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I need a reduction....Gearbox. 2:1 or so.


simonr
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When I built my electric freelander, I used a Suzuki SJ410 transfer box to reduce the speed of the eleccy motor to feed to the rear diff.

Unfortunately, the transfer box could not cope with the high speed (10,000 rpm input) and self destructed! It was very old and pre-knackered though.

A very kind forum member gave me a volvo gearbox, I think out of a 240 to try - but this appears to have the same problem. It's quite happy up to about 3000 rpm then tries to shake itself to bits!

What I'm looking for is a simple reduction gearbox with a fixed ratio, single reduction with an offset between the input and output - so essentially a big cog and a little cog in a box.

I've looked at marine gearboxes - which look great, but the ones I've found have been very heavy and include an un-needed reverse gear (you can reverse the direction of the motor for reverse). The ratios look good - but not the price!

I looked at reduction hubs for agricultural vehicles - but they are few & far between these days - and expensive.

Do any of you have any ideas? The box wants to be fairly compact with an offset of as much as 150mm between the in and out, but the in & out must be parallel. It needs to be able to cope with about 150Nm torque and as high a speed as possible.

If all else fails, I guess I could make something out of old gears from ?????.

Si

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Should be fairly easy to make yourself really.. just to gears, two shafts and good quality bearing in C3 or C4 and of course good lubrication. You could also use a chain, there are plenty that are happy to run a lot of rpm's.. What about a double chain and sprocket setup as per RV8? There's your 2:1 reduction and gears that's not that noisy and very compact.

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Thanks for the suggestions so far.

I like the Milner boxes - but probably too much money.

I am erring towards the 'making my own' option - I was just hoping for something easy, off the shelf.

I looked at V8 timing chain which would yield gears for 2:1. Just not so convinced it would cope so well with the torque & speed so well.

Best option is probably to dismantle a car or bike gearbox and re-use the two gears which give closest to 2:1 mounted on new shafts in a new housing etc.

NP203 or NP205 - I read somewhere that the low range gears although very strong, are noisy and need to be lapped / re-ground to a better accuracy if you want to use it all the time. May be wrong though.

I guess Bike parts are a good option. Any ideas what ratios they are or which are easiest to hack in to having shaft in and out?

Si

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I'll cut you a pair of gears if you want. You machine the blanks in EN36, I'll do the cutting and we'll pop them in the next batch of heat treatment. I'm sure we can work out some kind of exchange :rolleyes:

3 MOD 25 PA is as big as I can hob if you want helical but can go to 8DP 20 PA on the shaper as a spur gear

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That sounds a good plan! If I can't find something off the shelf - I'll be in touch!

Si

I'll cut you a pair of gears if you want. You machine the blanks in EN36, I'll do the cutting and we'll pop them in the next batch of heat treatment. I'm sure we can work out some kind of exchange :rolleyes:

3 MOD 25 PA is as big as I can hob if you want helical but can go to 8DP 20 PA on the shaper as a spur gear

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I was looking for a 1:2 gearbox for my electric reverse trike conversion a while ago but wanting to speed up a motor from 2500-5000. I also looked and asked about a V8 duplex timing chain and agricultural boxes. It wasn't promising.

I looked into using the gearbox BMW K100 motorbike, it is an under drive box hence wanting to speed uo the motor drive to it. It has very small straight cut gears on big splines with lots of backlask in the splines due to lack of syncro. I don't think they would cope with the torque. They feel very, very hard (glassy hard) and will probably shatter before you get to wear them out.

I am now opting for a Honda VFR chain drive swing arm but thinking of getting my single drive reduction with a duplex chain to the rear wheel.

If you make your own you should use helical cut gears to keep the noise down and for strength. There may be some Land Rover Tbox gears that might help but if you can do a deal to have ones made then all the better.

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Thanks Alfred,

I've been offered a gearbox out of a new BMW which had been in a crash and the box split open. I'm going to split it open some more to see if there are any useful gears!

If I'm assembling a gearbox, is there a rule of thumb to work out the separation / backlash? It's easy for known (MOD or DP) gears - but I don't imagine BMW use either! Obviously it needs to be right - but how so I work out what is right?

Si

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Not sure what motors you have used nor much else about this project but. Wouldn't it be easier to have 2 brushless motors or indeed 4 (no diffs) brushless motors and just maniulate the electronics to get what you require? The torque from an electric motor can be far more substantial than an engine. also with sensors either crude speed sensors or load sensors you could have a truly awsome offroad able serious articulating independant suspensioned motor. The technology in batteries alone have come on since the first Lipos and the enegry stroed in them can be awsome combined to a decent brushless setup it sounds like a winner. I'm very interested in your project!

