Hpr 135 cog

[Francois Coulloudon]

Hello everyone,

I'm currently building an HPR135.
I will be running on twin 12S2P packs.
I need to make sure the center of gravity is not too far from the "ideal" spot.

Anyone has a reco on where it should be? I can't find the information using the search on the forum.

Thank you!

Regards,

Francois

[srislash]

This seems to be a mystery, or at least the search for it. You can find pics of where everything appears to be placed but NOBODY seems to actually test the CG on a balance rod or anything. I have a number of friends here with dihedral design boats and nobody has given me a % either. I have a daytona and just getting on a HPR and it would sure be nice to know. I do know that they are a bit different than the flat pad boats. and more sensitive.

Shawn

[Lone-Wolf]

I'm running my MHZ138 today and once loaded up with batt's I'll measure mine for you. I run 10S/side...when you say "twin 12S2P", just to clarify, do you mean 12S/side or 12S2P/side?...I'm thinking 12S/side as 2P/side is alot of weight. I have run 10S2P/side and it was not easy getting everything in there.

I've got lipo sleds installed and they basically put the batt's way up there about 4" in front of motors, hull loves forward weight more than the common setups. Even with weight far forward the bow will easily lift if you are running props that are 1.5 pitch and up, I would recommend 1.4 pitch props like reduced X470's for speed and Prop Shop reduced 6514's, X457's are great but only come in 3/16 hub, those got me to 104mph running cool on 10S through 1167Kv 3040 motor. Why am I mentioning so much about props?...because that is really where you will get the hull dialed, mainly just get the weight as far forward as reasonable then use the props and of course the drive angle to get things perfect. Sorry to get off topic here. Will report back later with my CG.

[kfxguy]

I've given up a long time ago worrying with Cg. Every boat seems to be a touch different even if it's the same hull. I just shoot to have things heavy in the front at first and the prop level or even pointing down a touch.....then start moving weight back and bringing the prop angle up until it is running stBle and dry. It's a process but pays off in the long run

[Lone-Wolf]

Well said kfx!...agree fully as always.

OK, CG today was 40% on the 54" hull, I did have a blow over around 100mph but that was with 1.5 pitch props, kinda thought that was going to happen...but there ya go. First run with 1.4 pitch (reduced X470's to 60mm) and perfect in all aspect with the CG there at 40%. Hope this helps but kfx said it best.

[srislash]

40% from? Transom? Where drive enters hull? And 40% of overall length(138)?oops, got that with the 54" part.

So that makes 21.5 inches measured from?? Is what I am asking

[Lone-Wolf]

Here's an example from today of a 40% CG on 54" hull and 1.5 pitch props, 15 seconds into video....good distance!


https://youtu.be/HCR82xrLtMc

[srislash]

Just doesn't like those ABC's eh?

[Lone-Wolf]

40% from? Transom? Where drive enters hull? And 40% of overall length(138)?oops, got that with the 54" part.

So that makes 21.5 inches measured from?? Is what I am asking

Yeah dead-on...21.5" from transom overhang. I am going to move the "red brick" esc's more forward next time so will be around 45%.

[Lone-Wolf]

Just doesn't like those ABC's eh?

Does not like the ABC 2215's unless I am running 8S and even then sketchy. The video and crash today was with my new reduced (60mm) Prop Shops, 6515's...red bricks (Flier 400's) had some trouble pushing them actually but that will be in another thread shortly. Sorry to hijack thread Francois!

[Lone-Wolf]

And for comparison, here's the same boat but with 1.4 pitch X470's reduced to 60mm...and with MGM esc's...how nice is that! CG should be about the same at 40%.


https://www.youtube.com/watch?v=USA0xveh3Oo

[Francois Coulloudon]

Yes 12S2P on each side => needed to deliver the amount of power/current I need.

I got a message from Chris: "CG should be around 1/2 way up on the second step of hull measuring from transom". I think it's not too far from the 40%
I will run 1.4 in pitch, X470 downsized to X460. Will also try "X465" as I have two sets.

I understand kfxguy comment, but the closest I start from a good COG, the quicker I will find the "ideal spot" :-).

Thanks again guys. I will let you know, when I'm done, precisely where COG is. I need to find ways to move the motors bit more to the back and put all the Lipos. :-)

Cheers!

