To regulate or to buy a wierd battery, that is the question...

[MrForbes]

Originally Posted by Qbranch

As you can guess, making a throttle cable system to pull all five throttles EXACTLY the same amount at the same time would be a lot of trouble.

Then why bother? does it really matter if one engine puts out a bit more power than another?

(I'm just looking at it from the KISS perspective...electronics and servos and tractor pulls seems like a tough mix to me)

[vivek16]

Originally Posted by squirrel

Then why bother? does it really matter if one engine puts out a bit more power than another?

(I'm just looking at it from the KISS perspective...electronics and servos and tractor pulls seems like a tough mix to me)

Thats exactly what I was thinking, it may be different for gas motors but under any significant load, dc motors help in the end. I would probably just go with the KISS perspective too.

[Qbranch]

I think I should have described the throttle situation a little differently... the system used previously to pull all the throttle cables together caused gross throttle variances accross the tractor, causing some engines to pull hard and others to backfire against the torque. I could also put this a different way... the team tried the kiss method before, and found it wanting.

Unfortunately, unlike DC motors, these engines don't like a power mis-match too much. Plus, in this game every horsepower counts when your whole tractors at around 80hp...

-q

[MrForbes]

Are the throttles governed like they are on most little industrial engines?

[VEI Dude]

My 2 cents, on the original question...

Buying a wierd/custom battery is not good, due to the uneven drain.

Regulating is the correct answer, but I would avoid linear regulators. If you lose 6V in the linear regulator (12V in - 6V out), and doing this at 4A, you're losing 24Watts in heat! That is significant! Also, most 78xx regulators are rated for 1A (some at 1.5A), but that is with a lower drop voltage. Dropping 6V would probably cut you back to well under 1A, so you'd need more than 4 regulators. And to dissipate 24W, you'd need *significant* heatsinking, plus some type of air movement. And also make sure that the specific brand of regulators allow paralleling outputs.

The DC-DC converter is the correct answer. That Lineage Power dc-dc converter that Kevin pointed to is really nice for the price. Another option is to build your own, with the circuit designed for you automatically by one of the online switcher tools. One of my favourites is National's Webench. Enter your requirements and it will select appropriate switching regulator IC's for you, and then design the circuit for you. You can then tweak component values and see how the circuit responds (regulation, efficiency, etc). You can usually even order a kit with all the selected components, but then it gets costly. There are other manufacturers that do this too, btw.

For your requirements, I'd think one of the ready-made dc-dc converters would be best, but look through the datasheets to see if they require any external capacitors, as some do.

Cheers,
-Neil.

[MrForbes]

Does each engine have a generator that can be used to recharge the battery? if so then 24 watts being wasted probably isn't a big deal. Do the servos actually draw that much current when they're just holding a position, or is the rating for maximum power draw at maximum slew? Can you just use one 7805 or 7806 per servo?

again, trying to keep it simple....

[Qbranch]

squirrel: I think they are governed to avoid redlining... but I'm not entirely sure... this is the first project I've ever worked on that involves internal combustion (other than changing the oil on my hybrid).

VEI dude: Thanks for the suggestions.

squirrel: We've tried using six regulators for six servos... but this needed heatsinks on each regulator and a cooling fan. Trouble is, the very dusty environment didn't jive very well with the fan, and (mainly due to bad placement on the part of last year's design team... they put it on top of the nice n hot rear diff) still occasionally went out.

For now, we're going to order up one of those TI regulator boards Kevin mentioned. It looks like it should work, and we should be able to use a passive heatsink then encapsulate the rest of it.

-q