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Jal - I agree, but even now there are no practical hub motors which can deliver the wheel torque required for on, never mind off road use. They will innevitably come though.

My motor is capable of producing 400 Nm and 12,000 rpm (at opposite ends of the rev band). It tales about 4,000 Nm to break a half shaft - so even with one of those per wheel, you still need to gear it 10:1 to give you the same kind of torque of torque as a Land Rover.

The motor is a Siemens, 3 phase AC with vector phase control - which gives a similar performance envelope to brushless DC of the same size. I bet you've not seen many 120kg, 300 x 300 x 600mm brushless DC motors!

With the Siemens motor geared at about 9:1, it gives better performance than a 1.6 Petrol Freelander with a top speed of about 90 - err, I mean 70 Officer ;)!

This morning I did a bit of an experiment with the volvo gearbox. I mounted it in the lathe which can run up to 4000 rpm. In 3rd and 4th gear, it is quite smooth and quiet at 4000 rpm. In 1st and 2nd however, it is OK (but not that great) up to about 2500 and then by 3500 it is making a terrible racket and trying to escape from the clamps!

On the vehicle, I'm running it in 2nd gear which is a 2.2:1 reduction.

Also, the efficiency is very different between 2nd and 3rd. At the same speed (1500rpm), the lathe motor was drawing 3A in 2nd but only 2.2A in 3rd or 4th.

My conclusion is that the gears for 1st & 2nd are just not as well made as those for 3rd & 4th. In a car, if you were traveling at 70 in 2nd gear, any noise from the gearbox would be drowned out by the engine anyway. You'd probably also be worrying about your engine, which is now doing 7 or 8 thousand rpm, throwing a rod or something worse!

Si

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Thanks Alfred,

I've been offered a gearbox out of a new BMW which had been in a crash and the box split open. I'm going to split it open some more to see if there are any useful gears!

If I'm assembling a gearbox, is there a rule of thumb to work out the separation / backlash? It's easy for known (MOD or DP) gears - but I don't imagine BMW use either! Obviously it needs to be right - but how so I work out what is right?

Si

When I have 'borrowed' gears from another application I used a feeler guage to check the backlash before dismantelling and then recreated it afterwards.

Automotive gearboxes don;t need to be efficient in the lower gears as they are not used for long and there is plenty of expendable power to play with. Also straight cut gears will be noiser but more efficient then helical cut gears as there is no sliding contact area on the tooth profile, just a rolling one, however, helical gears would still be a better choice due to noise and overall strength.

If you can get into the BMW box with a feeler guage, then count teeth you might be able to find what you want but it could be the first gear set and that would mean a big hole in the middle of one gearwheel where the syncros go and the other gearwheel will be a forged part of the layshaft. Don't know if it would be much use that way.

I remember you advising me, on my BMW box, that it might not be weldable if the shaft wasn't what I wanted.

Machinery gears might be easier to work with then automotive.

Have you thought about an epicyclic gear train from an automatic box? It may be worth asking Ian Ashcroft if there is a simple gear set that will offer a 2:1 reduction like an old Laycock overdrive unit.

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My only dealings with brushless is with RC models the last 5 years the cost and performance has rocketed I can now get a 2.5Kg model to accelerate vertically on a motor and controller setup costing around £25/£30 the batteries are still expensive ish around £40-50 but in the scheme of things very cheap. I guess the tech will come and with brushless effeciencies it will be very very good and not that far away.

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Thanks Alfred,

I've been offered a gearbox out of a new BMW which had been in a crash and the box split open. I'm going to split it open some more to see if there are any useful gears!

If I'm assembling a gearbox, is there a rule of thumb to work out the separation / backlash? It's easy for known (MOD or DP) gears - but I don't imagine BMW use either! Obviously it needs to be right - but how so I work out what is right?

Si

Machinery Handbook gives 0.005-0.015" on 10-20DP gears up to 5" centres and 0.010-0.020" on 6-10DP on 5-10" centres. Our 10 DP gears run about 0.006" on 2.35" centres FWIW

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Thanks all,

Luke, the Protean Electric Performance hub motors look good on paper. A Land rover wheel is say 33" or 42cm radius. That means that the force the wheel can exert on the road to move it forward is 800 / 0.42 = 1904 N or 190kg

That means that it would lift 190kg vertically or 400kg up a 1:1 so a 1.6ton vehicle up a 1:1 with 4 motors with a top speed of about 60mph

Trouble is, if they were really that good - everyone would be beating a path to their door! With most of these companies, PML Flightlink, Wavecrest and many more, I have a strong suspicion that these pages are to attract venture capital. From experience, if you phone up and ask to buy a set - you discover that they have the patents, drawings and prototypes - but have yet to produce something workable for production.

