I'm going to be doing another 1/12 scale panzer tank and I'm planning on using two sets of gear boxes to drive it.I could use the typical single set of HL gear boxes and belt drive system and gain more power by gearing it down,but then I would loose to much speed.So I would like to try two sets of gear boxes,one set in the back and one set in the front.Instead of a front idler there would be another sprocket and drive motor.These tanks are a lot heavyer than a typical 1/16 tank,and I know they are putting a heavy load on the HL system I used.With 2 sets of HL gearboxes, boards and batterys there would be lots of power without sacraficing speed.My question being,does anyone know if I can run two of the main boards with just one of the little boards.Thought it might work by using a Y-harness from the little board to each of the big boards. Can anyone offer any help or suggestions here.???
Thanks, BIGMIG

It may work but not 100% sure but if it did you would need to use the right motor side of the boards output for the right motor from one board and use the same from the other board to extra motor on the right side and do the same for the left side this way the trims still work acordingly....I am not sure you will have to go ahead and try it it may not even work at all...

Getting the motors all working in the right direction will be easy enough,the big question is will the little board have enough power to run two main boards.Will it be over-loaded trying to do this.?? Would there be any kind of a conflict between the two boards that may feed back to the little board and cause problems.??? We have some smart electrical guys on here that may be able to give me advice on this.If no one knows or has tried this,I will give it a shot and see what happens.My new parts tanks will be here friday,so will be trying this out mabe this week-end.Hope I can get an answer to this question before that though.
Thanks BIGMIG

An important point to consider is the motors could try to drive at different rates without a differential transmission.

Basically even though exact same model number motors and gearboxes, slight tolerance differences in speed at a particular voltage could have the transmissions counter-competing with each other, potentially increasing gear wear.

Think of it like a 4WD with positive lock on all wheels, wears some rubber.

Thanks for the reply on that point.There will for sure be some minor load variance on the motors,I think the difference will be with-in the ability of the motors and boards to handle(I HOPE ).Don't think it will affect the gear boxes them selves,just the motors and boards.Thanks for your in-put,It all helps toward the final out-come. BIGMIG

In theory, good idea. The lines from the rcvr to the driver board are signal, not drive level. So, using one driver board for the front and one for the rear, both driven by signals from thew one rcvr board should be no big deal. But, as Lead pointed out, the actual loads on the individual motors will be slightly differend and result in speed/torque mismatch. Shouldn't cause much problem, other than tendency to pull to one side without the ability to trim out the diff. Should work without burning the driver board's outpu transistors. Might want to put extra effort into venting the driver boards, just to be cautious.

Keep us posted on results.

and, BTW, good to have ya back.

Splat

Just an idea when and if you do this you might reverse the polarity on the rear motors this would give you your back motors in the same direction and would not have to worry about changing to much as far as electronics and still hook up to the motor control board the same way, reverse the motor on the rear what would be black is now red on the motors. The I see thing is the current would divide between the 2 motor control boards from the single control board, that is if the 2 sides were equal in resistance. this would lower your current to the motor control boards and I think would slow down the motors and would not have any torque. AN easy way to find this out is where the motor control board plugs into the control board measure the resistance if the 2 boards are the same you should have no problem, can be different but would be better if the same ( difference would maybe 1 board measures 5K ohms and the other board is 7K ohms) . In a parallel circuit the voltage stays the same and the current is split between the sides (the split) of 2 motor drive boards. Think of it this way a river that is flowing when comes to a split in the main, the water is divided between the 2 rivers now (this would be your electrical current) but the force driving the 2 rivers does not change the speed of the 2 waters they they are the same (this would be your voltage). hey electronics 101. Now why the need for the same resistance on both sides, gets complicated, but if the 2 sides where not he same one side would try to draw more current but would not be able too and could end in damaging the control board because it would be trying to drive both sides equally. Again think of it this way, one side of the 2 rivers has a slight up grade the water is still coming at the same speed (voltage) but the water wants to back up to the main river and the slightly lower side (this would be your current) but cannot not do so because the main river is stronger ( from the control board main) and makes the the split still occur, at some point the river will break down if the balance is not kept the same. Any body can correct me if I am wrong but I was trying to explain some electronics and what to watch out for.

Thanks sniper67 for the reply,
Think we are both tinking kind of in the same direction.I have the motor directions pretty much figured out,they of course need to run in the same matching direction on each side of the tank.In theory they being motors of the same kind and ratings,should be fairly close in the RPM range.(what ever the specs are for a motor costing a dollar or two to make)Knowing there will be a slight miss-match in RPM's,I think that may not be a problem for the motors or the main boards.(guessing here).

My two major question's would be (1) will the little board have the power and ability to run 2 of the main boards. (2)I plan on using 2 batterys,one to each board.Seeing the little board must get its power supply from the big board,will there be some kind of conflict between the two main boards and using just one of the little boards connected by a Y harness.Guess I'm wondering if the signals can get messed up trying to do this,and smoke a board.
Was hoping one of our tech-guru people who understand these boards,and there workings could give me some technical advice here if they happen to see this post.Trial and error is not the best way to go sometimes,but may have to go that route to find out.I think the Idea is good as far as what I want to achieve,but don't know if the controls are going to co-operate with my plan.Man I hate to see things smooking in the tank,it's usually always bad new to the pocket book. BIGMIG [:-][:-][:-]

1) You should be okay. The driver boards don't draw very much current, so two in parallel should be okay. Test it on the bench first though so you don't go to all that effort. Keep in mind that the Heng Long boards can sometimes be confused by signals (I've had boards spontaneously lockup or reboot on me), and it would be bad for one board to shutdown and the other to keep driving.

