mad rat setup

[Grandad]

Hello,
My two Grandson's , Sean and Ryan, were at the meeting this last Saturday with their Mad Rats. Neither of them managed to finish a race because the speed controllers on both cars were overheating and shutting down. One had a 10 turn brushed motor, the other a 12 turn. In fact one of the leads of the 10 turn motor got so hot that it un-soldered itself -- let me say thanks to the person who let them borrow a soldering iron!

Both cars were built by us from kits, the small gear on the motor shaft is marked 21T, the large gear on the 'clutch' assembly is marked 80T. They both have 5000mA/H lipo batteries. We would like some advice on how to proceed.

I have a feeling that we fried the motors, so would it be better to convert to brushless motors? Bearing in mind that I have to buy two lots -- so cost is an issue -- what would be a sensible selection of motor/esc/gearing for beginners, so that we can at least not have to leave early and disappointed like we did last week!

Thanks and regards
Ian

[DazLee]

Hi Ian,

It certainly sounds as though the motors / Speed Controllers got a little too hot.

This I would imagine would be more likely due to the higher voltage of Lipo batteries (Nominal 7.4v) over the Nimh / NiCd (7.2v Nominal) we used to use with brushed motors.....rather than a gearing problem.

Although when charged a Lipo pack and Nimh pack are around the same voltage (8.4v) the Lipo pack maintains its voltage with very little drop off throughout the run which will generate extra heat in the motor and speed controller.

There are a few things you could check though before spending on new brushless systems:

1). The condition of the motors - Is the comm / brushes blackened and do they need a good clean? New brushes?
It could be that with a quick clean and new brushes they will be fine?
2). Are there any punch / power settings on the speed controller that can be turned down a little?
3). With the pinion gear (21t) removed, does the transmission on the car feel free and smooth? Is anything binding up and making the motor work harder than it should?
4). What sort of ride height (Chassis height) is being used. Grass can cause a lot of drag if this is too low which will cause extra work for the motor and extra heat.
5). Is there a little bit of 'rock' between the pinion gear (21t) and spur gear (80t). These should be meshed tightly enough not to strip teeth but loose enough to not cause unnecessary drag.

In an ideal world, upgrading to brushless would be your best option as this reduces the level of motor maintenance required massively and they are much more reliable.........but its best to check items 3, 4 & 5 above as these could cause extra heat to a brushless motor too......and perhaps end up damaging it.
A brushed motor will always need regular rebuilds, replacement brushes, comm skim etc....whereas a brushless motor will perhaps need bearings oiling and a clean out once every couple of months.

As fror recommending brushless systems, there are quite a few around and these can vary massively in price........I have seen motor & spped controller combination sets for around £69.99 upwards.
I run a GM speed controller which is massively complicated and quite expensive so would not recommend this for a beginner. I have been using it 5 years and still dont have a clue what most of the settings do!!!!!

Perhaps others on here can offer advice on what they are using and how they have found them??

I would think somewhere around a 10.5t brushless motor would be about the right speed for a beginner. It is slow enough to not break stuff everytime you hit a corner or make a mistake, but fast enough to teach throttle control and to be reasonably quick on a lap if you hook it up right.
Unfortunately, I have never owned or used a Mad rat so cannot really offer any advice on gearing.........I will leave this to someone with more experience of this particular car.
The gearing you are using though doesnt seem far enough out to be the sole cause of the motor heat problems.

Hope this helps
Darren

[Wacker1]

Hi Ian,

I think that Daz has covered most things to try/check, up on his List above

.......but personally, Upgrading to the Brushless Technology is the way forward!

If your Budget can Handle Purchasing a Brushless Motor/Speedo Combo(unfortunately x2 ), then I could pretty much Guarantee, you'll never look back!
Once Installed, your'll find it has Better Performance, virtually no Maintainance & far more Reliability than the old Brushed Systems.........the hardest thing to do before you Race then, will be Charging your Batteries!

There are plenty of Speedo/Motor Combos outthere to choose from, with High-End Brands such as GM, LRP, Nosram, Speed Passion, Novak, Tekin etc, but as your just Entering into the RC World of Buggy Racing, I'm sure something like the Following would be the ideal stepping stone for your Grandsons :

http://www.modelsport.co.uk/etronix-pho ... cts/368726

OR

http://www.modelsport.co.uk/ansmann-rac ... ucts/35886

Hope this Info helps!

[BazzerH]

Try looking for hobbywing xerun combos on eBay. You won't find much better value for money. U could spend 4 times as much and your lads won't notice any difference at all. You can even set 'boost' and 'turbo' levels which all young men find extremely exciting! Some old ones too.

I use the V 2.1 esc and it's brill, it's also just been outdated so might be a few bargains about

[Grandad]

Thanks to all for comments.
Yes, ride height was an issue. They are both set to what appears to be maximum. The only adjustment seems to be by fitting spacers between the top of the shock absorber mountings and the spring. Each car has got all of the spacers fitted, so I don't think we can improve that much.

The amount of grass cuttings that clogged the rear driveshafts I think caused the motors to work harder than normal, hopefully the track will be a bit drier next time.