A few years ago I talked to a company who had what sounded like a fantastic hub motor. Their prototype was almost there and was just waiting for a 'small' technological advance before every car would have one (or four). It turned out that the motor used gold wire to get the efficiency and performance (making it quite an expensive motor with 20kg or so of gold!) and the small technological advance they were waiting for was high temperature superconductors - which according to him were months away! Also, they were not interested in selling me motors, more in selling me a great investment opportunity!

Sorry if that sounds skeptical or cynical for that matter. We will get there - and I hope it's them that do it - but I'm yet to be convinced!

Jai, have you got any links to the highest power BDC motors available? There was a chap on one of the electric vehicle forums who was going to arrange a load of motors around one big central gear to give about 1:6 reduction. The idea being that 24 smaller motors and controllers would be cheaper than ine big motor.

I've had the BM box apart. The casing was smashed so there was no point in trying to measure the gear separation. I could get my fingers between some of the gears! Unfortunately, there is no pair of gears which mesh and give more than about 1.8:1. They also look a bit of a sod to interface to with all the synchro gubbins.

Zoltan, have you tested the mesh of your helical gears to anything 10k rpm? I worry because of how the volvo gears behaved at high speeds when at low speeds they felt fine.

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They only have puny motors and the specs are rubbish made for big RC Planes don't think it'll be any good for your idea but here is the biggest tey have:

http://www.giantcod.co.uk/xyh80100a-130kv-brushless-outrunner-7055-p-404608.html

I was very tempted to try and get 2 or 3 and modify a winch but after seeing my small Brushless RC car submerged under water I gave up on the idea. Still i have a diff pinning jig to finish so can't have too many projects on the go at once aye!

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That's the most impressive RC motor I've seen. At 12v it is only going to spin at 1300rpm. A winch motor spins up to 5000 rpm and has a stall torque of about 30Nm. The combination of motors therefore needs 115Nm torque to give the same pull and line speed.

Sadly, they do not quote torque. I would guess at needing 5 to 10 of those motors to compete with a Bowmotor 2.

So

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I'm in the process of moving interstate and can't put my hands on my gear handbooks and standards - I used to design gears in a previous life.You are not going to get 150 mm separation between input and output from a bike or car gearbox - the LT77 and R380 are 77 mm, LT85 is 85 mm, LT95 95 mm, LT230 (using an idler gear) is 230 mm.I would expect automotive gearboxes to be cut with standard equipment in either module or DP tooth forms. But they will have addendum modification to adjust the centre distance as each ratio pair have to operate on the same centre distance as the other pairs in the box.Addendum modification should also be used as ratio increases and for better strength and operation - with 2:1 you can get away without addendum modification. Often gear teeth will need tip modification to compensate for tooth deflection - it is something that has to be checked on a case by case basis. There is a lot more stuff that a gear designer needs to know that can not be found in machinerys handbook. At the speed you want to run, I doubt it will be satisfactory using hobbed or shaped gears - IMHO you need to have the gears ground after hardening. Precision (profile error and tooth to tooth pitch error) is very important when determining gear ratings, because of the effects/inducement of dynamic forces (these dynamics reduce capacity and increase noise and vibration). Gear design uses a 'quality number' (the table for quality number gives the limits for various allowable errors for each number) in the the process of determining the capacity of a gear pair. Case hardened and ground gears also benefit from having greater power rating.

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Zoltan, have you tested the mesh of your helical gears to anything 10k rpm? I worry because of how the volvo gears behaved at high speeds when at low speeds they felt fine.

Our helical gears are only running 10 degrees of helix, we are limited on how much side loading we can introduce through the flimsy standard casings. They are the Mini final drive gears so typically have a 13/54 or 13/56 tooth count (4.1 and 4.3 ratios) The pinions will be running at 9000rpm on 1:1 drop gears. They are noisy but since these are racing gearboxes no-one worries too much. On a road car I think at those rpm's people will hear you coming.

Bush's suggestion of ground gears post heat-treat would be best for noise but how expensive do you want to make this project? Gears that have run together for several thousand miles will have bedded nicely so using recycled gears would be best for noise

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