2) You should disconnect the V+ line from one of the driver boards to the RX board if you're using two batteries.. Step 9 of my DBC instructions (http://darkith.dyndns.org/~darkith/html/dbc_inst.shtml) make reference to this line, so compare it to your connector (the wire colors aren't reliable). Make sure you don't make any other connections between the boards (e.g. don't connect the turret outputs together, etc).

D.

Design criteria as I recall: One recvr signal driving two main driver (for motor drive) boards ( I assume one board for front and one for rear);

The only problem I see is that without a way to trim the speeds of each motor ( at neutral switch, no drive current on any motor; at selected forward, and/or backward, speed you get the same torque on all motors) you WILL experience mechanical feedback from the slower motor(s), which may induce back-voltage to the h-bridge(s) for that/those motor(s). Probablly not a big issue in well designed electronics, but, remember that the HL boards are designed to meet almost minimum requirements.

The above will also cause some dis-symetry in the mechanical drive (you may have some amount of trouble going in a straight line... but, then again, you could always say "it's a tactical evasive drive system, like TOW or Lase targeted tactical missiles. they never go to target in a straight line (yeah, I know it's really the electronics 'hunting' for the targeting signal, but the sales guys say it is to confuse enemy observers).

Back on topic. I don't know what to suggest for a simple trim for the motors. The only thing I can come up with is to hack +/- trims into the h-bridges on the two driver boards. But, that may be a little beyound what you want to get envolved with.

I deffer to darkith on this one.

Splat

To darkith,and 123Splat
Thank you both for your replys,think I'm getting closer to having enough confidence to give this a try.I will test this out first on the bench like you suggest,that should tell me if the basic idea is going to work.If that seems to work on the bench,then the real test will be what they do under an actual load.And yes 123splat, one board will run the front motors and the other the back motors.
Only one board will handle all the other functions on the tank.
Darkith could you give me a little more info on the V-+ wire you refered to,is that one of the three wires that plug into the two boards.I will try to find the DBC instructions you refered to,but I have not had very good luck on here trying to find some of the info on past subjects.Not very good with a computer,pretty new at it. Thanks very much BIGMIG

Bullyhys did rig up four (4) HL drives in an old Tamiya KT. He did NOT uses HL electronics. You could always PM him for more info.

After seeing that last picture, you could give this some thought. use only one board and put the 2 back motors to the same motor control board this is still having it in parallel. You most likely would not have to worry about delay to each motor control board and the way they respond delays and such again would the motor control board handle the load. In this case I would make it as light as possible. This is another idea use 1 motor control board use a 1 to 1 transformer to the motors and you would isolate the motors from the motor control boards this allows isolation of the current from the motors. If you need help on this design radio shack here in the state sometimes have little books on designs and circuits for applications such as this a kind of beginners book into electronics. I do not have an electronic CAD any more or i would let you see what i am talking about more. Transformers are used all the time to isolate a circuit from another one so as not to allow feed back or heavy current applications to muck up another board or circuit. Have fun heck I do. It's kind of fun when the smoke is let out and you get to fix it. good Luck, Sniper 67[&:]

Hey thanks ksoc,
Thats a thread I missed seeing,but is almost exactly what I was planning on doing.thanks for pulling up the picture.I do however want to use the HL boards and radio if I can make it work right. BIGMIG

Sniper, you can't use transformers with DC current. Plus transformers in AC isolate the voltage potential, but the primary is still loaded by the secondary, plus the additional efficiency loss.
Putting four motors on a Heng Long board will result in one of these options:
1) Half voltage to each motor (series wiring) with resulting half speed...blech.
2) Double current to each motor (parallel wiring) with resulting smoking Heng Long board...double blech.


BIGMIG,
In the pic below, the orange wire supplies battery power from the driver board to the RX (small) board. If you want to run two separate batteries (1 on each driver board), only one of these wires should connect to the RX board (disconnect the other). Note that your wire may be a different color.

I'd actually highly recommend you either use one big battery or use a y connector and use your two batteries in parallel..this will prevent this problem and help ensure that the motors receive the same voltage and prevent any variation in load/current between the front and back pairs. Just connect the vcc (batt+) and gnd (batt-) between the boards.

Cheers,
D.

Hello Darkith,
It looks like you have hit the nail on the head here.Using a seperate battery to each board may cause additional unwanted problems.I think I'm very close to fully understanding what you are trying to explain to me.(I'm a monkey see,monkey do type of guy-LOL).If I use two batterys on a Y-connector going to the first board,hot leg to its normal mounting position and ground to its normal mounting position on the board.Then tought I would run a jumper wire from hot leg on first board to hot side of second board.Same for ground,Jumper from ground on first board to second board.This will insure power to both boards being equal.
Hope the way I wrote this so far makes sense.
But one more time if I go this route,in your opinion can I make up a Y-connector for the three wire plug and connect the little board to both big boards.Or even in this case the one wire still must not be used on one of the boards.
BIGMIG

Yup, you got it.

If you go this route, you can y-connect the three wire RX cable with no voltage problems.

D.

Thank you very,very much.It will be a short time before I get to this part of the project but if it works out like I hope, I think it will be usefull info to pass on to others to use.I will post the results good or bad.Lets hope just good news.
Again,thank you very much. BIGMIG

Hey Mig,

How ya doin' on this project?

I would really like to hear how it's goin ang what kind of issues have arrisen. I suspect you will have drive symetry problems (can not go in a straight line) any am really interrested a=in anf fixes you come up with.

Good luck, Look forward to hearing some good news on it.
Splat

LOL, he has it all here: http://www.rcuniverse.com/forum/m_6487594/tm.htm