Running NIMH? Weigh in...

[Meniscus]

I'm looking for some input from anyone that still hasn't made the jump to Lion or Lipo. I'm running 6-cells Intellect 3800's and 6-cells Venom 5000's. I don't have the funds to move to Lipo, unless someone is looking for a charity case (just kidding).

Anyway, I was wonder what some would recommend for longer run times and overall performance with regards to charging amps for these batteries. I've tried different setups with mixed results. Right now, due to the weight of the NIMH batts, I'm losing a lot of speed with the hull in the water. I'm also interested in the Good, the Bad, and the Ugly of prop angles.

Any recommendations would be greatly appreciated.

Background: BJ BL owner for 4 or so weeks now. Running stock hardware plus antenna relocate and push-pull switch. JR XR2i TX and RX. Have programming card and removed Styrofoam, supplementing buoyancy with pool noodles. Run times are about 4-5 mins tops. Using MRC SuperBrain 977 for charging.

Experience: I used to run hovercrafts back about 10 or so years ago, but am reorienting with the rc boat world nowadays after a brief stint in rc dirt bikes.

[Meniscus]

What can I say, I'm staying in my budget.

Am I best off replacing the prop next?

[ReddyWatts]

I never went over 3 amps while charging NiMH's. A slow charge of .3 amps is good to equalize the cells every once in a while.

Reduce your amps for longer run times using a smaller prop, but sacrifices speed.

Usually an up tilt of 1 - 2 degrees on the back of the strut on a cat is good. You can also raise the bottom of the strut above the bottom of the hull. Not sure how much works best on this hull. Maybe 1/4 to 3/16?

[Meniscus]

I don't' want to sacrifice speed necessarily, I'd like to keep speed comparable. What props might everyone recommend for the near term and long term. I have access to various resources and don't see balancing too much of an issue (maybe naive).

Thanks for the input.

[obrien]

The bj really seems to like running the x642 detounged for a prop. For top speed, tilt the drive as high as it will go, and move the batteries back against the transom. If you want the boat turn better, keep the batteries more or less between the steps. I will say that the stock shaft will not last very long, so start making plans for atleast upgrading to a good flex shaft.

[Meniscus]

Yeah, I could guess that I might have to move to a flex shaft fairly soon. I just keep greasing and crossing my fingers.

I will try to tilt the drive to the extreme and try the x642 prop. I'm hoping that this will help to reduce some of the drag. If I get desperate, I'll have to the dollar store and start pumping the thing with helium, LOL! At least I haven't seen that approach here thus far.

Does anyone think that I could get any gains anywhere else, without moving to Lipo and going crazy?

[Spot Me 2]

Run more cells. It will increase your speed! How many 5000 packs do you have? You can run up to 3 at one time. You just need to make a tri y harness and find somewhere to put the 3rd pack. I just got done making to 9 cell 5000 packs for mine.

[Meniscus]

I've read various opinions on more than 6 or 7 cells. I know that some have used 7 cells successfully, but are you implying 18 cells (9 plus 9 is what you are running or 6+6+6)? I'd venture to guess that they gain vs. weight may not be worth it and I don't know enough about this esc and what it will take without shutting down. Have you experienced any issues?

I do appreciate your input and ideas.

[Apples1]

the gain is always worth the weight..... i charge at 1amp for run times and 5amps for outright speed, (about 5-7mph difference), but then made the jump to Lipo,

7 cells is good too.

[Meniscus]

Spot, how long have you been running with all of those cells? Any issues thus far?

Apples, I'll try some other charging amps and see how it works out.

Well I guess I have a list of things to try, but I'm the type to try one thing at a time and then make a determination, rather than putting a lot of variables in the mix.

Any insight for the number of NIMH cells the BJ ESC will support? I don't want to go too extreme and end up frying the thing. The whole point is that I, as well as others from what I can tell, don't have the funds available to move to Lipo. Hopefully, everyone that is using the NIMH batts can benefit from your input.

[Meniscus]

ReddyWatts, I tied equalizing the cells, that helped a lot.

Apples1, I experimented some more this weekend after equalizing the cells with the amps. It seems that now I'm moving in the right direction.

Thanks for all the input.

[Meniscus]

Alright, it looks like I have found the happy medium, at least with my setup. On Intellect 3800's NIMH 6-cells, charging at 3.2 or 3.3 amps and topping off at 4.7 before the run works best for me.

Moved the CG down and back a little and have to say that PropNut was right on regarding the distance back for the batteries. No experience with Lion or Lipo yet (still counting change for those!).

[Jesse J]

A comment on lipo

I jumped straight into the Lipo scene after I got the Triton 2 for Xmas. I got several 3S and 2S packs (2500 and 3300 mah resp) and was surprised at the short run times. I expressed these times on the forums and the guys are talking about their run times in seconds!! They are saying full throttle with high mah packs 1-2 minutes.

I am now waiting on the 4500 NiMhs to arrive to run them with the BJ 26 motor/esc in a cat I am modeling after the BJ 26.

In my hydros (22" and 28"), 24" cat and V (28") I have brushless motors and have used my Lipos (never over 3 minutes). Realize, with the Lipos you have to time your runs, compare that to the time it takes to recharge them and then stay under 75% of complete discharge to be safe and maintain longevity of the packs. You can get two NiMHs for the price of one Lipo (of similar voltage and lower capacity).

I have backed off on my encouragement of going Lipo unless you are really going to race and try to be competitive. I like the comparison with deflating a balloon, "NiMH is like a pin hole, Lipo is like a golf ball sized hole"

I am going to go NiMH with my BJ26" scratch build and try the 7cell packs (also thinking for the rest of my apps). I just want more run time and not have to bring it back to shore when the timer goes off.

Hope this helps

[crazzy maxx]

you can get a 4800 3s1p 11.1v zippy lipo for like $60

[Jesse J]

what kind of run times of the BJ26?