Lynxmotion Tech Support

I finished assembling my Terminator kit with a bot board. I have built a few other robots before, but I really have to say I am very happy with both the chassis and bot-board.

My bot is working but I suspect in present form it would be quite uncompetitive due to motor issues. Here are my problems:
- Because they fit so well, I put in two 7.2 V 3000 mah RC batteries. I used one for each set of two motors. This makes my voltage < 12 volts and my motors slow. I love the idea of having each bank of motors have its own battery, but I am not sure how to fit in two 12 or 14 v motors. Any advice on good batteries to use for the terminator? Space is a big concern.

- I currently have the motors on each side wired in series:
(+)______ Battery (7.2v)______ (-)
| |
|_(L Motor 1)_______(L Motor 2)_|

When one motor loses traction with the ground, it spins quickly and the other stalls. I can that happening often in Sumo against a wedge/

It would be nice to shift all the power to the stalled motor but I don't have any easy ways to do this. Has anyone experimented with shifting power from one set of wheels to the other.

Thank you for your help and advice

- George

Never wire motors together in series like you show here. What you are experiencing is exactly what will happen.

Wire your motors in parallel. This problem will go away. You will also see that your motors will spin faster with this configuration.

The batteries you have are fine. I use the same type of batteries in my sumo robots.

Let me know if you have any other questions.

Pete

Thank you, I will try that.

Is a 7.2 volt battery really going to move a 12 v motor fast enough for sumo? It really seems like it needs to go faster.

I think what Pete wanted to tell you is to wire your batteries in series (14.4vdc) and your motors is parallel. This will give your 12vdc motors 14.4vdc which is a little high but no problem for a short sumo match. Some people overvolt much more than this. BTW your original design was actually putting 7.2vdc across two motors which results in 3.6vdc across each motor.

Look at step 11 in here for the instructions to wire two batteries in series.
http://www.lynxmotion.com/images/html/build122.htm

_________________
Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

I recently saw on TV how the ultra fast electric drag bike works!

http://www.killacycle.com/

When the bike start the motors are wired in serie to get max torque(current) and while rolling it change from serie to parallel to get more voltage to the motor thus getting more speed!

Pretty cool!

I think that a sumo ring is to small to try this

ciao

Jerome

Wow!

The reason they can use two motors in series, is because the output of both motors is tied directly together via the chain. The sumo bots don't really have this ability.

0 to 60 in less than one second. wow, just wow!

_________________
Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

I seem to remember a few years ago one of the 1100cc production bikes could do 0-60 in under 2 seconds but I forget which... I want to say honda magna or something like that but I don't really remember. must be getting old or something... the only bikes I think about these days are harleys... and then I look at my paycheck and say maybe next year.

you realize 0-60 in under a second is about 3Gs...

gulp... all the blood would go to my feet and I would pass out! lol

_________________
Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...

3Gs? I would flip backwards by not being able to hang on to the handle grips!

_________________
Mike

The robotics nut.

Not really true! I saw a picture of Pete Mile sumo and he has attach his motors together with a chain!

If his robot get lift up he want the non-touching motor to give power to the rear motor via a chain to get more push instead of wasting energy!

I saw the picture in servo magazine

ciao

Jerome

Whoops, I did not know that. I stand corrected.

_________________
Jim Frye, the Robot Guy
http://www.lynxmotion.com
I've always tried to do my best...