My brushless Revo
 

Thought I'd start a thread on my BL Revo. I based it on Dafni's and Brian's and a few other's I've seen, with a few tweaks of my own. I decided to use an Emaxx tranny (sold the rest to fund this, should cover it entirely!) locked in 2nd gear. I removed the 1st gear idler and metal input gear to remove as much rotational mass as possible. The 2nd output gear is bolted to the dog gear w/ 12.9 screws. Should be very strong, but reversable in case I blow up a bearing (vs epoxy.) I am happy to report the tranny weight w/ steel idler was ~220g, about the same as a stock Revo tranny (~220g.)

the Batt trays are made from UMWPE, nearly indestructable with the weight close to CF (1.71 g/ml vs 1.61 g/ml CF.) 6061 alu is listed as ~4.1 g/ml. They are made form 2" angle, 1/4" thick. Works very well as was very easy to mold and cut, as easy as wood. Total weight was ~100g.

I was able to flush mount all the screws and bolts onto the existing chassis mounts. The bottom side is very smooth, and the whole mount very strong. I may trim alot of material out when I get a chance, but they are light enough now they are not a high priority now. Hopefully I can dye these later.

http://img199.imageshack.us/img199/8093/img2924xj5.jpg
http://img330.imageshack.us/img330/5204/img2925bm7.jpg
http://img173.imageshack.us/img173/639/img2927tg3.jpg

I just need to finish the front drive shaft install, the mount for the Rx and the Esc and its pretty much done. I may or may not put all 8 screws in the tranny The middle 4 don't seem to be critical, and I wonder if they are there more for the Maxx chassis the way it ties the chassis to lower braces. I will eventually going to 1 steering servo, but its good enough for now. Overall the conversion was very easy. The hardest part was the batt trays, but even then it was easy.

I will be be running an 8xl with 14 and 16 cells. I have a strobe and will be getting the 51t spur. Does anyone have any recommendations on a pinion? They are $12 ea so I don't want to do a lot of experimenting. LMK what you think and thanks to those who have already helped me get this far! I will eventually radar this to get some solid Bl #'s.

you may need some protection on the inside of the battries, because it looks like it might short if knocked the right way

Nice motor and dogbones. ;)

Have you tried to fit a body on there yet? It looks a little on the wide side. That's actually why I'm limited on battery size on my V2 Revo. And as crazyjr says; either protect the inside of those batts or just use some velcro strips and wrap them across and around the batteries/holders. Interesting choice of material - nice, lightweight, and sturdy. It looks like the type of material used in some cutting boards. Where do you get that stuff?

It doesn't look like it, but the batts fit in there very tight with the straps and up against the servos. I do have some other straps, not pictured, that wrap around the whole batt tray width wise.

Yes, they are very nice. :)

The one side fits the body perfect, the other side pooches out just a bit next to the steering servo. I really don't mind it, but some sticklers may. :P

I got the materials from McMaster-Carr, possibly the coolest website I've ever played with.:) They seem to have everything, including all sorts of very nifty stuff and easy to find. Metals, plastics, screws, etc etc. Cheap fast shipping too. Overnight was $4. The 2ft angle was only $5.

It may be the stuff they make cutting boards of as well. Its stiff and strong and insulating. As mentioned, I got velcro straps from them as well to wrap around the batts for overkill. You may be able to see there is some room to wrap a strap between the chassis and the trays. I like the width tho. Low CG w/o losing clearance. Once I get the gears, I'll be able to take it out for a spin.

What gearing did you use? 14/51? How did you like that, or do yuou think it could go up a bit? Sounds like yours ran really cool.

I might check that site out. I'm always looking for good places to get raw materials. OnlineMetals.com is good for metals, but I'm always looking for plastics and the like. Local retailers are worthless for this - at least around here.

14/51 worked well for me (you should've mentioned you wanted a 14T pinion). However, since yours may be lighter, you may want to go to 15T, but I'd get it all together and try it out first. Mine wouldn't wheelie because of the weight distribution, but all four tires would spin easily. I don't think you'll be disappointed in the power. What ESC do you plan to use?

I don't think you need to worry about that because it appears you have heatshrink on your batteries.

I've checked out OM.com, they seem pretty good too, just a narrow selection of raw materials (metals only.) I'm leaning towards a 15t, but it always takes a bit of experimenting for me to get it where I want. Just a bit pricey at $12 ea. I'm looking to get a good balance of speed, TQ and runtime (aren't we all?) If it doesn't wheelie its ok, I have the Rusty for that :) Gets to be a bit of a trouble at times.

