Using diodes to reduce volatage... Help needed!?!

[Minimole]

Hi guys,

Basically, in my thread:
http://www.rcgroups.com/forums/showthread.php?t=408988&page=2

I want to change from a 2S (7.4V) lipo to 3S(11.1V) lipo. Unfortunately, the tail motors dont like that much volts, so someone suggested using diodes on the tail motor to reduce the volatge the little motor will be getting.

I was told I should use these:
http://www.maplin.co.uk/Module.aspx?ModuleNo=46385&doy=27m8D

A few questions...

1. Are the the correct ones?

2. How many would I need to reduce the voltage to about 8.0V?

3. Do they need to be soldered to the negative (black) tail motor wire right?

I will be phoning up Maplins on Monday to find out more about these diodes, how much they reduce the voltage e.t.c.

Many thanks guys, Duane. :D

[pmackenzie]

You need a diode rated for some amount over the maximum current draw of the motor. 1 amp sounds low to me.
Each diode will drop about .65 volts, so to go from 11 to 8 you will need between 4 and 5 diodes.
They can be in the positive or negative lead or some in both. It doesn't matter.

One problem I can see is that you have more than doubled the main rotor power, but by keeping the tail rotor voltage the same as before
you have not increased the power in the tail. I am not sure it will work. It should be OK in hover, but you will run out of tail rotor power during climb outs.

I think you need a new larger motor for the tail that can handle the power.

Pat MacKenzie

[radfordc]

One problem I can see is that you have more than doubled the main rotor power, but by keeping the tail rotor voltage the same as before
you have not increased the power in the tail. I am not sure it will work. It should be OK in hover, but you will run out of tail rotor power during climb outs.
Pat MacKenzie

In theory, you're correct. In practice there's not a problem. This is for a fixed pitch heli. The main rotor will turn at "x" rpm in order for the heli to hover and the tail has to counter the torque. Adding power causes the main rotor to turn faster and the mixer also adds power to the tail motor so it turns faster.

You mostly only hover with FP heli's anyway as they don't do fast forward flight very well.

Adding two or three diodes should drop the voltage enough to prevent the motor brushes from burning out.

Charlie

[pmackenzie]

That is why I said in hover it will be fine, but in a climb out it might not.
Pat MacKenzie

[Minimole]

Hi guys,

Thanks for the replies.

So Ill probably order 5 (to be safe) of those diodes.

So 3 should be a good amount to put on the motor?

If I put too many on, would it reduce the tail performance much?


Thanks, Duane. :D

[Minimole]

Hey guys,

I got the diodes, put some on, but have been having a few problems.

Here:
http://www.rcgroups.com/forums/showthread.php?t=408988&page=3&pp=15

Thanks guys, Duane. :D

[Ron van Sommeren]

... Unfortunately, the tail motors dont like that much volts...Motors don't mind a higher voltage, high currents kill motors. A higher voltage will make your motor run faster AND current will increase. Therefore, shortening your tail rotor blades could also do the trick.

Vriendelijke groeten ;) Ron
• diy motor building tips & tricks (http://www.rcgroups.com/forums/showthread.php?t=240993)
• diy outrunner discussion group (http://www.yahoogroups.com/group/lrk-torquemax)

[Dan Baldwin]

Did the leads break off the diodes, or did they just come loose like they were unsoldered?

Dan

[Minimole]

It looks like they became unsoldered.

I suppose I could try cutitng down the blades, just that I only have one good blade ATM, and knowing me, Id mess up badly... ;)

Thanks, Duane. :D

[Acetronics]

Have a look Here:

http://www.rcgroups.com/forums/showthread.php?t=408988&page=3&pp=15

Message #49

Alain