Spartan, tear it down to build it up

[Brushless55]

I really like this info you keep posting for us!
Great job..
I wonder how my Medusa 3680 1600kv motor would fair in a spartan?

[GeoVW72]

Thank You Brushless55

Got a Feiago 10XL installed.

thinking the lower kv might help.

Ambient: 60*f

4s
esc: 71*
motor: 78*
VAS
SST
VR
6s
esc: 82*
motor: 104*
VAS
SST
VR
6s
esc: 92*
motor: 114*
VAS
SST
VR



I bring this SST graph from the 4s run out because from the 5.5-6.5min time frame I ran a right circle and then a left circle at the same relative speed. This illustrates my point that the rudder pickup, with the half-moon mod and enlarged to 3/32, flows poorly and causes the motor temp to increase. Not to say that a simple left turn will overheat the system, but I have seen a few vids where people run the boats on a left arch and that may limit the system's flow.


Given what I learned from the previous run, I made a point to stop periodically to see if the temp would rise on the log. Seeing that the temps does not immediately rise I would say that the motor is operating efficiently and not trying to fry itself to death.

However, I didn't exactly reach the 5-0 on the box, but that is to be expected going to a lower kv.
Upon disassembly the motor, had a tinge of the toasted smell
I just don't see any 2 pole pushing this hull to 50 reliably with their esc settings.

Off to find a better motor

[Brushless55]

temps looked better

[GeoVW72]

The temps are good, but it doesn't go 50+
messing with props would just raise the temp and we're back to a motor with no guts.

How about Pro boat's standby motor


Ambient: 72*f

4s
esc: 70*
motor: 95*
VAS
SST
VR

Tried running 6s, but the esc is limited in it's drive frequency and cut out at half throttle.

Nothing ventured, nothing gained.
Found the stock esc limits and that a 6 pole is too much. gonna need a 4 pole

Also should go with out saying but;

Nasty gunk, now with sparkles


And teflon flakes

Now to think of a motor with more gut, but not too amp hungry

Let ya know if I find one, any ideas?

[Brushless55]

Cool idea trying out a PB motor

[GeoVW72]

Well, found a motor that works OK.



Team Losi 1700kv 1/8 buggy motor (4pole)
I would recommend it, but it seems that losi discontinued them.

The one problem that I did find is the motor is on the limit of the esc's drive frequency. unloaded it will rev out and if the prop goes airborne in a run it will cog out, not that it's a major issue, you just have to let off.

It got the esc temps down into the 90*s on the esc and motor with the stock jacket. max speed I got was 42mph
Which really makes me wonder if we got what we paid the price of admission to see.
Chicken or the Egg argument in my mind, which we will never know the answer to

Makes me wonder if we're approaching the problem from the right angle

Open your mind...

[GeoVW72]

... to all that is possible.

We have all, including myself, moved in the direction of quenching the heat that the stock motor makes and just written it off as inefficient (which to some extent it is).
However, many have moved to more powerful setups and still have issues with torque roll and stuffing tube meltdowns.

Perhaps the stuffing tube/ drive line is the root of the problem;

1. Teflon: the first batch of spartans came with poor plastic liners
old shown on left, new on right

If your liner looks clear as the one on the left, I would contact Traxxas for a replacement(rolling change) or purchase some Octura .150 liner

2. Brass stuffing tube: This is something we have all overlooked because we expected the norm, unfortunately it is not.
Stock
OD: .254"
ID: .207"
wall thickness: .024"

K&S 1/4"
OD: .255"
ID: .222"
wall thickness: .017"

Changed the overall ID of the tube by ~.02"
Why this was done is only something I can speculate at; keep water out, retained the liner.
It would seem to me that this change can create a bind in the drive line.
After making a stuffing tube out of 1/4" K&S I noticed that the presence of teflon flakes was less and they were not "golden brown" as before.
I also made the tube longer to allow accurate temp readings and the standard trick of water line over the shaft

After 30sec the cable had turned the tubing into a 200* piece of goo, which lead me to..

3. Cable: Given that the cable damaged the tubing so quickly, I believe that an incorrect relationship exists between the cable/liner/brass where the cable is too aggressive on the liner which causes the liner to spin excessively in the brass.
This creates excessive drive line heat, 100*f(4s) 130*(6s) 160*(6s failures), which causes a bind of the drive line that leads to the motor heat and failures.