I appreciate the suggestions that brushless will mean less maintenance, which can only be a good thing, so I had a look on Ebay using your advice and ended up buying qty two ezrun 10turn motors with speed controllers and programming gadgets -- new from a shop I'd used before for £200. They arrived this afternoon. Looking at them quickly I'm slightly concerned that the height of the fan on the speed controllers isn't going to fit under the mad rat body without cutting holes, but we'll have a closer look at that later.

Whilst on ebay, I had a bit of a search for different spur and pinion gears for the mad rat but could only find the original parts 21/80, so I suppose we'll stick with that for now. I just remember experience from the indoor season with our three TT-01's, where even I had a go!, that the original spur/pinion combination supplied with the kits was useless in competion. So I don't know what the 'ideal' gear ratio would be for our grass track with the mad rats.

We use cheap and cheerful ansmann branded 2.4GHz radio sets with our cars, but we always have difficulty when it comes to fitting the receiver aerial in the car. The mounting and tube supplied with the madrat is obviously designed for maybe the old 27MHz equipment where the aerial is a single thin length of wire which easily fits into the aerial tube mounting slot and up into the tube. But the 2.4GHz receiver aerial, as you probably know, actually consists of a short length of coaxial cable with the outer sleeve removed at the end, which is a stuggle to fit inside the tube. Has any one had any success with just fitting the aerial inside the body of the car without using the tube?

So thanks for the help, and no doubt we'll have more questions with brushless setup in the future.

Thanks and regards
Ian

[DazLee]

Hi Ian,

I have had some limited experience of Hobbywing products and actually have one of the their speed controllers in my spare touring car. I run a 10.5t motor in that car and have never had a fan fitted to it. This has run with no problems at all for some time now.
Having said that, I would always recommend running the fan if you can get it to fit under the bodyshell....It is always going to aid cooling.
I have seen a number of cars with cuts in the bodyshell in the area that the speed controller fits..........perhaps this is to overcome that issue or simply to aid cooling. Its certainly an option.

As for the gearing, I would suspect that any 48dp 'pitch' pinion gear would fit as with most cars. These should be readily available from most hobby/model suppliers and are available from around 15t to 38t........usally at around £3.00 each.
I would try with the gearing you currently have and see how you get on, It doesnt sound far away from what I am running (although I am running 6.5t brushless motor) on my 2wd buggy so i certainly wouldnt expect it to cause any issues with heat. It would probably only require fine tuning for performance and this can be tackled at a later date once you have overcome the current 'reliability' issues.

As for the 2.4ghz aerial, I am led to understand that they will work with the antenna inside the car, although as I am an 'old school' racer from the days of 27Mhz and 40Mhz I still like to have the aerial antenna pointing upwards!!!
On my car I have cut the aerial tube down to about 10-12cm (4-5 inches) which is about the right length for the bit with the sleeve removed to poke out of the top. Whilst this doesnt help with the diameter issue and fitting the antenna inside the aerial tube, it can be fitted through because of the much shorter distance it has to travel through....sometimes with the help of a little lubricant. (I run futaba 2.4Ghz and I am not sure on the diameter of the co-ax antenna in comparison to others but would suspect they are all very similar).

If you have any other questions, feel free to ask and I will do what I can to help.

See you at the club soon........although dont think I will be there for the next couple of weekends as I have other 'touring car' commitments.

Thanks
Darren

[Hail Ming]

Hi Ian, if you want a cost effective way of changing to brushless (approx £100), I can recommend the following. I'd go for either a 60A or 120A Xerun Hobbywing esc (available from Giantshark here in the UK or on eBay from HK) and a 10.5T Speed Passion Sportmans V2 or V3 motor (you get these on eBay for around £25 shipped from HK). Gearing to use would be the kit spur (80T) and a 27T pinion - that will solve your running problems and provide a sensible amount of speed in order to be competitive.

Hope that helps.

James

[Grandad]

Thanks James,
Well we tried to fit the esc and motors into the madrats, but there was no way that the esc was going to fit without major surgery to the body.
So we decided to fit them into their Ansmann Macnum cars. These have much more internal headroom. The installation went well, a test down the local tarmac road showed good speed with cool motor.

However on race day, both failed to finish the first heat due to stripped gears in the gearbox unit. Sean raced again later in the afternoon after we fitted a spare complete gearbox unit, but it too was damaged in the end. So, a bit of time with google this afternoon came up with a few people complaining of stripped idler gears - asking whether metal replacements were available?

So, the slipper clutch unit that is fitted to these things, I'm not sure of its function or how to adjust it correctly. Presumably the tighter the spring tension on the plates the more power is transferred from the motor, so maybe loosening this a bit will save the gearbox? But presumably wear and tear would be reduced if the drivers didn't try and go around the track at full blast ?! The esc's came with programming cards, not really studied these in detail but it looks as though there might be an adjustment that would slow down the acceleration a bit.

With what we have, I'm not sure how to proceed. Anyone any experience of these budget ansmann models with brushless motors?

regards
Ian