At your suggestion, I went to Ratshack and got a cheap cap for the 9920. Put it in the Rusty, worked great, but just not as smooth as the Mtroniks I have. Allelectronics.com has better caps which I may pick up when I order some fans. I can't find any "fast-switching" caps in that spec tho, so I don't know what diff this will make long term. I'd like something like the Q125, just don't want to spend another $280 when that's about what I've spend on the whole truck so far. :( We'll see.

Yeah, radioshack isn't known for their quality parts. You could also try smaller value caps, just more of them. For example; if you need 100uF @ 25v, try two 50uF@25v caps instead. Using more caps helps transient response.

About the ESC; I know, that's usually the hard part to get (as long as you don't get those LMT motors).

That plastic is basically nylon, I'm not certain if you will be able to dye it. That type may be the oil impregnated version (usually referred to as UHMW), but I'd have to double check. It does have a decent strength to weight ratio, but like all plastics, its succeptible to threads pulling out. If anyone else tries to use some, just watch your cutting speeds (it gets to the melt temp fairl quick), and if your drilling keep the speed down, or have it clamped up good as it will tend pull your bit through too fast.

If its basically nylon, you should be able to dye it fairly easily.

I would recommend RIT dye available even at Wal-Mart. There is another major brand that I know of but it doesn't work well at all on nylons/plastics. You could try it on a small scrap first to make sure it won't be all spotchy.

Hey all. Actually UHMWPE (ultra-high Molecular Weight Polyethylene) is not nylon, that is a different plastic. Unfortunately it does not dye easily like nylon, it is more like polyester, which requires a "disperse dye" and not a simple acid bath dye like RIT. The procedure is simular, but requires an extra activator chemical to be boiled with the plastic. It can be done, just a bit more trouble. I did read somewhere that some use crayons for fabric, then use heat transfer to dye the materials, but the angle shape would be difficult to do this way. ProChem USA has dyes that will do this. ~$5-10 total. Shoot, looks like the only real drawback to this, but I don't really care about the color.

I have to make some corrections to the specs, I needed to look at my notes. UHMWPE is about half the weight of CF. ~.95g/ml, ie lighter than water (floats.) CF is ~1.75g/mL, 6061 is ~2.7g/ml and Titanium is ~4.7g/ml. Steel was 7.5-8 g/ml or so.

If you wanted to screw directly into the plastic you wouldn't want to use machine screws, but more like self tapping sheet metal screws that have a much bigger bite. I have all my screws going into SS standoff nuts and are recessed flat head screws. You can just see the standoffs in pic 3, they go through the 4mm bolt holes in the chassis and provide a 4-40 thread for the screws. There is no way they are coming out. MMC also has 2"x1" U-channels if you wanted to guard both sides of the batt, but the way the batt sits and the extra strap IMO are more than sufficent. The batts are shrinkwrapped, but I did have an experience where a batt shorted on a Alu Emaxx chassis I do not want to repeat.:eek:

Lastly, I don't think the plastic is oil-impreged. Some nylon is, but this is approved for 3A sanitary/FDA usage (dairy and food contact.) It is very slippery tho, close to teflon. This is often used as machinery guardrails, slides and such.

No one else on pinion rec's? 15t it is then? Ack, I need to do some more research. Brian, you had bigger tires on yours w/ the 14t as well, correct?

BTW, I drilled out all the holes by hand. It really doesn't take much and you really could screw things up by going to fast. Patience is a virtue. :)

I would say a 14 or 15T pinion should be about right.

Yeah, that's what it looked like - the stuff restaurants use as a food prep surface/cutting board. I was thinking of the Subway food prep area when I saw that.

Actually, my tires were the standard size, just heavy due to the tread design. The whole truck was heavier due to material choices, and I used 14T. My truck was a little over 14lbs with 14 GP3300 cells. I'd increase a tooth for every two pounds lighter than 14. So, if you are at 12lbs loaded, I'd try a 15T. When I went with 15T, my ESC heated up more, so it should be just about right if yours is lighter. If you had the cash, I'd say get a 15T and a 16T, but I think 15T will be just about right for that motor.

Chingame! I got the 15t, its was $4 extra for a total of $16... I hope I got the right one. Now I am wishing I got that 14t as well.. Oh well. The little gear ratio proggy puts the truck at 42mph with 15/51 and 40K rpm. Sounds about right, just hope its not too high. The weight should be a bit less than your V1, but I'm not sure by how much. The NIMH batts add 2 lbs themselves. 5s lipos would be great, but I have 4 pairs of NIMH I share with the rusty, so Its really the best for me right now. I can't wait!

Chingame? :032:

Well I got the esc mounted, now just waiting for the gears from Mike and I should be about set. I ended up getting a 15t and a 16t.

What's the deal on BK upgrading 7720s and 9920s I keep reading about?

You can send your 7020 in for a small fee they will make it a 9920, and if you send in your 9920 they will upgrade it to a 12020, and so on and so forth...

nice revo dude!

