ZZSE many modding questions

[mcbradshaw]

-Tears of Joy-
It purrs like a dentist's drill, with the whole drivetrain(motor, wheels and gears) hooked up to a 6volt lantern battery and under low loads. The final project will be 7.2V. It should have at least the same torque as the un-modded ZZSE, but hella fast. The wheels arn't stopped very easily with fingers.
Going that fast it started to smell like burning plastic, not electronics or motor. I need to start lubing the gears and axle generously. Next time I do this: metal gears, ball bearings. I can't wait to get this thing on the ground and under control and get a m.p.h speed. I'm using blue gears so far. I think the gym floor is the only place i can drive this.
All I need is a relay or large FET that will trigger with the current I mentioned earlier and can handle 7.2V. I think I will mod the relays that I have, tonight, to serve this purpose.
This has got to go at least 12 m.p.h.

(?????) By the way what is the speed to beat? How are you guys measuring it ("quarter-mile", unlimited head start)?

[codesuidae]

Which mosfets you would use would depend on how much current you expect to run, and if you can handle using surface mount parts.

I'm guessing you will not want to use surface mount parts, mostly because they tend to be difficult to use without making a PCB. You could use something like the IRLR3714, its on resistance is very low and it will handle very high currents. You'd probably want to use a simple switching transistor on the 2.4v input so you can use your higher voltage battery supply on the fet gates. You could do this with your relays too, so you can get enough power to turn them on.

To do it with mosfets you could build a full h-bridge so you can have forward and reverse, which would take 4 mosfets (preferably 2 n-channel and 2 p-channel). If you just want to go forward one will do.

If you are only pushing about 1A for the motor you could use this H-bridge IC.

If you want to stick with the relays you can use a transistor on the 2.4v output from the car to switch the 7v battery to your relay coil to turn it on fully. This is probaby much less trouble than using mosfets since you already have the parts. runtime won't be as good, but I don't think your going to be too concerned about that at this point

[mcbradshaw]

Thanks that is helpful.

Think im just going to one direction for now. Once I'm happy with that, I will have 2.4 reverse.


(????) When motors fry, do the go to heaven?

I was wondering how motors "go" when the do so at high voltage/rpm. Does the whole motor case get hot then....? Or does the motor fry from the inside out?

The only time I have fried motor so far happened when I was soldering wire leads to it.

I am running this thing at serious rpms and the motor stays "cool". Granted, this is at low loads for long times or accelerating the whole weight (batteries and all) for a foot or so. I have it heat sunk pretty good, but if it goes from the inside out, i can just cross my fingers.

[codesuidae]

You can power your relay with a circuit like this:

                       VCC7.2v
                        +
                        |
                     o--o
                     |  |
             snubber V  C relay
              diode  -  C coil
                     |  C
                     o--o
                        |
                 ___  |/
 From ZZSE >--o-|___|-| ne2222
   2.4v       |  2k   |>
              |  ___    |
              o-|___|---o
                10k     |
                       ===
                       GND

This way the relay coil will be energized using your higher voltage circuit. The 10k resistor can probably be omitted. The transistor is any N-channel small signal transistor, Radio Shack has them.

A motor will use the most power when it is stalled, so they tend to get hot under load. Running unloaded they only get hot if you are exceeding their rated voltage by quite a bit. The armature, the spinning part inside with the wires wound around it, is what gets hot. The current flows through the wires and heats them up.

Failure modes vary, usually it will just get hot enough to melt the wires somewhere (often near connections since they have higher resistance). Sometimes high temperatures can melt solder connections or cause moving parts to bind or seize.

Good heat sinking on the motor case helps, but heat can only leave the armature so fast, so you can still burn up the motor at high power.

[mcbradshaw]

Thanks. I'll give it a try. I can only get to rs on weekends. In the mean time i will play with the last relay i have. I bet i'l just break it, but i need to be doing something.

[wild03]

Originally posted by mcbradshaw
-Tears of Joy-
This has got to go at least 12 m.p.h.

(?????) By the way what is the speed to beat? How are you guys measuring it ("quarter-mile", unlimited head start)?

You can always try my site for ideas on a tachcometer or lap timer.
HAve fun

http://www.geocities.com/wdiaz03/miniRCstuff.html

[codesuidae]

I built a similar device, although mine measures linear speed instead of RPM.

I used the same mouse sensor idea, except I used cut down the base of the mouse to keep the whole axle assembly and the ball contact part of the sensor. I filled the slots and drilled a new hole then mounted IR sensor/receiver pair. The output runs through a small transistor circuit to digitize the output pulse.

Rather than go to the trouble of building a real interface for it (microcontroller and LCD display), I just connect it to the 'scope and to determine the frequency, then multiply by the diameter of the input shaft.

Works well to determine the top speed of the car, although its not very self-contained, since I have to keep the 'scope around to use it.

[mcbradshaw]

I've been off of my zzse project for a little while now. I've been playing around with some superslicks because they are larger and bit more forgiving. I miss having the propo controls. I'm getting more comfortable with using FETs. I plan to finish up my superslicks project by MOSFET modding it before I start back on with the zzse. The batteries and motor that I am using in the zzse are more or less the same as what I have in the superslick, so I expect equal and better results in the smaller propo car. The slick had 4 cells running on a stock PCB until I fried the FETs (hence FETs mod). So far the slick gets a top speed of >8mph (average over 10ft with 3ft head start.) I'll be starting new thread in the superslicks section for this car soon.

[mcbradshaw]

Even thought I have gotten great results from FET modding a super slick, I still like the simplicity of using a relay. http://www.mouser.com/ has a good selection of micro solid-state relays. The are reasonabily priced. I plan on continuing my experimentation on my zzse on this note.

[codesuidae]

Mouser is one of my favorite supply houses.

I'm looking forward to hearing what kind of results you end up with.

What are you doing for wheels? I find that with powerful motors I end up doing rather more doughnuts rather than acutal racing.