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  1. #1
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    Slash-Pede 4x4 MT and SCT Combo 4S Findings

    There was a thread a bit ago asking some questions about running the SCT Combo (MMP and 2400kV) on 4S and I have some findings to report. I have just gone 4S (35C 4500mah) with my Slash-Pede 4x4 MT and had it geared 17 / 54 with pro-line trencher tires. The slash chassis is 1.75 in longer and a couple oz heavier (due to extra length and larger body) than a 4x4 pede, but is otherwise the same truck for reference.

    After running several packs I found the peak temp to be around 160F ~ 170F, the MMP fan would start and run after about 1 minute and stay running as long as I kept driving, but would turn off after about 30 seconds of stopping. This was through tall thick yard grass, goning up and down hills, and doing some speed runs on the pavement.

    I also found a warehouse building nearby that's about a 100 meters long with rough asphalt that has some nice little hills and what not, but also a straight away running the length of the building. Its very high traction with those trenchers (about as high traction as you can get). I hammered the truck the entire pack, running full throttle (or as close as I could get without entirely loosing control), would turn around and do it again and again until the LVC stopped my fun. Hit 199F~200F at the end of the pack. Slipper is set to act almost like the launch control feature on the MMP so it slips just enough that it usually doesn't pull a wheelie from a dead stop (although once going about 20mph it will wheelie on demand if I blip the throttle or hit a bump). Run time was about 20~25 minute range, outside was dry and ambient temp was about 65F.

    I'm going to say that 16 / 54 is about max safe gearing for this combo, 17 / 54 is a bit over geared and can be done if care is taken (cold weather or shorter run times), but for bashing or hard long racing I would suggest not going over 16 / 54. I have not even tested that gearing yet, but one tooth should be enough to give me a bit of a safety margin to keep it under 200F in the most extreme use and it is also what the castle gearing chart stated as max recommended for the 2400kV on 4S in a slash 4x4, at least the booklet that came with my SCT combo.

    Also note that castles revised version in .pdf now states 14t / 54 as max instead of the 16t / 54 my booklet did, but I'm guessing that's with a 10 deg timing advance. I'm running 0 advance which is equivalent to dropping 2 teeth, so I am still within their guidelines. If I'm not mistaken this is also what Thomas-P ran in his 4x4 Pede before he went to the Hobby Wing motor (although I don't know if he ran 0 advance or left it on the default 10).

    I hope this helps anyone looking to run their SCT on 4S! Any additional thoughts, comments or experiences are always appreciated so feel free.

  2. #2
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    Got a chance to run it again today, only for about 12 to 15 minutes doing speed runs again, but the motor temp was 175F this time. I would expect by the end of the pack for it to be in the 180 range, which is still reasonable. Had to stop running though because one of my tires came untaped, thus it turned oval when doing speed runs :-(. I am not looking forward to un-gluing, re-taping and re-gluing it, but alas, I must!

  3. #3
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    Sounds like you have found the sweet spot on your combo man
    Famous last words...watch this!!!!

  4. #4
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    Got a chance to run again today, for a full pack this time. Temp reached max of 207F at the hottest part of the motor (the shaft end where its mounted to the motor plate), that's too hot and doesn't leave any room for a higher ambient temp. Gearing is 16 / 54, with a some what loose clutch (too loose as it slips for a good 10 feet or so).

    However I did notice that the end of the motor (207F) was much warmer than the center, which measured around 195~199F max when I scooted the shroud aside. I'm wondering if a heatsink motor mount would help along with a tighter slipper. If that slipper generates a lot of heat from constantly slipping i'd imagine that heat will very rapidly transfer through the motor mount onto the motor. Also perhaps setting everything back to default in my MMP may make a difference as well. I"ll play around some more and see how she responds, but it seems 16 / 54 is a reasonable gearing for this truck on 4S based on other's experiences.

  5. #5
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    Good reading. Good bit of usefull data. I am going to the park today where I can try a few speed runs without worrys of mail boxes and speed limit signs. I have 19/54 installed and running on g-loc street tires. I will be using a ******* 4s 40-50c 5000mah LIPO. I will also have the weight of my cell phone on it for max speed. I will take the phone off when I am satisfied with the #'s. I will update my temps later, if I don't destroy my pede!lol

  6. #6
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    Sounds good, if you can, run it for as long as you can, your packs have about the same capacity as mine, so your run time is around 20~25 min (I have 4500mah 35C 4S packs). Also what is the outside diameter of the g-lock street tires? The trenchers are about 4.8~4.9 in according to my calipers, I'm guessing those g-locks are a bit smaller, otherwise I think you may be over geared a couple of teeth. I seem to be pushing things to their thermal limits with trenchers, 16 / 54 even using the blower fan (hence my 200F temp by the end of the run). However there are a few things I can play with to see if I can drop those temps. Thanks for the info, looking forward to seeing your results!

    BTW, I have not had any issues with this motor producing power even running at those higher temps, which I have hit now twice, so I can confirm the motor is still within operating range right around 200F (give or take a few degrees of course). However, since I'm running on the edge now, if I push it even harder (if I can find a way) or run it on a hot day I will likely exceed that, so I will continue trying to create more headroom and get those temps down to around 180 or lower.

    Also note that a common max temperature of wire wrap wire (the wire used on the stator) has an enamel coating to insulate it, the max temp of that enamal coating is around 105C to 110C, which is the weakest part of the motor. The glue on the rotor may also have those temp limits and those two areas are where the failure would occure.
    Last edited by WiNandLeGeNd; 10-02-2012 at 02:27 PM.