Top is Octura .150, center is traxxas, bottom is pro boat
The strands are obviously thinner than octura and the angle of attack is higher, the traxxas cable also doesn't have the cadmium coating of the pro boat cable and they are asking much more from the cabling than pro boat.
Lubrication doesn't have much to do with it, anyone that has run a spartan with grease knows that most of it ends up on the transom. Some say it's sucked out, but I think it is simply extruded by the cable.

EZ-Lube mod that I came up with to grease the cable between runs, need less to say it's just succeeded in making a mess and water line again did not work to keep the mess in, just melted down.

The "fluttering" defect:
All these modifications have not prevented the fluttering defect from occurring again (ordered the proper cable from Jeff to put this to rest).
However, no one, including traxxas, as come up with the root of this defect.
All simply write it off as an esc defect because continued use lets the magic smoke out of the esc.
The defect is high speed cogging, caused by the weakened motor from heat cycles that demagnetize the rotor.

Same rotor as in post#165
The esc loses and finds the poles causing the limited speed and pulsation. Cogging is one of the highest amp draw situations that an esc can go through.
Replace the motor and the problem vanishes, the problem is not the esc!

Thread's getting a little long, if Jeff's cable works out how I think it will, the problems should be put to bead and "The" fix should be easy.

Until then

[dag-nabit]

We are thinking somewhat along the same line.

I was leaning toward the possibility the flex cable was "augering" the grease out of the stuffing tube, rather than being sucked out by venturi effect.

I was thinking maybe the fit was tight enough between the liner and cable that the cable wind might be acting like a flighting and forcing the grease out the end.

After two runs my flex cable had no visible "excess" of grease left on it. It still had a grease "sheen" on it and left some grease behind on the rag when wiped, but it was really more a film of grease than a coating.

I was running a Jeff Wohlt cable, and had the extra grommet installed between the transom and the strut, which should eliminate or greatly reduce the venturi effect.

With the grommet in place it appears most of the grease squeezes out the vent hole in the strut. there is always a glob of grease around the hole and along that side of the strut.

I was hoping when I made the last couple runs with the liner removed the larger annulus would result in more residual grease left on the cable, but this was not the case. If there was any extra grease left behind, it was too minute an amount to account for.

Conversely, I ran a couple sets of batts in my SV27 and, as per normal, the flex cable had a generous coating of grease remaining after two runs. Emulsified a bit, but still lots of grease clinging to the flex cable.

I know I'm not any closer to figuring it out. I will be interested to hear your results George.

Kevin

[GeoVW72]

Exactly

If it was just being sucked out it wouldn't be all over the right side of the transom.
The glob will always be on the strut, I don't use the grommet method and still have it on mine. You can also make the K&S stuffing tube longer to take up that space.

The first batch of plastic liners did seem tight, I also think that the smaller ID brass tube would not allow the teflon or anything else to expand slightly due to heat, then extrude any remaining runny grease.
The stock tube also seems to be what most call brass-is. It may be a little "soft" and maybe what caused the golden brown teflon flakes.

I would also say, based on what I note from running my MG, with an OSE cable(not an entirely valid direct comparison), the the relatively high drive line temps (vs. 85*f 5s) causes the grease to break down, discolor, and run. After running the MG a few times the blue pro boat grease is still fairly blue without a green tint that I get when I run the spartan.

I am hopeful a whole new drive line will solve the heat issue

[mave]

Grease coming out from the back

Yes, it is the shaft that is pushing the grease out from the back.

A small experiment you can do is put a small section(waste material) of the teflon on the shaft, grip it lightly with a plier, then the shaft in the direction that the prop should turn, you will notice that the teflon will move towards the prop end.
So, in the same note, the grease will move from the motor end to the prop end.

[dag-nabit]

Stuffing Tube and Strut Mod

Based on the the the thoughts/theory discussed above about the drive line augering grease out of the stuffing tube, I have completed the following mod on my driveline, based in part on recommendations by George (GeoVW72).

I drilled out the back strut bushing to 1/4" diameter and approx. 4mm depth using a 1/4" drill bit and drill press.

I then made a new stuffing tube out of 1/4" K&S tubing approx. 8mm longer than the stock stuffing tube. (ballpark length, take your own measurements to be certain)

I lined it with Octura teflon liner.

