Outline · Standard · [ Linear+ ] me needs some help

[mrbob1000]

on my super awsome zippy zap monster truck the little black wire from the steering motor came undone... so i soldered it back on. but i accedentally bridged it to the wire next to it and didnt notice it untill i drove it and it wouldnt turn left. so i unpluged the battery. resoldered the 2 wires and no left turning... so i replaced the little black rectangles (they say s1a and s2a) that go to the pads for the black steering wire and sadly it didnt do anything except improve my sodering skills.

now it wont steer left.

[baratacus]

I believe S1 is the N channel and S2 is the P channel. Those black rectangles are the FETs (Field Effect Transistor) there are three connections that must be made on each one, the Source Voltage, the Gate pole and the Drain Voltage. They must be placed properly and not overheated while soldering or you will burn out the FET. Its very hard to solder a surface mount FET without bridging something.

Also its very important that you get the N and P channel FETs in the right places. N (negative) channel and P (positive) channel conduct the current that their name implies. trying to send a positive load through an N channel FET isn't going to work.

The ZZMT boards are dual layer if I remember right. Did you check the FETs on the bottom as well as the top? How did you determine which ones needed replacing? did you use a volt meter to check their output on the Drain pole?

[mrbob1000]

I believe S1 is the N channel and S2 is the P channel.  Those black rectangles are the FETs (Field Effect Transistor)  there are three connections that must be made on each one, the Source Voltage, the Gate pole and the Drain Voltage. They must be placed properly and not overheated while soldering or you will burn out the FET.  Its very hard to solder a surface mount FET without bridging something. 

Also its very important that you get the N and P channel FETs in the right places.  N (negative) channel and  P (positive) channel conduct the  current that  their name implies.  trying to send a positive load through an N channel FET isn't going to work.

The ZZMT boards are dual layer if I remember right. Did you check the FETs on the bottom as well as the top? How did you determine which ones needed replacing? did you use a volt meter to check their output on the Drain pole?

yes... i replaced the n and the p.

how do i test them?

[baratacus]

the poles on the FET are for a high supply voltage, a low voltage gate signal, and the Drain voltage.

The input voltage to the fet should be constant regardless of the motor being on. When the reciever accepts a signal to turn left or right, the gate voltage on the respective FET will be charged and the drain on that FET will put out voltage to the motor.

A lot of times with a bi-directional motor you run an NPN FET so that you can control the motor with just 2 FETs. You have Negative current coming from both FETs to the wires and when you activate the gate on one of the FETs it switches the current to positive to that FET's wire.

With N and P channel FETs you need 2 FETs per wire. to control the positive and negative voltage. So you have 4 FETs that you need to test to find out which one is keeping the motor from turning left. You can narrow it down by checking the motor wires with a volt meter to see which one of them is not recieving a signal. From there you only have to check 2 of the FETs. You then need to check the input voltage to those two FETs. If they both have voltage at their supply pole then the FET is probably bad, or the signal pole is not connected properly. If the supply voltage to one of the FETs is not there, then you need to trace the problem back further.

This post has been edited by baratacus: Dec 15 2007, 06:34 PM

[mrbob1000]

the poles on the FET are for a high supply voltage, a low voltage gate signal, and the Drain voltage.

The input voltage to the fet should be constant regardless of the motor being on.  When the reciever accepts a signal to turn left or right, the gate voltage on the respective FET will be charged and the drain on that FET will put out voltage to the motor.   

A lot of times with a bi-directional motor you run an NPN FET so that you can control the motor with just 2 FETs.  You have Negative current coming from  both FETs to the wires and when you activate the gate on one of the FETs it switches the current to positive to that FET's wire.

With N and P channel FETs you need 2 FETs per wire. to control the positive and negative voltage.  So you have 4 FETs that you need to test to find out which one is keeping the motor from turning left.  You can narrow it down by checking the motor wires with a volt meter to see which one of them is not recieving a signal.  From there you only have to check 2 of the FETs.  You then need to check the input voltage to those two FETs.  If they both have voltage at their supply pole then the FET is probably bad, or the signal pole is not connected properly.  If the supply voltage to one of the FETs is not there, then you need to trace the problem back further.

ok... im off to the basement!

its lovely to have lots of donor parts from bits.