I was going to run to the LHS to pick up some parts and I wanted to stiffen the springs, esp in the rear now that it sags under the batt weight. I was going to go to tan springs in the rear, and move the greens upto the front. How does this sound? Thinking of repacking w/ 50 (or 60?) wt oil as well. What has everyone else found works well? I'm def will be going off road and taking some good 5-6ft jumps.

60 weight and try the silver 120 mm springs - ( even if your running the 90 mm rockers ) - the blacks were too soft for my revo running 2 5 cell lipos - i think you likey..

Hmmm....

So mixed results. I got it my gears and got it finshed, but the ESC is still having trouble. Even w/ 16 cells and 16/51 the top speed was ~25 mph. Very torquey, wheelies easy, but just no speed and a lot of stuttering from a stop.

I ran it for ~5 min, the checked the motor and esc temps. The motor was ~125, but the ESC was 200! Def something not right w. the 9920. Crap.

I was expecting 40 mph+, this is reasonable right? i think I will have to send the Bk off fopr repair or get bite the bullet and get a new ESC, maybe a Q125.

I really only see 3 esc that can handle 16 cells. The Bks, Q125 and the MGM 160. I guess the Q125 is it although I'm a bit annoyed with the heatsink thing.

Thoughts? I had replaced a bad cap on the 9920. Works now, but not perfectly. WTH would cause such high temps? I'm worried perhaps the FETs are messed or something major like that. So smoke or burned components that I can see. BEC jumper is removed BTW.

Thats awesome :):005:

:005:

I would get the Quark 125 and a pack or two of ram heatsink.

Heheh, I'll have to remember that when I get worried about my crappy typing. Popele wlil be albe to fgirure it out aynway.

Has anyone radared or GPS'd a BL revo? What kind of speeds are acheivble with "normal" setups (ie 14-18 cells)? I always assumed 40 mph as the Novak does mid 30's, and these sensorless are be quite a bit more powerful. Hmm Right now the titans woud give a strong run to the 9920/8xl which just isn't right.

The Q125 sounds good, just not the $280. :007: I was hoping to be able to run until the CC MMMaxx comes out and compare, tho this may be forever and a day.

25mph can't be right. I don't know if I ever hit 40mph with my 8XL, but it was very fast and my truck was heavy and I was only using 14 cells.

That 9920 might be bad as you pointed out. If you were running on fewer FETs due to some being burnt out, that could cause the heat and reduced performance. Too bad you didn't know anyone that lived near you who would let you try another ESC.

Are your batteries up to the task? That 8XL can pull some current. If they can't supply the current required, the truck will be slower and also cause the ESC to heat up. When I first put my V1 Revo together, I used less-than-high quality cells (just to try it out) and there was definitely a performance difference when switching to GP cells.

Did you wire the batteries in series or parrellal?
I looked at pic but no esc.

I was going to ask the same thing.

:007: :007: :007: :007: :007: :031: :031: :031: :mad:1 :mad:1
Stupid me. I wired the batts in parallel. I forgot to buy a set of male deans when I went to the LHS. I was so anxious to try it out I tried just putting the second wire back onto the esc like it was when I got it. (maybe thats how the dope blew the cap and then just sold it...hmmm) The 2nd lead was sodlered onto the =/- posts like I soldered the ubec, giving it of course, parallel config.

This is why not to do this in the middle of the night. The two mistakes I've made have been past 1am. The little baby at home makes any other time playing with it difficult tho. Dang it.

It makes sense now. My gear ratio is giving about 1000rpm/mph. The 8 cell pack is 10.5V on the voltmeter, which th kv rating would give ~20-25K rpm = ~20-25 mph. Doh. Nice wheelies tho.

I put the 9920 in the rusty w/ the 6L for 2 min to test the cap I replaced earlier this week. It ran ok but stuttery, so I just assumed it was still a bit fubared from this prob. The wiring didn't cross my mind. Damn damn damn. Time to get another male deans and make a proper Y like I should have. Maybe this esc will work after all....Oh they are good cells, GPs 3300 and 3700s. Excellent in the rusty.

Thanks guys again. You saved a considerable amount of money and hairpulling a few times now.

It is always the little things that get you. :D

Lol. Those little things can bite ya. :)

If you think it wheelies good at ~9.6v, just wait until you get it working right at 19.2v!

If you got 25 like that you should hit the 45 mark.

Hmm mixed bag of results... I made a y and wired it correctly. Lots of power now. :017: Surprizingly it doesn't want to wheelie now?:032:

Part of the prob is that it still stutters from a start. It surges *vroom...vroom vroom...vroom* then get to ~10 mph then just bolts to full speed. The back end def squats down and takes off. I would guess top speed to be high mid 30's currently.