The stuffing tube now fits into the rear bushing on the strut, Because drilling the bushing out with a 1/4" drill bit and drill press is hardly "precision" milling, the fit is a bit loose. (not an interference fit)

I adjusted the length of the stuffing tube a wee bit by sanding off the end until I got the correct length so the stuffing tube is "bottomed" out on the lip inside the strut bushing. This provides forward support for the strut to help hold it in place and maintain the correct negative/neutral/positive trim.

I have mine set at approx. 1mm positive trim. Minor adjustments can be made either by sliding the component tray forward or backward a mm or so, or by loosing off the stuffing tube clamp at the front of the tray and moving the stuffing tube forward or back a mm or so. (Be sure to leave clearance for the collet.

I also plugged the vent hole in the strut with silicone.

I'm hoping this might help retain grease on the flex shaft.

Hopefully can run it sometime this weekend to see if it works.





Kevin

[GeoVW72]

Nice

I wasn't thinking of going that far with the stuffing tube, but that should work great and fix any alignment issues. Silicone might not stay put in the smooth aluminum, just be sure it doesn't get ingested into the bushing.

Not sure that you need positive pitch with the torque you're getting out of that motor. I could never really get the strut to hold a positive pitch, but that mod will make it easy to set, just watch out for wear on the stub.


Hey mave, welcome to OSE, where all the real spartan info is.
Anything will be pushed by the cable that way because it acts like a corkscrew, that's how I clean all the gunk out of the cable. Everything should fit loosely enough to spin freely.

hope Jeff wasn't out of stock on cables

George

[dag-nabit]

Nice

I wasn't thinking of going that far with the stuffing tube, but that should work great and fix any alignment issues. Silicone might not stay put in the smooth aluminum, just be sure it doesn't get ingested into the bushing.

Not sure that you need positive pitch with the torque you're getting out of that motor. I could never really get the strut to hold a positive pitch, but that mod will make it easy to set, just watch out for wear on the stub.


Hey mave, welcome to OSE, where all the real spartan info is.
Anything will be pushed by the cable that way because it acts like a corkscrew, that's how I clean all the gunk out of the cable. Everything should fit loosely enough to spin freely.

hope Jeff wasn't out of stock on cables

George

I roughed it up with a needle file first. Still might not hold, but try it and see.

Not sure it will make any difference and hopefully won't cause any problems. I can't see there being much, if any, real pressure created by the flex shaft, but hopefully it will push out past the bushings if there is.

I was trying to run a bit of positive pitch on my strut, but it seemed to keep working it's way back to neutral or negative, no matter how tight the bolt was.

This should keep it in place.

The mod will either work, or it will blow apart, only way to know is to try it.

Kevin

[mave]

Hi Kevin,

since you have all the tools to do modifications. Can I suggest something?
what about forgetting the radio tray totally, reposition the motor. This will definitely shorten the length of the shaft and thus reduce the chance for the long shaft to wobble and generate excess heat. but of course doing that you will need to figure out the change in CG and etc. :)


Mave

I roughed it up with a needle file first. Still might not hold, but try it and see.

Not sure it will make any difference and hopefully won't cause any problems. I can't see there being much, if any, real pressure created by the flex shaft, but hopefully it will push out past the bushings if there is.

I was trying to run a bit of positive pitch on my strut, but it seemed to keep working it's way back to neutral or negative, no matter how tight the bolt was.

This should keep it in place.

The mod will either work, or it will blow apart, only way to know is to try it.

Kevin

[dag-nabit]

Hi Kevin,

since you have all the tools to do modifications. Can I suggest something?
what about forgetting the radio tray totally, reposition the motor. This will definitely shorten the length of the shaft and thus reduce the chance for the long shaft to wobble and generate excess heat. but of course doing that you will need to figure out the change in CG and etc. :)


Mave

Hey Mave,

Your suggestion is not without merit, shortening the drive shaft might eliminate some of the issues you have described.

I'm not really motivated to try a modification as extensive as you have suggested. if I'm going to put that much energy into a boat, I'll do a fiberglass build.

Most of the mods I have done on the Spartan have been more or less "bolt on" or have taken probably not much more than an hour or so to do.

I will keep picking away at this for a bit longer, but I'm quickly reaching the point where I'm just going to want to run it and see how long it lasts.

The component tray is actually one of the things I really like about the Spartan, and feel Traxxas did not too bad a job with it. A bit restrictive for doing component mods, but I really like being able to remove it and work on it without the hull restricting access and movement.

Kevin