EDIT: well... sadly its totally dead.

what do you suggest i do? (propo system, board swap,etc)

This post has been edited by mrbob1000: Dec 16 2007, 06:56 AM

[baratacus]

hmm...it didn't take my post...

anyway, If you've been putting bi-polar FETs from a Bit-clone that can pass pos AND neg voltage in place of single pole FETs that can only pass pos OR neg voltage then you might just need to change out the FETs with the correct ones. The trouble it would take to find the right components and correctly install them would probably be greater than its worth. Even then it still might not work. I'd advise going with a different board, especially if you have that much room to work with. You can put an epoch board and servo in for about 20 bucks, or you can go with I-waver electronics. You can find I-waver 0-1s for pretty cheap or you can just buy the board if you already have a 27mhz A.M. propo controller

[mrbob1000]

hmm...it didn't take my post...

anyway, If you've been putting bi-polar FETs from a Bit-clone that can pass pos AND neg voltage in place of single pole FETs that can only pass pos OR neg voltage then you might just need to change out the FETs with the correct ones.    The trouble it would take to find the right components and correctly install them would probably be greater than its worth.  Even then it still might not work.  I'd advise going with a different board, especially if you have that much room to work with.  You can put an epoch board and servo in for about 20 bucks, or you can go with I-waver electronics.  You can find I-waver 0-1s for pretty cheap or you can just buy the board if you already have a 27mhz A.M. propo controller

i already have a 27mhz am controller. Where might i find epoch boards and the servo. also how do i mount that servo. and can it take 4.8 volts?

[baratacus]

oh wow I totally forgot the micro-t reciever. http://www.rcslot.com/pc-radio-control-slo...s/LOSB0803.html Thats a stronger piece of equipment right there than the epoch has and more readily available. That price is about as low as they go... you might find a used on on ebay from someone that's upgrading to the brushless system.

[mrbob1000]

are micro t motors the same size as zip zap motors?

also. how do i mount the servo and where? (i want to plan this all out)

EDIT: i googled for propo zzmt and http://bitpimps.lixlink.com/pages/phpForum...25d270eac601f15

anything is possible. but his runs lipos.

el cheapo http://bitpimps.lixlink.com/pages/phpForum...opic.php?t=8290

This post has been edited by mrbob1000: Dec 17 2007, 01:30 PM

[baratacus]

the one with the spy esc isn't necessary since the MicroT has a built in esc. It runs motors a little smaller than an xmod motor, but larger than a ZZMT motor. you can also use it with a dual lipo cell.

That's an old tutortial, they didn't have micro-t's back then. They did have epochs though... dunno why he didn't go that rout. LBRC made a sweet one with an I-waver board and lipo.

The one with the SE board would give you full propo, but you wouldn't have any power. You couldn't effectively run the MT motor with an SE board, and the SE motor would be working way too hard to run 4WD on the MT, especially with your oversized setup.

This post has been edited by baratacus: Dec 17 2007, 09:01 PM

[mrbob1000]

the one with the spy esc isn't necessary since the MicroT has a built in esc.  It runs motors a little smaller than an xmod motor, but larger than a ZZMT motor.  you can also use it with a dual lipo cell.   

That's an old tutortial, they didn't have micro-t's back then. They did have epochs though... dunno why he didn't go that rout.  LBRC made a sweet one with an I-waver board and lipo.

  The one with the SE board would give you full propo, but you wouldn't have any power.  You couldn't effectively run the MT motor with an SE board, and the SE motor would be working way too hard to run 4WD on the MT, especially with your oversized setup.

i crippled the vehicle and made it 2wd by removing the drive shaft... a long time ago.

anyway. i cant wait to go to the hobby store. ima get me some new electronics. and possibly some small lipos with a cutoff circuit. and most likely also some deans.

[baratacus]

I don't know of any stores that sell micro electronics.... All my hobby shops think that micro means 1:18 and 1:24. check some of the airplane sites for good micro products for your lipo needs. Also deans connectors are too large for micro. you need some smaller connectors and smaller wires.

http://www.bphobbies.com/view.asp?id=V426371
this page has some low voltage indicators for 10 bucks that are pretty small. You have to get one for the application you are using though, single, double, or tripple cell pack.

http://www.bphobbies.com/view.asp?id=A0320181
this page has connectors.. probably the JST connectors would be more the size you need.

there are other sites with specialized gadgets and micro plane development going on, but BPH is a good General store for just about any scale RC. and they have a lot of micro stuff compared to other general hobby shops.