Fabricating a Bevel gear box – tether car

[Paul McDonoughParticipant @paulmcdonough43628]

I want to build a tethered race car to be driven by a 3.5cc model engine. It has been recommend that I use angle grinder bevel gears (like these sourcingmap Electric Tool Parts Spiral Bevel Gear for Hitachi G10SF3 Angle Grinder : Amazon.co.uk: DIY & Tools) to drive the rear axle.

I don't need or especially want a differential, but it needs to be robust to cope with push starts with the driven shaft 10 to 12mm in diameter and 200 to 250 mm in length.

I am struggling to find a proven simple and robust design.

The best i can come up with is a thick piece of aluminium angle with bearings recessed into the two 90 deg faces to hold one side of the main rear wheel shaft with the crown gear mounted on this shaft and the pinion gear on a short shaft in the other face. This all feels a bit crude and i worry about fine setting and maintaining the gear alignment.

In my head I can see a solution involving hollowing out a cube of ali, but this seems very wasteful and chuncky but at least it would be able to accommodate both left and right main shaft bearings.

I have also though of adapting a complete an angle grinder gear box but worry about drilling the grinder shaft to take a smaller dia rear axle and dealing with the bulk of the thing!

Many thanks for your thoughts.

[Paul McDonoughParticipant @paulmcdonough43628]

[bernard towersParticipant @bernardtowers37738]

How about channel with an endplate? Considering the work that an angle grinder does that gears is a bargain!

Edited By bernard towers on 28/07/2023 16:24:14

[JasonBModerator @jasonb]

I'd go with two flat side plates bored to take suitable bearings for the solid rear axle. Tap the bottom edges to fit to the chassis. Have front and rear plates that fit between the side plates the front one of which has bearings for the prop shaft

I made similar years ago for a 1/8th scale buggy

Quite a few tether cars run transverse engines which could be done with a belt or spur gears or if you are feeling adventurous then a slave crankshaft can be used driven by the existing crankshaft to take your two rear wheels

 

Edited By JasonB on 28/07/2023 16:43:29

[Paul McDonoughParticipant @paulmcdonough43628]

Thanks for your ideas I like the idea of a box made up from channel and I agree the angle grinder gears are good value and apparently quite hard.

I am also taken by the idea of using spur gears, the engine, taken from an old RC car, is currently fitted with a centrifugal clutch and spur gear but the current gears are quite small and don't allow for the main drive shaft to pass the engine crankcase, but I could add an intermediate gear to get some distance between them. obviously dealing with the shaft reverse direction.

[JasonBModerator @jasonb]

Other option would be a bigger pinion on the engine, as you will be doing away with the clutch that usually has the gear attached you are half way there already. Just size the axle gear to suit. Big advantage with a setup like this is you can easily change ratios which you can't do without a complete new gearbox if the angle grinder option has too low a ratio. Though tyre diameter can be brought into play.

Couple of examples here, bit on gearboxes here

Edited By JasonB on 28/07/2023 18:27:23

[Paul McDonoughParticipant @paulmcdonough43628]

Cheers I like the spur gear solutions, I agree it allows for a change of ratio although I am a bit limited for tyres trying to stick with 75 to 85mm in diameter.

it is telling that the 1940’s book I have shows that gearboxes were once relatively available so many purpose built units on show. As were engines with slave crank shafts which are probably a bit beyond my skill set!

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