rheostat speed control

[more coffee]

hi
i was wondering if anyone had used a rheostat out of a cordless drill as a speed control.the forward drive is straight forward ,but what about reverse.
ive fiddled with a few schematics, but it always seems ,even with diodes i'll excite the forward circut when reversing.
im trying to use 2 rheostats.one forward one reverse,the servo is the actuator.it seems that reversing the polarity through a rheostat isnt a good idea. to reverse the motors from forward ,i'll just reverse the polarity at the motors.
anybody ever try to use some thing like this.
i can get the motors and rheostats for under 25 dollars per pair,which is why im considering this as an alternative.
any thoughts appreciated

chris

[LtDoc]

Chris,
What you are talking about is the older style of speed controler, variable resistor. As far as using the 'trigger' assembly from a drill, it ought to be at least comparable. And in a nut shell, a terrible way of doing things. Instead of the current all going to the motor a lot of it gets turned into heat and is totally wasted. Run time will suffer to some extent. Then theres the fact that if the components used (and wire) isn't heavy enough, you get to handle an on-board fire. (If you think seeing smoke come out of your boat isn't exciting, take my word for it, it is - lol!)
I can also understand wanting to save a little money, but there are ways of doing that that are not exactly the wisest choice...
- 'Doc

[CG Bob]

im trying to use 2 rheostats.one forward one reverse,the servo is the actuator.it seems that reversing the polarity through a rheostat isnt a good idea. to reverse the motors from forward ,i'll just reverse the polarity at the motors.
This plan will tie up two radio channels as one will be used to operate the rheostat and the second will be operating a DPDT switch mechanism to reverse the polarity. You'll need at least a three channel radio to make this plan work: channel 1 is rudder; channel 2 to reverse polarity; and channel 3 for the rheostats. You're better off with an ESC or mechanical speed control that connects to a servo.

[more coffee]

thanks for the replies guys
LtDoc
i know its not the best way of doing things ,but worth a look.i'll try anthing once.it actually peaked the intrest of our mechanic.at worst my boat would get a viking funeral :eek:. i once used eggs to get home from a camping trip.that was funny ,a week later the smell wasnt.
its a little old school but replacement parts are cheap,and easy to attain.i dont have to sink a small wad into spare parts..i could put a smoke alarm in the hull. hooked up to a pump to fill the hull and put out the fire :p :D
CG Bob
the switching became aparent when we roughed up a few schematics.using diodes would cause some problems ,either by leaking or by not allowing the current to flow. so we came up with a idea to mount the switches, just before the rheostat engages to excite the circut ,while it would open the other as the servo arm moved to engage either forward or revese. a lever style micro switch(normally off) was thought to work well, after looking a little longer.the polarity would stay the same on both rehostats ,but would switch at the motor terminals, hence the problem with current flow and more than likley a short circut
we also figure that with the right servo linkage we could get away with one rheostat,an idea im not crazy about because there is already alot of moving parts(weight).

[Umi_Ryuzuki]

It shouldn't be that difficult if you are determined to make it work mechanically. It still takes two channels.

One reostat to control the voltage.
Two push on - push off SPDT or momentary SPDT switches.
I prefer the momentary switches with a normally closed contact.

You wire the ground to the normally closed contact(NC) of both switches, the Common tab runs to the motor leads (one to each switch).
The positive lead runs through your reostat, and from the reostat to the normally open(NO) contact of each switch.

The motor is now grounded. throw the "switching servo" to one side, and it connects the reostat(and the positive power) to one side of the motor.
Run up the reostat, and you have high, or low power.

Re center the switching servo, and you have all stop. Motor is grounded again.

Throw the switching servo to switch 2, and you have reverse

[more coffee]

thanks umi
think i'll mock something up in a piece of ply wood ,give it a shot. i really dont want to chew up two channels. i think i'll first try to mount the switches within the sweep of the servo running the rheostats. with the servo in nuetral it well be dead stop .as you move to engage forward or reverse the servo would actuate the switch first,closing the circut and allowing the rehostat to start running up the motor.still would require 2 rheostats.an after thought is that it would lessen the duty cycle on each, given they have their own specific function.not one performing both.
then it dawned on me that i may have to use a seprate battery to run the reciever ,servo gear. battery voltage for the motors well be around 13v DC,i dont know much about the recievers ,but i dont think you can put 13v through them outright.

i guess at the end of the day it boils down to time and what its worth.2 ESC's that run 12v or better are ,from what ive seen, a little pricey.

let the smoke and sparks fly

[more coffee]

some smoke ,a few sparks.
i'll have to find a pair of 12v ESC's.

[Umi_Ryuzuki]

It's possible that you are drawing more amps than the reostats can handle.

[more coffee]

umi
your probably right,that was no load ,i dont have an ammeter handy.
the motors look like johnson 500 series,only they seem to like 12v better than 6v.they dont wind up or they sound like they are underpowered on the 6v area.
can you recommend a decent 12v contol?

chris

[AmokCrow]

I'd use a board like this if I wanted fully mechanical control. Reverse without an extra switch. And it's easy to make from the striped copperboard found in every electric store.
Just my 2c.

-Michael

p.s. Remember to use resistors of sufficient wattage rating.

[Umi_Ryuzuki]

Model Control Devices is right there in Ontario...
http://www.modelcontrol.com/page1.htm

Of course there are cheaper options
http://www.proboatmodels.com/Products/Default.aspx?ProdID=PRB2314
I am sure more than a few people here use the proboat.


I have something similar by Mtroniks I believe it is a Sonik4 ECO20
http://www.mtroniks.net/
At the time it was $39
http://www.hobbypeople.net/guru/HPS_475421628.asp