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UKNerfWar

Khaos/HyperFire Variable ROF

So I did a bit of an experiment and it seems to work (quite well in fact) but I'm wondering if the theory backs up the results.

I have a HyperFire running on 3S and for shits and giggles I decided to add a switch that changes the ROF between something reasonable to full on dart hose. Theoretically this could also be used on the Rival Khaos too since it has a similar feed mech. I don't really like the HyperFire but I do like to be innovative. Essentially I have a SPDT switch with a string of diodes on one side for low ROF and nothing on the other side for all out silliness.

I'm appealing to the more electronic minded of you to chime in with a better alternative if there is one. Otherwise let me know if you think it's a dumb idea.
daniel k

Sounds awesome, and with an actual utility. I want a hyperfire to make a hyper-pistol, and a variable ROF would help that out a lot.
Twibz

Re: Khaos/HyperFire Variable ROF

So currently you have:
Bat pos --- switch --- then:
1: motor --- bat neg
2: diode(s) --- motor --- bat neg

?

The only thing I'd suggest that could be an improvement would be to use a zener to clamp the  voltages on both modes....but given that you're no doubt using lithium chemistries, voltage drop under load won't be a problem, and it would be sledgehammer to crack a nut. Carry on!
SSGT

Re: Khaos/HyperFire Variable ROF

Switch mode power/PWM would be better in that it's more efficient (it effectively steps the voltage down and current up as opposed to diodes/resistors which draw the same current from the pack that they supply to the motor and effectively convert the dropped voltage into heat) but otherwise using diodes is fine. You could do the same with a RS/Rhino Fire (switch in/out diodes where you'd normally put them in to prevent runaway firing in a stock pusher motor build).
UKNerfWar

Re: Khaos/HyperFire Variable ROF

SSGT wrote:
Switch mode power/PWM would be better in that it's more efficient...


I must admit, I thought about this but drew a blank trying to find a suitable SMPS on RS. I have diodes and switches so I felt that the simple solution was the best. I haven't really used the HyperFire in anger yet so I'm not really sure how much of an issue the heat will be.
SSGT

As long as the diodes are rated for the current you'll be putting through them the heat itself shouldn't be too much of an issue, it'll just be a little more wasteful. In practice the only major difference you'd notice would be that it draws more current from the pack compared to switch-mode voltage regulation resulting in reduced battery life between charges.

For example, assume a motor draws 5A at 6V (30W) and you're using a 12V pack. If you use diodes to drop from 12V to 6V the pack will be supplying 5A at 12v (60W), because current into the diode equals current out, whereas if you use a switch-mode regulator the pack will supply closer to 2.5A at 12V (30W), because a switch mode regulator acts more like an AC transformer in that it can step-down the voltage and step-up the current (the overall power in/out is still the same). So with diodes, or any other linear regulator, you're putting in 60W electrical and getting out 30W electrical (30W is dissipated as heat) whereas with a switching regulator you get almost the same electrical power out as the electrical power you put in as almost nothing is lost to heat (there will still be some small resistance losses). 30W seems a lot for a diode to dissipate but, because you'd need between 6-9 diodes to drop 6V, each diode would only have to dissipate around 3-5W in heat.

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