Jammin X1-CR HV conversion

Hey!

I finally ran my car with the DPR. Results are in my blog.

I was also experimenting with the Jazz throttle/brake control. Here is my understanding of how it works, based on how it responds.

When the trigger is moved anywhere above center, the Jazz tries to speed the motor to that level immediately. It does that for both positive AND negative acceleration, meaning that if you're running at 70% throttle, and you slow to 30%, the Jazz will apply brakes to get the car to 30% quickly. If you're on 70% throttle and you quickly release to 0%, it will brake very quickly as the trigger decreases, but once 0 is reached it lets the wheels run free. If you speed up again to 30% while it is coasting above 30%, it will brake to get you to 30% before applying power to maintain 30%.

Well this is very weird behaviour, but I guess one could get used to it. I'm going to pop a mail to Kontronik to question them about it and see if there's any way to disable that "feature" without a firmware upgrade.

Othello, would be cool if you could confirm the same behaviour and also mail Kontronik. :)

Oh, I might need cooling when I get my closed crowdpleazer body. Motor temps hitting 140 with the stock nitro body installed (the one with the big precut engine/tank holes). Or maybe it'll stay cooler on dirt. I get enough traction on tar to pull a wheelie atm. :)

I'm running Maxamps 2100 packs btw. They appear to be coping with 30C discharge rates! They dump alot of voltage under those loads, but they're not puffing. Time will tell how they last... :)

[othello]

>Maybe we should both take this up with Kontronik? Would be nice to get a fix from them. :) I would guess it's just a firmware issue...

A german guy did exactly this and had some talk with kontronik. But he was only told to use the "car" specific controllers and that he was the only one experiencing this behaviour (he used a Jazz 80-6-18). Seems to me they will not be too cooperative about this. But when more and more people will complain they might change their firmware. But you mainly see those ESC in air/heli application.

I too saw regenerative braking in my logs: graph. The eagletree micropower does not get confused by the current flowing to the battery when braking. Weird that the DPR resets it's zero point to 26A. Average Watt and amperes are hard to tell this way. 1077 watts average would dump your battery rather quickly ;-))

I can absolutely confirm your findings but obviously got used to this behaviour (i drive Jazz ESCs in 1:8 conversions since half a year) especially as i mainly drive on loose surfaces with quick throttle position changes where it does not get so obvious as if you would drive on a high grip surface with gentler throttle impulses. It sure would be better if the ESC would not kind of brake to get from 70% throttle to 30%. It is worth a try to shoot kontronik a mail about this but i do not think there is an easy way to change this behaviour by ourselves. It sure implies a firmware change.

The more traction, the higher your Amp Peaks will be and your ESC and motor will heat up accordingly. My findings were that even if you see almost the same average Amps on different tracks, temperature levels of the ESC and motor are quite different when you drive on loose or on hard packed tracks. On grass i pulled up to 2,27KW (95A with 10s A123). So the jazz is up to the task and is able to provide more than 65A but will heat up easely when used constantly up to this power levels. No thermal shut down as of yet but I might need a small heat sink especially when ambient temps will rise here during summer. I never needed one when i used the jazz 55 in my lighter buggy with power levels up to 1.7KW, but the truggy needs more power (obviously) and thus heats up the ESC quicker.

140F is more than i expected from this big motor, but it is not critical at all. What was your outside temp when you drove?

EDIT: can't see the firmware version, as i mounted my Jazz with the cooling plate facing upwards.

For a Jazz 80-6-18, I guess their car specific ESCs are an option. They don't have any HV ones though. :) Another idea I have is to try forward/reverse mode to see if the throttle responds the same as forward only. Will let ya know.

After thinking about it for a while, for dirt track racing the brake-to-speed behaviour might be advantageous. Kontronik must have had a reason to program it like that - maybe they know something we don't. :)

Temperature started at 80F, which is 26C which sounds right for today's ambient temperature. Summer here. :) I think these motors max out at 200F (magnet limit) so there is some headroom. I'll see how things go when I get my closed body and take it on the track. If it's still bad I might attach a heatsink that protrudes through the top of the body.

I think your Jazz will be version 8 too. I don't recall this behaviour from my version 7 Jazzes. Heck, if version 7 doesn't do this, we could ask Kontronik to downgrade our Jazzes. :) Only improvement I noticed in version 8 was that forward/reverse mode was made usable.

[othello]

You should see the same behaviour with forward/reverse mode as i'm using this mode with my jazz 55.

>After thinking about it for a while, for dirt track racing the brake-to-speed behaviour might be advantageous. Kontronik must have had a reason to program it like that - maybe they know something we don't.

True. I drove my truggy today on grass and never felt that it braked too heavely when i reduced throttle. It's only on tarmac where this behaviour can start to annoy me. I think it really depends how the car is geared, how much the car wheighs and the resistance of the motor when turned without actually applying current. The braking behaviour actually was more obvious in my lighter buggy than now in my truggy.

140F max with 80F ambient temp is nothing to get too worried about.

Interesting that your jazz v7 did not show the same behaviour. Seems to me it's only firmware related then. A downgrade should be possible, but to be honest it doesn't bother me this much ... A firmware up/downgrade would certainly take a good week at least (Austria is a neighbouring country to germany).

You're lucky to live so close. If the problem ever bugs you enough you could pop them a visit and take your car with. :D

Will let you know if I mail them about it. Probably only in the new year as I think they're closed for the holidays atm...

Thanks for sharing. :)

Hi,

I finally got the opportunity to drag race my X1-CR. Against nitros too! The venue was Boyz Toyz, a local RC car shop here, where a 40 meter straight track was setup (1:10 equivalent of a quarter mile).

I WHIPPED ASS.

Best time of the day by moi - 3.24 seconds
Best nitro time of the day - 3.62 seconds

And I have some evidence too!

Video High Quality (h.264 MP4, 20 MB)
Video Low Quality (XviD AVI, 20 MB)

All my heats are at the end. I'm the dude in the safari hat!

[lutach]

Originally Posted by Aragon

Hi,

I finally got the opportunity to drag race my X1-CR. Against nitros too! The venue was Boyz Toyz, a local RC car shop here, where a 40 meter straight track was setup (1:10 equivalent of a quarter mile).

I WHIPPED ASS.

Best time of the day by moi - 3.24 seconds
Best nitro time of the day - 3.62 seconds

And I have some evidence too!

Video High Quality (h.264 MP4, 20 MB)
Video Low Quality (XviD AVI, 20 MB)

All my heats are at the end. I'm the dude in the safari hat!

Those nitros were slow. Man your buggy is nice. Great job on the nitro .

Hi all,

I finally got around to sealing my motor. I made a front cap up of fibreglass which turned out really well. Fits like a glove and only 3 grams. Should hold up to heat too.

Taking a short cut for the motor's rear - just some aluminium tape. Not sure how the contact adhesive will hold up.

I'm hoping to take some nitros on on the track. :)

[BL_RV0]

Very cool. Are you planning to make a video?

If I can find a camera man, definitely. :)

[BL_RV0]

Cool. I'll be watching.