[HELP] 9398 Crawler on 10V using DC/DC Regulator

[ddimkin]

Hi guys, I am just expecting my 9398 to arrive soon and would like to be prepared with rechargeble battery supply. I do have a bike lamp which operates with this Li-ion battery pack here:

http://www.ebay.co.uk/itm/Led-Lamp-6400Mah-18650-8-4v-battery-Pack-for-xml-T6-P7-LED-lamp-/251001613660?pt=UK_SportsLeisure_Camping_LightsLanternsTorches&hash=item3a70dcad5c

and the charger for it. So, I would like to use the pack also on the crawler. The pack consists of 2 x 2 18650s connected in parallel and then connected together in serial. I am not an electrician but the output voltage should be something between 8,1 volt (measured today after a fully charging) and 7,4 volt after some usage.

So I was thinking to use the above battery and increase the voltage on the motors by using 2 of this regulators:

http://www.ebay.com/itm/321283653204?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

One regulator after the IR-receiver and before each motor.

Possible?? If not, how about connecting the battery pack directly to the IR-receiver? I saw some tests and the crawler performs quite well with the Lego Li-Po battery. What do you think performance-wise??

Best regards,

Daniel

[Rockbrick]

performance is pretty good with the Lego Li-po battery but partly due to the weight saving too

I only recently bought a rechargeable box to try on the 9398

previously with the large battery box I use 1.2v rechargeables anyway so the voltage is very similar

though with 6 new 1.5v alkalines ts goes great but not for long as you will waste them wanting to play with it all the time...

Edited May 19, 2014 by Rockbrick

[ddimkin]

Thanks!! The idea is to increase voltage on on the both L-motors but not on the servo - this should improve performance a lot

Still need to know if it is possible at all with the intended setup.. thanks a lot!!

[1974]

The ouput from the IR reciever is not DC but PWM

Anyway, this is a waste of time, imo. You'll most likely stress the motors (and not to mention the actual LEGO parts) by boosting the voltage/power

If you want proper RC performance, buy proper RC cars

[ddimkin]

Wow.. thanks!! This is really important. Are there any PWM regulators that will work?

If there are none - how about connecting the battery pack to the IR reciever directly and run the crawler on 7,4 volt?

Maybe any other ideas on how to increase voltage on the motors by using this same battery pack? I know about the Eneloops and using eight of them.. but I want to use my present battery and charger. Plus it might be interesting for other crawler owners

Thanks!!

p.p. I love Lego Don't expect same performance as of RC car but want to get the maximum of the crawler.

Edited May 19, 2014 by ddimkin

[Blakbird]

If there are none - how about connecting the battery pack to the IR reciever directly and run the crawler on 7,4 volt?

Maybe any other ideas on how to increase voltage on the motors by using this same battery pack? I know about the Eneloops and using eight of them.. but I want to use my present battery and charger. Plus it might be interesting for other crawler owners

You are going to a lot of work to avoid the obvious solutions. Performance is very good on 6 x 1.5V AA batteries. Everything will operate just fine on a 2 cell lithium battery at 7.4V. In fact, this is exactly what the LEGO rechargeable battery is. Everything will also operate fine using 6 x 1.2V NiMH batteries which are inexpensive and rechargeable. Your battery pack is massive overkill at 6400 mAh, but that extra capacity doesn't buy you anything except longer run time. It won't add performance. I'd say skip the regulator and just use your battery directly. Performance will be at least as good as the LEGO rechargeable pack. There have been people who have run 8043 on a 3-cell pack at 11.2V, but there is almost universal agreement that it will cause problems with the motors in the long term.

[ddimkin]

Thank you.. but as Philo states on his site you get a whole lot more RPMs with 9 or 10 volt:

7.5 V

6.48 N.cm

203 rpm

0.48 A

1.38 W

3.60 W

38 %

9 V

6.48 N.cm

272 rpm

0.49 A

1.85 W

4.41 W

42 %

10.5V

6.48 N.cm

338 rpm

0.49 A

2.30 W

5.15 W

44 %

http://www.philohome.com/motors/motorcomp.htm

Then using the 8/24 gears you get a lot more torque, right? If I could run it on 9 volt it would be just great.. if I am not mistaking something

[hrontos]

The price for these seems to be too optimistic.

Google for 18650 to check what the stated capacity means in real and what is the experience of others with these cells. There are quite big differences between brands and some of them have very poor real capacity.

To stay on topic: I wouldn't go over 9.6V to prevent damage to motors and IR receivers. Make some tests with the battery you already have and you will see if it makes sense to buy other or increase the voltage by the regulator.

[ddimkin]

Thanks Hrontos!! I know about the capacity of the battery - thats why I already ordered this one:

http://www.ebay.com/...984.m1497.l2649

even if it has only 1/3 of the promised capacity combined with the one I already have it should give me hours of fun with the Crawler :)

Today I will order the regulator - it is also available in my country so I will get it very soon.

9.6V sound fantastic!

On the regulator I will buy I get 3 something usable amper on the output. At 4A it switches off.

Do you guys think this will be enough for the 2 x L-motors and the new servo motor? Stalled current 2 x 1.3A (L-motor) + 900mA (Servo motor) = 3.5A. I don't think I can bring all 3 motors to their stalled current at the same time very often. Especially with the 8/24 gears. Do I get this right?

Here a refference to the motors:

Servo (see at the very bottom):

http://www.philohome...rvo/pfservo.htm

and the L-motors:

http://www.philohome.com/motors/motorcomp.htm

Edited May 22, 2014 by ddimkin