  7. #7
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    Quote Originally Posted by dirty don View Post
    Good reading. Good bit of usefull data. I am going to the park today where I can try a few speed runs without worrys of mail boxes and speed limit signs. I have 19/54 installed and running on g-loc street tires. I will be using a 4s 40-50c 5000mah LIPO. I will also have the weight of my cell phone on it for max speed. I will take the phone off when I am satisfied with the #'s. I will update my temps later, if I don't destroy my pede!lol
    just got back from the park. Wanted to catch Monster Jam on tv! Lol I ran the set-up listed above with the MM2400 combo. I made six teeth grinding speed runs. Outside temps are 82 deg. My motor temp was 135 deg and I managed to hit 62 mph. I was using the Ulysse speedometer app. Made several more high speed runs. 15 min runtime total. I then drove it off the blacktop on to a gravel road then straight to a unseen pothole full of water. I then shut it down. My max temp after all of this was 160deg. Don't seem to have done any damage to the esc from the water. A couple of months ago I sprayed the circuit board of the esc with some Kon Form. We use this stuff to protect electronics offshore. It's kind of like spraying polyurethane.
    Last edited by dirty don; 10-02-2012 at 02:59 PM.

  8. #8
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    Sounds good. I will try re-setting my MMP to factory defaults. My truck geared 16 / 54 produces a top speed a bit lower than what you have (by about 6mph), so I don't think I should be seeing temps that high after a 20+ minute run on pavement in 65 deg ambient. Its possible the current FW I'm using is causing this since its a beta version (or a combination of setting and FW), what version of FW are you using on the MMP? I have the latest beta (1.38 beta I think).

  9. #9
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    I have the same update as you I think. I just loaded the software and got a update notice. Release date was 9-27-12. Man your ambient temps are awesome. It's stays hot and humid down south.

  10. #10
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    Had a chance to run for a bout 15 minutes last night...and the moral of the story is don't drive a 55mph RC truck in the dark with no lights :-). Hit a telephone pole at full throttle because I could barely see, but I did see the truck hit so hard it launched about 10 feet in the air! Amazingly the only thing that broke was the ball cup on the bottom of one of my rear shocks, it ripped in half, but the shaft, shock and rest of the truck is some how un-damaged!

    During that 15 minutes the max motor temp I saw was about 165~170F which is inline with everyone else. I think the reason I see 190~210F range is because when I drive during the day on the pavement, I run back and fourth full throttle for the whole pack. You can't push the motor any harder than that. When I drive off-road on grass or dirt, I don't get to use the throttle nearly as much to maintain control, so the motor isn't being pushed ot the extreme and I see temps in the 150 to 170F range.'

    Also, castle states the max reccomended gearing for the 2400kV in a slash 4x4 (that's with 4.2" slash tires) is 14 / 54 for this motor. The RC speed calculator gives the truck a max speed of 40mph flat on 4S. When I change the tire size to 4.9 and gearing to 16 / 54 I get a top speed of 54mph on 4S. That's a 26% increase in gearing and easily accounts for the extra heat when I REALLY push the motor. So I don't think there is anything wrong with the motor, controller or my setup, I've just found a way to push it its absolute limits.

    There are a couple of solutions:
    1. Get the 2650kV (which at this time I don't want to do because of cost and I just got this system)
    2. Gear down to 13 / 54 or 14 / 54 as per castle's recomendations
    3. Add thermal mass and surface area to the motor to compensate for the added waste heat

    I am going to leave my gearing at 16 / 54 and try adding additional heatsinking to see if I can get my max temp to around 185F or lower at the end of a pack when I hammer it for 20+ minutes straight. If I can do that then I think the system should remain reliable enough that I don't have to monitor it constantly even when I really push it (which I do often). Eventually I may go the 2650kv route and get some insane 65+ mph speeds, but 54 is pretty fast and I'm more than satisfied with it right now as long as I can get it run at reasonable temps under the abuse I dish out.

    I am gonig to try the traxxas heatsink motor plate (the added thickness increases thermal mass and thus requires more energy to heat up and maintain that temperature) in conjunction with the Novak HV heatsink (for 550 size motors), again increasing the thermal mass of the motor as well as significantly increasing surface area for better thermal transfer (will use PC heatsink thermal compound for better conduction). Lastly I will cut the sides of the CC blower shroud off and zip-tie the blower to the top of the heatsink to privide constant airflow as well as cut / drill holes right below the motor to allow for better convection cooling. It is my hopes that the combination of all of these modifications togeather will be enough to accomplish my goals. The King Headz bearing carrier I already have, so there is additional thermal mass as well. The parts come friday, so we shall see this weekend!

    Motor Heatsink: http://www.amainhobbies.com/product_...otor-Heat-Sink

    Motor Plate Heatsink: http://www.amainhobbies.com/product_...tor-Plate-Blue

  11. #11
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    I have the Hot Racing motor plate... It fits well and looks pretty cool too!



    http://www.hobbyetc.com/item.cgi?par...6PVcbsrvECqFUQ
    When Boy When, Are You Gonna Get Your Act Together

  12. #12
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    I saw that motor plate and really liked it, but I decided to go with the traxxas one because the Novak HV heat sink is for a 550 motor and will cover most of the motor. I believe those radial heat sinks on that plate would prevent the HV heat sink from fitting properly and I need the added cooling of a full can length radial heat sink.

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