forbes@aries.scs.uiuc.edu (Jeff Forbes) (01/04/91)
Does anyone have the schematic for an electric motor speed control that will operate with a standard RC receiver? I don't care to spend $40++ for $10 worth of parts, and I would like to build one. Jeff Forbes "....I have not failed. I've just found 10,000 ways that won't work." Thomas Edison
tgm@psuecl.bitnet (01/19/91)
In article <1991Jan4.051028.24807@ux1.cso.uiuc.edu>, forbes@aries.scs.uiuc.edu (Jeff Forbes) writes: > Does anyone have the schematic for an electric motor speed control that > will operate with a standard RC receiver? I don't care to spend $40++ > for $10 worth of parts, and I would like to build one. > > Jeff Forbes I don't know much about standard RC receivers, but if you can get a voltage from it, you could build a Pulse Width Modulation motor controller, dirt cheap. What you need is a 556C low-power timer IC, a rugged NPN transistor for switching the motor on/off, a couple misc components like 2N2222 transistors, caps, resistors... The theory behind the circuit is to switch the motor full-on to full-off repeatedly and very quickly. The amount of time the motor is on in relation to the period of the on/off cycle determines how fast the motor runs. I don't have a schematic, but the idea is simple, and 555-type oscillator and PWM shematics are in just about any manufacturer's application books. Here it goes: ^ ^ Vhi | | | *----| | | | | Motor _ Diode prevents spikes RC Receiver--------| | | ^ V | *----| +----------+ +-----+ / | |OSCILLATOR|--->| PWM |----| / +----------+ +-----+ \---| TIP-31 2N2222 \ | V GND 1. Set up 1/2 of the 556C as an oscillator with a frequency of 100-1000 Hz. The higher the frequency, the less "jerky" the switching action will be. The output should be high almost all of the time, briefly dropping low once per cycle. This is necessary because the PWM's output is held high, and thus the motor on, when the oscillator is low--no matter what the PWM control voltage (RC receiver) is. So, even when your receiver says "off", the motor will be partially on, but only a teensy bit. 2. Set up the other 1/2 of the 556C as a Pulse Width Modulator, triggered off the osciallator's output. The control voltage for the PWM will come from your RC receiver. Here's the tricky part: Pick your timing resistor and capacitor such that when your receiver says "full tilt", the PWM's output's high time is equal to the oscillator's period. 3. Use a 2N2222 and TIP-31 (for up to 3 Amp capability) in the above setup to switch the motor on and off in accordance with the PWM's output. Don't forget a clamping diode across the motor's leads or else the spikes built up across the motor could fry your TIP-31. That about does it. BTW, all the above parts can be found at Radio Shack. --Tom Moertel thor@chopin.psu.edu
ntaib@silver.ucs.indiana.edu (Nur Iskandar Taib) (01/23/91)
>3. Use a 2N2222 and TIP-31 (for up to 3 Amp capability) in the above setup > to switch the motor on and off in accordance with the PWM's output. Don't > forget a clamping diode across the motor's leads or else the spikes built > up across the motor could fry your TIP-31. Hmmm... The TIP-31 could be replaced by a MOSFET (Radio Shack sells the IRF-511 for $2) for lower "on" resistance. Does anyone know how the 555 in a plug driver is used? I tried to reverse-engineer an old Polk power panel and it seems like they hooked it up as a monostable instead of a regular oscillator. One of the advertised features of these power panels is the ability to send extra current to the plug when the plug gets wet (I suppose the lowered resistance is somehow used to increase the duty cycle of the pulse output on pin 3 of the 555). How is this done? -- ------------------------------------------------------------------------------- Iskandar Taib | The only thing worse than Peach ala Internet: NTAIB@AQUA.UCS.INDIANA.EDU | Frog is Frog ala Peach Bitnet: NTAIB@IUBACS ! -------------------------------------------------------------------------------