[Roy Van De Sande]

If you need 12s2p on each side in a HPR135 to deliver enough power, I would be looking for better batteries :)
I have 1 HPR135 on 8s5000mAh/side with 1170kv TP4070, another HPR135 on 12s5000mAh/side with TP5850 820kv.
Batteries are never hot so 12s2p/side is a bit over the top I guess.

[Francois Coulloudon]

If you need 12s2p on each side in a HPR135 to deliver enough power, I would be looking for better batteries :)
I have 1 HPR135 on 8s5000mAh/side with 1170kv TP4070, another HPR135 on 12s5000mAh/side with TP5850 820kv.
Batteries are never hot so 12s2p/side is a bit over the top I guess.

I'm using 8 of these: https://hobbyking.com/en_us/turnigy-nano-tech-a-spec-g2-2600mah-6s-60-90c-lipoly-pack.html

I need 280A @ 50V. Will try with only 1P but I would like to be able to add another P.

Cheers,

Francois

[Lone-Wolf]

Most likely the limiting factor power-wise will be the esc's not the cells as long as they are strong, what esc's are you going to run?...motors?

I was assuming you were using 5000ma packs which is why I was mentioning about the weight, of course those smaller packs will fit no problem. Just in case you don't know, the C-rating will of course double when you parallel but because your packs are half the capacity of a 5000ma pack you will still only get the same discharge rating as a typical 60C 5000ma pack in 1P. In other words; Your packs (2600ma 60C = 2.6x60=156amps in 2P=312amps) comparing to a 1P Revo 5000ma 70C (5x70=350amps). The only way you are going to allow for more safe amp draw is by using larger cells or just stick to high quality cells in 1P but 5000's, like Roy said above, I agree, no need for 2P but maybe you already have those cells in which case use them of course but a nice set of 70C Revo's (or comparable quality cells) will get you the best speeds with your setup. Hope that wasn't confusing.

[Francois Coulloudon]

Most likely the limiting factor power-wise will be the esc's not the cells as long as they are strong, what esc's are you going to run?...motors?

I was assuming you were using 5000ma packs which is why I was mentioning about the weight, of course those smaller packs will fit no problem. Just in case you don't know, the C-rating will of course double when you parallel but because your packs are half the capacity of a 5000ma pack you will still only get the same discharge rating as a typical 60C 5000ma pack in 1P. In other words; Your packs (2600ma 60C = 2.6x60=156amps in 2P=312amps) comparing to a 1P Revo 5000ma 70C (5x70=350amps). The only way you are going to allow for more safe amp draw is by using larger cells or just stick to high quality cells in 1P but 5000's, like Roy said above, I agree, no need for 2P but maybe you already have those cells in which case use them of course but a nice set of 70C Revo's (or comparable quality cells) will get you the best speeds with your setup. Hope that wasn't confusing.


Twin : http://www.offshoreelectrics.com/proddetail.php?prod=hef-HBF1300L
The problem is that having this setup split the current over twice the amount of conductor reducing the stress/resistance for current.
I'm quite sure total weight is not too far from twin 5000mAh. Also, I have more flexibility in weight distribution.

Thanks. Will stick to my plan, but can try other setups later.

Cheers,

Francois

[Lone-Wolf]

By all means stick to your plan, I'm looking forward to hearing how she runs! Keep us updated.

[Lone-Wolf]

It's come to my attention that I gave some slightly incorrect info when referring to proper CG with a hull like this, just want to get this out there before Francois starts gluing anything! Anyways, an observation I made since installing the quite heavy Flier 400 esc's into my hull is that the CG seems too far back compared to when the much lighter MGM's where installed, bow noticeably lifting under full power with Flier's. I measured the CG as mentioned above from the transom overhang of the hull, I should have measured from where the drives meet the transom!! Some time ago Keith B mentioned this to me and faded away in my mind...but you guys don't miss anything! So that being said, I am moving my heavy esc's forward to the point where the hull is at 40% CG. I'm certain this is where the hull will be best suited to top speeds but will update with results after I next run, maybe today. Of course this is just what works for my hull, installing Lipo sled's will be a great help in fine tuning CG.

Updates to come shortly. Sorry about that Francois!