharge), and one/several cheap, low capacity (4A max discharge) batterypacks would be coupled in parallell to facilitate the charging of the capacitorbanks and increasing Ah rating of the total powersupply. Seems like a pretty bad idea with the current technology in batteries and capacitors

If you just parallel "enough" of those 4A packs, the current per pack will stay below the maximum. Even if a cell is rated for 4A max (continuous), it doesn't mean it's incapable of providing much more current, just that it can't handle it continuously. The internal resistance of the lower max discharge-cells is likely much higher than for the high-discharge ones, so it will drop more voltage in the resistance with high currents, and might heat up to dangerous levels. Put 5 packs in parallel, and you still stay within the 4A per pack rating at 20A.

For an average voltage of 60V, 20A would already mean 1200W of power, something which you likely won't be using continuously (but which will discharge even a relatively large capacitor bank to too low voltage in less than a second). Capacitors are good for high pulse currents (like spot welding), compensating for stray inductance, filtering and the like, but not really for continuous power supply by themselves.

 

34 minutes ago, Cryptonitor said:

Screw the batterynonsense.. I'll just get a 20A pack and be done with it. I'd rather focus my efforts on making the surfboard add-on look like something from Back To The Future, with a "hood" ontop to replace the shattered shell.  http://www.instructables.com/id/How-to-build-scale-Hoverboards-from-Back-to-the-fu/

Take a look at the private-sales section, you might get a good used wheel for the price of the packs (depending where you're ordering from). Then you could keep your old wheel for modding and such. Just remember safety, especially when working with the batteries.

Edited by esaj
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3 minutes ago, esaj said:

If you just parallel "enough" of those 4A packs, the current per pack will stay below the maximum. Even if a cell is rated for 4A max (continuous), it doesn't mean it's incapable of providing much more current, just that it can't handle it continuously. The internal resistance of the lower max discharge-cells is likely much higher than for the high-discharge ones, so it will drop more voltage in the resistance with high currents, and might heat up to dangerous levels. Put 5 packs in parallel, and you still stay within the 4A per pack rating at 20A.

For an average voltage of 60V, 20A would already mean 1200W of power, something which you likely won't be using continuously (but which will discharge even a relatively large capacitor bank to too low voltage in less than a second). Capacitors are good for high pulse currents (like spot welding), compensating for stray inductance, filtering and the like, but not really for continuous power supply by themselves.

Aw I might just have to let this go completely. The idea was (with the surfboard being able to fit large batterypacks) that lesser quality batteries could be coupled in with limiting diodes to only be part of the circuit when the load was under 4A. Would still have a main pack able to deliver 20A continous and would have to ride smooth to avoid having the limiting diodes on the auxiliary packs cutting too often

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Posted (edited)

30 minutes ago, esaj said:

Take a look at the private-sales section, you might get a good used wheel for the price of the packs (depending where you're ordering from). Then you could keep your old wheel for modding and such. Just remember safety, especially when working with the batteries.

The surfboard is made to be slip-on so no modification at all is required=) Batterymods I'm now considering are just stand-alone packs with limiting diodes coupled on the existing setup, if I went for the easiest add-on/relieving method. I'll draw up some schematic and simulations of the circuits since I'm not so good at explaining. Putting my efforts with regards to practical work on making the surfmod better and making the "hood" ontop. Late evening for studies and simulations on circuits

Edited by Cryptonitor
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New shell (not completely finished designing yet). Going to cut out (roughly) this shape from thick brass plates. Now the motor will have more solid mounts for the electronics. Ontop of these 2 fancy brass plates I will rivet on boxes made of glassfiber to house the batteries and electronics. Those boxes will be fitted with a pressure-seal gasket and coated with heavy leather. Planning on securing the battery and electronics in fiberglass casings that are airtight and watertight seperate from the main frame and connected through copperspringloaded connections to make it more service-friendly. Over the driveaxle there will be a small cover only fastened with a clip for easy access to the driveshaft. Ideally I would remove the charger plug and mount an induction charger but cannot afford parts now.

image.jpeg

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I'd advise building a shell that's designed to be more be functional than flamboyant.

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This started as a functional square metal plate (with boxes on to house battery/electronics). In my opinion the most pracical way of securing the footboards and electronics while keeping it easy to take apart. I just added some lines to shave off weight to begin with and ended up with this. Fiberglass, plastic or aluminium is just too weak for use in the arctic. Will probably fit some spring-loaded bolts to be able to slip on a cover for protection when winter comes. Also planned a canvas made from leather shaped with aluminium rods for a slip-on cover/mudguard for use in the summer

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Posted (edited)

Thought of how sharkteeth look when I started reducing weight (from a square metal plate on each side). They have incredibly strong teeth because of rounded lines on the inside of each jagged edge. Same principle works with metal. If you round off the shapes that stretch inward the result is a much stronger structure than if you just cut out a square.

Future plans: induction charge station to get rid of the charging plug (weak link), bluetooth control bracelet with power indicators (no more lights or holes for moisture to get in), servo hooked up to the driveaxlenut set at the momentum specified, wake-on bios to remove power button completely (to make a completely sealed device totally sealed against moisture). At this point the battery and electronics would be sealed in completely and all wires could be fastened permanently to avoid the problems I've had with wear due to vibrations. Tire could be changed by removing a few connecting rods between the metal plates on each side (rods bolted on the shapes that go further out than tire). I would like to fit a pressure gauge on the tire (bluetooth to send signal to controlbracelet) and wire up a circuit to check the condition of the battery (or maybe the condition of each cell) at certain intervals.

EDIT: Controlbracelet is for now with a arduino that is quite big... Once I can afford it I plan to get a Raspberry Pi or programmable blueooth watch so its smaller.

Edited by Cryptonitor
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