Help requested - using a DPDT Switch plus a DPDT Relay to create low-speed reverse

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wilse
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Help requested - using a DPDT Switch plus a DPDT Relay to create low-speed reverse

Post by wilse »

Hello!

I'm a beginner working on my first project. I'm working on converting a small 6V single-gearbox Mini Cooper to 12V two-gearbox. I'm having trouble figuring out how to do some shifter/motor wiring. Conceptually, I can think about the problem broadly enough to design a general solution, but I just can't grasp the mechanics quite well enough to put forth the wiring design that makes it all work. I will continue to think about it, but I figured I'd ask the experts here in case anyone could help out with some advice or instruction.

So, my little car now has two 12V gearboxes/motors. However, because it was just a little 6V car to begin with, its shifter only supports a single two-position DPDT switch (ON/ON). This is used to select forward or reverse. If this was all I needed to accomplish, I understand (thanks to the great resources on this forum!) how to wire that switch to the motors for polarity reversal.

However, I do want an extra function. I want reverse to be "low speed". So, when in reverse, not only do I want the polarity reversed, I also want the motors to be running in series. When in forward, I want the motors to be running normal polarity and in parallel.

I've seen the diagrams that show how to accomplish this with two physical DPDT switches, but the little shifter in this car doesn't allow for that. It seems that I should be able to accomplish this by using a DPDT relay instead of the second physical switch, but this is where I'm running into trouble designing how to implement the wiring. Does anyone know how this could be accomplished?

Any assistance is much appreciated. Thank you!


wilse
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Re: Help requested - using a DPDT Switch plus a DPDT Relay to create low-speed reverse

Post by wilse »

Well, one thought did just occur to me, and maybe now I'm on the way to cracking this nut. Seems like I might need two of the relays to accomplish this.
wilse
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Re: Help requested - using a DPDT Switch plus a DPDT Relay to create low-speed reverse

Post by wilse »

Ok, I think I have it figured out. In this scenario, the shifter switch can actually just be a simple on/off switch (I think).

In this example, I'm also using relays along with my on/off and throttle switches, but with sturdy switches in those location I don't think those relays would be necessary.

Anyone care to double check my work here? The idea is that when the shifter switch is open (FORWARD), then both motors get normal polarity in parallel configuration. When the shifter switch is closed (REVERSE), then both relays are triggered to close, and both motors receive reversed polarity in series configuration (for half-speed reverse).

Does it work? Thanks!
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wilse
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Re: Help requested - using a DPDT Switch plus a DPDT Relay to create low-speed reverse

Post by wilse »

For some reason, the diagram uploaded/attached at a pretty small size. Here's an attempt at a full-size:

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CJB
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Re: Help requested - using a DPDT Switch plus a DPDT Relay to create low-speed reverse

Post by CJB »

You lost me at the 12v ESC module and the way the throttle is hooked up.
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wired
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Re: Help requested - using a DPDT Switch plus a DPDT Relay to create low-speed reverse

Post by wired »

Proposed request does not match your diagram. How about just using a standard 12v power wheel harness and shifter to get the hi/lo fwd and lo rev functions?
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