I wonder if that cheap Ratshack cap is not upto the job. Seems like its missing a phase or something. The basic specs are the same 220uf, but it only 35V and 60*C rated, and non-fast switching. I've ordered some better caps from allelectronics.com, but I don't see them listed as fast-switching. I hope they can do better. I can't find a replacement Rubycon cap in a quant less than 400, so I'm a bit stuck. Also, the esc is still heating way up. It got to ~200F again within a pack (4-5 min really.) I may have already partially killed the RS cap with the temps. Perhaps that's why its misbehaving more badly at low speeds (was ~ok first run.) I should have just bought the esc new. Thought that as soon as I won it and have been regretting since. Maybe I'll get it working, its almost there.

May have to wait till mon/tues when the new caps come and see what happens. I will def need a roll bar. Got too used to flinging the rusty in the turns, and you just can't do that on such a big MT and expect to stay on the wheels.

I don't see why those caps don't work right. Maybe it is the temperature since the traces may get quite warm and the heat will tend to be sinked through them.

High speed caps would be more of an issue for oscillator or high frequency filter, but I think (please correct me if I'm wrong) those caps are actually to provide a little amperage oomph during high current spikes.

Anyway, it will be interesting to see how those new caps work. If you are concerned about the working voltage, I found some inexpensive ones here. Temp ranges from -40 to 85C. These are from partsexpress so they tend to use the higher quality caps for use in audio crossovers so they may be faster switching as a result even though they don't specifically say that.

Honestly I don't know why they are used as such. But pulling the Rubycon part # off the caps, the spec sheet lists the caps as high freq switching (or whatever exactly.) I'm just trying to replace the caps with as close a match as possible. The whole spec was 220uf, 50V, 105C. The allelectronics caps I bought are exactly that. If that does not correct teh problem (I'm worried it may not) I will have no choice but to sent it off. My best hope is that it is the caps as its something I can repair cheaply.

I know what you are saying about the amp spikes, but on the other hand I don't know why BK would have used 4 small caps for that. It seems easier and more reliable to have used 1 large cap. The caps are only 220uf, so they aren't really that large at that. When one of the caps was bad, the esc did not work properly at all.

I'm concerned about the heat build up, something is casuing a high amp draw.I don't see it being the setup. It got warm even whenI tested it in a 2 min drive in my rusty. Worst case would be some internal short Would a bad FET do something like this? Dunno, I don't see a whole lot else there. Nothing smaoking or burning, so not a whole lot for me to go off of. I have a feeling there is more power there too which is not getting to the wheels. I would think the 8xl/16 cells could break 40. Its still off that by a bit. We'll see what Monday brings I guess.

In the meantime I've got to figure out a roll bar. I don't want to crush the motor or esc on a bad flip or landing. The stock body is pretty light& flimsy and doesn't offer a whole lot of protection in a crash. When I get everything together I'll put up some more pics.

Finnster, a wing works wonders :p.

Actually, several smaller caps in parallel have a better transient response (charges and discharges faster) than a single large cap. Plus, multiple smaller ones are usually cheaper and easier to mount, but may take up more physical space than one would. Those four 220uF 50v caps have the same capacity as one 50v 880uF cap, if in fact they are all wired in parallel.

As to your heat question; FETs have an "on" resistance. Having several in parallel (like these ESCs do) effectively decreases this total "on" resistance. If one FET has, say, 0.1ohm of resistance, then ten of them in parallel will have 0.01 ohms of resistance. Higher resistance creates more of a voltage drop which, combined with the current, generates heat. Less resistance, less heat. The point to this "lecture" is to say that if you have one or more burnt out FETs, then the total resistance goes up, creating more heat for the same current. I don't know if this is the case in your situation, but it is a possibility.

Something like the Eagletree system would record your battery current for you and tell you if you had too much amp draw.

Could be one or more phases on the motor itself is bad but I doubt it's that since it ran perfectly fine with my Bk 12020, and I really didn't use it all that much anyway. If you had a meter with a "conductance" mode, you could get accurate readings of the windings. With a regular meter, the winding resistance is so low that it will look like a short when it isn't. The most you could do here is check the resistance from each terminal to the motor case - it should be an open circuit for all phases.

An interal short would definitely blow something, but how would that happen? Even water doesn't short electricity unless it is very high voltage, it's the corrosion that gets ya. Most semiconductors usually open when they give up the ghost as opposed to shorting. Kinda like a fuse; too much current will burn up the small parts inside the devices.

Sounds like the ESC to me, hopefully the new cap will help. While you are at it, you might want to replace all of them. If they are all in parallel, what happened to one happened to them all. Maybe only one totally crapped out, but the others may be weakened.